# Copyright 2010 United States Government as represented by the
# Administrator of the National Aeronautics and Space Administration.
# Copyright 2011 Justin Santa Barbara
# All Rights Reserved.
#
#    Licensed under the Apache License, Version 2.0 (the "License"); you may
#    not use this file except in compliance with the License. You may obtain
#    a copy of the License at
#
#         http://www.apache.org/licenses/LICENSE-2.0
#
#    Unless required by applicable law or agreed to in writing, software
#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
#    License for the specific language governing permissions and limitations
#    under the License.

"""Handles all processes relating to instances (guest vms).

The :py:class:`ComputeManager` class is a :py:class:`nova.manager.Manager` that
handles RPC calls relating to creating instances.  It is responsible for
building a disk image, launching it via the underlying virtualization driver,
responding to calls to check its state, attaching persistent storage, and
terminating it.

"""

import base64
import contextlib
import functools
import socket
import sys
import time
import traceback
import uuid

from cinderclient import exceptions as cinder_exception
import eventlet.event
from eventlet import greenthread
import eventlet.semaphore
import eventlet.timeout
from keystoneclient import exceptions as keystone_exception
from oslo_config import cfg
from oslo_log import log as logging
import oslo_messaging as messaging
from oslo_serialization import jsonutils
from oslo_service import loopingcall
from oslo_service import periodic_task
from oslo_utils import excutils
from oslo_utils import strutils
from oslo_utils import timeutils
import six
from six.moves import range

from nova import block_device
from nova.cells import rpcapi as cells_rpcapi
from nova.cloudpipe import pipelib
from nova import compute
from nova.compute import build_results
from nova.compute import claims
from nova.compute import power_state
from nova.compute import resource_tracker
from nova.compute import rpcapi as compute_rpcapi
from nova.compute import task_states
from nova.compute import utils as compute_utils
from nova.compute import vm_states
from nova import conductor
from nova import consoleauth
import nova.context
from nova import exception
from nova import hooks
from nova.i18n import _
from nova.i18n import _LE
from nova.i18n import _LI
from nova.i18n import _LW
from nova import image
from nova.image import glance
from nova import manager
from nova import network
from nova.network import base_api as base_net_api
from nova.network import model as network_model
from nova.network.security_group import openstack_driver
from nova import objects
from nova.objects import base as obj_base
from nova import paths
from nova import rpc
from nova import safe_utils
from nova.scheduler import client as scheduler_client
from nova import utils
from nova.virt import block_device as driver_block_device
from nova.virt import configdrive
from nova.virt import driver
from nova.virt import event as virtevent
from nova.virt import storage_users
from nova.virt import virtapi
from nova import volume
from nova.volume import encryptors


compute_opts = [
    cfg.StrOpt('console_host',
               default=socket.gethostname(),
               help='Console proxy host to use to connect '
                    'to instances on this host.'),
    cfg.StrOpt('default_access_ip_network_name',
               help='Name of network to use to set access IPs for instances'),
    cfg.BoolOpt('defer_iptables_apply',
                default=False,
                help='Whether to batch up the application of IPTables rules'
                     ' during a host restart and apply all at the end of the'
                     ' init phase'),
    cfg.StrOpt('instances_path',
               default=paths.state_path_def('instances'),
               help='Where instances are stored on disk'),
    cfg.BoolOpt('instance_usage_audit',
                default=False,
                help="Generate periodic compute.instance.exists"
                     " notifications"),
    cfg.IntOpt('live_migration_retry_count',
               default=30,
               help="Number of 1 second retries needed in live_migration"),
    cfg.BoolOpt('resume_guests_state_on_host_boot',
                default=False,
                help='Whether to start guests that were running before the '
                     'host rebooted'),
    cfg.IntOpt('network_allocate_retries',
               default=0,
               help="Number of times to retry network allocation on failures"),
    cfg.IntOpt('max_concurrent_builds',
               default=10,
               help='Maximum number of instance builds to run concurrently'),
    cfg.IntOpt('max_concurrent_live_migrations',
               default=1,
               help='Maximum number of live migrations to run concurrently. '
                    'This limit is enforced to avoid outbound live migrations '
                    'overwhelming the host/network and causing failures. It '
                    'is not recommended that you change this unless you are '
                    'very sure that doing so is safe and stable in your '
                    'environment.'),
    cfg.IntOpt('block_device_allocate_retries',
               default=60,
               help='Number of times to retry block device'
                    ' allocation on failures')
    ]

interval_opts = [
    cfg.IntOpt('bandwidth_poll_interval',
               default=600,
               help='Interval to pull network bandwidth usage info. Not '
                    'supported on all hypervisors. Set to -1 to disable. '
                    'Setting this to 0 will run at the default rate.'),
    cfg.IntOpt('sync_power_state_interval',
               default=600,
               help='Interval to sync power states between the database and '
                    'the hypervisor. Set to -1 to disable. '
                    'Setting this to 0 will run at the default rate.'),
    cfg.IntOpt("heal_instance_info_cache_interval",
               default=60,
               help="Number of seconds between instance network information "
                    "cache updates"),
    cfg.IntOpt('reclaim_instance_interval',
               default=0,
               help='Interval in seconds for reclaiming deleted instances'),
    cfg.IntOpt('volume_usage_poll_interval',
               default=0,
               help='Interval in seconds for gathering volume usages'),
    cfg.IntOpt('shelved_poll_interval',
               default=3600,
               help='Interval in seconds for polling shelved instances to '
                    'offload. Set to -1 to disable.'
                    'Setting this to 0 will run at the default rate.'),
    cfg.IntOpt('shelved_offload_time',
               default=0,
               help='Time in seconds before a shelved instance is eligible '
                    'for removing from a host. -1 never offload, 0 offload '
                    'immediately when shelved'),
    cfg.IntOpt('instance_delete_interval',
               default=300,
               help='Interval in seconds for retrying failed instance file '
                    'deletes. Set to -1 to disable. '
                    'Setting this to 0 will run at the default rate.'),
    cfg.IntOpt('block_device_allocate_retries_interval',
               default=3,
               help='Waiting time interval (seconds) between block'
                    ' device allocation retries on failures'),
    cfg.IntOpt('scheduler_instance_sync_interval',
               default=120,
               help='Waiting time interval (seconds) between sending the '
                    'scheduler a list of current instance UUIDs to verify '
                    'that its view of instances is in sync with nova. If the '
                    'CONF option `scheduler_tracks_instance_changes` is '
                    'False, changing this option will have no effect.'),
    cfg.IntOpt('update_resources_interval',
               default=0,
               help='Interval in seconds for updating compute resources. A '
                    'number less than 0 means to disable the task completely. '
                    'Leaving this at the default of 0 will cause this to run '
                    'at the default periodic interval. Setting it to any '
                    'positive value will cause it to run at approximately '
                    'that number of seconds.'),
]

timeout_opts = [
    cfg.IntOpt("reboot_timeout",
               default=0,
               help="Automatically hard reboot an instance if it has been "
                    "stuck in a rebooting state longer than N seconds. "
                    "Set to 0 to disable."),
    cfg.IntOpt("instance_build_timeout",
               default=0,
               help="Amount of time in seconds an instance can be in BUILD "
                    "before going into ERROR status. "
                    "Set to 0 to disable."),
    cfg.IntOpt("rescue_timeout",
               default=0,
               help="Automatically unrescue an instance after N seconds. "
                    "Set to 0 to disable."),
    cfg.IntOpt("resize_confirm_window",
               default=0,
               help="Automatically confirm resizes after N seconds. "
                    "Set to 0 to disable."),
    cfg.IntOpt("shutdown_timeout",
               default=60,
               help="Total amount of time to wait in seconds for an instance "
                    "to perform a clean shutdown."),
]

running_deleted_opts = [
    cfg.StrOpt("running_deleted_instance_action",
               default="reap",
               choices=('noop', 'log', 'shutdown', 'reap'),
               help="Action to take if a running deleted instance is detected."
                    "Set to 'noop' to take no action."),
    cfg.IntOpt("running_deleted_instance_poll_interval",
               default=1800,
               help="Number of seconds to wait between runs of the cleanup "
                    "task."),
    cfg.IntOpt("running_deleted_instance_timeout",
               default=0,
               help="Number of seconds after being deleted when a running "
                    "instance should be considered eligible for cleanup."),
]

instance_cleaning_opts = [
    cfg.IntOpt('maximum_instance_delete_attempts',
               default=5,
               help='The number of times to attempt to reap an instance\'s '
                    'files.'),
]

CONF = cfg.CONF
CONF.register_opts(compute_opts)
CONF.register_opts(interval_opts)
CONF.register_opts(timeout_opts)
CONF.register_opts(running_deleted_opts)
CONF.register_opts(instance_cleaning_opts)
CONF.import_opt('console_topic', 'nova.console.rpcapi')
CONF.import_opt('host', 'nova.netconf')
CONF.import_opt('enabled', 'nova.vnc', group='vnc')
CONF.import_opt('enabled', 'nova.spice', group='spice')
CONF.import_opt('enable', 'nova.cells.opts', group='cells')
CONF.import_opt('image_cache_manager_interval', 'nova.virt.imagecache')
CONF.import_opt('enabled', 'nova.rdp', group='rdp')
CONF.import_opt('html5_proxy_base_url', 'nova.rdp', group='rdp')
CONF.import_opt('enabled', 'nova.mks', group='mks')
CONF.import_opt('mksproxy_base_url', 'nova.mks', group='mks')
CONF.import_opt('enabled', 'nova.console.serial', group='serial_console')
CONF.import_opt('base_url', 'nova.console.serial', group='serial_console')
CONF.import_opt('destroy_after_evacuate', 'nova.utils', group='workarounds')
CONF.import_opt('scheduler_tracks_instance_changes',
                'nova.scheduler.host_manager')

LOG = logging.getLogger(__name__)

get_notifier = functools.partial(rpc.get_notifier, service='compute')
wrap_exception = functools.partial(exception.wrap_exception,
                                   get_notifier=get_notifier)


@utils.expects_func_args('migration')
def errors_out_migration(function):
    """Decorator to error out migration on failure."""

    @functools.wraps(function)
    def decorated_function(self, context, *args, **kwargs):
        try:
            return function(self, context, *args, **kwargs)
        except Exception as ex:
            with excutils.save_and_reraise_exception():
                wrapped_func = utils.get_wrapped_function(function)
                keyed_args = safe_utils.getcallargs(wrapped_func, context,
                                                    *args, **kwargs)
                migration = keyed_args['migration']

                # NOTE(rajesht): If InstanceNotFound error is thrown from
                # decorated function, migration status should be set to
                # 'error', without checking current migration status.
                if not isinstance(ex, exception.InstanceNotFound):
                    status = migration.status
                    if status not in ['migrating', 'post-migrating']:
                        return

                migration.status = 'error'
                try:
                    with migration.obj_as_admin():
                        migration.save()
                except Exception:
                    LOG.debug('Error setting migration status '
                              'for instance %s.',
                              migration.instance_uuid, exc_info=True)

    return decorated_function


@utils.expects_func_args('instance')
def reverts_task_state(function):
    """Decorator to revert task_state on failure."""

    @functools.wraps(function)
    def decorated_function(self, context, *args, **kwargs):
        try:
            return function(self, context, *args, **kwargs)
        except exception.UnexpectedTaskStateError as e:
            # Note(maoy): unexpected task state means the current
            # task is preempted. Do not clear task state in this
            # case.
            with excutils.save_and_reraise_exception():
                LOG.info(_LI("Task possibly preempted: %s"),
                         e.format_message())
        except Exception:
            with excutils.save_and_reraise_exception():
                wrapped_func = utils.get_wrapped_function(function)
                keyed_args = safe_utils.getcallargs(wrapped_func, context,
                                                    *args, **kwargs)
                # NOTE(mriedem): 'instance' must be in keyed_args because we
                # have utils.expects_func_args('instance') decorating this
                # method.
                instance = keyed_args['instance']
                try:
                    self._instance_update(context, instance, task_state=None)
                except exception.InstanceNotFound:
                    # We might delete an instance that failed to build shortly
                    # after it errored out this is an expected case and we
                    # should not trace on it.
                    pass
                except Exception as e:
                    msg = _LW("Failed to revert task state for instance. "
                              "Error: %s")
                    LOG.warning(msg, e, instance=instance)

    return decorated_function


@utils.expects_func_args('instance')
def wrap_instance_fault(function):
    """Wraps a method to catch exceptions related to instances.

    This decorator wraps a method to catch any exceptions having to do with
    an instance that may get thrown. It then logs an instance fault in the db.
    """

    @functools.wraps(function)
    def decorated_function(self, context, *args, **kwargs):
        try:
            return function(self, context, *args, **kwargs)
        except exception.InstanceNotFound:
            raise
        except Exception as e:
            # NOTE(gtt): If argument 'instance' is in args rather than kwargs,
            # we will get a KeyError exception which will cover up the real
            # exception. So, we update kwargs with the values from args first.
            # then, we can get 'instance' from kwargs easily.
            kwargs.update(dict(zip(function.func_code.co_varnames[2:], args)))

            with excutils.save_and_reraise_exception():
                compute_utils.add_instance_fault_from_exc(context,
                        kwargs['instance'], e, sys.exc_info())

    return decorated_function


@utils.expects_func_args('instance')
def wrap_instance_event(function):
    """Wraps a method to log the event taken on the instance, and result.

    This decorator wraps a method to log the start and result of an event, as
    part of an action taken on an instance.
    """

    @functools.wraps(function)
    def decorated_function(self, context, *args, **kwargs):
        wrapped_func = utils.get_wrapped_function(function)
        keyed_args = safe_utils.getcallargs(wrapped_func, context, *args,
                                       **kwargs)
        instance_uuid = keyed_args['instance']['uuid']

        event_name = 'compute_{0}'.format(function.func_name)
        with compute_utils.EventReporter(context, event_name, instance_uuid):
            return function(self, context, *args, **kwargs)

    return decorated_function


@utils.expects_func_args('image_id', 'instance')
def delete_image_on_error(function):
    """Used for snapshot related method to ensure the image created in
    compute.api is deleted when an error occurs.
    """

    @functools.wraps(function)
    def decorated_function(self, context, image_id, instance,
                           *args, **kwargs):
        try:
            return function(self, context, image_id, instance,
                            *args, **kwargs)
        except Exception:
            with excutils.save_and_reraise_exception():
                LOG.debug("Cleaning up image %s", image_id,
                          exc_info=True, instance=instance)
                try:
                    self.image_api.delete(context, image_id)
                except Exception:
                    LOG.exception(_LE("Error while trying to clean up "
                                      "image %s"), image_id,
                                  instance=instance)

    return decorated_function


# TODO(danms): Remove me after Icehouse
# NOTE(mikal): if the method being decorated has more than one decorator, then
# put this one first. Otherwise the various exception handling decorators do
# not function correctly.
def object_compat(function):
    """Wraps a method that expects a new-world instance

    This provides compatibility for callers passing old-style dict
    instances.
    """

    @functools.wraps(function)
    def decorated_function(self, context, *args, **kwargs):
        def _load_instance(instance_or_dict):
            if isinstance(instance_or_dict, dict):
                # try to get metadata and system_metadata for most cases but
                # only attempt to load those if the db instance already has
                # those fields joined
                metas = [meta for meta in ('metadata', 'system_metadata')
                         if meta in instance_or_dict]
                instance = objects.Instance._from_db_object(
                    context, objects.Instance(), instance_or_dict,
                    expected_attrs=metas)
                instance._context = context
                return instance
            return instance_or_dict

        try:
            kwargs['instance'] = _load_instance(kwargs['instance'])
        except KeyError:
            args = (_load_instance(args[0]),) + args[1:]

        migration = kwargs.get('migration')
        if isinstance(migration, dict):
            migration = objects.Migration._from_db_object(
                    context.elevated(), objects.Migration(),
                    migration)
            kwargs['migration'] = migration

        return function(self, context, *args, **kwargs)

    return decorated_function


class InstanceEvents(object):
    def __init__(self):
        self._events = {}

    @staticmethod
    def _lock_name(instance):
        return '%s-%s' % (instance.uuid, 'events')

    def prepare_for_instance_event(self, instance, event_name):
        """Prepare to receive an event for an instance.

        This will register an event for the given instance that we will
        wait on later. This should be called before initiating whatever
        action will trigger the event. The resulting eventlet.event.Event
        object should be wait()'d on to ensure completion.

        :param instance: the instance for which the event will be generated
        :param event_name: the name of the event we're expecting
        :returns: an event object that should be wait()'d on
        """
        if self._events is None:
            # NOTE(danms): We really should have a more specific error
            # here, but this is what we use for our default error case
            raise exception.NovaException('In shutdown, no new events '
                                          'can be scheduled')

        @utils.synchronized(self._lock_name(instance))
        def _create_or_get_event():
            instance_events = self._events.setdefault(instance.uuid, {})
            return instance_events.setdefault(event_name,
                                              eventlet.event.Event())
        LOG.debug('Preparing to wait for external event %(event)s',
                  {'event': event_name}, instance=instance)
        return _create_or_get_event()

    def pop_instance_event(self, instance, event):
        """Remove a pending event from the wait list.

        This will remove a pending event from the wait list so that it
        can be used to signal the waiters to wake up.

        :param instance: the instance for which the event was generated
        :param event: the nova.objects.external_event.InstanceExternalEvent
                      that describes the event
        :returns: the eventlet.event.Event object on which the waiters
                  are blocked
        """
        no_events_sentinel = object()
        no_matching_event_sentinel = object()

        @utils.synchronized(self._lock_name(instance))
        def _pop_event():
            if not self._events:
                LOG.debug('Unexpected attempt to pop events during shutdown',
                          instance=instance)
                return no_events_sentinel
            events = self._events.get(instance.uuid)
            if not events:
                return no_events_sentinel
            _event = events.pop(event.key, None)
            if not events:
                del self._events[instance.uuid]
            if _event is None:
                return no_matching_event_sentinel
            return _event

        result = _pop_event()
        if result is no_events_sentinel:
            LOG.debug('No waiting events found dispatching %(event)s',
                      {'event': event.key},
                      instance=instance)
            return None
        elif result is no_matching_event_sentinel:
            LOG.debug('No event matching %(event)s in %(events)s',
                      {'event': event.key,
                       'events': self._events.get(instance.uuid, {}).keys()},
                      instance=instance)
            return None
        else:
            return result

    def clear_events_for_instance(self, instance):
        """Remove all pending events for an instance.

        This will remove all events currently pending for an instance
        and return them (indexed by event name).

        :param instance: the instance for which events should be purged
        :returns: a dictionary of {event_name: eventlet.event.Event}
        """
        @utils.synchronized(self._lock_name(instance))
        def _clear_events():
            if self._events is None:
                LOG.debug('Unexpected attempt to clear events during shutdown',
                          instance=instance)
                return dict()
            return self._events.pop(instance.uuid, {})
        return _clear_events()

    def cancel_all_events(self):
        our_events = self._events
        # NOTE(danms): Block new events
        self._events = None

        for instance_uuid, events in our_events.items():
            for event_name, eventlet_event in events.items():
                LOG.debug('Canceling in-flight event %(event)s for '
                          'instance %(instance_uuid)s',
                          {'event': event_name,
                           'instance_uuid': instance_uuid})
                name, tag = event_name.rsplit('-', 1)
                event = objects.InstanceExternalEvent(
                    instance_uuid=instance_uuid,
                    name=name, status='failed',
                    tag=tag, data={})
                eventlet_event.send(event)


class ComputeVirtAPI(virtapi.VirtAPI):
    def __init__(self, compute):
        super(ComputeVirtAPI, self).__init__()
        self._compute = compute

    def provider_fw_rule_get_all(self, context):
        return self._compute.conductor_api.provider_fw_rule_get_all(context)

    def _default_error_callback(self, event_name, instance):
        raise exception.NovaException(_('Instance event failed'))

    @contextlib.contextmanager
    def wait_for_instance_event(self, instance, event_names, deadline=300,
                                error_callback=None):
        """Plan to wait for some events, run some code, then wait.

        This context manager will first create plans to wait for the
        provided event_names, yield, and then wait for all the scheduled
        events to complete.

        Note that this uses an eventlet.timeout.Timeout to bound the
        operation, so callers should be prepared to catch that
        failure and handle that situation appropriately.

        If the event is not received by the specified timeout deadline,
        eventlet.timeout.Timeout is raised.

        If the event is received but did not have a 'completed'
        status, a NovaException is raised.  If an error_callback is
        provided, instead of raising an exception as detailed above
        for the failure case, the callback will be called with the
        event_name and instance, and can return True to continue
        waiting for the rest of the events, False to stop processing,
        or raise an exception which will bubble up to the waiter.

        :param instance: The instance for which an event is expected
        :param event_names: A list of event names. Each element can be a
                            string event name or tuple of strings to
                            indicate (name, tag).
        :param deadline: Maximum number of seconds we should wait for all
                         of the specified events to arrive.
        :param error_callback: A function to be called if an event arrives

        """

        if error_callback is None:
            error_callback = self._default_error_callback
        events = {}
        for event_name in event_names:
            if isinstance(event_name, tuple):
                name, tag = event_name
                event_name = objects.InstanceExternalEvent.make_key(
                    name, tag)
            try:
                events[event_name] = (
                    self._compute.instance_events.prepare_for_instance_event(
                        instance, event_name))
            except exception.NovaException:
                error_callback(event_name, instance)
                # NOTE(danms): Don't wait for any of the events. They
                # should all be canceled and fired immediately below,
                # but don't stick around if not.
                deadline = 0
        yield
        with eventlet.timeout.Timeout(deadline):
            for event_name, event in events.items():
                actual_event = event.wait()
                if actual_event.status == 'completed':
                    continue
                decision = error_callback(event_name, instance)
                if decision is False:
                    break


class ComputeManager(manager.Manager):
    """Manages the running instances from creation to destruction."""

    target = messaging.Target(version='4.5')

    # How long to wait in seconds before re-issuing a shutdown
    # signal to an instance during power off.  The overall
    # time to wait is set by CONF.shutdown_timeout.
    SHUTDOWN_RETRY_INTERVAL = 10

    def __init__(self, compute_driver=None, *args, **kwargs):
        """Load configuration options and connect to the hypervisor."""
        self.virtapi = ComputeVirtAPI(self)
        self.network_api = network.API()
        self.volume_api = volume.API()
        self.image_api = image.API()
        self._last_host_check = 0
        self._last_bw_usage_poll = 0
        self._bw_usage_supported = True
        self._last_bw_usage_cell_update = 0
        self.compute_api = compute.API()
        self.compute_rpcapi = compute_rpcapi.ComputeAPI()
        self.conductor_api = conductor.API()
        self.compute_task_api = conductor.ComputeTaskAPI()
        self.is_neutron_security_groups = (
            openstack_driver.is_neutron_security_groups())
        self.consoleauth_rpcapi = consoleauth.rpcapi.ConsoleAuthAPI()
        self.cells_rpcapi = cells_rpcapi.CellsAPI()
        self.scheduler_client = scheduler_client.SchedulerClient()
        self._resource_tracker_dict = {}
        self.instance_events = InstanceEvents()
        self._sync_power_pool = eventlet.GreenPool()
        self._syncs_in_progress = {}
        self.send_instance_updates = CONF.scheduler_tracks_instance_changes
        if CONF.max_concurrent_builds != 0:
            self._build_semaphore = eventlet.semaphore.Semaphore(
                CONF.max_concurrent_builds)
        else:
            self._build_semaphore = compute_utils.UnlimitedSemaphore()
        if max(CONF.max_concurrent_live_migrations, 0) != 0:
            self._live_migration_semaphore = eventlet.semaphore.Semaphore(
                CONF.max_concurrent_live_migrations)
        else:
            self._live_migration_semaphore = compute_utils.UnlimitedSemaphore()

        super(ComputeManager, self).__init__(service_name="compute",
                                             *args, **kwargs)

        # NOTE(russellb) Load the driver last.  It may call back into the
        # compute manager via the virtapi, so we want it to be fully
        # initialized before that happens.
        self.driver = driver.load_compute_driver(self.virtapi, compute_driver)
        self.use_legacy_block_device_info = \
                            self.driver.need_legacy_block_device_info

    def _get_resource_tracker(self, nodename):
        rt = self._resource_tracker_dict.get(nodename)
        if not rt:
            if not self.driver.node_is_available(nodename):
                raise exception.NovaException(
                        _("%s is not a valid node managed by this "
                          "compute host.") % nodename)

            rt = resource_tracker.ResourceTracker(self.host,
                                                  self.driver,
                                                  nodename)
            self._resource_tracker_dict[nodename] = rt
        return rt

    def _update_resource_tracker(self, context, instance):
        """Let the resource tracker know that an instance has changed state."""

        if (instance.host == self.host and
                self.driver.node_is_available(instance.node)):
            rt = self._get_resource_tracker(instance.node)
            rt.update_usage(context, instance)

    def _instance_update(self, context, instance, **kwargs):
        """Update an instance in the database using kwargs as value."""

        for k, v in kwargs.items():
            setattr(instance, k, v)
        instance.save()
        self._update_resource_tracker(context, instance)

    def _nil_out_instance_obj_host_and_node(self, instance):
        # NOTE(jwcroppe): We don't do instance.save() here for performance
        # reasons; a call to this is expected to be immediately followed by
        # another call that does instance.save(), thus avoiding two writes
        # to the database layer.
        instance.host = None
        instance.node = None

    def _set_instance_obj_error_state(self, context, instance,
                                      clean_task_state=False):
        try:
            instance.vm_state = vm_states.ERROR
            if clean_task_state:
                instance.task_state = None
            instance.save()
        except exception.InstanceNotFound:
            LOG.debug('Instance has been destroyed from under us while '
                      'trying to set it to ERROR', instance=instance)

    def _get_instances_on_driver(self, context, filters=None):
        """Return a list of instance records for the instances found
        on the hypervisor which satisfy the specified filters. If filters=None
        return a list of instance records for all the instances found on the
        hypervisor.
        """
        if not filters:
            filters = {}
        try:
            driver_uuids = self.driver.list_instance_uuids()
            if len(driver_uuids) == 0:
                # Short circuit, don't waste a DB call
                return objects.InstanceList()
            filters['uuid'] = driver_uuids
            local_instances = objects.InstanceList.get_by_filters(
                context, filters, use_slave=True)
            return local_instances
        except NotImplementedError:
            pass

        # The driver doesn't support uuids listing, so we'll have
        # to brute force.
        driver_instances = self.driver.list_instances()
        instances = objects.InstanceList.get_by_filters(context, filters,
                                                        use_slave=True)
        name_map = {instance.name: instance for instance in instances}
        local_instances = []
        for driver_instance in driver_instances:
            instance = name_map.get(driver_instance)
            if not instance:
                continue
            local_instances.append(instance)
        return local_instances

    def _destroy_evacuated_instances(self, context):
        """Destroys evacuated instances.

        While nova-compute was down, the instances running on it could be
        evacuated to another host. Check that the instances reported
        by the driver are still associated with this host.  If they are
        not, destroy them, with the exception of instances which are in
        the MIGRATING, RESIZE_MIGRATING, RESIZE_MIGRATED, RESIZE_FINISH
        task state or RESIZED vm state.
        """
        filters = {
            'source_compute': self.host,
            'status': 'accepted',
            'migration_type': 'evacuation',
        }
        evacuations = objects.MigrationList.get_by_filters(context, filters)
        if not evacuations:
            return
        evacuations = {mig.instance_uuid: mig for mig in evacuations}

        filters = {'deleted': False}
        local_instances = self._get_instances_on_driver(context, filters)
        evacuated = [inst for inst in local_instances
                     if inst.uuid in evacuations]
        for instance in evacuated:
            migration = evacuations[instance.uuid]
            LOG.info(_LI('Deleting instance as it has been evacuated from '
                         'this host'), instance=instance)
            try:
                network_info = self.network_api.get_instance_nw_info(
                    context, instance)
                bdi = self._get_instance_block_device_info(context,
                                                           instance)
                destroy_disks = not (self._is_instance_storage_shared(
                    context, instance))
            except exception.InstanceNotFound:
                network_info = network_model.NetworkInfo()
                bdi = {}
                LOG.info(_LI('Instance has been marked deleted already, '
                             'removing it from the hypervisor.'),
                         instance=instance)
                # always destroy disks if the instance was deleted
                destroy_disks = True
            self.driver.destroy(context, instance,
                                network_info,
                                bdi, destroy_disks)
            migration.status = 'completed'
            migration.save()

    def _is_instance_storage_shared(self, context, instance, host=None):
        shared_storage = True
        data = None
        try:
            data = self.driver.check_instance_shared_storage_local(context,
                                                       instance)
            if data:
                shared_storage = (self.compute_rpcapi.
                                  check_instance_shared_storage(context,
                                  instance, data, host=host))
        except NotImplementedError:
            LOG.debug('Hypervisor driver does not support '
                      'instance shared storage check, '
                      'assuming it\'s not on shared storage',
                      instance=instance)
            shared_storage = False
        except Exception:
            LOG.exception(_LE('Failed to check if instance shared'),
                      instance=instance)
        finally:
            if data:
                self.driver.check_instance_shared_storage_cleanup(context,
                                                                  data)
        return shared_storage

    def _complete_partial_deletion(self, context, instance):
        """Complete deletion for instances in DELETED status but not marked as
        deleted in the DB
        """
        system_meta = instance.system_metadata
        instance.destroy()
        bdms = objects.BlockDeviceMappingList.get_by_instance_uuid(
                context, instance.uuid)
        quotas = objects.Quotas(context=context)
        project_id, user_id = objects.quotas.ids_from_instance(context,
                                                               instance)
        quotas.reserve(project_id=project_id, user_id=user_id, instances=-1,
                       cores=-instance.vcpus, ram=-instance.memory_mb)
        self._complete_deletion(context,
                                instance,
                                bdms,
                                quotas,
                                system_meta)

    def _complete_deletion(self, context, instance, bdms,
                           quotas, system_meta):
        if quotas:
            quotas.commit()

        # ensure block device mappings are not leaked
        for bdm in bdms:
            bdm.destroy()

        self._notify_about_instance_usage(context, instance, "delete.end",
                system_metadata=system_meta)

        self._clean_instance_console_tokens(context, instance)
        self._delete_scheduler_instance_info(context, instance.uuid)

    def _create_reservations(self, context, instance, project_id, user_id):
        vcpus = instance.vcpus
        mem_mb = instance.memory_mb

        quotas = objects.Quotas(context=context)
        quotas.reserve(project_id=project_id,
                       user_id=user_id,
                       instances=-1,
                       cores=-vcpus,
                       ram=-mem_mb)
        return quotas

    def _init_instance(self, context, instance):
        '''Initialize this instance during service init.'''

        # NOTE(danms): If the instance appears to not be owned by this
        # host, it may have been evacuated away, but skipped by the
        # evacuation cleanup code due to configuration. Thus, if that
        # is a possibility, don't touch the instance in any way, but
        # log the concern. This will help avoid potential issues on
        # startup due to misconfiguration.
        if instance.host != self.host:
            LOG.warning(_LW('Instance %(uuid)s appears to not be owned '
                            'by this host, but by %(host)s. Startup '
                            'processing is being skipped.'),
                        {'uuid': instance.uuid,
                         'host': instance.host})
            return

        # Instances that are shut down, or in an error state can not be
        # initialized and are not attempted to be recovered. The exception
        # to this are instances that are in RESIZE_MIGRATING or DELETING,
        # which are dealt with further down.
        if (instance.vm_state == vm_states.SOFT_DELETED or
            (instance.vm_state == vm_states.ERROR and
            instance.task_state not in
            (task_states.RESIZE_MIGRATING, task_states.DELETING))):
            LOG.debug("Instance is in %s state.",
                      instance.vm_state, instance=instance)
            return

        if instance.vm_state == vm_states.DELETED:
            try:
                self._complete_partial_deletion(context, instance)
            except Exception:
                # we don't want that an exception blocks the init_host
                msg = _LE('Failed to complete a deletion')
                LOG.exception(msg, instance=instance)
            return

        if (instance.vm_state == vm_states.BUILDING or
            instance.task_state in [task_states.SCHEDULING,
                                    task_states.BLOCK_DEVICE_MAPPING,
                                    task_states.NETWORKING,
                                    task_states.SPAWNING]):
            # NOTE(dave-mcnally) compute stopped before instance was fully
            # spawned so set to ERROR state. This is safe to do as the state
            # may be set by the api but the host is not so if we get here the
            # instance has already been scheduled to this particular host.
            LOG.debug("Instance failed to spawn correctly, "
                      "setting to ERROR state", instance=instance)
            instance.task_state = None
            instance.vm_state = vm_states.ERROR
            instance.save()
            return

        if (instance.vm_state in [vm_states.ACTIVE, vm_states.STOPPED] and
            instance.task_state in [task_states.REBUILDING,
                                    task_states.REBUILD_BLOCK_DEVICE_MAPPING,
                                    task_states.REBUILD_SPAWNING]):
            # NOTE(jichenjc) compute stopped before instance was fully
            # spawned so set to ERROR state. This is consistent to BUILD
            LOG.debug("Instance failed to rebuild correctly, "
                      "setting to ERROR state", instance=instance)
            instance.task_state = None
            instance.vm_state = vm_states.ERROR
            instance.save()
            return

        if (instance.vm_state != vm_states.ERROR and
            instance.task_state in [task_states.IMAGE_SNAPSHOT_PENDING,
                                    task_states.IMAGE_PENDING_UPLOAD,
                                    task_states.IMAGE_UPLOADING,
                                    task_states.IMAGE_SNAPSHOT]):
            LOG.debug("Instance in transitional state %s at start-up "
                      "clearing task state",
                      instance.task_state, instance=instance)
            try:
                self._post_interrupted_snapshot_cleanup(context, instance)
            except Exception:
                # we don't want that an exception blocks the init_host
                msg = _LE('Failed to cleanup snapshot.')
                LOG.exception(msg, instance=instance)
            instance.task_state = None
            instance.save()

        if (instance.vm_state != vm_states.ERROR and
            instance.task_state in [task_states.RESIZE_PREP]):
            LOG.debug("Instance in transitional state %s at start-up "
                      "clearing task state",
                      instance['task_state'], instance=instance)
            instance.task_state = None
            instance.save()

        if instance.task_state == task_states.DELETING:
            try:
                LOG.info(_LI('Service started deleting the instance during '
                             'the previous run, but did not finish. Restarting'
                             ' the deletion now.'), instance=instance)
                instance.obj_load_attr('metadata')
                instance.obj_load_attr('system_metadata')
                bdms = objects.BlockDeviceMappingList.get_by_instance_uuid(
                        context, instance.uuid)
                project_id, user_id = objects.quotas.ids_from_instance(
                    context, instance)
                quotas = self._create_reservations(context, instance,
                                                   project_id, user_id)

                self._delete_instance(context, instance, bdms, quotas)
            except Exception:
                # we don't want that an exception blocks the init_host
                msg = _LE('Failed to complete a deletion')
                LOG.exception(msg, instance=instance)
                self._set_instance_obj_error_state(context, instance)
            return

        try_reboot, reboot_type = self._retry_reboot(context, instance)
        current_power_state = self._get_power_state(context, instance)

        if try_reboot:
            LOG.debug("Instance in transitional state (%(task_state)s) at "
                      "start-up and power state is (%(power_state)s), "
                      "triggering reboot",
                      {'task_state': instance.task_state,
                       'power_state': current_power_state},
                      instance=instance)

            # NOTE(mikal): if the instance was doing a soft reboot that got as
            # far as shutting down the instance but not as far as starting it
            # again, then we've just become a hard reboot. That means the
            # task state for the instance needs to change so that we're in one
            # of the expected task states for a hard reboot.
            soft_types = [task_states.REBOOT_STARTED,
                          task_states.REBOOT_PENDING,
                          task_states.REBOOTING]
            if instance.task_state in soft_types and reboot_type == 'HARD':
                instance.task_state = task_states.REBOOT_PENDING_HARD

            self.reboot_instance(context, instance, block_device_info=None,
                                 reboot_type=reboot_type)
            return

        elif (current_power_state == power_state.RUNNING and
              instance.task_state in [task_states.REBOOT_STARTED,
                                      task_states.REBOOT_STARTED_HARD,
                                      task_states.PAUSING,
                                      task_states.UNPAUSING]):
            LOG.warning(_LW("Instance in transitional state "
                            "(%(task_state)s) at start-up and power state "
                            "is (%(power_state)s), clearing task state"),
                        {'task_state': instance.task_state,
                         'power_state': current_power_state},
                        instance=instance)
            instance.task_state = None
            instance.vm_state = vm_states.ACTIVE
            instance.save()
        elif (current_power_state == power_state.PAUSED and
              instance.task_state == task_states.UNPAUSING):
            LOG.warning(_LW("Instance in transitional state "
                            "(%(task_state)s) at start-up and power state "
                            "is (%(power_state)s), clearing task state "
                            "and unpausing the instance"),
                        {'task_state': instance.task_state,
                         'power_state': current_power_state},
                        instance=instance)
            try:
                self.unpause_instance(context, instance)
            except NotImplementedError:
                # Some virt driver didn't support pause and unpause
                pass
            except Exception:
                LOG.exception(_LE('Failed to unpause instance'),
                              instance=instance)
            return

        if instance.task_state == task_states.POWERING_OFF:
            try:
                LOG.debug("Instance in transitional state %s at start-up "
                          "retrying stop request",
                          instance.task_state, instance=instance)
                self.stop_instance(context, instance, True)
            except Exception:
                # we don't want that an exception blocks the init_host
                msg = _LE('Failed to stop instance')
                LOG.exception(msg, instance=instance)
            return

        if instance.task_state == task_states.POWERING_ON:
            try:
                LOG.debug("Instance in transitional state %s at start-up "
                          "retrying start request",
                          instance.task_state, instance=instance)
                self.start_instance(context, instance)
            except Exception:
                # we don't want that an exception blocks the init_host
                msg = _LE('Failed to start instance')
                LOG.exception(msg, instance=instance)
            return

        net_info = compute_utils.get_nw_info_for_instance(instance)
        try:
            self.driver.plug_vifs(instance, net_info)
        except NotImplementedError as e:
            LOG.debug(e, instance=instance)
        except exception.VirtualInterfacePlugException:
            # we don't want an exception to block the init_host
            LOG.exception(_LE("Vifs plug failed"), instance=instance)
            self._set_instance_obj_error_state(context, instance)
            return

        if instance.task_state == task_states.RESIZE_MIGRATING:
            # We crashed during resize/migration, so roll back for safety
            try:
                # NOTE(mriedem): check old_vm_state for STOPPED here, if it's
                # not in system_metadata we default to True for backwards
                # compatibility
                power_on = (instance.system_metadata.get('old_vm_state') !=
                            vm_states.STOPPED)

                block_dev_info = self._get_instance_block_device_info(context,
                                                                      instance)

                self.driver.finish_revert_migration(context,
                    instance, net_info, block_dev_info, power_on)

            except Exception:
                LOG.exception(_LE('Failed to revert crashed migration'),
                              instance=instance)
            finally:
                LOG.info(_LI('Instance found in migrating state during '
                             'startup. Resetting task_state'),
                         instance=instance)
                instance.task_state = None
                instance.save()
        if instance.task_state == task_states.MIGRATING:
            # Live migration did not complete, but instance is on this
            # host, so reset the state.
            instance.task_state = None
            instance.save(expected_task_state=[task_states.MIGRATING])

        db_state = instance.power_state
        drv_state = self._get_power_state(context, instance)
        expect_running = (db_state == power_state.RUNNING and
                          drv_state != db_state)

        LOG.debug('Current state is %(drv_state)s, state in DB is '
                  '%(db_state)s.',
                  {'drv_state': drv_state, 'db_state': db_state},
                  instance=instance)

        if expect_running and CONF.resume_guests_state_on_host_boot:
            LOG.info(_LI('Rebooting instance after nova-compute restart.'),
                     instance=instance)

            block_device_info = \
                self._get_instance_block_device_info(context, instance)

            try:
                self.driver.resume_state_on_host_boot(
                    context, instance, net_info, block_device_info)
            except NotImplementedError:
                LOG.warning(_LW('Hypervisor driver does not support '
                                'resume guests'), instance=instance)
            except Exception:
                # NOTE(vish): The instance failed to resume, so we set the
                #             instance to error and attempt to continue.
                LOG.warning(_LW('Failed to resume instance'),
                            instance=instance)
                self._set_instance_obj_error_state(context, instance)

        elif drv_state == power_state.RUNNING:
            # VMwareAPI drivers will raise an exception
            try:
                self.driver.ensure_filtering_rules_for_instance(
                                       instance, net_info)
            except NotImplementedError:
                LOG.warning(_LW('Hypervisor driver does not support '
                                'firewall rules'), instance=instance)

    def _retry_reboot(self, context, instance):
        current_power_state = self._get_power_state(context, instance)
        current_task_state = instance.task_state
        retry_reboot = False
        reboot_type = compute_utils.get_reboot_type(current_task_state,
                                                    current_power_state)

        pending_soft = (current_task_state == task_states.REBOOT_PENDING and
                        instance.vm_state in vm_states.ALLOW_SOFT_REBOOT)
        pending_hard = (current_task_state == task_states.REBOOT_PENDING_HARD
                        and instance.vm_state in vm_states.ALLOW_HARD_REBOOT)
        started_not_running = (current_task_state in
                               [task_states.REBOOT_STARTED,
                                task_states.REBOOT_STARTED_HARD] and
                               current_power_state != power_state.RUNNING)

        if pending_soft or pending_hard or started_not_running:
            retry_reboot = True

        return retry_reboot, reboot_type

    def handle_lifecycle_event(self, event):
        LOG.info(_LI("VM %(state)s (Lifecycle Event)"),
                 {'state': event.get_name()},
                 instance_uuid=event.get_instance_uuid())
        context = nova.context.get_admin_context(read_deleted='yes')
        instance = objects.Instance.get_by_uuid(context,
                                                event.get_instance_uuid(),
                                                expected_attrs=[])
        vm_power_state = None
        if event.get_transition() == virtevent.EVENT_LIFECYCLE_STOPPED:
            vm_power_state = power_state.SHUTDOWN
        elif event.get_transition() == virtevent.EVENT_LIFECYCLE_STARTED:
            vm_power_state = power_state.RUNNING
        elif event.get_transition() == virtevent.EVENT_LIFECYCLE_PAUSED:
            vm_power_state = power_state.PAUSED
        elif event.get_transition() == virtevent.EVENT_LIFECYCLE_RESUMED:
            vm_power_state = power_state.RUNNING
        elif event.get_transition() == virtevent.EVENT_LIFECYCLE_SUSPENDED:
            vm_power_state = power_state.SUSPENDED
        else:
            LOG.warning(_LW("Unexpected power state %d"),
                        event.get_transition())

        # Note(lpetrut): The event may be delayed, thus not reflecting
        # the current instance power state. In that case, ignore the event.
        current_power_state = self._get_power_state(context, instance)
        if current_power_state == vm_power_state:
            LOG.debug('Synchronizing instance power state after lifecycle '
                      'event "%(event)s"; current vm_state: %(vm_state)s, '
                      'current task_state: %(task_state)s, current DB '
                      'power_state: %(db_power_state)s, VM power_state: '
                      '%(vm_power_state)s',
                      {'event': event.get_name(),
                       'vm_state': instance.vm_state,
                       'task_state': instance.task_state,
                       'db_power_state': instance.power_state,
                       'vm_power_state': vm_power_state},
                      instance_uuid=instance.uuid)
            self._sync_instance_power_state(context,
                                            instance,
                                            vm_power_state)

    def handle_events(self, event):
        if isinstance(event, virtevent.LifecycleEvent):
            try:
                self.handle_lifecycle_event(event)
            except exception.InstanceNotFound:
                LOG.debug("Event %s arrived for non-existent instance. The "
                          "instance was probably deleted.", event)
        else:
            LOG.debug("Ignoring event %s", event)

    def init_virt_events(self):
        if CONF.workarounds.handle_virt_lifecycle_events:
            self.driver.register_event_listener(self.handle_events)
        else:
            # NOTE(mriedem): If the _sync_power_states periodic task is
            # disabled we should emit a warning in the logs.
            if CONF.sync_power_state_interval < 0:
                LOG.warn(_LW('Instance lifecycle events from the compute '
                             'driver have been disabled. Note that lifecycle '
                             'changes to an instance outside of the compute '
                             'service will not be synchronized '
                             'automatically since the _sync_power_states '
                             'periodic task is also disabled.'))
            else:
                LOG.info(_LI('Instance lifecycle events from the compute '
                             'driver have been disabled. Note that lifecycle '
                             'changes to an instance outside of the compute '
                             'service will only be synchronized by the '
                             '_sync_power_states periodic task.'))

    def init_host(self):
        """Initialization for a standalone compute service."""
        self.driver.init_host(host=self.host)
        context = nova.context.get_admin_context()
        instances = objects.InstanceList.get_by_host(
            context, self.host, expected_attrs=['info_cache', 'metadata'])

        if CONF.defer_iptables_apply:
            self.driver.filter_defer_apply_on()

        self.init_virt_events()

        try:
            # checking that instance was not already evacuated to other host
            self._destroy_evacuated_instances(context)
            for instance in instances:
                self._init_instance(context, instance)
        finally:
            if CONF.defer_iptables_apply:
                self.driver.filter_defer_apply_off()
            self._update_scheduler_instance_info(context, instances)

    def cleanup_host(self):
        self.driver.register_event_listener(None)
        self.instance_events.cancel_all_events()
        self.driver.cleanup_host(host=self.host)

    def pre_start_hook(self):
        """After the service is initialized, but before we fully bring
        the service up by listening on RPC queues, make sure to update
        our available resources (and indirectly our available nodes).
        """
        self.update_available_resource(nova.context.get_admin_context())

    def _get_power_state(self, context, instance):
        """Retrieve the power state for the given instance."""
        LOG.debug('Checking state', instance=instance)
        try:
            return self.driver.get_info(instance).state
        except exception.InstanceNotFound:
            return power_state.NOSTATE

    def get_console_topic(self, context):
        """Retrieves the console host for a project on this host.

        Currently this is just set in the flags for each compute host.

        """
        # TODO(mdragon): perhaps make this variable by console_type?
        return '%s.%s' % (CONF.console_topic, CONF.console_host)

    @wrap_exception()
    def get_console_pool_info(self, context, console_type):
        return self.driver.get_console_pool_info(console_type)

    @wrap_exception()
    def refresh_security_group_rules(self, context, security_group_id):
        """Tell the virtualization driver to refresh security group rules.

        Passes straight through to the virtualization driver.

        """
        return self.driver.refresh_security_group_rules(security_group_id)

    @wrap_exception()
    def refresh_security_group_members(self, context, security_group_id):
        """Tell the virtualization driver to refresh security group members.

        Passes straight through to the virtualization driver.

        """
        return self.driver.refresh_security_group_members(security_group_id)

    @object_compat
    @wrap_exception()
    def refresh_instance_security_rules(self, context, instance):
        """Tell the virtualization driver to refresh security rules for
        an instance.

        Passes straight through to the virtualization driver.

        Synchronise the call because we may still be in the middle of
        creating the instance.
        """
        @utils.synchronized(instance.uuid)
        def _sync_refresh():
            try:
                return self.driver.refresh_instance_security_rules(instance)
            except NotImplementedError:
                LOG.warning(_LW('Hypervisor driver does not support '
                                'security groups.'), instance=instance)

        return _sync_refresh()

    @wrap_exception()
    def refresh_provider_fw_rules(self, context):
        """This call passes straight through to the virtualization driver."""
        return self.driver.refresh_provider_fw_rules()

    def _await_block_device_map_created(self, context, vol_id):
        # TODO(yamahata): creating volume simultaneously
        #                 reduces creation time?
        # TODO(yamahata): eliminate dumb polling
        start = time.time()
        retries = CONF.block_device_allocate_retries
        if retries < 0:
            LOG.warning(_LW("Treating negative config value (%(retries)s) for "
                            "'block_device_retries' as 0."),
                        {'retries': retries})
        # (1) treat  negative config value as 0
        # (2) the configured value is 0, one attempt should be made
        # (3) the configured value is > 0, then the total number attempts
        #      is (retries + 1)
        attempts = 1
        if retries >= 1:
            attempts = retries + 1
        for attempt in range(1, attempts + 1):
            volume = self.volume_api.get(context, vol_id)
            volume_status = volume['status']
            if volume_status not in ['creating', 'downloading']:
                if volume_status == 'available':
                    return attempt
                LOG.warning(_LW("Volume id: %(vol_id)s finished being "
                                "created but its status is %(vol_status)s."),
                            {'vol_id': vol_id,
                             'vol_status': volume_status})
                break
            greenthread.sleep(CONF.block_device_allocate_retries_interval)
        raise exception.VolumeNotCreated(volume_id=vol_id,
                                         seconds=int(time.time() - start),
                                         attempts=attempt,
                                         volume_status=volume_status)

    def _decode_files(self, injected_files):
        """Base64 decode the list of files to inject."""
        if not injected_files:
            return []

        def _decode(f):
            path, contents = f
            try:
                decoded = base64.b64decode(contents)
                return path, decoded
            except TypeError:
                raise exception.Base64Exception(path=path)

        return [_decode(f) for f in injected_files]

    def _validate_instance_group_policy(self, context, instance,
            filter_properties):
        # NOTE(russellb) Instance group policy is enforced by the scheduler.
        # However, there is a race condition with the enforcement of
        # the policy.  Since more than one instance may be scheduled at the
        # same time, it's possible that more than one instance with an
        # anti-affinity policy may end up here.  It's also possible that
        # multiple instances with an affinity policy could end up on different
        # hosts.  This is a validation step to make sure that starting the
        # instance here doesn't violate the policy.

        scheduler_hints = filter_properties.get('scheduler_hints') or {}
        group_hint = scheduler_hints.get('group')
        if not group_hint:
            return

        @utils.synchronized(group_hint)
        def _do_validation(context, instance, group_hint):
            group = objects.InstanceGroup.get_by_hint(context, group_hint)
            if 'anti-affinity' in group.policies:
                group_hosts = group.get_hosts(exclude=[instance.uuid])
                if self.host in group_hosts:
                    msg = _("Anti-affinity instance group policy "
                            "was violated.")
                    raise exception.RescheduledException(
                            instance_uuid=instance.uuid,
                            reason=msg)
            elif 'affinity' in group.policies:
                group_hosts = group.get_hosts(exclude=[instance.uuid])
                if group_hosts and self.host not in group_hosts:
                    msg = _("Affinity instance group policy was violated.")
                    raise exception.RescheduledException(
                            instance_uuid=instance.uuid,
                            reason=msg)

        _do_validation(context, instance, group_hint)

    def _log_original_error(self, exc_info, instance_uuid):
        LOG.error(_LE('Error: %s'), exc_info[1], instance_uuid=instance_uuid,
                  exc_info=exc_info)

    def _reschedule(self, context, request_spec, filter_properties,
            instance, reschedule_method, method_args, task_state,
            exc_info=None):
        """Attempt to re-schedule a compute operation."""

        instance_uuid = instance.uuid
        retry = filter_properties.get('retry')
        if not retry:
            # no retry information, do not reschedule.
            LOG.debug("Retry info not present, will not reschedule",
                      instance_uuid=instance_uuid)
            return

        if not request_spec:
            LOG.debug("No request spec, will not reschedule",
                      instance_uuid=instance_uuid)
            return

        LOG.debug("Re-scheduling %(method)s: attempt %(num)d",
                  {'method': reschedule_method.func_name,
                   'num': retry['num_attempts']}, instance_uuid=instance_uuid)

        # reset the task state:
        self._instance_update(context, instance, task_state=task_state)

        if exc_info:
            # stringify to avoid circular ref problem in json serialization:
            retry['exc'] = traceback.format_exception_only(exc_info[0],
                                    exc_info[1])

        reschedule_method(context, *method_args)
        return True

    @periodic_task.periodic_task
    def _check_instance_build_time(self, context):
        """Ensure that instances are not stuck in build."""
        timeout = CONF.instance_build_timeout
        if timeout == 0:
            return

        filters = {'vm_state': vm_states.BUILDING,
                   'host': self.host}

        building_insts = objects.InstanceList.get_by_filters(context,
                           filters, expected_attrs=[], use_slave=True)

        for instance in building_insts:
            if timeutils.is_older_than(instance.created_at, timeout):
                self._set_instance_obj_error_state(context, instance)
                LOG.warning(_LW("Instance build timed out. Set to error "
                                "state."), instance=instance)

    def _check_instance_exists(self, context, instance):
        """Ensure an instance with the same name is not already present."""
        if self.driver.instance_exists(instance):
            raise exception.InstanceExists(name=instance.name)

    def _allocate_network_async(self, context, instance, requested_networks,
                                macs, security_groups, is_vpn, dhcp_options):
        """Method used to allocate networks in the background.

        Broken out for testing.
        """
        LOG.debug("Allocating IP information in the background.",
                  instance=instance)
        retries = CONF.network_allocate_retries
        if retries < 0:
            LOG.warning(_LW("Treating negative config value (%(retries)s) for "
                            "'network_allocate_retries' as 0."),
                        {'retries': retries})
            retries = 0
        attempts = retries + 1
        retry_time = 1
        for attempt in range(1, attempts + 1):
            try:
                nwinfo = self.network_api.allocate_for_instance(
                        context, instance, vpn=is_vpn,
                        requested_networks=requested_networks,
                        macs=macs,
                        security_groups=security_groups,
                        dhcp_options=dhcp_options)
                LOG.debug('Instance network_info: |%s|', nwinfo,
                          instance=instance)
                instance.system_metadata['network_allocated'] = 'True'
                # NOTE(JoshNang) do not save the instance here, as it can cause
                # races. The caller shares a reference to instance and waits
                # for this async greenthread to finish before calling
                # instance.save().
                return nwinfo
            except Exception:
                exc_info = sys.exc_info()
                log_info = {'attempt': attempt,
                            'attempts': attempts}
                if attempt == attempts:
                    LOG.exception(_LE('Instance failed network setup '
                                      'after %(attempts)d attempt(s)'),
                                  log_info)
                    six.reraise(*exc_info)
                LOG.warning(_LW('Instance failed network setup '
                                '(attempt %(attempt)d of %(attempts)d)'),
                            log_info, instance=instance)
                time.sleep(retry_time)
                retry_time *= 2
                if retry_time > 30:
                    retry_time = 30
        # Not reached.

    def _build_networks_for_instance(self, context, instance,
            requested_networks, security_groups):

        # If we're here from a reschedule the network may already be allocated.
        if strutils.bool_from_string(
                instance.system_metadata.get('network_allocated', 'False')):
            # NOTE(alex_xu): The network_allocated is True means the network
            # resource already allocated at previous scheduling, and the
            # network setup is cleanup at previous. After rescheduling, the
            # network resource need setup on the new host.
            self.network_api.setup_instance_network_on_host(
                context, instance, instance.host)
            return self.network_api.get_instance_nw_info(context, instance)

        if not self.is_neutron_security_groups:
            security_groups = []

        macs = self.driver.macs_for_instance(instance)
        dhcp_options = self.driver.dhcp_options_for_instance(instance)
        network_info = self._allocate_network(context, instance,
                requested_networks, macs, security_groups, dhcp_options)

        return network_info

    def _allocate_network(self, context, instance, requested_networks, macs,
                          security_groups, dhcp_options):
        """Start network allocation asynchronously.  Return an instance
        of NetworkInfoAsyncWrapper that can be used to retrieve the
        allocated networks when the operation has finished.
        """
        # NOTE(comstud): Since we're allocating networks asynchronously,
        # this task state has little meaning, as we won't be in this
        # state for very long.
        instance.vm_state = vm_states.BUILDING
        instance.task_state = task_states.NETWORKING
        instance.save(expected_task_state=[None])
        self._update_resource_tracker(context, instance)

        is_vpn = pipelib.is_vpn_image(instance.image_ref)
        return network_model.NetworkInfoAsyncWrapper(
                self._allocate_network_async, context, instance,
                requested_networks, macs, security_groups, is_vpn,
                dhcp_options)

    def _default_root_device_name(self, instance, image_meta, root_bdm):
        try:
            return self.driver.default_root_device_name(instance,
                                                        image_meta,
                                                        root_bdm)
        except NotImplementedError:
            return compute_utils.get_next_device_name(instance, [])

    def _default_device_names_for_instance(self, instance,
                                           root_device_name,
                                           *block_device_lists):
        try:
            self.driver.default_device_names_for_instance(instance,
                                                          root_device_name,
                                                          *block_device_lists)
        except NotImplementedError:
            compute_utils.default_device_names_for_instance(
                instance, root_device_name, *block_device_lists)

    def _get_device_name_for_instance(self, instance, bdms, block_device_obj):
        # NOTE(ndipanov): Copy obj to avoid changing the original
        block_device_obj = block_device_obj.obj_clone()
        try:
            return self.driver.get_device_name_for_instance(
                instance, bdms, block_device_obj)
        except NotImplementedError:
            return compute_utils.get_device_name_for_instance(
                instance, bdms, block_device_obj.get("device_name"))

    def _default_block_device_names(self, context, instance,
                                    image_meta, block_devices):
        """Verify that all the devices have the device_name set. If not,
        provide a default name.

        It also ensures that there is a root_device_name and is set to the
        first block device in the boot sequence (boot_index=0).
        """
        root_bdm = block_device.get_root_bdm(block_devices)
        if not root_bdm:
            return

        # Get the root_device_name from the root BDM or the instance
        root_device_name = None
        update_root_bdm = False

        if root_bdm.device_name:
            root_device_name = root_bdm.device_name
            instance.root_device_name = root_device_name
        elif instance.root_device_name:
            root_device_name = instance.root_device_name
            root_bdm.device_name = root_device_name
            update_root_bdm = True
        else:
            root_device_name = self._default_root_device_name(instance,
                                                              image_meta,
                                                              root_bdm)

            instance.root_device_name = root_device_name
            root_bdm.device_name = root_device_name
            update_root_bdm = True

        if update_root_bdm:
            root_bdm.save()

        ephemerals = filter(block_device.new_format_is_ephemeral,
                            block_devices)
        swap = filter(block_device.new_format_is_swap,
                      block_devices)
        block_device_mapping = filter(
              driver_block_device.is_block_device_mapping, block_devices)

        self._default_device_names_for_instance(instance,
                                                root_device_name,
                                                ephemerals,
                                                swap,
                                                block_device_mapping)

    def _block_device_info_to_legacy(self, block_device_info):
        """Convert BDI to the old format for drivers that need it."""

        if self.use_legacy_block_device_info:
            ephemerals = driver_block_device.legacy_block_devices(
                driver.block_device_info_get_ephemerals(block_device_info))
            mapping = driver_block_device.legacy_block_devices(
                driver.block_device_info_get_mapping(block_device_info))
            swap = block_device_info['swap']
            if swap:
                swap = swap.legacy()

            block_device_info.update({
                'ephemerals': ephemerals,
                'swap': swap,
                'block_device_mapping': mapping})

    def _prep_block_device(self, context, instance, bdms,
                           do_check_attach=True):
        """Set up the block device for an instance with error logging."""
        try:
            block_device_info = driver.get_block_device_info(instance, bdms)
            mapping = driver.block_device_info_get_mapping(block_device_info)
            driver_block_device.attach_block_devices(
                mapping, context, instance, self.volume_api, self.driver,
                do_check_attach=do_check_attach,
                wait_func=self._await_block_device_map_created)

            self._block_device_info_to_legacy(block_device_info)
            return block_device_info

        except exception.OverQuota:
            msg = _LW('Failed to create block device for instance due to '
                      'being over volume resource quota')
            LOG.warn(msg, instance=instance)
            raise exception.VolumeLimitExceeded()

        except Exception:
            LOG.exception(_LE('Instance failed block device setup'),
                          instance=instance)
            raise exception.InvalidBDM()

    def _update_instance_after_spawn(self, context, instance):
        instance.power_state = self._get_power_state(context, instance)
        instance.vm_state = vm_states.ACTIVE
        instance.task_state = None
        instance.launched_at = timeutils.utcnow()
        configdrive.update_instance(instance)

    def _update_scheduler_instance_info(self, context, instance):
        """Sends an InstanceList with created or updated Instance objects to
        the Scheduler client.

        In the case of init_host, the value passed will already be an
        InstanceList. Other calls will send individual Instance objects that
        have been created or resized. In this case, we create an InstanceList
        object containing that Instance.
        """
        if not self.send_instance_updates:
            return
        if isinstance(instance, objects.Instance):
            instance = objects.InstanceList(objects=[instance])
        context = context.elevated()
        self.scheduler_client.update_instance_info(context, self.host,
                                                   instance)

    def _delete_scheduler_instance_info(self, context, instance_uuid):
        """Sends the uuid of the deleted Instance to the Scheduler client."""
        if not self.send_instance_updates:
            return
        context = context.elevated()
        self.scheduler_client.delete_instance_info(context, self.host,
                                                   instance_uuid)

    @periodic_task.periodic_task(spacing=CONF.scheduler_instance_sync_interval)
    def _sync_scheduler_instance_info(self, context):
        if not self.send_instance_updates:
            return
        context = context.elevated()
        instances = objects.InstanceList.get_by_host(context, self.host,
                                                     expected_attrs=[],
                                                     use_slave=True)
        uuids = [instance.uuid for instance in instances]
        self.scheduler_client.sync_instance_info(context, self.host, uuids)

    def _notify_about_instance_usage(self, context, instance, event_suffix,
                                     network_info=None, system_metadata=None,
                                     extra_usage_info=None, fault=None):
        compute_utils.notify_about_instance_usage(
            self.notifier, context, instance, event_suffix,
            network_info=network_info,
            system_metadata=system_metadata,
            extra_usage_info=extra_usage_info, fault=fault)

    def _deallocate_network(self, context, instance,
                            requested_networks=None):
        LOG.debug('Deallocating network for instance', instance=instance)
        self.network_api.deallocate_for_instance(
            context, instance, requested_networks=requested_networks)

    def _get_instance_block_device_info(self, context, instance,
                                        refresh_conn_info=False,
                                        bdms=None):
        """Transform block devices to the driver block_device format."""

        if not bdms:
            bdms = objects.BlockDeviceMappingList.get_by_instance_uuid(
                    context, instance.uuid)
        block_device_info = driver.get_block_device_info(instance, bdms)

        if not refresh_conn_info:
            # if the block_device_mapping has no value in connection_info
            # (returned as None), don't include in the mapping
            block_device_info['block_device_mapping'] = [
                bdm for bdm in driver.block_device_info_get_mapping(
                                    block_device_info)
                if bdm.get('connection_info')]
        else:
            driver_block_device.refresh_conn_infos(
                driver.block_device_info_get_mapping(block_device_info),
                context, instance, self.volume_api, self.driver)

        self._block_device_info_to_legacy(block_device_info)

        return block_device_info

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_fault
    def build_and_run_instance(self, context, instance, image, request_spec,
                     filter_properties, admin_password=None,
                     injected_files=None, requested_networks=None,
                     security_groups=None, block_device_mapping=None,
                     node=None, limits=None):

        @utils.synchronized(instance.uuid)
        def _locked_do_build_and_run_instance(*args, **kwargs):
            # NOTE(danms): We grab the semaphore with the instance uuid
            # locked because we could wait in line to build this instance
            # for a while and we want to make sure that nothing else tries
            # to do anything with this instance while we wait.
            with self._build_semaphore:
                self._do_build_and_run_instance(*args, **kwargs)

        # NOTE(danms): We spawn here to return the RPC worker thread back to
        # the pool. Since what follows could take a really long time, we don't
        # want to tie up RPC workers.
        utils.spawn_n(_locked_do_build_and_run_instance,
                      context, instance, image, request_spec,
                      filter_properties, admin_password, injected_files,
                      requested_networks, security_groups,
                      block_device_mapping, node, limits)

    @hooks.add_hook('build_instance')
    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @wrap_instance_fault
    def _do_build_and_run_instance(self, context, instance, image,
            request_spec, filter_properties, admin_password, injected_files,
            requested_networks, security_groups, block_device_mapping,
            node=None, limits=None):

        try:
            LOG.info(_LI('Starting instance...'), context=context,
                  instance=instance)
            instance.vm_state = vm_states.BUILDING
            instance.task_state = None
            instance.save(expected_task_state=
                    (task_states.SCHEDULING, None))
        except exception.InstanceNotFound:
            msg = 'Instance disappeared before build.'
            LOG.debug(msg, instance=instance)
            return build_results.FAILED
        except exception.UnexpectedTaskStateError as e:
            LOG.debug(e.format_message(), instance=instance)
            return build_results.FAILED

        # b64 decode the files to inject:
        decoded_files = self._decode_files(injected_files)

        if limits is None:
            limits = {}

        if node is None:
            node = self.driver.get_available_nodes(refresh=True)[0]
            LOG.debug('No node specified, defaulting to %s', node,
                      instance=instance)

        try:
            self._build_and_run_instance(context, instance, image,
                    decoded_files, admin_password, requested_networks,
                    security_groups, block_device_mapping, node, limits,
                    filter_properties)
            return build_results.ACTIVE
        except exception.RescheduledException as e:
            retry = filter_properties.get('retry')
            if not retry:
                # no retry information, do not reschedule.
                LOG.debug("Retry info not present, will not reschedule",
                    instance=instance)
                self._cleanup_allocated_networks(context, instance,
                    requested_networks)
                compute_utils.add_instance_fault_from_exc(context,
                        instance, e, sys.exc_info())
                self._nil_out_instance_obj_host_and_node(instance)
                self._set_instance_obj_error_state(context, instance,
                                                   clean_task_state=True)
                return build_results.FAILED
            LOG.debug(e.format_message(), instance=instance)
            retry['exc'] = traceback.format_exception(*sys.exc_info())
            # NOTE(comstud): Deallocate networks if the driver wants
            # us to do so.
            if self.driver.deallocate_networks_on_reschedule(instance):
                self._cleanup_allocated_networks(context, instance,
                        requested_networks)
            else:
                # NOTE(alex_xu): Network already allocated and we don't
                # want to deallocate them before rescheduling. But we need
                # to cleanup those network resources setup on this host before
                # rescheduling.
                self.network_api.cleanup_instance_network_on_host(
                    context, instance, self.host)

            self._nil_out_instance_obj_host_and_node(instance)
            instance.task_state = task_states.SCHEDULING
            instance.save()

            self.compute_task_api.build_instances(context, [instance],
                    image, filter_properties, admin_password,
                    injected_files, requested_networks, security_groups,
                    block_device_mapping)
            return build_results.RESCHEDULED
        except (exception.InstanceNotFound,
                exception.UnexpectedDeletingTaskStateError):
            msg = 'Instance disappeared during build.'
            LOG.debug(msg, instance=instance)
            self._cleanup_allocated_networks(context, instance,
                    requested_networks)
            return build_results.FAILED
        except exception.BuildAbortException as e:
            LOG.exception(e.format_message(), instance=instance)
            self._cleanup_allocated_networks(context, instance,
                    requested_networks)
            self._cleanup_volumes(context, instance.uuid,
                    block_device_mapping, raise_exc=False)
            compute_utils.add_instance_fault_from_exc(context, instance,
                    e, sys.exc_info())
            self._nil_out_instance_obj_host_and_node(instance)
            self._set_instance_obj_error_state(context, instance,
                                               clean_task_state=True)
            return build_results.FAILED
        except Exception as e:
            # Should not reach here.
            msg = _LE('Unexpected build failure, not rescheduling build.')
            LOG.exception(msg, instance=instance)
            self._cleanup_allocated_networks(context, instance,
                    requested_networks)
            self._cleanup_volumes(context, instance.uuid,
                    block_device_mapping, raise_exc=False)
            compute_utils.add_instance_fault_from_exc(context, instance,
                    e, sys.exc_info())
            self._nil_out_instance_obj_host_and_node(instance)
            self._set_instance_obj_error_state(context, instance,
                                               clean_task_state=True)
            return build_results.FAILED

    def _build_and_run_instance(self, context, instance, image, injected_files,
            admin_password, requested_networks, security_groups,
            block_device_mapping, node, limits, filter_properties):

        image_name = image.get('name')
        self._notify_about_instance_usage(context, instance, 'create.start',
                extra_usage_info={'image_name': image_name})
        try:
            rt = self._get_resource_tracker(node)
            with rt.instance_claim(context, instance, limits):
                # NOTE(russellb) It's important that this validation be done
                # *after* the resource tracker instance claim, as that is where
                # the host is set on the instance.
                self._validate_instance_group_policy(context, instance,
                        filter_properties)
                with self._build_resources(context, instance,
                        requested_networks, security_groups, image,
                        block_device_mapping) as resources:
                    instance.vm_state = vm_states.BUILDING
                    instance.task_state = task_states.SPAWNING
                    # NOTE(JoshNang) This also saves the changes to the
                    # instance from _allocate_network_async, as they aren't
                    # saved in that function to prevent races.
                    instance.save(expected_task_state=
                            task_states.BLOCK_DEVICE_MAPPING)
                    block_device_info = resources['block_device_info']
                    network_info = resources['network_info']
                    self.driver.spawn(context, instance, image,
                                      injected_files, admin_password,
                                      network_info=network_info,
                                      block_device_info=block_device_info)
        except (exception.InstanceNotFound,
                exception.UnexpectedDeletingTaskStateError) as e:
            with excutils.save_and_reraise_exception():
                self._notify_about_instance_usage(context, instance,
                    'create.end', fault=e)
        except exception.ComputeResourcesUnavailable as e:
            LOG.debug(e.format_message(), instance=instance)
            self._notify_about_instance_usage(context, instance,
                    'create.error', fault=e)
            raise exception.RescheduledException(
                    instance_uuid=instance.uuid, reason=e.format_message())
        except exception.BuildAbortException as e:
            with excutils.save_and_reraise_exception():
                LOG.debug(e.format_message(), instance=instance)
                self._notify_about_instance_usage(context, instance,
                    'create.error', fault=e)
        except (exception.FixedIpLimitExceeded,
                exception.NoMoreNetworks, exception.NoMoreFixedIps) as e:
            LOG.warning(_LW('No more network or fixed IP to be allocated'),
                        instance=instance)
            self._notify_about_instance_usage(context, instance,
                    'create.error', fault=e)
            msg = _('Failed to allocate the network(s) with error %s, '
                    'not rescheduling.') % e.format_message()
            raise exception.BuildAbortException(instance_uuid=instance.uuid,
                    reason=msg)
        except (exception.VirtualInterfaceCreateException,
                exception.VirtualInterfaceMacAddressException) as e:
            LOG.exception(_LE('Failed to allocate network(s)'),
                          instance=instance)
            self._notify_about_instance_usage(context, instance,
                    'create.error', fault=e)
            msg = _('Failed to allocate the network(s), not rescheduling.')
            raise exception.BuildAbortException(instance_uuid=instance.uuid,
                    reason=msg)
        except (exception.FlavorDiskTooSmall,
                exception.FlavorMemoryTooSmall,
                exception.ImageNotActive,
                exception.ImageUnacceptable) as e:
            self._notify_about_instance_usage(context, instance,
                    'create.error', fault=e)
            raise exception.BuildAbortException(instance_uuid=instance.uuid,
                    reason=e.format_message())
        except Exception as e:
            self._notify_about_instance_usage(context, instance,
                    'create.error', fault=e)
            raise exception.RescheduledException(
                    instance_uuid=instance.uuid, reason=six.text_type(e))

        # NOTE(alaski): This is only useful during reschedules, remove it now.
        instance.system_metadata.pop('network_allocated', None)

        # If CONF.default_access_ip_network_name is set, grab the
        # corresponding network and set the access ip values accordingly.
        network_name = CONF.default_access_ip_network_name
        if (network_name and not instance.access_ip_v4 and
                not instance.access_ip_v6):
            # Note that when there are multiple ips to choose from, an
            # arbitrary one will be chosen.
            for vif in network_info:
                if vif['network']['label'] == network_name:
                    for ip in vif.fixed_ips():
                        if not instance.access_ip_v4 and ip['version'] == 4:
                            instance.access_ip_v4 = ip['address']
                        if not instance.access_ip_v6 and ip['version'] == 6:
                            instance.access_ip_v6 = ip['address']
                    break

        self._update_instance_after_spawn(context, instance)

        try:
            instance.save(expected_task_state=task_states.SPAWNING)
        except (exception.InstanceNotFound,
                exception.UnexpectedDeletingTaskStateError) as e:
            with excutils.save_and_reraise_exception():
                self._notify_about_instance_usage(context, instance,
                    'create.end', fault=e)

        self._update_scheduler_instance_info(context, instance)
        self._notify_about_instance_usage(context, instance, 'create.end',
                extra_usage_info={'message': _('Success')},
                network_info=network_info)

    @contextlib.contextmanager
    def _build_resources(self, context, instance, requested_networks,
            security_groups, image, block_device_mapping):
        resources = {}
        network_info = None
        try:
            network_info = self._build_networks_for_instance(context, instance,
                    requested_networks, security_groups)
            resources['network_info'] = network_info
        except (exception.InstanceNotFound,
                exception.UnexpectedDeletingTaskStateError):
            raise
        except exception.UnexpectedTaskStateError as e:
            raise exception.BuildAbortException(instance_uuid=instance.uuid,
                    reason=e.format_message())
        except Exception:
            # Because this allocation is async any failures are likely to occur
            # when the driver accesses network_info during spawn().
            LOG.exception(_LE('Failed to allocate network(s)'),
                          instance=instance)
            msg = _('Failed to allocate the network(s), not rescheduling.')
            raise exception.BuildAbortException(instance_uuid=instance.uuid,
                    reason=msg)

        try:
            # Verify that all the BDMs have a device_name set and assign a
            # default to the ones missing it with the help of the driver.
            self._default_block_device_names(context, instance, image,
                    block_device_mapping)

            instance.vm_state = vm_states.BUILDING
            instance.task_state = task_states.BLOCK_DEVICE_MAPPING
            instance.save()

            block_device_info = self._prep_block_device(context, instance,
                    block_device_mapping)
            resources['block_device_info'] = block_device_info
        except (exception.InstanceNotFound,
                exception.UnexpectedDeletingTaskStateError):
            with excutils.save_and_reraise_exception():
                # Make sure the async call finishes
                if network_info is not None:
                    network_info.wait(do_raise=False)
        except (exception.UnexpectedTaskStateError,
                exception.VolumeLimitExceeded,
                exception.InvalidBDM) as e:
            # Make sure the async call finishes
            if network_info is not None:
                network_info.wait(do_raise=False)
            raise exception.BuildAbortException(instance_uuid=instance.uuid,
                    reason=e.format_message())
        except Exception:
            LOG.exception(_LE('Failure prepping block device'),
                    instance=instance)
            # Make sure the async call finishes
            if network_info is not None:
                network_info.wait(do_raise=False)
            msg = _('Failure prepping block device.')
            raise exception.BuildAbortException(instance_uuid=instance.uuid,
                    reason=msg)

        try:
            yield resources
        except Exception as exc:
            with excutils.save_and_reraise_exception() as ctxt:
                if not isinstance(exc, (exception.InstanceNotFound,
                    exception.UnexpectedDeletingTaskStateError)):
                        LOG.exception(_LE('Instance failed to spawn'),
                                instance=instance)
                # Make sure the async call finishes
                if network_info is not None:
                    network_info.wait(do_raise=False)
                # if network_info is empty we're likely here because of
                # network allocation failure. Since nothing can be reused on
                # rescheduling it's better to deallocate network to eliminate
                # the chance of orphaned ports in neutron
                deallocate_networks = False if network_info else True
                try:
                    self._shutdown_instance(context, instance,
                            block_device_mapping, requested_networks,
                            try_deallocate_networks=deallocate_networks)
                except Exception:
                    ctxt.reraise = False
                    msg = _('Could not clean up failed build,'
                            ' not rescheduling')
                    raise exception.BuildAbortException(
                            instance_uuid=instance.uuid, reason=msg)

    def _cleanup_allocated_networks(self, context, instance,
            requested_networks):
        try:
            self._deallocate_network(context, instance, requested_networks)
        except Exception:
            msg = _LE('Failed to deallocate networks')
            LOG.exception(msg, instance=instance)
            return

        instance.system_metadata['network_allocated'] = 'False'
        try:
            instance.save()
        except exception.InstanceNotFound:
            # NOTE(alaski): It's possible that we're cleaning up the networks
            # because the instance was deleted.  If that's the case then this
            # exception will be raised by instance.save()
            pass

    def _try_deallocate_network(self, context, instance,
                                requested_networks=None):
        try:
            # tear down allocated network structure
            self._deallocate_network(context, instance, requested_networks)
        except Exception:
            with excutils.save_and_reraise_exception():
                LOG.error(_LE('Failed to deallocate network for instance.'),
                          instance=instance)
                self._set_instance_obj_error_state(context, instance)

    def _get_power_off_values(self, context, instance, clean_shutdown):
        """Get the timing configuration for powering down this instance."""
        if clean_shutdown:
            timeout = compute_utils.get_value_from_system_metadata(instance,
                          key='image_os_shutdown_timeout', type=int,
                          default=CONF.shutdown_timeout)
            retry_interval = self.SHUTDOWN_RETRY_INTERVAL
        else:
            timeout = 0
            retry_interval = 0

        return timeout, retry_interval

    def _power_off_instance(self, context, instance, clean_shutdown=True):
        """Power off an instance on this host."""
        timeout, retry_interval = self._get_power_off_values(context,
                                        instance, clean_shutdown)
        self.driver.power_off(instance, timeout, retry_interval)

    def _shutdown_instance(self, context, instance,
                           bdms, requested_networks=None, notify=True,
                           try_deallocate_networks=True):
        """Shutdown an instance on this host.

        :param:context: security context
        :param:instance: a nova.objects.Instance object
        :param:bdms: the block devices for the instance to be torn
                     down
        :param:requested_networks: the networks on which the instance
                                   has ports
        :param:notify: true if a final usage notification should be
                       emitted
        :param:try_deallocate_networks: false if we should avoid
                                        trying to teardown networking
        """
        context = context.elevated()
        LOG.info(_LI('%(action_str)s instance') %
                 {'action_str': 'Terminating'},
                  context=context, instance=instance)

        if notify:
            self._notify_about_instance_usage(context, instance,
                                              "shutdown.start")

        network_info = compute_utils.get_nw_info_for_instance(instance)

        # NOTE(vish) get bdms before destroying the instance
        vol_bdms = [bdm for bdm in bdms if bdm.is_volume]
        block_device_info = self._get_instance_block_device_info(
            context, instance, bdms=bdms)

        # NOTE(melwitt): attempt driver destroy before releasing ip, may
        #                want to keep ip allocated for certain failures
        try:
            self.driver.destroy(context, instance, network_info,
                    block_device_info)
        except exception.InstancePowerOffFailure:
            # if the instance can't power off, don't release the ip
            with excutils.save_and_reraise_exception():
                pass
        except Exception:
            with excutils.save_and_reraise_exception():
                # deallocate ip and fail without proceeding to
                # volume api calls, preserving current behavior
                if try_deallocate_networks:
                    self._try_deallocate_network(context, instance,
                                                 requested_networks)

        if try_deallocate_networks:
            self._try_deallocate_network(context, instance, requested_networks)

        for bdm in vol_bdms:
            try:
                # NOTE(vish): actual driver detach done in driver.destroy, so
                #             just tell cinder that we are done with it.
                connector = self.driver.get_volume_connector(instance)
                self.volume_api.terminate_connection(context,
                                                     bdm.volume_id,
                                                     connector)
                self.volume_api.detach(context, bdm.volume_id)
            except exception.DiskNotFound as exc:
                LOG.debug('Ignoring DiskNotFound: %s', exc,
                          instance=instance)
            except exception.VolumeNotFound as exc:
                LOG.debug('Ignoring VolumeNotFound: %s', exc,
                          instance=instance)
            except (cinder_exception.EndpointNotFound,
                    keystone_exception.EndpointNotFound) as exc:
                LOG.warning(_LW('Ignoring EndpointNotFound: %s'), exc,
                            instance=instance)
            except cinder_exception.ClientException as exc:
                LOG.warning(_LW('Ignoring Unknown cinder exception: %s'), exc,
                            instance=instance)

        if notify:
            self._notify_about_instance_usage(context, instance,
                                              "shutdown.end")

    def _cleanup_volumes(self, context, instance_uuid, bdms, raise_exc=True):
        exc_info = None

        for bdm in bdms:
            LOG.debug("terminating bdm %s", bdm,
                      instance_uuid=instance_uuid)
            if bdm.volume_id and bdm.delete_on_termination:
                try:
                    self.volume_api.delete(context, bdm.volume_id)
                except Exception as exc:
                    exc_info = sys.exc_info()
                    LOG.warning(_LW('Failed to delete volume: %(volume_id)s '
                                    'due to %(exc)s'),
                                {'volume_id': bdm.volume_id, 'exc': exc})
        if exc_info is not None and raise_exc:
            six.reraise(exc_info[0], exc_info[1], exc_info[2])

    @hooks.add_hook("delete_instance")
    def _delete_instance(self, context, instance, bdms, quotas):
        """Delete an instance on this host.  Commit or rollback quotas
        as necessary.

        :param context: nova request context
        :param instance: nova.objects.instance.Instance object
        :param bdms: nova.objects.block_device.BlockDeviceMappingList object
        :param quotas: nova.objects.quotas.Quotas object
        """
        was_soft_deleted = instance.vm_state == vm_states.SOFT_DELETED
        if was_soft_deleted:
            # Instances in SOFT_DELETED vm_state have already had quotas
            # decremented.
            try:
                quotas.rollback()
            except Exception:
                pass

        try:
            events = self.instance_events.clear_events_for_instance(instance)
            if events:
                LOG.debug('Events pending at deletion: %(events)s',
                          {'events': ','.join(events.keys())},
                          instance=instance)
            self._notify_about_instance_usage(context, instance,
                                              "delete.start")
            self._shutdown_instance(context, instance, bdms)
            # NOTE(dims): instance.info_cache.delete() should be called after
            # _shutdown_instance in the compute manager as shutdown calls
            # deallocate_for_instance so the info_cache is still needed
            # at this point.
            if instance.info_cache is not None:
                instance.info_cache.delete()
            else:
                # NOTE(yoshimatsu): Avoid AttributeError if instance.info_cache
                # is None. When the root cause that instance.info_cache becomes
                # None is fixed, the log level should be reconsidered.
                LOG.warning(_LW("Info cache for instance could not be found. "
                                "Ignore."), instance=instance)

            # NOTE(vish): We have already deleted the instance, so we have
            #             to ignore problems cleaning up the volumes. It
            #             would be nice to let the user know somehow that
            #             the volume deletion failed, but it is not
            #             acceptable to have an instance that can not be
            #             deleted. Perhaps this could be reworked in the
            #             future to set an instance fault the first time
            #             and to only ignore the failure if the instance
            #             is already in ERROR.
            self._cleanup_volumes(context, instance.uuid, bdms,
                    raise_exc=False)
            # if a delete task succeeded, always update vm state and task
            # state without expecting task state to be DELETING
            instance.vm_state = vm_states.DELETED
            instance.task_state = None
            instance.power_state = power_state.NOSTATE
            instance.terminated_at = timeutils.utcnow()
            instance.save()
            self._update_resource_tracker(context, instance)
            system_meta = instance.system_metadata
            instance.destroy()
        except Exception:
            with excutils.save_and_reraise_exception():
                quotas.rollback()

        self._complete_deletion(context,
                                instance,
                                bdms,
                                quotas,
                                system_meta)

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @wrap_instance_fault
    def terminate_instance(self, context, instance, bdms, reservations):
        """Terminate an instance on this host."""
        quotas = objects.Quotas.from_reservations(context,
                                                  reservations,
                                                  instance=instance)

        @utils.synchronized(instance.uuid)
        def do_terminate_instance(instance, bdms):
            try:
                self._delete_instance(context, instance, bdms, quotas)
            except exception.InstanceNotFound:
                LOG.info(_LI("Instance disappeared during terminate"),
                         instance=instance)
            except Exception:
                # As we're trying to delete always go to Error if something
                # goes wrong that _delete_instance can't handle.
                with excutils.save_and_reraise_exception():
                    LOG.exception(_LE('Setting instance vm_state to ERROR'),
                                  instance=instance)
                    self._set_instance_obj_error_state(context, instance)

        do_terminate_instance(instance, bdms)

    # NOTE(johannes): This is probably better named power_off_instance
    # so it matches the driver method, but because of other issues, we
    # can't use that name in grizzly.
    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @wrap_instance_fault
    def stop_instance(self, context, instance, clean_shutdown):
        """Stopping an instance on this host."""

        @utils.synchronized(instance.uuid)
        def do_stop_instance():
            current_power_state = self._get_power_state(context, instance)
            LOG.debug('Stopping instance; current vm_state: %(vm_state)s, '
                      'current task_state: %(task_state)s, current DB '
                      'power_state: %(db_power_state)s, current VM '
                      'power_state: %(current_power_state)s',
                      {'vm_state': instance.vm_state,
                       'task_state': instance.task_state,
                       'db_power_state': instance.power_state,
                       'current_power_state': current_power_state},
                      instance_uuid=instance.uuid)

            # NOTE(mriedem): If the instance is already powered off, we are
            # possibly tearing down and racing with other operations, so we can
            # expect the task_state to be None if something else updates the
            # instance and we're not locking it.
            expected_task_state = [task_states.POWERING_OFF]
            # The list of power states is from _sync_instance_power_state.
            if current_power_state in (power_state.NOSTATE,
                                       power_state.SHUTDOWN,
                                       power_state.CRASHED):
                LOG.info(_LI('Instance is already powered off in the '
                             'hypervisor when stop is called.'),
                         instance=instance)
                expected_task_state.append(None)

            self._notify_about_instance_usage(context, instance,
                                              "power_off.start")
            self._power_off_instance(context, instance, clean_shutdown)
            instance.power_state = self._get_power_state(context, instance)
            instance.vm_state = vm_states.STOPPED
            instance.task_state = None
            instance.save(expected_task_state=expected_task_state)
            self._notify_about_instance_usage(context, instance,
                                              "power_off.end")

        do_stop_instance()

    def _power_on(self, context, instance):
        network_info = self.network_api.get_instance_nw_info(context, instance)
        block_device_info = self._get_instance_block_device_info(context,
                                                                 instance)
        self.driver.power_on(context, instance,
                             network_info,
                             block_device_info)

    def _delete_snapshot_of_shelved_instance(self, context, instance,
                                             snapshot_id):
        """Delete snapshot of shelved instance."""
        try:
            self.image_api.delete(context, snapshot_id)
        except (exception.ImageNotFound,
                exception.ImageNotAuthorized) as exc:
            LOG.warning(_LW("Failed to delete snapshot "
                            "from shelved instance (%s)."),
                        exc.format_message(), instance=instance)
        except Exception:
            LOG.exception(_LE("Something wrong happened when trying to "
                              "delete snapshot from shelved instance."),
                          instance=instance)

    # NOTE(johannes): This is probably better named power_on_instance
    # so it matches the driver method, but because of other issues, we
    # can't use that name in grizzly.
    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @wrap_instance_fault
    def start_instance(self, context, instance):
        """Starting an instance on this host."""
        self._notify_about_instance_usage(context, instance, "power_on.start")
        self._power_on(context, instance)
        instance.power_state = self._get_power_state(context, instance)
        instance.vm_state = vm_states.ACTIVE
        instance.task_state = None

        # Delete an image(VM snapshot) for a shelved instance
        snapshot_id = instance.system_metadata.get('shelved_image_id')
        if snapshot_id:
            self._delete_snapshot_of_shelved_instance(context, instance,
                                                      snapshot_id)

        # Delete system_metadata for a shelved instance
        compute_utils.remove_shelved_keys_from_system_metadata(instance)

        instance.save(expected_task_state=task_states.POWERING_ON)
        self._notify_about_instance_usage(context, instance, "power_on.end")

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @wrap_instance_fault
    def soft_delete_instance(self, context, instance, reservations):
        """Soft delete an instance on this host."""

        quotas = objects.Quotas.from_reservations(context,
                                                  reservations,
                                                  instance=instance)
        try:
            self._notify_about_instance_usage(context, instance,
                                              "soft_delete.start")
            try:
                self.driver.soft_delete(instance)
            except NotImplementedError:
                # Fallback to just powering off the instance if the
                # hypervisor doesn't implement the soft_delete method
                self.driver.power_off(instance)
            instance.power_state = self._get_power_state(context, instance)
            instance.vm_state = vm_states.SOFT_DELETED
            instance.task_state = None
            instance.save(expected_task_state=[task_states.SOFT_DELETING])
        except Exception:
            with excutils.save_and_reraise_exception():
                quotas.rollback()
        quotas.commit()
        self._notify_about_instance_usage(context, instance, "soft_delete.end")

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @wrap_instance_fault
    def restore_instance(self, context, instance):
        """Restore a soft-deleted instance on this host."""
        self._notify_about_instance_usage(context, instance, "restore.start")
        try:
            self.driver.restore(instance)
        except NotImplementedError:
            # Fallback to just powering on the instance if the hypervisor
            # doesn't implement the restore method
            self._power_on(context, instance)
        instance.power_state = self._get_power_state(context, instance)
        instance.vm_state = vm_states.ACTIVE
        instance.task_state = None
        instance.save(expected_task_state=task_states.RESTORING)
        self._notify_about_instance_usage(context, instance, "restore.end")

    def _rebuild_default_impl(self, context, instance, image_meta,
                              injected_files, admin_password, bdms,
                              detach_block_devices, attach_block_devices,
                              network_info=None,
                              recreate=False, block_device_info=None,
                              preserve_ephemeral=False):
        if preserve_ephemeral:
            # The default code path does not support preserving ephemeral
            # partitions.
            raise exception.PreserveEphemeralNotSupported()

        if recreate:
            detach_block_devices(context, bdms)
        else:
            self._power_off_instance(context, instance, clean_shutdown=True)
            detach_block_devices(context, bdms)
            self.driver.destroy(context, instance,
                                network_info=network_info,
                                block_device_info=block_device_info)

        instance.task_state = task_states.REBUILD_BLOCK_DEVICE_MAPPING
        instance.save(expected_task_state=[task_states.REBUILDING])

        new_block_device_info = attach_block_devices(context, instance, bdms)

        instance.task_state = task_states.REBUILD_SPAWNING
        instance.save(
            expected_task_state=[task_states.REBUILD_BLOCK_DEVICE_MAPPING])

        self.driver.spawn(context, instance, image_meta, injected_files,
                          admin_password, network_info=network_info,
                          block_device_info=new_block_device_info)

    @messaging.expected_exceptions(exception.PreserveEphemeralNotSupported)
    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @wrap_instance_fault
    def rebuild_instance(self, context, instance, orig_image_ref, image_ref,
                         injected_files, new_pass, orig_sys_metadata,
                         bdms, recreate, on_shared_storage=None,
                         preserve_ephemeral=False, migration=None,
                         scheduled_node=None, limits=None):
        """Destroy and re-make this instance.

        A 'rebuild' effectively purges all existing data from the system and
        remakes the VM with given 'metadata' and 'personalities'.

        :param context: `nova.RequestContext` object
        :param instance: Instance object
        :param orig_image_ref: Original image_ref before rebuild
        :param image_ref: New image_ref for rebuild
        :param injected_files: Files to inject
        :param new_pass: password to set on rebuilt instance
        :param orig_sys_metadata: instance system metadata from pre-rebuild
        :param bdms: block-device-mappings to use for rebuild
        :param recreate: True if the instance is being recreated (e.g. the
            hypervisor it was on failed) - cleanup of old state will be
            skipped.
        :param on_shared_storage: True if instance files on shared storage.
                                  If not provided then information from the
                                  driver will be used to decide if the instance
                                  files are available or not on the target host
        :param preserve_ephemeral: True if the default ephemeral storage
                                   partition must be preserved on rebuild
        :param migration: a Migration object if one was created for this
                          rebuild operation (if it's a part of evacaute)
        :param scheduled_node: A node of the host chosen by the scheduler. If a
                               host was specified by the user, this will be
                               None
        :param limits: Overcommit limits set by the scheduler. If a host was
                       specified by the user, this will be None
        """
        context = context.elevated()

        LOG.info(_LI("Rebuilding instance"), context=context,
                    instance=instance)
        if scheduled_node is not None:
            rt = self._get_resource_tracker(scheduled_node)
            rebuild_claim = rt.rebuild_claim
        else:
            rebuild_claim = claims.NopClaim

        image_meta = {}
        if image_ref:
            image_meta = self.image_api.get(context, image_ref)

        # NOTE(mriedem): On a recreate (evacuate), we need to update
        # the instance's host and node properties to reflect it's
        # destination node for the recreate.
        if not scheduled_node:
            try:
                compute_node = self._get_compute_info(context, self.host)
                scheduled_node = compute_node.hypervisor_hostname
            except exception.ComputeHostNotFound:
                LOG.exception(_LE('Failed to get compute_info for %s'),
                                self.host)

        def _fail_migration(migration):
            if migration:
                migration.status = 'failed'
                migration.save()

        with self._error_out_instance_on_exception(context, instance):
            try:
                claim_ctxt = rebuild_claim(
                    context, instance, limits=limits, image_meta=image_meta,
                    migration=migration)
                self._do_rebuild_instance_with_claim(
                    claim_ctxt, context, instance, orig_image_ref,
                    image_ref, injected_files, new_pass, orig_sys_metadata,
                    bdms, recreate, on_shared_storage, preserve_ephemeral)
            except exception.ComputeResourcesUnavailable as e:
                LOG.debug("Could not rebuild instance on this host, not "
                          "enough resources available.", instance=instance)

                # NOTE(ndipanov): We just abort the build for now and leave a
                # migration record for potential cleanup later
                _fail_migration(migration)

                self._notify_about_instance_usage(context, instance,
                        'rebuild.error', fault=e)
                raise exception.BuildAbortException(
                    instance_uuid=instance.uuid, reason=e.format_message())
            except Exception as e:
                _fail_migration(migration)
                self._notify_about_instance_usage(context, instance,
                        'rebuild.error', fault=e)
                raise
            else:
                instance.apply_migration_context()
                # NOTE (ndipanov): This save will now update the host and node
                # attributes making sure that next RT pass is consistent since
                # it will be based on the instance and not the migration DB
                # entry.
                instance.host = self.host
                instance.node = scheduled_node
                instance.save()
                instance.drop_migration_context()

                # NOTE (ndipanov): Mark the migration as done only after we
                # mark the instance as belonging to this host.
                if migration:
                    migration.status = 'done'
                    migration.save()

    def _do_rebuild_instance_with_claim(self, claim_context, *args, **kwargs):
        """Helper to avoid deep nesting in the top-level method."""

        with claim_context:
            self._do_rebuild_instance(*args, **kwargs)

    def _do_rebuild_instance(self, context, instance, orig_image_ref,
                             image_ref, injected_files, new_pass,
                             orig_sys_metadata, bdms, recreate,
                             on_shared_storage, preserve_ephemeral):
        orig_vm_state = instance.vm_state

        if recreate:
            if not self.driver.capabilities["supports_recreate"]:
                raise exception.InstanceRecreateNotSupported

            self._check_instance_exists(context, instance)

            if on_shared_storage is None:
                LOG.debug('on_shared_storage is not provided, using driver'
                            'information to decide if the instance needs to'
                            'be recreated')
                on_shared_storage = self.driver.instance_on_disk(instance)

            elif (on_shared_storage !=
                    self.driver.instance_on_disk(instance)):
                # To cover case when admin expects that instance files are
                # on shared storage, but not accessible and vice versa
                raise exception.InvalidSharedStorage(
                        _("Invalid state of instance files on shared"
                            " storage"))

            if on_shared_storage:
                LOG.info(_LI('disk on shared storage, recreating using'
                                ' existing disk'))
            else:
                image_ref = orig_image_ref = instance.image_ref
                LOG.info(_LI("disk not on shared storage, rebuilding from:"
                                " '%s'"), str(image_ref))

        if image_ref:
            image_meta = self.image_api.get(context, image_ref)
        else:
            image_meta = {}

        # This instance.exists message should contain the original
        # image_ref, not the new one.  Since the DB has been updated
        # to point to the new one... we have to override it.
        # TODO(jaypipes): Move generate_image_url() into the nova.image.api
        orig_image_ref_url = glance.generate_image_url(orig_image_ref)
        extra_usage_info = {'image_ref_url': orig_image_ref_url}
        compute_utils.notify_usage_exists(
                self.notifier, context, instance,
                current_period=True, system_metadata=orig_sys_metadata,
                extra_usage_info=extra_usage_info)

        # This message should contain the new image_ref
        extra_usage_info = {'image_name': image_meta.get('name', '')}
        self._notify_about_instance_usage(context, instance,
                "rebuild.start", extra_usage_info=extra_usage_info)

        instance.power_state = self._get_power_state(context, instance)
        instance.task_state = task_states.REBUILDING
        instance.save(expected_task_state=[task_states.REBUILDING])

        if recreate:
            # Needed for nova-network, does nothing for neutron
            self.network_api.setup_networks_on_host(
                    context, instance, self.host)
            # For nova-network this is needed to move floating IPs
            # For neutron this updates the host in the port binding
            # TODO(cfriesen): this network_api call and the one above
            # are so similar, we should really try to unify them.
            self.network_api.setup_instance_network_on_host(
                    context, instance, self.host)

        network_info = compute_utils.get_nw_info_for_instance(instance)
        if bdms is None:
            bdms = objects.BlockDeviceMappingList.get_by_instance_uuid(
                    context, instance.uuid)

        block_device_info = \
            self._get_instance_block_device_info(
                    context, instance, bdms=bdms)

        def detach_block_devices(context, bdms):
            for bdm in bdms:
                if bdm.is_volume:
                    self._detach_volume(context, bdm.volume_id, instance,
                                        destroy_bdm=False)

        files = self._decode_files(injected_files)

        kwargs = dict(
            context=context,
            instance=instance,
            image_meta=image_meta,
            injected_files=files,
            admin_password=new_pass,
            bdms=bdms,
            detach_block_devices=detach_block_devices,
            attach_block_devices=self._prep_block_device,
            block_device_info=block_device_info,
            network_info=network_info,
            preserve_ephemeral=preserve_ephemeral,
            recreate=recreate)
        try:
            self.driver.rebuild(**kwargs)
        except NotImplementedError:
            # NOTE(rpodolyaka): driver doesn't provide specialized version
            # of rebuild, fall back to the default implementation
            self._rebuild_default_impl(**kwargs)
        self._update_instance_after_spawn(context, instance)
        instance.save(expected_task_state=[task_states.REBUILD_SPAWNING])

        if orig_vm_state == vm_states.STOPPED:
            LOG.info(_LI("bringing vm to original state: '%s'"),
                        orig_vm_state, instance=instance)
            instance.vm_state = vm_states.ACTIVE
            instance.task_state = task_states.POWERING_OFF
            instance.progress = 0
            instance.save()
            self.stop_instance(context, instance, False)
        self._update_scheduler_instance_info(context, instance)
        self._notify_about_instance_usage(
                context, instance, "rebuild.end",
                network_info=network_info,
                extra_usage_info=extra_usage_info)

    def _handle_bad_volumes_detached(self, context, instance, bad_devices,
                                     block_device_info):
        """Handle cases where the virt-layer had to detach non-working volumes
        in order to complete an operation.
        """
        for bdm in block_device_info['block_device_mapping']:
            if bdm.get('mount_device') in bad_devices:
                try:
                    volume_id = bdm['connection_info']['data']['volume_id']
                except KeyError:
                    continue

                # NOTE(sirp): ideally we'd just call
                # `compute_api.detach_volume` here but since that hits the
                # DB directly, that's off limits from within the
                # compute-manager.
                #
                # API-detach
                LOG.info(_LI("Detaching from volume api: %s"), volume_id)
                volume = self.volume_api.get(context, volume_id)
                self.volume_api.check_detach(context, volume)
                self.volume_api.begin_detaching(context, volume_id)

                # Manager-detach
                self.detach_volume(context, volume_id, instance)

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @wrap_instance_fault
    def reboot_instance(self, context, instance, block_device_info,
                        reboot_type):
        """Reboot an instance on this host."""
        # acknowledge the request made it to the manager
        if reboot_type == "SOFT":
            instance.task_state = task_states.REBOOT_PENDING
            expected_states = (task_states.REBOOTING,
                               task_states.REBOOT_PENDING,
                               task_states.REBOOT_STARTED)
        else:
            instance.task_state = task_states.REBOOT_PENDING_HARD
            expected_states = (task_states.REBOOTING_HARD,
                               task_states.REBOOT_PENDING_HARD,
                               task_states.REBOOT_STARTED_HARD)
        context = context.elevated()
        LOG.info(_LI("Rebooting instance"), context=context, instance=instance)

        block_device_info = self._get_instance_block_device_info(context,
                                                                 instance)

        network_info = self.network_api.get_instance_nw_info(context, instance)

        self._notify_about_instance_usage(context, instance, "reboot.start")

        instance.power_state = self._get_power_state(context, instance)
        instance.save(expected_task_state=expected_states)

        if instance.power_state != power_state.RUNNING:
            state = instance.power_state
            running = power_state.RUNNING
            LOG.warning(_LW('trying to reboot a non-running instance:'
                            ' (state: %(state)s expected: %(running)s)'),
                        {'state': state, 'running': running},
                        context=context, instance=instance)

        def bad_volumes_callback(bad_devices):
            self._handle_bad_volumes_detached(
                    context, instance, bad_devices, block_device_info)

        try:
            # Don't change it out of rescue mode
            if instance.vm_state == vm_states.RESCUED:
                new_vm_state = vm_states.RESCUED
            else:
                new_vm_state = vm_states.ACTIVE
            new_power_state = None
            if reboot_type == "SOFT":
                instance.task_state = task_states.REBOOT_STARTED
                expected_state = task_states.REBOOT_PENDING
            else:
                instance.task_state = task_states.REBOOT_STARTED_HARD
                expected_state = task_states.REBOOT_PENDING_HARD
            instance.save(expected_task_state=expected_state)
            self.driver.reboot(context, instance,
                               network_info,
                               reboot_type,
                               block_device_info=block_device_info,
                               bad_volumes_callback=bad_volumes_callback)

        except Exception as error:
            with excutils.save_and_reraise_exception() as ctxt:
                exc_info = sys.exc_info()
                # if the reboot failed but the VM is running don't
                # put it into an error state
                new_power_state = self._get_power_state(context, instance)
                if new_power_state == power_state.RUNNING:
                    LOG.warning(_LW('Reboot failed but instance is running'),
                                context=context, instance=instance)
                    compute_utils.add_instance_fault_from_exc(context,
                            instance, error, exc_info)
                    self._notify_about_instance_usage(context, instance,
                            'reboot.error', fault=error)
                    ctxt.reraise = False
                else:
                    LOG.error(_LE('Cannot reboot instance: %s'), error,
                              context=context, instance=instance)
                    self._set_instance_obj_error_state(context, instance)

        if not new_power_state:
            new_power_state = self._get_power_state(context, instance)
        try:
            instance.power_state = new_power_state
            instance.vm_state = new_vm_state
            instance.task_state = None
            instance.save()
        except exception.InstanceNotFound:
            LOG.warning(_LW("Instance disappeared during reboot"),
                        context=context, instance=instance)

        self._notify_about_instance_usage(context, instance, "reboot.end")

    @delete_image_on_error
    def _do_snapshot_instance(self, context, image_id, instance, rotation):
        if rotation < 0:
            raise exception.RotationRequiredForBackup()
        self._snapshot_instance(context, image_id, instance,
                                task_states.IMAGE_BACKUP)

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_fault
    def backup_instance(self, context, image_id, instance, backup_type,
                        rotation):
        """Backup an instance on this host.

        :param backup_type: daily | weekly
        :param rotation: int representing how many backups to keep around
        """
        self._do_snapshot_instance(context, image_id, instance, rotation)
        self._rotate_backups(context, instance, backup_type, rotation)

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_fault
    @delete_image_on_error
    def snapshot_instance(self, context, image_id, instance):
        """Snapshot an instance on this host.

        :param context: security context
        :param instance: a nova.objects.instance.Instance object
        :param image_id: glance.db.sqlalchemy.models.Image.Id
        """
        # NOTE(dave-mcnally) the task state will already be set by the api
        # but if the compute manager has crashed/been restarted prior to the
        # request getting here the task state may have been cleared so we set
        # it again and things continue normally
        try:
            instance.task_state = task_states.IMAGE_SNAPSHOT
            instance.save(
                        expected_task_state=task_states.IMAGE_SNAPSHOT_PENDING)
        except exception.InstanceNotFound:
            # possibility instance no longer exists, no point in continuing
            LOG.debug("Instance not found, could not set state %s "
                      "for instance.",
                      task_states.IMAGE_SNAPSHOT, instance=instance)
            return

        except exception.UnexpectedDeletingTaskStateError:
            LOG.debug("Instance being deleted, snapshot cannot continue",
                      instance=instance)
            return

        self._snapshot_instance(context, image_id, instance,
                                task_states.IMAGE_SNAPSHOT)

    def _snapshot_instance(self, context, image_id, instance,
                           expected_task_state):
        context = context.elevated()

        instance.power_state = self._get_power_state(context, instance)
        try:
            instance.save()

            LOG.info(_LI('instance snapshotting'), context=context,
                  instance=instance)

            if instance.power_state != power_state.RUNNING:
                state = instance.power_state
                running = power_state.RUNNING
                LOG.warning(_LW('trying to snapshot a non-running instance: '
                                '(state: %(state)s expected: %(running)s)'),
                            {'state': state, 'running': running},
                            instance=instance)

            self._notify_about_instance_usage(
                context, instance, "snapshot.start")

            def update_task_state(task_state,
                                  expected_state=expected_task_state):
                instance.task_state = task_state
                instance.save(expected_task_state=expected_state)

            self.driver.snapshot(context, instance, image_id,
                                 update_task_state)

            instance.task_state = None
            instance.save(expected_task_state=task_states.IMAGE_UPLOADING)

            self._notify_about_instance_usage(context, instance,
                                              "snapshot.end")
        except (exception.InstanceNotFound,
                exception.UnexpectedDeletingTaskStateError):
            # the instance got deleted during the snapshot
            # Quickly bail out of here
            msg = 'Instance disappeared during snapshot'
            LOG.debug(msg, instance=instance)
            try:
                image_service = glance.get_default_image_service()
                image = image_service.show(context, image_id)
                if image['status'] != 'active':
                    image_service.delete(context, image_id)
            except Exception:
                LOG.warning(_LW("Error while trying to clean up image %s"),
                            image_id, instance=instance)
        except exception.ImageNotFound:
            instance.task_state = None
            instance.save()
            msg = _LW("Image not found during snapshot")
            LOG.warn(msg, instance=instance)

    def _post_interrupted_snapshot_cleanup(self, context, instance):
        self.driver.post_interrupted_snapshot_cleanup(context, instance)

    @messaging.expected_exceptions(NotImplementedError)
    @wrap_exception()
    def volume_snapshot_create(self, context, instance, volume_id,
                               create_info):
        self.driver.volume_snapshot_create(context, instance, volume_id,
                                           create_info)

    @messaging.expected_exceptions(NotImplementedError)
    @wrap_exception()
    def volume_snapshot_delete(self, context, instance, volume_id,
                               snapshot_id, delete_info):
        self.driver.volume_snapshot_delete(context, instance, volume_id,
                                           snapshot_id, delete_info)

    @wrap_instance_fault
    def _rotate_backups(self, context, instance, backup_type, rotation):
        """Delete excess backups associated to an instance.

        Instances are allowed a fixed number of backups (the rotation number);
        this method deletes the oldest backups that exceed the rotation
        threshold.

        :param context: security context
        :param instance: Instance dict
        :param backup_type: a user-defined type, like "daily" or "weekly" etc.
        :param rotation: int representing how many backups to keep around;
            None if rotation shouldn't be used (as in the case of snapshots)
        """
        filters = {'property-image_type': 'backup',
                   'property-backup_type': backup_type,
                   'property-instance_uuid': instance.uuid}

        images = self.image_api.get_all(context, filters=filters,
                                        sort_key='created_at', sort_dir='desc')
        num_images = len(images)
        LOG.debug("Found %(num_images)d images (rotation: %(rotation)d)",
                  {'num_images': num_images, 'rotation': rotation},
                  instance=instance)

        if num_images > rotation:
            # NOTE(sirp): this deletes all backups that exceed the rotation
            # limit
            excess = len(images) - rotation
            LOG.debug("Rotating out %d backups", excess,
                      instance=instance)
            for i in range(excess):
                image = images.pop()
                image_id = image['id']
                LOG.debug("Deleting image %s", image_id,
                          instance=instance)
                self.image_api.delete(context, image_id)

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @wrap_instance_fault
    def set_admin_password(self, context, instance, new_pass):
        """Set the root/admin password for an instance on this host.

        This is generally only called by API password resets after an
        image has been built.

        @param context: Nova auth context.
        @param instance: Nova instance object.
        @param new_pass: The admin password for the instance.
        """

        context = context.elevated()
        if new_pass is None:
            # Generate a random password
            new_pass = utils.generate_password()

        current_power_state = self._get_power_state(context, instance)
        expected_state = power_state.RUNNING

        if current_power_state != expected_state:
            instance.task_state = None
            instance.save(expected_task_state=task_states.UPDATING_PASSWORD)
            _msg = _('instance %s is not running') % instance.uuid
            raise exception.InstancePasswordSetFailed(
                instance=instance.uuid, reason=_msg)

        try:
            self.driver.set_admin_password(instance, new_pass)
            LOG.info(_LI("Root password set"), instance=instance)
            instance.task_state = None
            instance.save(
                expected_task_state=task_states.UPDATING_PASSWORD)
        except NotImplementedError:
            LOG.warning(_LW('set_admin_password is not implemented '
                            'by this driver or guest instance.'),
                        instance=instance)
            instance.task_state = None
            instance.save(
                expected_task_state=task_states.UPDATING_PASSWORD)
            raise NotImplementedError(_('set_admin_password is not '
                                        'implemented by this driver or guest '
                                        'instance.'))
        except exception.UnexpectedTaskStateError:
            # interrupted by another (most likely delete) task
            # do not retry
            raise
        except Exception:
            # Catch all here because this could be anything.
            LOG.exception(_LE('set_admin_password failed'),
                          instance=instance)
            self._set_instance_obj_error_state(context, instance)
            # We create a new exception here so that we won't
            # potentially reveal password information to the
            # API caller.  The real exception is logged above
            _msg = _('error setting admin password')
            raise exception.InstancePasswordSetFailed(
                instance=instance.uuid, reason=_msg)

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_fault
    def inject_file(self, context, path, file_contents, instance):
        """Write a file to the specified path in an instance on this host."""
        # NOTE(russellb) Remove this method, as well as the underlying virt
        # driver methods, when the compute rpc interface is bumped to 4.x
        # as it is no longer used.
        context = context.elevated()
        current_power_state = self._get_power_state(context, instance)
        expected_state = power_state.RUNNING
        if current_power_state != expected_state:
            LOG.warning(_LW('trying to inject a file into a non-running '
                            '(state: %(current_state)s expected: '
                            '%(expected_state)s)'),
                        {'current_state': current_power_state,
                         'expected_state': expected_state},
                        instance=instance)
        LOG.info(_LI('injecting file to %s'), path,
                    instance=instance)
        self.driver.inject_file(instance, path, file_contents)

    def _get_rescue_image(self, context, instance, rescue_image_ref=None):
        """Determine what image should be used to boot the rescue VM."""
        # 1. If rescue_image_ref is passed in, use that for rescue.
        # 2. Else, use the base image associated with instance's current image.
        #       The idea here is to provide the customer with a rescue
        #       environment which they are familiar with.
        #       So, if they built their instance off of a Debian image,
        #       their rescue VM will also be Debian.
        # 3. As a last resort, use instance's current image.
        if not rescue_image_ref:
            system_meta = utils.instance_sys_meta(instance)
            rescue_image_ref = system_meta.get('image_base_image_ref')

        if not rescue_image_ref:
            LOG.warning(_LW('Unable to find a different image to use for '
                            'rescue VM, using instance\'s current image'),
                        instance=instance)
            rescue_image_ref = instance.image_ref

        image_meta = self.image_api.get(context, rescue_image_ref)
        # NOTE(belliott) bug #1227350 - xenapi needs the actual image id
        image_meta['id'] = rescue_image_ref
        return image_meta

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @wrap_instance_fault
    def rescue_instance(self, context, instance, rescue_password,
                        rescue_image_ref, clean_shutdown):
        context = context.elevated()
        LOG.info(_LI('Rescuing'), context=context, instance=instance)

        admin_password = (rescue_password if rescue_password else
                      utils.generate_password())

        network_info = self.network_api.get_instance_nw_info(context, instance)

        rescue_image_meta = self._get_rescue_image(context, instance,
                                                   rescue_image_ref)

        extra_usage_info = {'rescue_image_name':
                            rescue_image_meta.get('name', '')}
        self._notify_about_instance_usage(context, instance,
                "rescue.start", extra_usage_info=extra_usage_info,
                network_info=network_info)

        try:
            self._power_off_instance(context, instance, clean_shutdown)

            self.driver.rescue(context, instance,
                               network_info,
                               rescue_image_meta, admin_password)
        except Exception as e:
            LOG.exception(_LE("Error trying to Rescue Instance"),
                          instance=instance)
            raise exception.InstanceNotRescuable(
                instance_id=instance.uuid,
                reason=_("Driver Error: %s") % e)

        compute_utils.notify_usage_exists(self.notifier, context, instance,
                                          current_period=True)

        instance.vm_state = vm_states.RESCUED
        instance.task_state = None
        instance.power_state = self._get_power_state(context, instance)
        instance.launched_at = timeutils.utcnow()
        instance.save(expected_task_state=task_states.RESCUING)

        self._notify_about_instance_usage(context, instance,
                "rescue.end", extra_usage_info=extra_usage_info,
                network_info=network_info)

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @wrap_instance_fault
    def unrescue_instance(self, context, instance):
        context = context.elevated()
        LOG.info(_LI('Unrescuing'), context=context, instance=instance)

        network_info = self.network_api.get_instance_nw_info(context, instance)
        self._notify_about_instance_usage(context, instance,
                "unrescue.start", network_info=network_info)
        with self._error_out_instance_on_exception(context, instance):
            self.driver.unrescue(instance,
                                 network_info)

        instance.vm_state = vm_states.ACTIVE
        instance.task_state = None
        instance.power_state = self._get_power_state(context, instance)
        instance.save(expected_task_state=task_states.UNRESCUING)

        self._notify_about_instance_usage(context,
                                          instance,
                                          "unrescue.end",
                                          network_info=network_info)

    @wrap_exception()
    @wrap_instance_fault
    def change_instance_metadata(self, context, diff, instance):
        """Update the metadata published to the instance."""
        LOG.debug("Changing instance metadata according to %r",
                  diff, instance=instance)
        self.driver.change_instance_metadata(context, instance, diff)

    def _cleanup_stored_instance_types(self, instance, restore_old=False):
        """Clean up "old" and "new" instance_type information stored in
        instance's system_metadata. Optionally update the "current"
        instance_type to the saved old one first.

        Returns the updated system_metadata as a dict, the
        post-cleanup current instance type and the to-be dropped
        instance type.
        """
        sys_meta = instance.system_metadata
        if restore_old:
            instance_type = instance.get_flavor('old')
            drop_instance_type = instance.get_flavor()
            instance.set_flavor(instance_type)
        else:
            instance_type = instance.get_flavor()
            drop_instance_type = instance.get_flavor('old')

        instance.delete_flavor('old')
        instance.delete_flavor('new')

        return sys_meta, instance_type, drop_instance_type

    @wrap_exception()
    @wrap_instance_event
    @wrap_instance_fault
    def confirm_resize(self, context, instance, reservations, migration):

        quotas = objects.Quotas.from_reservations(context,
                                                  reservations,
                                                  instance=instance)

        @utils.synchronized(instance.uuid)
        def do_confirm_resize(context, instance, migration_id):
            # NOTE(wangpan): Get the migration status from db, if it has been
            #                confirmed, we do nothing and return here
            LOG.debug("Going to confirm migration %s", migration_id,
                      context=context, instance=instance)
            try:
                # TODO(russellb) Why are we sending the migration object just
                # to turn around and look it up from the db again?
                migration = objects.Migration.get_by_id(
                                    context.elevated(), migration_id)
            except exception.MigrationNotFound:
                LOG.error(_LE("Migration %s is not found during confirmation"),
                          migration_id, context=context, instance=instance)
                quotas.rollback()
                return

            if migration.status == 'confirmed':
                LOG.info(_LI("Migration %s is already confirmed"),
                         migration_id, context=context, instance=instance)
                quotas.rollback()
                return
            elif migration.status not in ('finished', 'confirming'):
                LOG.warning(_LW("Unexpected confirmation status '%(status)s' "
                                "of migration %(id)s, exit confirmation "
                                "process"),
                            {"status": migration.status, "id": migration_id},
                            context=context, instance=instance)
                quotas.rollback()
                return

            # NOTE(wangpan): Get the instance from db, if it has been
            #                deleted, we do nothing and return here
            expected_attrs = ['metadata', 'system_metadata', 'flavor']
            try:
                instance = objects.Instance.get_by_uuid(
                        context, instance.uuid,
                        expected_attrs=expected_attrs)
            except exception.InstanceNotFound:
                LOG.info(_LI("Instance is not found during confirmation"),
                         context=context, instance=instance)
                quotas.rollback()
                return

            self._confirm_resize(context, instance, quotas,
                                 migration=migration)

        do_confirm_resize(context, instance, migration.id)

    def _confirm_resize(self, context, instance, quotas,
                        migration=None):
        """Destroys the source instance."""
        self._notify_about_instance_usage(context, instance,
                                          "resize.confirm.start")

        with self._error_out_instance_on_exception(context, instance,
                                                   quotas=quotas):
            # NOTE(danms): delete stashed migration information
            sys_meta, instance_type, old_instance_type = (
                self._cleanup_stored_instance_types(instance))
            sys_meta.pop('old_vm_state', None)

            instance.system_metadata = sys_meta
            instance.save()

            # NOTE(tr3buchet): tear down networks on source host
            self.network_api.setup_networks_on_host(context, instance,
                               migration.source_compute, teardown=True)

            network_info = self.network_api.get_instance_nw_info(context,
                                                                 instance)
            self.driver.confirm_migration(migration, instance,
                                          network_info)

            migration.status = 'confirmed'
            with migration.obj_as_admin():
                migration.save()

            rt = self._get_resource_tracker(migration.source_node)
            rt.drop_move_claim(context, instance, old_instance_type)

            # NOTE(mriedem): The old_vm_state could be STOPPED but the user
            # might have manually powered up the instance to confirm the
            # resize/migrate, so we need to check the current power state
            # on the instance and set the vm_state appropriately. We default
            # to ACTIVE because if the power state is not SHUTDOWN, we
            # assume _sync_instance_power_state will clean it up.
            p_state = instance.power_state
            vm_state = None
            if p_state == power_state.SHUTDOWN:
                vm_state = vm_states.STOPPED
                LOG.debug("Resized/migrated instance is powered off. "
                          "Setting vm_state to '%s'.", vm_state,
                          instance=instance)
            else:
                vm_state = vm_states.ACTIVE

            instance.vm_state = vm_state
            instance.task_state = None
            instance.save(expected_task_state=[None, task_states.DELETING])

            self._notify_about_instance_usage(
                context, instance, "resize.confirm.end",
                network_info=network_info)

            quotas.commit()

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @errors_out_migration
    @wrap_instance_fault
    def revert_resize(self, context, instance, migration, reservations):
        """Destroys the new instance on the destination machine.

        Reverts the model changes, and powers on the old instance on the
        source machine.

        """

        quotas = objects.Quotas.from_reservations(context,
                                                  reservations,
                                                  instance=instance)

        # NOTE(comstud): A revert_resize is essentially a resize back to
        # the old size, so we need to send a usage event here.
        compute_utils.notify_usage_exists(self.notifier, context, instance,
                                          current_period=True)

        with self._error_out_instance_on_exception(context, instance,
                                                   quotas=quotas):
            # NOTE(tr3buchet): tear down networks on destination host
            self.network_api.setup_networks_on_host(context, instance,
                                                    teardown=True)

            migration_p = obj_base.obj_to_primitive(migration)
            self.network_api.migrate_instance_start(context,
                                                    instance,
                                                    migration_p)

            network_info = self.network_api.get_instance_nw_info(context,
                                                                 instance)
            bdms = objects.BlockDeviceMappingList.get_by_instance_uuid(
                    context, instance.uuid)
            block_device_info = self._get_instance_block_device_info(
                                context, instance, bdms=bdms)

            destroy_disks = not self._is_instance_storage_shared(
                context, instance, host=migration.source_compute)
            self.driver.destroy(context, instance, network_info,
                                block_device_info, destroy_disks)

            self._terminate_volume_connections(context, instance, bdms)

            migration.status = 'reverted'
            with migration.obj_as_admin():
                migration.save()

            # NOTE(ndipanov): We need to do this here because dropping the
            # claim means we lose the migration_context data. We really should
            # fix this by moving the drop_move_claim call to the
            # finish_revert_resize method as this is racy (revert is dropped,
            # but instance resources will be tracked with the new flavor until
            # it gets rolled back in finish_revert_resize, which is
            # potentially wrong for a period of time).
            instance.revert_migration_context()
            instance.save()

            rt = self._get_resource_tracker(instance.node)
            rt.drop_move_claim(context, instance)

            self.compute_rpcapi.finish_revert_resize(context, instance,
                    migration, migration.source_compute,
                    quotas.reservations)

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @errors_out_migration
    @wrap_instance_fault
    def finish_revert_resize(self, context, instance, reservations, migration):
        """Finishes the second half of reverting a resize.

        Bring the original source instance state back (active/shutoff) and
        revert the resized attributes in the database.

        """

        quotas = objects.Quotas.from_reservations(context,
                                                  reservations,
                                                  instance=instance)

        with self._error_out_instance_on_exception(context, instance,
                                                   quotas=quotas):
            network_info = self.network_api.get_instance_nw_info(context,
                                                                 instance)

            self._notify_about_instance_usage(
                    context, instance, "resize.revert.start")

            sys_meta, instance_type, drop_instance_type = (
                self._cleanup_stored_instance_types(instance, True))

            # NOTE(mriedem): delete stashed old_vm_state information; we
            # default to ACTIVE for backwards compatibility if old_vm_state
            # is not set
            old_vm_state = sys_meta.pop('old_vm_state', vm_states.ACTIVE)

            instance.system_metadata = sys_meta
            instance.memory_mb = instance_type.memory_mb
            instance.vcpus = instance_type.vcpus
            instance.root_gb = instance_type.root_gb
            instance.ephemeral_gb = instance_type.ephemeral_gb
            instance.instance_type_id = instance_type.id
            instance.host = migration.source_compute
            instance.node = migration.source_node
            instance.save()

            migration.dest_compute = migration.source_compute
            with migration.obj_as_admin():
                migration.save()

            self.network_api.setup_networks_on_host(context, instance,
                                                    migration.source_compute)

            block_device_info = self._get_instance_block_device_info(
                    context, instance, refresh_conn_info=True)

            power_on = old_vm_state != vm_states.STOPPED
            self.driver.finish_revert_migration(context, instance,
                                       network_info,
                                       block_device_info, power_on)

            instance.launched_at = timeutils.utcnow()
            instance.save(expected_task_state=task_states.RESIZE_REVERTING)

            migration_p = obj_base.obj_to_primitive(migration)
            self.network_api.migrate_instance_finish(context,
                                                     instance,
                                                     migration_p)

            # if the original vm state was STOPPED, set it back to STOPPED
            LOG.info(_LI("Updating instance to original state: '%s'"),
                     old_vm_state)
            if power_on:
                instance.vm_state = vm_states.ACTIVE
                instance.task_state = None
                instance.save()
            else:
                instance.task_state = task_states.POWERING_OFF
                instance.save()
                self.stop_instance(context, instance=instance,
                                   clean_shutdown=True)

            self._notify_about_instance_usage(
                    context, instance, "resize.revert.end")
            quotas.commit()

    def _prep_resize(self, context, image, instance, instance_type,
            quotas, request_spec, filter_properties, node,
            clean_shutdown=True):

        if not filter_properties:
            filter_properties = {}

        if not instance.host:
            self._set_instance_obj_error_state(context, instance)
            msg = _('Instance has no source host')
            raise exception.MigrationError(reason=msg)

        same_host = instance.host == self.host
        # if the flavor IDs match, it's migrate; otherwise resize
        if same_host and instance_type.id == instance['instance_type_id']:
            # check driver whether support migrate to same host
            if not self.driver.capabilities['supports_migrate_to_same_host']:
                raise exception.UnableToMigrateToSelf(
                    instance_id=instance.uuid, host=self.host)

        # NOTE(danms): Stash the new instance_type to avoid having to
        # look it up in the database later
        instance.set_flavor(instance_type, 'new')
        # NOTE(mriedem): Stash the old vm_state so we can set the
        # resized/reverted instance back to the same state later.
        vm_state = instance.vm_state
        LOG.debug('Stashing vm_state: %s', vm_state, instance=instance)
        instance.system_metadata['old_vm_state'] = vm_state
        instance.save()

        limits = filter_properties.get('limits', {})
        rt = self._get_resource_tracker(node)
        with rt.resize_claim(context, instance, instance_type,
                             image_meta=image, limits=limits) as claim:
            LOG.info(_LI('Migrating'), context=context, instance=instance)
            self.compute_rpcapi.resize_instance(
                    context, instance, claim.migration, image,
                    instance_type, quotas.reservations,
                    clean_shutdown)

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @wrap_instance_fault
    def prep_resize(self, context, image, instance, instance_type,
                    reservations, request_spec, filter_properties, node,
                    clean_shutdown):
        """Initiates the process of moving a running instance to another host.

        Possibly changes the RAM and disk size in the process.

        """
        if node is None:
            node = self.driver.get_available_nodes(refresh=True)[0]
            LOG.debug("No node specified, defaulting to %s", node,
                      instance=instance)

        # NOTE(melwitt): Remove this in version 5.0 of the RPC API
        # Code downstream may expect extra_specs to be populated since it
        # is receiving an object, so lookup the flavor to ensure this.
        if not isinstance(instance_type, objects.Flavor):
            instance_type = objects.Flavor.get_by_id(context,
                                                     instance_type['id'])

        quotas = objects.Quotas.from_reservations(context,
                                                  reservations,
                                                  instance=instance)
        with self._error_out_instance_on_exception(context, instance,
                                                   quotas=quotas):
            compute_utils.notify_usage_exists(self.notifier, context, instance,
                                              current_period=True)
            self._notify_about_instance_usage(
                    context, instance, "resize.prep.start")
            try:
                self._prep_resize(context, image, instance,
                                  instance_type, quotas,
                                  request_spec, filter_properties,
                                  node, clean_shutdown)
            # NOTE(dgenin): This is thrown in LibvirtDriver when the
            #               instance to be migrated is backed by LVM.
            #               Remove when LVM migration is implemented.
            except exception.MigrationPreCheckError:
                raise
            except Exception:
                # try to re-schedule the resize elsewhere:
                exc_info = sys.exc_info()
                self._reschedule_resize_or_reraise(context, image, instance,
                        exc_info, instance_type, quotas, request_spec,
                        filter_properties)
            finally:
                extra_usage_info = dict(
                        new_instance_type=instance_type.name,
                        new_instance_type_id=instance_type.id)

                self._notify_about_instance_usage(
                    context, instance, "resize.prep.end",
                    extra_usage_info=extra_usage_info)

    def _reschedule_resize_or_reraise(self, context, image, instance, exc_info,
            instance_type, quotas, request_spec, filter_properties):
        """Try to re-schedule the resize or re-raise the original error to
        error out the instance.
        """
        if not request_spec:
            request_spec = {}
        if not filter_properties:
            filter_properties = {}

        rescheduled = False
        instance_uuid = instance.uuid

        try:
            reschedule_method = self.compute_task_api.resize_instance
            scheduler_hint = dict(filter_properties=filter_properties)
            method_args = (instance, None, scheduler_hint, instance_type,
                           quotas.reservations)
            task_state = task_states.RESIZE_PREP

            rescheduled = self._reschedule(context, request_spec,
                    filter_properties, instance, reschedule_method,
                    method_args, task_state, exc_info)
        except Exception as error:
            rescheduled = False
            LOG.exception(_LE("Error trying to reschedule"),
                          instance_uuid=instance_uuid)
            compute_utils.add_instance_fault_from_exc(context,
                    instance, error,
                    exc_info=sys.exc_info())
            self._notify_about_instance_usage(context, instance,
                    'resize.error', fault=error)

        if rescheduled:
            self._log_original_error(exc_info, instance_uuid)
            compute_utils.add_instance_fault_from_exc(context,
                    instance, exc_info[1], exc_info=exc_info)
            self._notify_about_instance_usage(context, instance,
                    'resize.error', fault=exc_info[1])
        else:
            # not re-scheduling
            six.reraise(*exc_info)

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @errors_out_migration
    @wrap_instance_fault
    def resize_instance(self, context, instance, image,
                        reservations, migration, instance_type,
                        clean_shutdown):
        """Starts the migration of a running instance to another host."""

        quotas = objects.Quotas.from_reservations(context,
                                                  reservations,
                                                  instance=instance)
        with self._error_out_instance_on_exception(context, instance,
                                                   quotas=quotas):
            # TODO(chaochin) Remove this until v5 RPC API
            # Code downstream may expect extra_specs to be populated since it
            # is receiving an object, so lookup the flavor to ensure this.
            if (not instance_type or
                not isinstance(instance_type, objects.Flavor)):
                instance_type = objects.Flavor.get_by_id(
                    context, migration['new_instance_type_id'])

            network_info = self.network_api.get_instance_nw_info(context,
                                                                 instance)

            migration.status = 'migrating'
            with migration.obj_as_admin():
                migration.save()

            instance.task_state = task_states.RESIZE_MIGRATING
            instance.save(expected_task_state=task_states.RESIZE_PREP)

            self._notify_about_instance_usage(
                context, instance, "resize.start", network_info=network_info)

            bdms = objects.BlockDeviceMappingList.get_by_instance_uuid(
                    context, instance.uuid)
            block_device_info = self._get_instance_block_device_info(
                                context, instance, bdms=bdms)

            timeout, retry_interval = self._get_power_off_values(context,
                                            instance, clean_shutdown)
            disk_info = self.driver.migrate_disk_and_power_off(
                    context, instance, migration.dest_host,
                    instance_type, network_info,
                    block_device_info,
                    timeout, retry_interval)

            self._terminate_volume_connections(context, instance, bdms)

            migration_p = obj_base.obj_to_primitive(migration)
            self.network_api.migrate_instance_start(context,
                                                    instance,
                                                    migration_p)

            migration.status = 'post-migrating'
            with migration.obj_as_admin():
                migration.save()

            instance.host = migration.dest_compute
            instance.node = migration.dest_node
            instance.task_state = task_states.RESIZE_MIGRATED
            instance.save(expected_task_state=task_states.RESIZE_MIGRATING)

            self.compute_rpcapi.finish_resize(context, instance,
                    migration, image, disk_info,
                    migration.dest_compute, reservations=quotas.reservations)

            self._notify_about_instance_usage(context, instance, "resize.end",
                                              network_info=network_info)
            self.instance_events.clear_events_for_instance(instance)

    def _terminate_volume_connections(self, context, instance, bdms):
        connector = self.driver.get_volume_connector(instance)
        for bdm in bdms:
            if bdm.is_volume:
                self.volume_api.terminate_connection(context, bdm.volume_id,
                                                     connector)

    @staticmethod
    def _set_instance_info(instance, instance_type):
        instance.instance_type_id = instance_type.id
        instance.memory_mb = instance_type.memory_mb
        instance.vcpus = instance_type.vcpus
        instance.root_gb = instance_type.root_gb
        instance.ephemeral_gb = instance_type.ephemeral_gb
        instance.set_flavor(instance_type)

    def _finish_resize(self, context, instance, migration, disk_info,
                       image):
        resize_instance = False
        old_instance_type_id = migration['old_instance_type_id']
        new_instance_type_id = migration['new_instance_type_id']
        old_instance_type = instance.get_flavor()
        # NOTE(mriedem): Get the old_vm_state so we know if we should
        # power on the instance. If old_vm_state is not set we need to default
        # to ACTIVE for backwards compatibility
        old_vm_state = instance.system_metadata.get('old_vm_state',
                                                    vm_states.ACTIVE)
        instance.set_flavor(old_instance_type, 'old')

        if old_instance_type_id != new_instance_type_id:
            instance_type = instance.get_flavor('new')
            self._set_instance_info(instance, instance_type)
            for key in ('root_gb', 'swap', 'ephemeral_gb'):
                if old_instance_type[key] != instance_type[key]:
                    resize_instance = True
                    break
        instance.apply_migration_context()

        # NOTE(tr3buchet): setup networks on destination host
        self.network_api.setup_networks_on_host(context, instance,
                                                migration['dest_compute'])

        migration_p = obj_base.obj_to_primitive(migration)
        self.network_api.migrate_instance_finish(context,
                                                 instance,
                                                 migration_p)

        network_info = self.network_api.get_instance_nw_info(context, instance)

        instance.task_state = task_states.RESIZE_FINISH
        instance.save(expected_task_state=task_states.RESIZE_MIGRATED)

        self._notify_about_instance_usage(
            context, instance, "finish_resize.start",
            network_info=network_info)

        block_device_info = self._get_instance_block_device_info(
                            context, instance, refresh_conn_info=True)

        # NOTE(mriedem): If the original vm_state was STOPPED, we don't
        # automatically power on the instance after it's migrated
        power_on = old_vm_state != vm_states.STOPPED

        try:
            self.driver.finish_migration(context, migration, instance,
                                         disk_info,
                                         network_info,
                                         image, resize_instance,
                                         block_device_info, power_on)
        except Exception:
            with excutils.save_and_reraise_exception():
                if old_instance_type_id != new_instance_type_id:
                    self._set_instance_info(instance,
                                            old_instance_type)

        migration.status = 'finished'
        with migration.obj_as_admin():
            migration.save()

        instance.vm_state = vm_states.RESIZED
        instance.task_state = None
        instance.launched_at = timeutils.utcnow()
        instance.save(expected_task_state=task_states.RESIZE_FINISH)

        self._update_scheduler_instance_info(context, instance)
        self._notify_about_instance_usage(
            context, instance, "finish_resize.end",
            network_info=network_info)

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @errors_out_migration
    @wrap_instance_fault
    def finish_resize(self, context, disk_info, image, instance,
                      reservations, migration):
        """Completes the migration process.

        Sets up the newly transferred disk and turns on the instance at its
        new host machine.

        """
        quotas = objects.Quotas.from_reservations(context,
                                                  reservations,
                                                  instance=instance)
        try:
            self._finish_resize(context, instance, migration,
                                disk_info, image)
            quotas.commit()
        except Exception:
            LOG.exception(_LE('Setting instance vm_state to ERROR'),
                          instance=instance)
            with excutils.save_and_reraise_exception():
                try:
                    quotas.rollback()
                except Exception:
                    LOG.exception(_LE("Failed to rollback quota for failed "
                                      "finish_resize"),
                                  instance=instance)
                self._set_instance_obj_error_state(context, instance)

    @wrap_exception()
    @wrap_instance_fault
    def add_fixed_ip_to_instance(self, context, network_id, instance):
        """Calls network_api to add new fixed_ip to instance
        then injects the new network info and resets instance networking.

        """
        self._notify_about_instance_usage(
                context, instance, "create_ip.start")

        network_info = self.network_api.add_fixed_ip_to_instance(context,
                                                                 instance,
                                                                 network_id)
        self._inject_network_info(context, instance, network_info)
        self.reset_network(context, instance)

        # NOTE(russellb) We just want to bump updated_at.  See bug 1143466.
        instance.updated_at = timeutils.utcnow()
        instance.save()

        self._notify_about_instance_usage(
            context, instance, "create_ip.end", network_info=network_info)

    @wrap_exception()
    @wrap_instance_fault
    def remove_fixed_ip_from_instance(self, context, address, instance):
        """Calls network_api to remove existing fixed_ip from instance
        by injecting the altered network info and resetting
        instance networking.
        """
        self._notify_about_instance_usage(
                context, instance, "delete_ip.start")

        network_info = self.network_api.remove_fixed_ip_from_instance(context,
                                                                      instance,
                                                                      address)
        self._inject_network_info(context, instance, network_info)
        self.reset_network(context, instance)

        # NOTE(russellb) We just want to bump updated_at.  See bug 1143466.
        instance.updated_at = timeutils.utcnow()
        instance.save()

        self._notify_about_instance_usage(
            context, instance, "delete_ip.end", network_info=network_info)

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @wrap_instance_fault
    def pause_instance(self, context, instance):
        """Pause an instance on this host."""
        context = context.elevated()
        LOG.info(_LI('Pausing'), context=context, instance=instance)
        self._notify_about_instance_usage(context, instance, 'pause.start')
        self.driver.pause(instance)
        instance.power_state = self._get_power_state(context, instance)
        instance.vm_state = vm_states.PAUSED
        instance.task_state = None
        instance.save(expected_task_state=task_states.PAUSING)
        self._notify_about_instance_usage(context, instance, 'pause.end')

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @wrap_instance_fault
    def unpause_instance(self, context, instance):
        """Unpause a paused instance on this host."""
        context = context.elevated()
        LOG.info(_LI('Unpausing'), context=context, instance=instance)
        self._notify_about_instance_usage(context, instance, 'unpause.start')
        self.driver.unpause(instance)
        instance.power_state = self._get_power_state(context, instance)
        instance.vm_state = vm_states.ACTIVE
        instance.task_state = None
        instance.save(expected_task_state=task_states.UNPAUSING)
        self._notify_about_instance_usage(context, instance, 'unpause.end')

    @wrap_exception()
    def host_power_action(self, context, action):
        """Reboots, shuts down or powers up the host."""
        return self.driver.host_power_action(action)

    @wrap_exception()
    def host_maintenance_mode(self, context, host, mode):
        """Start/Stop host maintenance window. On start, it triggers
        guest VMs evacuation.
        """
        return self.driver.host_maintenance_mode(host, mode)

    @wrap_exception()
    def set_host_enabled(self, context, enabled):
        """Sets the specified host's ability to accept new instances."""
        return self.driver.set_host_enabled(enabled)

    @wrap_exception()
    def get_host_uptime(self, context):
        """Returns the result of calling "uptime" on the target host."""
        return self.driver.get_host_uptime()

    @wrap_exception()
    @wrap_instance_fault
    def get_diagnostics(self, context, instance):
        """Retrieve diagnostics for an instance on this host."""
        current_power_state = self._get_power_state(context, instance)
        if current_power_state == power_state.RUNNING:
            LOG.info(_LI("Retrieving diagnostics"), context=context,
                      instance=instance)
            return self.driver.get_diagnostics(instance)
        else:
            raise exception.InstanceInvalidState(
                attr='power_state',
                instance_uuid=instance.uuid,
                state=instance.power_state,
                method='get_diagnostics')

    @object_compat
    @wrap_exception()
    @wrap_instance_fault
    def get_instance_diagnostics(self, context, instance):
        """Retrieve diagnostics for an instance on this host."""
        current_power_state = self._get_power_state(context, instance)
        if current_power_state == power_state.RUNNING:
            LOG.info(_LI("Retrieving diagnostics"), context=context,
                      instance=instance)
            diags = self.driver.get_instance_diagnostics(instance)
            return diags.serialize()
        else:
            raise exception.InstanceInvalidState(
                attr='power_state',
                instance_uuid=instance.uuid,
                state=instance.power_state,
                method='get_diagnostics')

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @wrap_instance_fault
    def suspend_instance(self, context, instance):
        """Suspend the given instance."""
        context = context.elevated()

        # Store the old state
        instance.system_metadata['old_vm_state'] = instance.vm_state
        self._notify_about_instance_usage(context, instance, 'suspend.start')

        with self._error_out_instance_on_exception(context, instance,
             instance_state=instance.vm_state):
            self.driver.suspend(context, instance)
        instance.power_state = self._get_power_state(context, instance)
        instance.vm_state = vm_states.SUSPENDED
        instance.task_state = None
        instance.save(expected_task_state=task_states.SUSPENDING)
        self._notify_about_instance_usage(context, instance, 'suspend.end')

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @wrap_instance_fault
    def resume_instance(self, context, instance):
        """Resume the given suspended instance."""
        context = context.elevated()
        LOG.info(_LI('Resuming'), context=context, instance=instance)

        self._notify_about_instance_usage(context, instance, 'resume.start')
        network_info = self.network_api.get_instance_nw_info(context, instance)
        block_device_info = self._get_instance_block_device_info(
                            context, instance)

        with self._error_out_instance_on_exception(context, instance,
             instance_state=instance.vm_state):
            self.driver.resume(context, instance, network_info,
                               block_device_info)

        instance.power_state = self._get_power_state(context, instance)

        # We default to the ACTIVE state for backwards compatibility
        instance.vm_state = instance.system_metadata.pop('old_vm_state',
                                                         vm_states.ACTIVE)

        instance.task_state = None
        instance.save(expected_task_state=task_states.RESUMING)
        self._notify_about_instance_usage(context, instance, 'resume.end')

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @wrap_instance_fault
    def shelve_instance(self, context, instance, image_id,
                        clean_shutdown):
        """Shelve an instance.

        This should be used when you want to take a snapshot of the instance.
        It also adds system_metadata that can be used by a periodic task to
        offload the shelved instance after a period of time.

        :param context: request context
        :param instance: an Instance object
        :param image_id: an image id to snapshot to.
        :param clean_shutdown: give the GuestOS a chance to stop
        """
        compute_utils.notify_usage_exists(self.notifier, context, instance,
                                          current_period=True)
        self._notify_about_instance_usage(context, instance, 'shelve.start')

        def update_task_state(task_state, expected_state=task_states.SHELVING):
            shelving_state_map = {
                    task_states.IMAGE_PENDING_UPLOAD:
                        task_states.SHELVING_IMAGE_PENDING_UPLOAD,
                    task_states.IMAGE_UPLOADING:
                        task_states.SHELVING_IMAGE_UPLOADING,
                    task_states.SHELVING: task_states.SHELVING}
            task_state = shelving_state_map[task_state]
            expected_state = shelving_state_map[expected_state]
            instance.task_state = task_state
            instance.save(expected_task_state=expected_state)

        self._power_off_instance(context, instance, clean_shutdown)
        self.driver.snapshot(context, instance, image_id, update_task_state)

        instance.system_metadata['shelved_at'] = timeutils.strtime()
        instance.system_metadata['shelved_image_id'] = image_id
        instance.system_metadata['shelved_host'] = self.host
        instance.vm_state = vm_states.SHELVED
        instance.task_state = None
        if CONF.shelved_offload_time == 0:
            instance.task_state = task_states.SHELVING_OFFLOADING
        instance.power_state = self._get_power_state(context, instance)
        instance.save(expected_task_state=[
                task_states.SHELVING,
                task_states.SHELVING_IMAGE_UPLOADING])

        self._notify_about_instance_usage(context, instance, 'shelve.end')

        if CONF.shelved_offload_time == 0:
            self.shelve_offload_instance(context, instance,
                                         clean_shutdown=False)

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_fault
    def shelve_offload_instance(self, context, instance, clean_shutdown):
        """Remove a shelved instance from the hypervisor.

        This frees up those resources for use by other instances, but may lead
        to slower unshelve times for this instance.  This method is used by
        volume backed instances since restoring them doesn't involve the
        potentially large download of an image.

        :param context: request context
        :param instance: nova.objects.instance.Instance
        :param clean_shutdown: give the GuestOS a chance to stop
        """
        self._notify_about_instance_usage(context, instance,
                'shelve_offload.start')

        self._power_off_instance(context, instance, clean_shutdown)
        current_power_state = self._get_power_state(context, instance)

        self.network_api.cleanup_instance_network_on_host(context, instance,
                                                          instance.host)
        network_info = self.network_api.get_instance_nw_info(context, instance)
        block_device_info = self._get_instance_block_device_info(context,
                                                                 instance)
        self.driver.destroy(context, instance, network_info,
                block_device_info)

        instance.power_state = current_power_state
        instance.host = None
        instance.node = None
        instance.vm_state = vm_states.SHELVED_OFFLOADED
        instance.task_state = None
        instance.save(expected_task_state=[task_states.SHELVING,
                                           task_states.SHELVING_OFFLOADING])
        self._delete_scheduler_instance_info(context, instance.uuid)
        self._notify_about_instance_usage(context, instance,
                'shelve_offload.end')

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_event
    @wrap_instance_fault
    def unshelve_instance(self, context, instance, image,
                          filter_properties, node):
        """Unshelve the instance.

        :param context: request context
        :param instance: a nova.objects.instance.Instance object
        :param image: an image to build from.  If None we assume a
            volume backed instance.
        :param filter_properties: dict containing limits, retry info etc.
        :param node: target compute node
        """
        if filter_properties is None:
            filter_properties = {}

        @utils.synchronized(instance.uuid)
        def do_unshelve_instance():
            self._unshelve_instance(context, instance, image,
                                    filter_properties, node)
        do_unshelve_instance()

    def _unshelve_instance_key_scrub(self, instance):
        """Remove data from the instance that may cause side effects."""
        cleaned_keys = dict(
                key_data=instance.key_data,
                auto_disk_config=instance.auto_disk_config)
        instance.key_data = None
        instance.auto_disk_config = False
        return cleaned_keys

    def _unshelve_instance_key_restore(self, instance, keys):
        """Restore previously scrubbed keys before saving the instance."""
        instance.update(keys)

    def _unshelve_instance(self, context, instance, image, filter_properties,
                           node):
        self._notify_about_instance_usage(context, instance, 'unshelve.start')
        instance.task_state = task_states.SPAWNING
        instance.save()

        bdms = objects.BlockDeviceMappingList.get_by_instance_uuid(
                context, instance.uuid)
        block_device_info = self._prep_block_device(context, instance, bdms,
                                                    do_check_attach=False)
        scrubbed_keys = self._unshelve_instance_key_scrub(instance)

        if node is None:
            node = self.driver.get_available_nodes()[0]
            LOG.debug('No node specified, defaulting to %s', node,
                      instance=instance)

        rt = self._get_resource_tracker(node)
        limits = filter_properties.get('limits', {})

        if image:
            shelved_image_ref = instance.image_ref
            instance.image_ref = image['id']
            image_meta = image
        else:
            image_meta = utils.get_image_from_system_metadata(
                instance.system_metadata)

        self.network_api.setup_instance_network_on_host(context, instance,
                                                        self.host)
        network_info = self.network_api.get_instance_nw_info(context, instance)
        try:
            with rt.instance_claim(context, instance, limits):
                self.driver.spawn(context, instance, image_meta,
                                  injected_files=[],
                                  admin_password=None,
                                  network_info=network_info,
                                  block_device_info=block_device_info)
        except Exception:
            with excutils.save_and_reraise_exception():
                LOG.exception(_LE('Instance failed to spawn'),
                              instance=instance)

        if image:
            instance.image_ref = shelved_image_ref
            self._delete_snapshot_of_shelved_instance(context, instance,
                                                      image['id'])

        self._unshelve_instance_key_restore(instance, scrubbed_keys)
        self._update_instance_after_spawn(context, instance)
        # Delete system_metadata for a shelved instance
        compute_utils.remove_shelved_keys_from_system_metadata(instance)

        instance.save(expected_task_state=task_states.SPAWNING)
        self._update_scheduler_instance_info(context, instance)
        self._notify_about_instance_usage(context, instance, 'unshelve.end')

    @messaging.expected_exceptions(NotImplementedError)
    @wrap_instance_fault
    def reset_network(self, context, instance):
        """Reset networking on the given instance."""
        LOG.debug('Reset network', context=context, instance=instance)
        self.driver.reset_network(instance)

    def _inject_network_info(self, context, instance, network_info):
        """Inject network info for the given instance."""
        LOG.debug('Inject network info', context=context, instance=instance)
        LOG.debug('network_info to inject: |%s|', network_info,
                  instance=instance)

        self.driver.inject_network_info(instance,
                                        network_info)

    @wrap_instance_fault
    def inject_network_info(self, context, instance):
        """Inject network info, but don't return the info."""
        network_info = self.network_api.get_instance_nw_info(context, instance)
        self._inject_network_info(context, instance, network_info)

    @messaging.expected_exceptions(NotImplementedError,
                                   exception.InstanceNotFound)
    @wrap_exception()
    @wrap_instance_fault
    def get_console_output(self, context, instance, tail_length):
        """Send the console output for the given instance."""
        context = context.elevated()
        LOG.info(_LI("Get console output"), context=context,
                  instance=instance)
        output = self.driver.get_console_output(context, instance)

        if tail_length is not None:
            output = self._tail_log(output, tail_length)

        return output.decode('utf-8', 'replace').encode('ascii', 'replace')

    def _tail_log(self, log, length):
        try:
            length = int(length)
        except ValueError:
            length = 0

        if length == 0:
            return ''
        else:
            return '\n'.join(log.split('\n')[-int(length):])

    @messaging.expected_exceptions(exception.ConsoleTypeInvalid,
                                   exception.InstanceNotReady,
                                   exception.InstanceNotFound,
                                   exception.ConsoleTypeUnavailable,
                                   NotImplementedError)
    @wrap_exception()
    @wrap_instance_fault
    def get_vnc_console(self, context, console_type, instance):
        """Return connection information for a vnc console."""
        context = context.elevated()
        LOG.debug("Getting vnc console", instance=instance)
        token = str(uuid.uuid4())

        if not CONF.vnc.enabled:
            raise exception.ConsoleTypeUnavailable(console_type=console_type)

        if console_type == 'novnc':
            # For essex, novncproxy_base_url must include the full path
            # including the html file (like http://myhost/vnc_auto.html)
            access_url = '%s?token=%s' % (CONF.vnc.novncproxy_base_url, token)
        elif console_type == 'xvpvnc':
            access_url = '%s?token=%s' % (CONF.vnc.xvpvncproxy_base_url, token)
        else:
            raise exception.ConsoleTypeInvalid(console_type=console_type)

        try:
            # Retrieve connect info from driver, and then decorate with our
            # access info token
            console = self.driver.get_vnc_console(context, instance)
            connect_info = console.get_connection_info(token, access_url)
        except exception.InstanceNotFound:
            if instance.vm_state != vm_states.BUILDING:
                raise
            raise exception.InstanceNotReady(instance_id=instance.uuid)

        return connect_info

    @messaging.expected_exceptions(exception.ConsoleTypeInvalid,
                                   exception.InstanceNotReady,
                                   exception.InstanceNotFound,
                                   exception.ConsoleTypeUnavailable,
                                   NotImplementedError)
    @wrap_exception()
    @wrap_instance_fault
    def get_spice_console(self, context, console_type, instance):
        """Return connection information for a spice console."""
        context = context.elevated()
        LOG.debug("Getting spice console", instance=instance)
        token = str(uuid.uuid4())

        if not CONF.spice.enabled:
            raise exception.ConsoleTypeUnavailable(console_type=console_type)

        if console_type == 'spice-html5':
            # For essex, spicehtml5proxy_base_url must include the full path
            # including the html file (like http://myhost/spice_auto.html)
            access_url = '%s?token=%s' % (CONF.spice.html5proxy_base_url,
                                          token)
        else:
            raise exception.ConsoleTypeInvalid(console_type=console_type)

        try:
            # Retrieve connect info from driver, and then decorate with our
            # access info token
            console = self.driver.get_spice_console(context, instance)
            connect_info = console.get_connection_info(token, access_url)
        except exception.InstanceNotFound:
            if instance.vm_state != vm_states.BUILDING:
                raise
            raise exception.InstanceNotReady(instance_id=instance.uuid)

        return connect_info

    @messaging.expected_exceptions(exception.ConsoleTypeInvalid,
                                   exception.InstanceNotReady,
                                   exception.InstanceNotFound,
                                   exception.ConsoleTypeUnavailable,
                                   NotImplementedError)
    @wrap_exception()
    @wrap_instance_fault
    def get_rdp_console(self, context, console_type, instance):
        """Return connection information for a RDP console."""
        context = context.elevated()
        LOG.debug("Getting RDP console", instance=instance)
        token = str(uuid.uuid4())

        if not CONF.rdp.enabled:
            raise exception.ConsoleTypeUnavailable(console_type=console_type)

        if console_type == 'rdp-html5':
            access_url = '%s?token=%s' % (CONF.rdp.html5_proxy_base_url,
                                          token)
        else:
            raise exception.ConsoleTypeInvalid(console_type=console_type)

        try:
            # Retrieve connect info from driver, and then decorate with our
            # access info token
            console = self.driver.get_rdp_console(context, instance)
            connect_info = console.get_connection_info(token, access_url)
        except exception.InstanceNotFound:
            if instance.vm_state != vm_states.BUILDING:
                raise
            raise exception.InstanceNotReady(instance_id=instance.uuid)

        return connect_info

    @messaging.expected_exceptions(exception.ConsoleTypeInvalid,
                                   exception.InstanceNotReady,
                                   exception.InstanceNotFound,
                                   exception.ConsoleTypeUnavailable,
                                   NotImplementedError)
    @wrap_exception()
    @wrap_instance_fault
    def get_mks_console(self, context, console_type, instance):
        """Return connection information for a MKS console."""
        context = context.elevated()
        LOG.debug("Getting MKS console", instance=instance)
        token = str(uuid.uuid4())

        if not CONF.mks.enabled:
            raise exception.ConsoleTypeUnavailable(console_type=console_type)

        if console_type == 'webmks':
            access_url = '%s?token=%s' % (CONF.mks.mksproxy_base_url,
                                          token)
        else:
            raise exception.ConsoleTypeInvalid(console_type=console_type)

        try:
            # Retrieve connect info from driver, and then decorate with our
            # access info token
            console = self.driver.get_mks_console(context, instance)
            connect_info = console.get_connection_info(token, access_url)
        except exception.InstanceNotFound:
            if instance.vm_state != vm_states.BUILDING:
                raise
            raise exception.InstanceNotReady(instance_id=instance.uuid)

        return connect_info

    @messaging.expected_exceptions(
        exception.ConsoleTypeInvalid,
        exception.InstanceNotReady,
        exception.InstanceNotFound,
        exception.ConsoleTypeUnavailable,
        exception.SocketPortRangeExhaustedException,
        exception.ImageSerialPortNumberInvalid,
        exception.ImageSerialPortNumberExceedFlavorValue,
        NotImplementedError)
    @wrap_exception()
    @wrap_instance_fault
    def get_serial_console(self, context, console_type, instance):
        """Returns connection information for a serial console."""

        LOG.debug("Getting serial console", instance=instance)

        if not CONF.serial_console.enabled:
            raise exception.ConsoleTypeUnavailable(console_type=console_type)

        context = context.elevated()

        token = str(uuid.uuid4())
        access_url = '%s?token=%s' % (CONF.serial_console.base_url, token)

        try:
            # Retrieve connect info from driver, and then decorate with our
            # access info token
            console = self.driver.get_serial_console(context, instance)
            connect_info = console.get_connection_info(token, access_url)
        except exception.InstanceNotFound:
            if instance.vm_state != vm_states.BUILDING:
                raise
            raise exception.InstanceNotReady(instance_id=instance.uuid)

        return connect_info

    @messaging.expected_exceptions(exception.ConsoleTypeInvalid,
                                   exception.InstanceNotReady,
                                   exception.InstanceNotFound)
    @wrap_exception()
    @wrap_instance_fault
    def validate_console_port(self, ctxt, instance, port, console_type):
        if console_type == "spice-html5":
            console_info = self.driver.get_spice_console(ctxt, instance)
        elif console_type == "rdp-html5":
            console_info = self.driver.get_rdp_console(ctxt, instance)
        elif console_type == "serial":
            console_info = self.driver.get_serial_console(ctxt, instance)
        elif console_type == "webmks":
            console_info = self.driver.get_mks_console(ctxt, instance)
        else:
            console_info = self.driver.get_vnc_console(ctxt, instance)

        return console_info.port == port

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_fault
    def reserve_block_device_name(self, context, instance, device,
                                  volume_id, disk_bus, device_type):
        @utils.synchronized(instance.uuid)
        def do_reserve():
            bdms = (
                objects.BlockDeviceMappingList.get_by_instance_uuid(
                    context, instance.uuid))

            # NOTE(ndipanov): We need to explicitly set all the fields on the
            #                 object so that obj_load_attr does not fail
            new_bdm = objects.BlockDeviceMapping(
                    context=context,
                    source_type='volume', destination_type='volume',
                    instance_uuid=instance.uuid, boot_index=None,
                    volume_id=volume_id or 'reserved',
                    device_name=device, guest_format=None,
                    disk_bus=disk_bus, device_type=device_type)

            new_bdm.device_name = self._get_device_name_for_instance(
                    instance, bdms, new_bdm)

            # NOTE(vish): create bdm here to avoid race condition
            new_bdm.create()
            return new_bdm

        return do_reserve()

    @wrap_exception()
    @wrap_instance_fault
    def attach_volume(self, context, instance, bdm):
        """Attach a volume to an instance."""
        driver_bdm = driver_block_device.convert_volume(bdm)

        @utils.synchronized(instance.uuid)
        def do_attach_volume(context, instance, driver_bdm):
            try:
                return self._attach_volume(context, instance, driver_bdm)
            except Exception:
                with excutils.save_and_reraise_exception():
                    bdm.destroy()

        do_attach_volume(context, instance, driver_bdm)

    def _attach_volume(self, context, instance, bdm):
        context = context.elevated()
        LOG.info(_LI('Attaching volume %(volume_id)s to %(mountpoint)s'),
                  {'volume_id': bdm.volume_id,
                  'mountpoint': bdm['mount_device']},
                 context=context, instance=instance)
        try:
            bdm.attach(context, instance, self.volume_api, self.driver,
                       do_check_attach=False, do_driver_attach=True)
        except Exception:
            with excutils.save_and_reraise_exception():
                LOG.exception(_LE("Failed to attach %(volume_id)s "
                                  "at %(mountpoint)s"),
                              {'volume_id': bdm.volume_id,
                               'mountpoint': bdm['mount_device']},
                              context=context, instance=instance)
                self.volume_api.unreserve_volume(context, bdm.volume_id)

        info = {'volume_id': bdm.volume_id}
        self._notify_about_instance_usage(
            context, instance, "volume.attach", extra_usage_info=info)

    def _driver_detach_volume(self, context, instance, bdm):
        """Do the actual driver detach using block device mapping."""
        mp = bdm.device_name
        volume_id = bdm.volume_id

        LOG.info(_LI('Detach volume %(volume_id)s from mountpoint %(mp)s'),
                  {'volume_id': volume_id, 'mp': mp},
                  context=context, instance=instance)

        connection_info = jsonutils.loads(bdm.connection_info)
        # NOTE(vish): We currently don't use the serial when disconnecting,
        #             but added for completeness in case we ever do.
        if connection_info and 'serial' not in connection_info:
            connection_info['serial'] = volume_id
        try:
            if not self.driver.instance_exists(instance):
                LOG.warning(_LW('Detaching volume from unknown instance'),
                            context=context, instance=instance)

            encryption = encryptors.get_encryption_metadata(
                context, self.volume_api, volume_id, connection_info)

            self.driver.detach_volume(connection_info,
                                      instance,
                                      mp,
                                      encryption=encryption)
        except exception.DiskNotFound as err:
            LOG.warning(_LW('Ignoring DiskNotFound exception while detaching '
                            'volume %(volume_id)s from %(mp)s: %(err)s'),
                        {'volume_id': volume_id, 'mp': mp, 'err': err},
                        instance=instance)
        except Exception:
            with excutils.save_and_reraise_exception():
                LOG.exception(_LE('Failed to detach volume %(volume_id)s '
                                  'from %(mp)s'),
                              {'volume_id': volume_id, 'mp': mp},
                              context=context, instance=instance)
                self.volume_api.roll_detaching(context, volume_id)

    def _detach_volume(self, context, volume_id, instance, destroy_bdm=True):
        """Detach a volume from an instance.

        :param context: security context
        :param volume_id: the volume id
        :param instance: the Instance object to detach the volume from
        :param destroy_bdm: if True, the corresponding BDM entry will be marked
                            as deleted. Disabling this is useful for operations
                            like rebuild, when we don't want to destroy BDM

        """

        bdm = objects.BlockDeviceMapping.get_by_volume_id(
                context, volume_id)
        if CONF.volume_usage_poll_interval > 0:
            vol_stats = []
            mp = bdm.device_name
            # Handle bootable volumes which will not contain /dev/
            if '/dev/' in mp:
                mp = mp[5:]
            try:
                vol_stats = self.driver.block_stats(instance, mp)
            except NotImplementedError:
                pass

            if vol_stats:
                LOG.debug("Updating volume usage cache with totals",
                          instance=instance)
                rd_req, rd_bytes, wr_req, wr_bytes, flush_ops = vol_stats
                vol_usage = objects.VolumeUsage(context)
                vol_usage.volume_id = volume_id
                vol_usage.instance_uuid = instance.uuid
                vol_usage.project_id = instance.project_id
                vol_usage.user_id = instance.user_id
                vol_usage.availability_zone = instance.availability_zone
                vol_usage.curr_reads = rd_req
                vol_usage.curr_read_bytes = rd_bytes
                vol_usage.curr_writes = wr_req
                vol_usage.curr_write_bytes = wr_bytes
                vol_usage.save(update_totals=True)
                self.notifier.info(context, 'volume.usage',
                                   compute_utils.usage_volume_info(vol_usage))

        self._driver_detach_volume(context, instance, bdm)
        connector = self.driver.get_volume_connector(instance)
        self.volume_api.terminate_connection(context, volume_id, connector)

        if destroy_bdm:
            bdm.destroy()

        info = dict(volume_id=volume_id)
        self._notify_about_instance_usage(
            context, instance, "volume.detach", extra_usage_info=info)
        self.volume_api.detach(context.elevated(), volume_id)

    @wrap_exception()
    @wrap_instance_fault
    def detach_volume(self, context, volume_id, instance):
        """Detach a volume from an instance."""

        self._detach_volume(context, volume_id, instance)

    def _init_volume_connection(self, context, new_volume_id,
                                old_volume_id, connector, instance, bdm):

        new_cinfo = self.volume_api.initialize_connection(context,
                                                          new_volume_id,
                                                          connector)
        old_cinfo = jsonutils.loads(bdm['connection_info'])
        if old_cinfo and 'serial' not in old_cinfo:
            old_cinfo['serial'] = old_volume_id
        new_cinfo['serial'] = old_cinfo['serial']
        return (old_cinfo, new_cinfo)

    def _swap_volume(self, context, instance, bdm, connector,
                     old_volume_id, new_volume_id, resize_to):
        mountpoint = bdm['device_name']
        failed = False
        new_cinfo = None
        try:
            old_cinfo, new_cinfo = self._init_volume_connection(context,
                                                                new_volume_id,
                                                                old_volume_id,
                                                                connector,
                                                                instance,
                                                                bdm)
            LOG.debug("swap_volume: Calling driver volume swap with "
                      "connection infos: new: %(new_cinfo)s; "
                      "old: %(old_cinfo)s",
                      {'new_cinfo': new_cinfo, 'old_cinfo': old_cinfo},
                      contex=context, instance=instance)
            self.driver.swap_volume(old_cinfo, new_cinfo, instance, mountpoint,
                                    resize_to)
        except Exception:
            failed = True
            with excutils.save_and_reraise_exception():
                if new_cinfo:
                    msg = _LE("Failed to swap volume %(old_volume_id)s "
                              "for %(new_volume_id)s")
                    LOG.exception(msg, {'old_volume_id': old_volume_id,
                                        'new_volume_id': new_volume_id},
                                  context=context,
                                  instance=instance)
                else:
                    msg = _LE("Failed to connect to volume %(volume_id)s "
                              "with volume at %(mountpoint)s")
                    LOG.exception(msg, {'volume_id': new_volume_id,
                                        'mountpoint': bdm['device_name']},
                                  context=context,
                                  instance=instance)
                self.volume_api.roll_detaching(context, old_volume_id)
                self.volume_api.unreserve_volume(context, new_volume_id)
        finally:
            conn_volume = new_volume_id if failed else old_volume_id
            if new_cinfo:
                LOG.debug("swap_volume: calling Cinder terminate_connection "
                          "for %(volume)s", {'volume': conn_volume},
                          context=context, instance=instance)
                self.volume_api.terminate_connection(context,
                                                     conn_volume,
                                                     connector)
            # If Cinder initiated the swap, it will keep
            # the original ID
            comp_ret = self.volume_api.migrate_volume_completion(
                                                      context,
                                                      old_volume_id,
                                                      new_volume_id,
                                                      error=failed)
            LOG.debug("swap_volume: Cinder migrate_volume_completion "
                      "returned: %(comp_ret)s", {'comp_ret': comp_ret},
                      context=context, instance=instance)

        return (comp_ret, new_cinfo)

    @wrap_exception()
    @reverts_task_state
    @wrap_instance_fault
    def swap_volume(self, context, old_volume_id, new_volume_id, instance):
        """Swap volume for an instance."""
        context = context.elevated()

        bdm = objects.BlockDeviceMapping.get_by_volume_id(
                context, old_volume_id, instance_uuid=instance.uuid)
        connector = self.driver.get_volume_connector(instance)

        resize_to = 0
        old_vol_size = self.volume_api.get(context, old_volume_id)['size']
        new_vol_size = self.volume_api.get(context, new_volume_id)['size']
        if new_vol_size > old_vol_size:
            resize_to = new_vol_size

        LOG.info(_LI('Swapping volume %(old_volume)s for %(new_volume)s'),
                  {'old_volume': old_volume_id, 'new_volume': new_volume_id},
                  context=context, instance=instance)
        comp_ret, new_cinfo = self._swap_volume(context, instance,
                                                         bdm,
                                                         connector,
                                                         old_volume_id,
                                                         new_volume_id,
                                                         resize_to)

        save_volume_id = comp_ret['save_volume_id']

        # Update bdm
        values = {
            'connection_info': jsonutils.dumps(new_cinfo),
            'delete_on_termination': False,
            'source_type': 'volume',
            'destination_type': 'volume',
            'snapshot_id': None,
            'volume_id': save_volume_id,
            'no_device': None}

        if resize_to:
            values['volume_size'] = resize_to

        LOG.debug("swap_volume: Updating volume %(volume_id)s BDM record with "
                  "%(updates)s", {'volume_id': bdm.volume_id,
                                  'updates': values},
                  context=context, instance=instance)
        bdm.update(values)
        bdm.save()

    @wrap_exception()
    def remove_volume_connection(self, context, volume_id, instance):
        """Remove a volume connection using the volume api."""
        # NOTE(vish): We don't want to actually mark the volume
        #             detached, or delete the bdm, just remove the
        #             connection from this host.

        try:
            bdm = objects.BlockDeviceMapping.get_by_volume_id(
                    context, volume_id)
            self._driver_detach_volume(context, instance, bdm)
            connector = self.driver.get_volume_connector(instance)
            self.volume_api.terminate_connection(context, volume_id, connector)
        except exception.NotFound:
            pass

    @wrap_exception()
    @wrap_instance_fault
    def attach_interface(self, context, instance, network_id, port_id,
                         requested_ip):
        """Use hotplug to add an network adapter to an instance."""
        network_info = self.network_api.allocate_port_for_instance(
            context, instance, port_id, network_id, requested_ip)
        if len(network_info) != 1:
            LOG.error(_LE('allocate_port_for_instance returned %(ports)s '
                          'ports'), {'ports': len(network_info)})
            raise exception.InterfaceAttachFailed(
                    instance_uuid=instance.uuid)
        image_meta = utils.get_image_from_system_metadata(
            instance.system_metadata)

        try:
            self.driver.attach_interface(instance, image_meta, network_info[0])
        except exception.NovaException as ex:
            port_id = network_info[0].get('id')
            LOG.warn(_LW("attach interface failed , try to deallocate "
                         "port %(port_id)s, reason: %(msg)s"),
                     {'port_id': port_id, 'msg': ex},
                     instance=instance)
            try:
                self.network_api.deallocate_port_for_instance(
                    context, instance, port_id)
            except Exception:
                LOG.warn(_LW("deallocate port %(port_id)s failed"),
                             {'port_id': port_id}, instance=instance)
            raise exception.InterfaceAttachFailed(
                instance_uuid=instance.uuid)

        return network_info[0]

    @wrap_exception()
    @wrap_instance_fault
    def detach_interface(self, context, instance, port_id):
        """Detach an network adapter from an instance."""
        network_info = instance.info_cache.network_info
        condemned = None
        for vif in network_info:
            if vif['id'] == port_id:
                condemned = vif
                break
        if condemned is None:
            raise exception.PortNotFound(_("Port %s is not "
                                           "attached") % port_id)
        try:
            self.driver.detach_interface(instance, condemned)
        except exception.NovaException as ex:
            LOG.warning(_LW("Detach interface failed, port_id=%(port_id)s,"
                            " reason: %(msg)s"),
                        {'port_id': port_id, 'msg': ex}, instance=instance)
            raise exception.InterfaceDetachFailed(instance_uuid=instance.uuid)
        else:
            try:
                self.network_api.deallocate_port_for_instance(
                    context, instance, port_id)
            except Exception as ex:
                with excutils.save_and_reraise_exception():
                    # Since this is a cast operation, log the failure for
                    # triage.
                    LOG.warning(_LW('Failed to deallocate port %(port_id)s '
                                    'for instance. Error: %(error)s'),
                                {'port_id': port_id, 'error': ex},
                                instance=instance)

    def _get_compute_info(self, context, host):
        return objects.ComputeNode.get_first_node_by_host_for_old_compat(
            context, host)

    @wrap_exception()
    def check_instance_shared_storage(self, ctxt, instance, data):
        """Check if the instance files are shared

        :param ctxt: security context
        :param instance: dict of instance data
        :param data: result of driver.check_instance_shared_storage_local

        Returns True if instance disks located on shared storage and
        False otherwise.
        """
        return self.driver.check_instance_shared_storage_remote(ctxt, data)

    @wrap_exception()
    @wrap_instance_event
    @wrap_instance_fault
    def check_can_live_migrate_destination(self, ctxt, instance,
                                           block_migration, disk_over_commit):
        """Check if it is possible to execute live migration.

        This runs checks on the destination host, and then calls
        back to the source host to check the results.

        :param context: security context
        :param instance: dict of instance data
        :param block_migration: if true, prepare for block migration
        :param disk_over_commit: if true, allow disk over commit
        :returns: a dict containing migration info
        """
        src_compute_info = obj_base.obj_to_primitive(
            self._get_compute_info(ctxt, instance.host))
        dst_compute_info = obj_base.obj_to_primitive(
            self._get_compute_info(ctxt, CONF.host))
        dest_check_data = self.driver.check_can_live_migrate_destination(ctxt,
            instance, src_compute_info, dst_compute_info,
            block_migration, disk_over_commit)
        migrate_data = {}
        try:
            migrate_data = self.compute_rpcapi.\
                                check_can_live_migrate_source(ctxt, instance,
                                                              dest_check_data)
        finally:
            self.driver.check_can_live_migrate_destination_cleanup(ctxt,
                    dest_check_data)
        if 'migrate_data' in dest_check_data:
            migrate_data.update(dest_check_data['migrate_data'])
        return migrate_data

    @wrap_exception()
    @wrap_instance_event
    @wrap_instance_fault
    def check_can_live_migrate_source(self, ctxt, instance, dest_check_data):
        """Check if it is possible to execute live migration.

        This checks if the live migration can succeed, based on the
        results from check_can_live_migrate_destination.

        :param ctxt: security context
        :param instance: dict of instance data
        :param dest_check_data: result of check_can_live_migrate_destination
        :returns: a dict containing migration info
        """
        is_volume_backed = self.compute_api.is_volume_backed_instance(ctxt,
                                                                      instance)
        dest_check_data['is_volume_backed'] = is_volume_backed
        block_device_info = self._get_instance_block_device_info(
                            ctxt, instance, refresh_conn_info=True)
        return self.driver.check_can_live_migrate_source(ctxt, instance,
                                                         dest_check_data,
                                                         block_device_info)

    @wrap_exception()
    @wrap_instance_event
    @wrap_instance_fault
    def pre_live_migration(self, context, instance, block_migration, disk,
                           migrate_data):
        """Preparations for live migration at dest host.

        :param context: security context
        :param instance: dict of instance data
        :param block_migration: if true, prepare for block migration
        :param migrate_data: if not None, it is a dict which holds data
                             required for live migration without shared
                             storage.

        """
        block_device_info = self._get_instance_block_device_info(
                            context, instance, refresh_conn_info=True)

        network_info = self.network_api.get_instance_nw_info(context, instance)
        self._notify_about_instance_usage(
                     context, instance, "live_migration.pre.start",
                     network_info=network_info)

        pre_live_migration_data = self.driver.pre_live_migration(context,
                                       instance,
                                       block_device_info,
                                       network_info,
                                       disk,
                                       migrate_data)

        # NOTE(tr3buchet): setup networks on destination host
        self.network_api.setup_networks_on_host(context, instance,
                                                         self.host)

        # Creating filters to hypervisors and firewalls.
        # An example is that nova-instance-instance-xxx,
        # which is written to libvirt.xml(Check "virsh nwfilter-list")
        # This nwfilter is necessary on the destination host.
        # In addition, this method is creating filtering rule
        # onto destination host.
        self.driver.ensure_filtering_rules_for_instance(instance,
                                            network_info)

        self._notify_about_instance_usage(
                     context, instance, "live_migration.pre.end",
                     network_info=network_info)

        return pre_live_migration_data

    def _do_live_migration(self, context, dest, instance, block_migration,
                           migration, migrate_data):
        # NOTE(danms): Remove these guards in v5.0 of the RPC API
        if migration:
            # NOTE(danms): We should enhance the RT to account for migrations
            # and use the status field to denote when the accounting has been
            # done on source/destination. For now, this is just here for status
            # reporting
            migration.status = 'preparing'
            migration.save()

        # Create a local copy since we'll be modifying the dictionary
        migrate_data = dict(migrate_data or {})
        try:
            if block_migration:
                block_device_info = self._get_instance_block_device_info(
                    context, instance)
                disk = self.driver.get_instance_disk_info(
                    instance, block_device_info=block_device_info)
            else:
                disk = None

            pre_migration_data = self.compute_rpcapi.pre_live_migration(
                context, instance,
                block_migration, disk, dest, migrate_data)
            migrate_data['pre_live_migration_result'] = pre_migration_data

        except Exception:
            with excutils.save_and_reraise_exception():
                LOG.exception(_LE('Pre live migration failed at %s'),
                              dest, instance=instance)
                if migration:
                    migration.status = 'failed'
                    migration.save()
                self._rollback_live_migration(context, instance, dest,
                                              block_migration, migrate_data)

        if migration:
            migration.status = 'running'
            migration.save()

        migrate_data['migration'] = migration
        try:
            self.driver.live_migration(context, instance, dest,
                                       self._post_live_migration,
                                       self._rollback_live_migration,
                                       block_migration, migrate_data)
        except Exception:
            # Executing live migration
            # live_migration might raises exceptions, but
            # nothing must be recovered in this version.
            LOG.exception(_LE('Live migration failed.'), instance=instance)
            with excutils.save_and_reraise_exception():
                if migration:
                    migration.status = 'failed'
                    migration.save()

    @wrap_exception()
    @wrap_instance_event
    @wrap_instance_fault
    def live_migration(self, context, dest, instance, block_migration,
                       migration, migrate_data):
        """Executing live migration.

        :param context: security context
        :param dest: destination host
        :param instance: a nova.objects.instance.Instance object
        :param block_migration: if true, prepare for block migration
        :param migration: an nova.objects.Migration object
        :param migrate_data: implementation specific params

        """

        # NOTE(danms): Remove these guards in v5.0 of the RPC API
        if migration:
            migration.status = 'queued'
            migration.save()

        def dispatch_live_migration(*args, **kwargs):
            with self._live_migration_semaphore:
                self._do_live_migration(*args, **kwargs)

        # NOTE(danms): We spawn here to return the RPC worker thread back to
        # the pool. Since what follows could take a really long time, we don't
        # want to tie up RPC workers.
        utils.spawn_n(dispatch_live_migration,
                      context, dest, instance,
                      block_migration, migration,
                      migrate_data)

    def _live_migration_cleanup_flags(self, block_migration, migrate_data):
        """Determine whether disks or instance path need to be cleaned up after
        live migration (at source on success, at destination on rollback)

        Block migration needs empty image at destination host before migration
        starts, so if any failure occurs, any empty images has to be deleted.

        Also Volume backed live migration w/o shared storage needs to delete
        newly created instance-xxx dir on the destination as a part of its
        rollback process

        :param block_migration: if true, it was a block migration
        :param migrate_data: implementation specific data
        :returns: (bool, bool) -- do_cleanup, destroy_disks
        """
        # NOTE(angdraug): block migration wouldn't have been allowed if either
        #                 block storage or instance path were shared
        is_shared_block_storage = not block_migration
        is_shared_instance_path = not block_migration
        if migrate_data:
            is_shared_block_storage = migrate_data.get(
                    'is_shared_block_storage', is_shared_block_storage)
            is_shared_instance_path = migrate_data.get(
                    'is_shared_instance_path', is_shared_instance_path)

        # No instance booting at source host, but instance dir
        # must be deleted for preparing next block migration
        # must be deleted for preparing next live migration w/o shared storage
        do_cleanup = block_migration or not is_shared_instance_path
        destroy_disks = not is_shared_block_storage

        return (do_cleanup, destroy_disks)

    @wrap_exception()
    @wrap_instance_fault
    def _post_live_migration(self, ctxt, instance,
                            dest, block_migration=False, migrate_data=None):
        """Post operations for live migration.

        This method is called from live_migration
        and mainly updating database record.

        :param ctxt: security context
        :param instance: instance dict
        :param dest: destination host
        :param block_migration: if true, prepare for block migration
        :param migrate_data: if not None, it is a dict which has data
        required for live migration without shared storage

        """
        LOG.info(_LI('_post_live_migration() is started..'),
                 instance=instance)

        bdms = objects.BlockDeviceMappingList.get_by_instance_uuid(
                ctxt, instance.uuid)

        # Cleanup source host post live-migration
        block_device_info = self._get_instance_block_device_info(
                            ctxt, instance, bdms=bdms)
        self.driver.post_live_migration(ctxt, instance, block_device_info,
                                        migrate_data)

        # Detaching volumes.
        connector = self.driver.get_volume_connector(instance)
        for bdm in bdms:
            # NOTE(vish): We don't want to actually mark the volume
            #             detached, or delete the bdm, just remove the
            #             connection from this host.

            # remove the volume connection without detaching from hypervisor
            # because the instance is not running anymore on the current host
            if bdm.is_volume:
                self.volume_api.terminate_connection(ctxt, bdm.volume_id,
                                                     connector)

        # Releasing vlan.
        # (not necessary in current implementation?)

        network_info = self.network_api.get_instance_nw_info(ctxt, instance)

        self._notify_about_instance_usage(ctxt, instance,
                                          "live_migration._post.start",
                                          network_info=network_info)
        # Releasing security group ingress rule.
        LOG.debug('Calling driver.unfilter_instance from _post_live_migration',
                  instance=instance)
        self.driver.unfilter_instance(instance,
                                      network_info)

        migration = {'source_compute': self.host,
                     'dest_compute': dest, }
        self.network_api.migrate_instance_start(ctxt,
                                                instance,
                                                migration)

        destroy_vifs = False
        try:
            self.driver.post_live_migration_at_source(ctxt, instance,
                                                      network_info)
        except NotImplementedError as ex:
            LOG.debug(ex, instance=instance)
            # For all hypervisors other than libvirt, there is a possibility
            # they are unplugging networks from source node in the cleanup
            # method
            destroy_vifs = True

        # Define domain at destination host, without doing it,
        # pause/suspend/terminate do not work.
        self.compute_rpcapi.post_live_migration_at_destination(ctxt,
                instance, block_migration, dest)

        do_cleanup, destroy_disks = self._live_migration_cleanup_flags(
                block_migration, migrate_data)

        if do_cleanup:
            LOG.debug('Calling driver.cleanup from _post_live_migration',
                      instance=instance)
            self.driver.cleanup(ctxt, instance, network_info,
                                destroy_disks=destroy_disks,
                                migrate_data=migrate_data,
                                destroy_vifs=destroy_vifs)

        self.instance_events.clear_events_for_instance(instance)

        # NOTE(timello): make sure we update available resources on source
        # host even before next periodic task.
        self.update_available_resource(ctxt)

        self._update_scheduler_instance_info(ctxt, instance)
        self._notify_about_instance_usage(ctxt, instance,
                                          "live_migration._post.end",
                                          network_info=network_info)
        LOG.info(_LI('Migrating instance to %s finished successfully.'),
                 dest, instance=instance)
        LOG.info(_LI("You may see the error \"libvirt: QEMU error: "
                     "Domain not found: no domain with matching name.\" "
                     "This error can be safely ignored."),
                 instance=instance)

        self._clean_instance_console_tokens(ctxt, instance)
        if migrate_data and migrate_data.get('migration'):
            migrate_data['migration'].status = 'completed'
            migrate_data['migration'].save()

    def _consoles_enabled(self):
        """Returns whether a console is enable."""
        return (CONF.vnc.enabled or CONF.spice.enabled or
                CONF.rdp.enabled or CONF.serial_console.enabled or
                CONF.mks.enabled)

    def _clean_instance_console_tokens(self, ctxt, instance):
        """Clean console tokens stored for an instance."""
        if self._consoles_enabled():
            if CONF.cells.enable:
                self.cells_rpcapi.consoleauth_delete_tokens(
                    ctxt, instance.uuid)
            else:
                self.consoleauth_rpcapi.delete_tokens_for_instance(
                    ctxt, instance.uuid)

    @wrap_exception()
    @wrap_instance_event
    @wrap_instance_fault
    def post_live_migration_at_destination(self, context, instance,
                                           block_migration):
        """Post operations for live migration .

        :param context: security context
        :param instance: Instance dict
        :param block_migration: if true, prepare for block migration

        """
        LOG.info(_LI('Post operation of migration started'),
                 instance=instance)

        # NOTE(tr3buchet): setup networks on destination host
        #                  this is called a second time because
        #                  multi_host does not create the bridge in
        #                  plug_vifs
        self.network_api.setup_networks_on_host(context, instance,
                                                         self.host)
        migration = {'source_compute': instance.host,
                     'dest_compute': self.host, }
        self.network_api.migrate_instance_finish(context,
                                                 instance,
                                                 migration)

        network_info = self.network_api.get_instance_nw_info(context, instance)
        self._notify_about_instance_usage(
                     context, instance, "live_migration.post.dest.start",
                     network_info=network_info)
        block_device_info = self._get_instance_block_device_info(context,
                                                                 instance)

        self.driver.post_live_migration_at_destination(context, instance,
                                            network_info,
                                            block_migration, block_device_info)
        # Restore instance state
        current_power_state = self._get_power_state(context, instance)
        node_name = None
        prev_host = instance.host
        try:
            compute_node = self._get_compute_info(context, self.host)
            node_name = compute_node.hypervisor_hostname
        except exception.ComputeHostNotFound:
            LOG.exception(_LE('Failed to get compute_info for %s'), self.host)
        finally:
            instance.host = self.host
            instance.power_state = current_power_state
            instance.task_state = None
            instance.node = node_name
            instance.save(expected_task_state=task_states.MIGRATING)

        # NOTE(tr3buchet): tear down networks on source host
        self.network_api.setup_networks_on_host(context, instance,
                                                prev_host, teardown=True)
        # NOTE(vish): this is necessary to update dhcp
        self.network_api.setup_networks_on_host(context, instance, self.host)
        self._notify_about_instance_usage(
                     context, instance, "live_migration.post.dest.end",
                     network_info=network_info)

    @wrap_exception()
    @wrap_instance_fault
    def _rollback_live_migration(self, context, instance,
                                 dest, block_migration, migrate_data=None):
        """Recovers Instance/volume state from migrating -> running.

        :param context: security context
        :param instance: nova.objects.instance.Instance object
        :param dest:
            This method is called from live migration src host.
            This param specifies destination host.
        :param block_migration: if true, prepare for block migration
        :param migrate_data:
            if not none, contains implementation specific data.

        """
        instance.task_state = None
        instance.save(expected_task_state=[task_states.MIGRATING])

        # NOTE(danms): Pop out the migration object so we don't pass
        # it over RPC unintentionally below
        if migrate_data:
            migration = migrate_data.pop('migration', None)
        else:
            migration = None

        # NOTE(tr3buchet): setup networks on source host (really it's re-setup)
        self.network_api.setup_networks_on_host(context, instance, self.host)

        bdms = objects.BlockDeviceMappingList.get_by_instance_uuid(
                context, instance.uuid)
        for bdm in bdms:
            if bdm.is_volume:
                self.compute_rpcapi.remove_volume_connection(
                        context, instance, bdm.volume_id, dest)

        self._notify_about_instance_usage(context, instance,
                                          "live_migration._rollback.start")

        do_cleanup, destroy_disks = self._live_migration_cleanup_flags(
                block_migration, migrate_data)

        if do_cleanup:
            self.compute_rpcapi.rollback_live_migration_at_destination(
                    context, instance, dest, destroy_disks=destroy_disks,
                    migrate_data=migrate_data)

        self._notify_about_instance_usage(context, instance,
                                          "live_migration._rollback.end")
        if migration:
            migration.status = 'error'
            migration.save()

    @wrap_exception()
    @wrap_instance_event
    @wrap_instance_fault
    def rollback_live_migration_at_destination(self, context, instance,
                                               destroy_disks,
                                               migrate_data):
        """Cleaning up image directory that is created pre_live_migration.

        :param context: security context
        :param instance: a nova.objects.instance.Instance object sent over rpc
        """
        network_info = self.network_api.get_instance_nw_info(context, instance)
        self._notify_about_instance_usage(
                      context, instance, "live_migration.rollback.dest.start",
                      network_info=network_info)

        # NOTE(tr3buchet): tear down networks on destination host
        self.network_api.setup_networks_on_host(context, instance,
                                                self.host, teardown=True)

        # NOTE(vish): The mapping is passed in so the driver can disconnect
        #             from remote volumes if necessary
        block_device_info = self._get_instance_block_device_info(context,
                                                                 instance)
        self.driver.rollback_live_migration_at_destination(
                        context, instance, network_info, block_device_info,
                        destroy_disks=destroy_disks, migrate_data=migrate_data)
        self._notify_about_instance_usage(
                        context, instance, "live_migration.rollback.dest.end",
                        network_info=network_info)

    @periodic_task.periodic_task(
        spacing=CONF.heal_instance_info_cache_interval)
    def _heal_instance_info_cache(self, context):
        """Called periodically.  On every call, try to update the
        info_cache's network information for another instance by
        calling to the network manager.

        This is implemented by keeping a cache of uuids of instances
        that live on this host.  On each call, we pop one off of a
        list, pull the DB record, and try the call to the network API.
        If anything errors don't fail, as it's possible the instance
        has been deleted, etc.
        """
        heal_interval = CONF.heal_instance_info_cache_interval
        if not heal_interval:
            return

        instance_uuids = getattr(self, '_instance_uuids_to_heal', [])
        instance = None

        LOG.debug('Starting heal instance info cache')

        if not instance_uuids:
            # The list of instances to heal is empty so rebuild it
            LOG.debug('Rebuilding the list of instances to heal')
            db_instances = objects.InstanceList.get_by_host(
                context, self.host, expected_attrs=[], use_slave=True)
            for inst in db_instances:
                # We don't want to refresh the cache for instances
                # which are building or deleting so don't put them
                # in the list. If they are building they will get
                # added to the list next time we build it.
                if (inst.vm_state == vm_states.BUILDING):
                    LOG.debug('Skipping network cache update for instance '
                              'because it is Building.', instance=inst)
                    continue
                if (inst.task_state == task_states.DELETING):
                    LOG.debug('Skipping network cache update for instance '
                              'because it is being deleted.', instance=inst)
                    continue

                if not instance:
                    # Save the first one we find so we don't
                    # have to get it again
                    instance = inst
                else:
                    instance_uuids.append(inst['uuid'])

            self._instance_uuids_to_heal = instance_uuids
        else:
            # Find the next valid instance on the list
            while instance_uuids:
                try:
                    inst = objects.Instance.get_by_uuid(
                            context, instance_uuids.pop(0),
                            expected_attrs=['system_metadata', 'info_cache'],
                            use_slave=True)
                except exception.InstanceNotFound:
                    # Instance is gone.  Try to grab another.
                    continue

                # Check the instance hasn't been migrated
                if inst.host != self.host:
                    LOG.debug('Skipping network cache update for instance '
                              'because it has been migrated to another '
                              'host.', instance=inst)
                # Check the instance isn't being deleting
                elif inst.task_state == task_states.DELETING:
                    LOG.debug('Skipping network cache update for instance '
                              'because it is being deleted.', instance=inst)
                else:
                    instance = inst
                    break

        if instance:
            # We have an instance now to refresh
            try:
                # Call to network API to get instance info.. this will
                # force an update to the instance's info_cache
                self.network_api.get_instance_nw_info(context, instance)
                LOG.debug('Updated the network info_cache for instance',
                          instance=instance)
            except exception.InstanceNotFound:
                # Instance is gone.
                LOG.debug('Instance no longer exists. Unable to refresh',
                          instance=instance)
                return
            except exception.InstanceInfoCacheNotFound:
                # InstanceInfoCache is gone.
                LOG.debug('InstanceInfoCache no longer exists. '
                          'Unable to refresh', instance=instance)
            except Exception:
                LOG.error(_LE('An error occurred while refreshing the network '
                              'cache.'), instance=instance, exc_info=True)
        else:
            LOG.debug("Didn't find any instances for network info cache "
                      "update.")

    @periodic_task.periodic_task
    def _poll_rebooting_instances(self, context):
        if CONF.reboot_timeout > 0:
            filters = {'task_state':
                       [task_states.REBOOTING,
                        task_states.REBOOT_STARTED,
                        task_states.REBOOT_PENDING],
                       'host': self.host}
            rebooting = objects.InstanceList.get_by_filters(
                context, filters, expected_attrs=[], use_slave=True)

            to_poll = []
            for instance in rebooting:
                if timeutils.is_older_than(instance.updated_at,
                                           CONF.reboot_timeout):
                    to_poll.append(instance)

            self.driver.poll_rebooting_instances(CONF.reboot_timeout, to_poll)

    @periodic_task.periodic_task
    def _poll_rescued_instances(self, context):
        if CONF.rescue_timeout > 0:
            filters = {'vm_state': vm_states.RESCUED,
                       'host': self.host}
            rescued_instances = objects.InstanceList.get_by_filters(
                context, filters, expected_attrs=["system_metadata"],
                use_slave=True)

            to_unrescue = []
            for instance in rescued_instances:
                if timeutils.is_older_than(instance.launched_at,
                                           CONF.rescue_timeout):
                    to_unrescue.append(instance)

            for instance in to_unrescue:
                self.compute_api.unrescue(context, instance)

    @periodic_task.periodic_task
    def _poll_unconfirmed_resizes(self, context):
        if CONF.resize_confirm_window == 0:
            return

        migrations = objects.MigrationList.get_unconfirmed_by_dest_compute(
                context, CONF.resize_confirm_window, self.host,
                use_slave=True)

        migrations_info = dict(migration_count=len(migrations),
                confirm_window=CONF.resize_confirm_window)

        if migrations_info["migration_count"] > 0:
            LOG.info(_LI("Found %(migration_count)d unconfirmed migrations "
                         "older than %(confirm_window)d seconds"),
                     migrations_info)

        def _set_migration_to_error(migration, reason, **kwargs):
            LOG.warning(_LW("Setting migration %(migration_id)s to error: "
                         "%(reason)s"),
                     {'migration_id': migration['id'], 'reason': reason},
                     **kwargs)
            migration.status = 'error'
            with migration.obj_as_admin():
                migration.save()

        for migration in migrations:
            instance_uuid = migration.instance_uuid
            LOG.info(_LI("Automatically confirming migration "
                         "%(migration_id)s for instance %(instance_uuid)s"),
                     {'migration_id': migration.id,
                      'instance_uuid': instance_uuid})
            expected_attrs = ['metadata', 'system_metadata']
            try:
                instance = objects.Instance.get_by_uuid(context,
                            instance_uuid, expected_attrs=expected_attrs,
                            use_slave=True)
            except exception.InstanceNotFound:
                reason = (_("Instance %s not found") %
                          instance_uuid)
                _set_migration_to_error(migration, reason)
                continue
            if instance.vm_state == vm_states.ERROR:
                reason = _("In ERROR state")
                _set_migration_to_error(migration, reason,
                                        instance=instance)
                continue
            # race condition: The instance in DELETING state should not be
            # set the migration state to error, otherwise the instance in
            # to be deleted which is in RESIZED state
            # will not be able to confirm resize
            if instance.task_state in [task_states.DELETING,
                                       task_states.SOFT_DELETING]:
                msg = ("Instance being deleted or soft deleted during resize "
                       "confirmation. Skipping.")
                LOG.debug(msg, instance=instance)
                continue

            # race condition: This condition is hit when this method is
            # called between the save of the migration record with a status of
            # finished and the save of the instance object with a state of
            # RESIZED. The migration record should not be set to error.
            if instance.task_state == task_states.RESIZE_FINISH:
                msg = ("Instance still resizing during resize "
                       "confirmation. Skipping.")
                LOG.debug(msg, instance=instance)
                continue

            vm_state = instance.vm_state
            task_state = instance.task_state
            if vm_state != vm_states.RESIZED or task_state is not None:
                reason = (_("In states %(vm_state)s/%(task_state)s, not "
                           "RESIZED/None") %
                          {'vm_state': vm_state,
                           'task_state': task_state})
                _set_migration_to_error(migration, reason,
                                        instance=instance)
                continue
            try:
                self.compute_api.confirm_resize(context, instance,
                                                migration=migration)
            except Exception as e:
                LOG.info(_LI("Error auto-confirming resize: %s. "
                             "Will retry later."),
                         e, instance=instance)

    @periodic_task.periodic_task(spacing=CONF.shelved_poll_interval)
    def _poll_shelved_instances(self, context):

        if CONF.shelved_offload_time <= 0:
            return

        filters = {'vm_state': vm_states.SHELVED,
                   'host': self.host}
        shelved_instances = objects.InstanceList.get_by_filters(
            context, filters=filters, expected_attrs=['system_metadata'],
            use_slave=True)

        to_gc = []
        for instance in shelved_instances:
            sys_meta = instance.system_metadata
            shelved_at = timeutils.parse_strtime(sys_meta['shelved_at'])
            if timeutils.is_older_than(shelved_at, CONF.shelved_offload_time):
                to_gc.append(instance)

        for instance in to_gc:
            try:
                instance.task_state = task_states.SHELVING_OFFLOADING
                instance.save()
                self.shelve_offload_instance(context, instance,
                                             clean_shutdown=False)
            except Exception:
                LOG.exception(_LE('Periodic task failed to offload instance.'),
                        instance=instance)

    @periodic_task.periodic_task
    def _instance_usage_audit(self, context):
        if not CONF.instance_usage_audit:
            return

        begin, end = utils.last_completed_audit_period()
        if objects.TaskLog.get(context, 'instance_usage_audit', begin, end,
                               self.host):
            return

        instances = objects.InstanceList.get_active_by_window_joined(
            context, begin, end, host=self.host,
            expected_attrs=['system_metadata', 'info_cache', 'metadata'],
            use_slave=True)
        num_instances = len(instances)
        errors = 0
        successes = 0
        LOG.info(_LI("Running instance usage audit for"
                     " host %(host)s from %(begin_time)s to "
                     "%(end_time)s. %(number_instances)s"
                     " instances."),
                 {'host': self.host,
                  'begin_time': begin,
                  'end_time': end,
                  'number_instances': num_instances})
        start_time = time.time()
        task_log = objects.TaskLog(context)
        task_log.task_name = 'instance_usage_audit'
        task_log.period_beginning = begin
        task_log.period_ending = end
        task_log.host = self.host
        task_log.task_items = num_instances
        task_log.message = 'Instance usage audit started...'
        task_log.begin_task()
        for instance in instances:
            try:
                compute_utils.notify_usage_exists(
                    self.notifier, context, instance,
                    ignore_missing_network_data=False)
                successes += 1
            except Exception:
                LOG.exception(_LE('Failed to generate usage '
                                  'audit for instance '
                                  'on host %s'), self.host,
                              instance=instance)
                errors += 1
        task_log.errors = errors
        task_log.message = (
            'Instance usage audit ran for host %s, %s instances in %s seconds.'
            % (self.host, num_instances, time.time() - start_time))
        task_log.end_task()

    @periodic_task.periodic_task(spacing=CONF.bandwidth_poll_interval)
    def _poll_bandwidth_usage(self, context):

        if not self._bw_usage_supported:
            return

        prev_time, start_time = utils.last_completed_audit_period()

        curr_time = time.time()
        if (curr_time - self._last_bw_usage_poll >
                CONF.bandwidth_poll_interval):
            self._last_bw_usage_poll = curr_time
            LOG.info(_LI("Updating bandwidth usage cache"))
            cells_update_interval = CONF.cells.bandwidth_update_interval
            if (cells_update_interval > 0 and
                   curr_time - self._last_bw_usage_cell_update >
                           cells_update_interval):
                self._last_bw_usage_cell_update = curr_time
                update_cells = True
            else:
                update_cells = False

            instances = objects.InstanceList.get_by_host(context,
                                                              self.host,
                                                              use_slave=True)
            try:
                bw_counters = self.driver.get_all_bw_counters(instances)
            except NotImplementedError:
                # NOTE(mdragon): Not all hypervisors have bandwidth polling
                # implemented yet.  If they don't it doesn't break anything,
                # they just don't get the info in the usage events.
                # NOTE(PhilDay): Record that its not supported so we can
                # skip fast on future calls rather than waste effort getting
                # the list of instances.
                LOG.warning(_LW("Bandwidth usage not supported by "
                                "hypervisor."))
                self._bw_usage_supported = False
                return

            refreshed = timeutils.utcnow()
            for bw_ctr in bw_counters:
                # Allow switching of greenthreads between queries.
                greenthread.sleep(0)
                bw_in = 0
                bw_out = 0
                last_ctr_in = None
                last_ctr_out = None
                usage = objects.BandwidthUsage.get_by_instance_uuid_and_mac(
                    context, bw_ctr['uuid'], bw_ctr['mac_address'],
                    start_period=start_time, use_slave=True)
                if usage:
                    bw_in = usage.bw_in
                    bw_out = usage.bw_out
                    last_ctr_in = usage.last_ctr_in
                    last_ctr_out = usage.last_ctr_out
                else:
                    usage = (objects.BandwidthUsage.
                             get_by_instance_uuid_and_mac(
                        context, bw_ctr['uuid'], bw_ctr['mac_address'],
                        start_period=prev_time, use_slave=True))
                    if usage:
                        last_ctr_in = usage.last_ctr_in
                        last_ctr_out = usage.last_ctr_out

                if last_ctr_in is not None:
                    if bw_ctr['bw_in'] < last_ctr_in:
                        # counter rollover
                        bw_in += bw_ctr['bw_in']
                    else:
                        bw_in += (bw_ctr['bw_in'] - last_ctr_in)

                if last_ctr_out is not None:
                    if bw_ctr['bw_out'] < last_ctr_out:
                        # counter rollover
                        bw_out += bw_ctr['bw_out']
                    else:
                        bw_out += (bw_ctr['bw_out'] - last_ctr_out)

                objects.BandwidthUsage(context=context).create(
                                              bw_ctr['uuid'],
                                              bw_ctr['mac_address'],
                                              bw_in,
                                              bw_out,
                                              bw_ctr['bw_in'],
                                              bw_ctr['bw_out'],
                                              start_period=start_time,
                                              last_refreshed=refreshed,
                                              update_cells=update_cells)

    def _get_host_volume_bdms(self, context, use_slave=False):
        """Return all block device mappings on a compute host."""
        compute_host_bdms = []
        instances = objects.InstanceList.get_by_host(context, self.host,
            use_slave=use_slave)
        for instance in instances:
            bdms = objects.BlockDeviceMappingList.get_by_instance_uuid(
                    context, instance.uuid, use_slave=use_slave)
            instance_bdms = [bdm for bdm in bdms if bdm.is_volume]
            compute_host_bdms.append(dict(instance=instance,
                                          instance_bdms=instance_bdms))

        return compute_host_bdms

    def _update_volume_usage_cache(self, context, vol_usages):
        """Updates the volume usage cache table with a list of stats."""
        for usage in vol_usages:
            # Allow switching of greenthreads between queries.
            greenthread.sleep(0)
            vol_usage = objects.VolumeUsage(context)
            vol_usage.volume_id = usage['volume']
            vol_usage.instance_uuid = usage['instance'].uuid
            vol_usage.project_id = usage['instance'].project_id
            vol_usage.user_id = usage['instance'].user_id
            vol_usage.availability_zone = usage['instance'].availability_zone
            vol_usage.curr_reads = usage['rd_req']
            vol_usage.curr_read_bytes = usage['rd_bytes']
            vol_usage.curr_writes = usage['wr_req']
            vol_usage.curr_write_bytes = usage['wr_bytes']
            vol_usage.save()
            self.notifier.info(context, 'volume.usage',
                               compute_utils.usage_volume_info(vol_usage))

    @periodic_task.periodic_task(spacing=CONF.volume_usage_poll_interval)
    def _poll_volume_usage(self, context, start_time=None):
        if CONF.volume_usage_poll_interval == 0:
            return

        if not start_time:
            start_time = utils.last_completed_audit_period()[1]

        compute_host_bdms = self._get_host_volume_bdms(context,
                                                       use_slave=True)
        if not compute_host_bdms:
            return

        LOG.debug("Updating volume usage cache")
        try:
            vol_usages = self.driver.get_all_volume_usage(context,
                                                          compute_host_bdms)
        except NotImplementedError:
            return

        self._update_volume_usage_cache(context, vol_usages)

    @periodic_task.periodic_task(spacing=CONF.sync_power_state_interval,
                                 run_immediately=True)
    def _sync_power_states(self, context):
        """Align power states between the database and the hypervisor.

        To sync power state data we make a DB call to get the number of
        virtual machines known by the hypervisor and if the number matches the
        number of virtual machines known by the database, we proceed in a lazy
        loop, one database record at a time, checking if the hypervisor has the
        same power state as is in the database.
        """
        db_instances = objects.InstanceList.get_by_host(context, self.host,
                                                        expected_attrs=[],
                                                        use_slave=True)

        num_vm_instances = self.driver.get_num_instances()
        num_db_instances = len(db_instances)

        if num_vm_instances != num_db_instances:
            LOG.warning(_LW("While synchronizing instance power states, found "
                            "%(num_db_instances)s instances in the database "
                            "and %(num_vm_instances)s instances on the "
                            "hypervisor."),
                        {'num_db_instances': num_db_instances,
                         'num_vm_instances': num_vm_instances})

        def _sync(db_instance):
            # NOTE(melwitt): This must be synchronized as we query state from
            #                two separate sources, the driver and the database.
            #                They are set (in stop_instance) and read, in sync.
            @utils.synchronized(db_instance.uuid)
            def query_driver_power_state_and_sync():
                self._query_driver_power_state_and_sync(context, db_instance)

            try:
                query_driver_power_state_and_sync()
            except Exception:
                LOG.exception(_LE("Periodic sync_power_state task had an "
                                  "error while processing an instance."),
                              instance=db_instance)

            self._syncs_in_progress.pop(db_instance.uuid)

        for db_instance in db_instances:
            # process syncs asynchronously - don't want instance locking to
            # block entire periodic task thread
            uuid = db_instance.uuid
            if uuid in self._syncs_in_progress:
                LOG.debug('Sync already in progress for %s' % uuid)
            else:
                LOG.debug('Triggering sync for uuid %s' % uuid)
                self._syncs_in_progress[uuid] = True
                self._sync_power_pool.spawn_n(_sync, db_instance)

    def _query_driver_power_state_and_sync(self, context, db_instance):
        if db_instance.task_state is not None:
            LOG.info(_LI("During sync_power_state the instance has a "
                         "pending task (%(task)s). Skip."),
                     {'task': db_instance.task_state}, instance=db_instance)
            return
        # No pending tasks. Now try to figure out the real vm_power_state.
        try:
            vm_instance = self.driver.get_info(db_instance)
            vm_power_state = vm_instance.state
        except exception.InstanceNotFound:
            vm_power_state = power_state.NOSTATE
        # Note(maoy): the above get_info call might take a long time,
        # for example, because of a broken libvirt driver.
        try:
            self._sync_instance_power_state(context,
                                            db_instance,
                                            vm_power_state,
                                            use_slave=True)
        except exception.InstanceNotFound:
            # NOTE(hanlind): If the instance gets deleted during sync,
            # silently ignore.
            pass

    def _sync_instance_power_state(self, context, db_instance, vm_power_state,
                                   use_slave=False):
        """Align instance power state between the database and hypervisor.

        If the instance is not found on the hypervisor, but is in the database,
        then a stop() API will be called on the instance.
        """

        # We re-query the DB to get the latest instance info to minimize
        # (not eliminate) race condition.
        db_instance.refresh(use_slave=use_slave)
        db_power_state = db_instance.power_state
        vm_state = db_instance.vm_state

        if self.host != db_instance.host:
            # on the sending end of nova-compute _sync_power_state
            # may have yielded to the greenthread performing a live
            # migration; this in turn has changed the resident-host
            # for the VM; However, the instance is still active, it
            # is just in the process of migrating to another host.
            # This implies that the compute source must relinquish
            # control to the compute destination.
            LOG.info(_LI("During the sync_power process the "
                         "instance has moved from "
                         "host %(src)s to host %(dst)s"),
                     {'src': db_instance.host,
                      'dst': self.host},
                     instance=db_instance)
            return
        elif db_instance.task_state is not None:
            # on the receiving end of nova-compute, it could happen
            # that the DB instance already report the new resident
            # but the actual VM has not showed up on the hypervisor
            # yet. In this case, let's allow the loop to continue
            # and run the state sync in a later round
            LOG.info(_LI("During sync_power_state the instance has a "
                         "pending task (%(task)s). Skip."),
                     {'task': db_instance.task_state},
                     instance=db_instance)
            return

        orig_db_power_state = db_power_state
        if vm_power_state != db_power_state:
            LOG.info(_LI('During _sync_instance_power_state the DB '
                         'power_state (%(db_power_state)s) does not match '
                         'the vm_power_state from the hypervisor '
                         '(%(vm_power_state)s). Updating power_state in the '
                         'DB to match the hypervisor.'),
                     {'db_power_state': db_power_state,
                      'vm_power_state': vm_power_state},
                     instance=db_instance)
            # power_state is always updated from hypervisor to db
            db_instance.power_state = vm_power_state
            db_instance.save()
            db_power_state = vm_power_state

        # Note(maoy): Now resolve the discrepancy between vm_state and
        # vm_power_state. We go through all possible vm_states.
        if vm_state in (vm_states.BUILDING,
                        vm_states.RESCUED,
                        vm_states.RESIZED,
                        vm_states.SUSPENDED,
                        vm_states.ERROR):
            # TODO(maoy): we ignore these vm_state for now.
            pass
        elif vm_state == vm_states.ACTIVE:
            # The only rational power state should be RUNNING
            if vm_power_state in (power_state.SHUTDOWN,
                                  power_state.CRASHED):
                LOG.warning(_LW("Instance shutdown by itself. Calling the "
                                "stop API. Current vm_state: %(vm_state)s, "
                                "current task_state: %(task_state)s, "
                                "original DB power_state: %(db_power_state)s, "
                                "current VM power_state: %(vm_power_state)s"),
                            {'vm_state': vm_state,
                             'task_state': db_instance.task_state,
                             'db_power_state': orig_db_power_state,
                             'vm_power_state': vm_power_state},
                            instance=db_instance)
                try:
                    # Note(maoy): here we call the API instead of
                    # brutally updating the vm_state in the database
                    # to allow all the hooks and checks to be performed.
                    if db_instance.shutdown_terminate:
                        self.compute_api.delete(context, db_instance)
                    else:
                        self.compute_api.stop(context, db_instance)
                except Exception:
                    # Note(maoy): there is no need to propagate the error
                    # because the same power_state will be retrieved next
                    # time and retried.
                    # For example, there might be another task scheduled.
                    LOG.exception(_LE("error during stop() in "
                                      "sync_power_state."),
                                  instance=db_instance)
            elif vm_power_state == power_state.SUSPENDED:
                LOG.warning(_LW("Instance is suspended unexpectedly. Calling "
                                "the stop API."), instance=db_instance)
                try:
                    self.compute_api.stop(context, db_instance)
                except Exception:
                    LOG.exception(_LE("error during stop() in "
                                      "sync_power_state."),
                                  instance=db_instance)
            elif vm_power_state == power_state.PAUSED:
                # Note(maoy): a VM may get into the paused state not only
                # because the user request via API calls, but also
                # due to (temporary) external instrumentations.
                # Before the virt layer can reliably report the reason,
                # we simply ignore the state discrepancy. In many cases,
                # the VM state will go back to running after the external
                # instrumentation is done. See bug 1097806 for details.
                LOG.warning(_LW("Instance is paused unexpectedly. Ignore."),
                            instance=db_instance)
            elif vm_power_state == power_state.NOSTATE:
                # Occasionally, depending on the status of the hypervisor,
                # which could be restarting for example, an instance may
                # not be found.  Therefore just log the condition.
                LOG.warning(_LW("Instance is unexpectedly not found. Ignore."),
                            instance=db_instance)
        elif vm_state == vm_states.STOPPED:
            if vm_power_state not in (power_state.NOSTATE,
                                      power_state.SHUTDOWN,
                                      power_state.CRASHED):
                LOG.warning(_LW("Instance is not stopped. Calling "
                                "the stop API. Current vm_state: %(vm_state)s,"
                                " current task_state: %(task_state)s, "
                                "original DB power_state: %(db_power_state)s, "
                                "current VM power_state: %(vm_power_state)s"),
                            {'vm_state': vm_state,
                             'task_state': db_instance.task_state,
                             'db_power_state': orig_db_power_state,
                             'vm_power_state': vm_power_state},
                            instance=db_instance)
                try:
                    # NOTE(russellb) Force the stop, because normally the
                    # compute API would not allow an attempt to stop a stopped
                    # instance.
                    self.compute_api.force_stop(context, db_instance)
                except Exception:
                    LOG.exception(_LE("error during stop() in "
                                      "sync_power_state."),
                                  instance=db_instance)
        elif vm_state == vm_states.PAUSED:
            if vm_power_state in (power_state.SHUTDOWN,
                                  power_state.CRASHED):
                LOG.warning(_LW("Paused instance shutdown by itself. Calling "
                                "the stop API."), instance=db_instance)
                try:
                    self.compute_api.force_stop(context, db_instance)
                except Exception:
                    LOG.exception(_LE("error during stop() in "
                                      "sync_power_state."),
                                  instance=db_instance)
        elif vm_state in (vm_states.SOFT_DELETED,
                          vm_states.DELETED):
            if vm_power_state not in (power_state.NOSTATE,
                                      power_state.SHUTDOWN):
                # Note(maoy): this should be taken care of periodically in
                # _cleanup_running_deleted_instances().
                LOG.warning(_LW("Instance is not (soft-)deleted."),
                            instance=db_instance)

    @periodic_task.periodic_task
    def _reclaim_queued_deletes(self, context):
        """Reclaim instances that are queued for deletion."""
        interval = CONF.reclaim_instance_interval
        if interval <= 0:
            LOG.debug("CONF.reclaim_instance_interval <= 0, skipping...")
            return

        # TODO(comstud, jichenjc): Dummy quota object for now See bug 1296414.
        # The only case that the quota might be inconsistent is
        # the compute node died between set instance state to SOFT_DELETED
        # and quota commit to DB. When compute node starts again
        # it will have no idea the reservation is committed or not or even
        # expired, since it's a rare case, so marked as todo.
        quotas = objects.Quotas.from_reservations(context, None)

        filters = {'vm_state': vm_states.SOFT_DELETED,
                   'task_state': None,
                   'host': self.host}
        instances = objects.InstanceList.get_by_filters(
            context, filters,
            expected_attrs=objects.instance.INSTANCE_DEFAULT_FIELDS,
            use_slave=True)
        for instance in instances:
            if self._deleted_old_enough(instance, interval):
                bdms = objects.BlockDeviceMappingList.get_by_instance_uuid(
                        context, instance.uuid)
                LOG.info(_LI('Reclaiming deleted instance'), instance=instance)
                try:
                    self._delete_instance(context, instance, bdms, quotas)
                except Exception as e:
                    LOG.warning(_LW("Periodic reclaim failed to delete "
                                    "instance: %s"),
                                e, instance=instance)

    @periodic_task.periodic_task(spacing=CONF.update_resources_interval)
    def update_available_resource(self, context):
        """See driver.get_available_resource()

        Periodic process that keeps that the compute host's understanding of
        resource availability and usage in sync with the underlying hypervisor.

        :param context: security context
        """
        new_resource_tracker_dict = {}

        compute_nodes_in_db = self._get_compute_nodes_in_db(context,
                                                            use_slave=True)
        nodenames = set(self.driver.get_available_nodes())
        for nodename in nodenames:
            rt = self._get_resource_tracker(nodename)
            try:
                rt.update_available_resource(context)
            except exception.ComputeHostNotFound:
                # NOTE(comstud): We can get to this case if a node was
                # marked 'deleted' in the DB and then re-added with a
                # different auto-increment id. The cached resource
                # tracker tried to update a deleted record and failed.
                # Don't add this resource tracker to the new dict, so
                # that this will resolve itself on the next run.
                LOG.info(_LI("Compute node '%s' not found in "
                             "update_available_resource."), nodename)
                continue
            except Exception as e:
                LOG.error(_LE("Error updating resources for node "
                              "%(node)s: %(e)s"),
                          {'node': nodename, 'e': e})
            new_resource_tracker_dict[nodename] = rt

        # NOTE(comstud): Replace the RT cache before looping through
        # compute nodes to delete below, as we can end up doing greenthread
        # switches there. Best to have everyone using the newest cache
        # ASAP.
        self._resource_tracker_dict = new_resource_tracker_dict

        # Delete orphan compute node not reported by driver but still in db
        for cn in compute_nodes_in_db:
            if cn.hypervisor_hostname not in nodenames:
                LOG.info(_LI("Deleting orphan compute node %s") % cn.id)
                cn.destroy()

    def _get_compute_nodes_in_db(self, context, use_slave=False):
        try:
            return objects.ComputeNodeList.get_all_by_host(context, self.host,
                                                           use_slave=use_slave)
        except exception.NotFound:
            LOG.error(_LE("No compute node record for host %s"), self.host)
            return []

    @periodic_task.periodic_task(
        spacing=CONF.running_deleted_instance_poll_interval)
    def _cleanup_running_deleted_instances(self, context):
        """Cleanup any instances which are erroneously still running after
        having been deleted.

        Valid actions to take are:

            1. noop - do nothing
            2. log - log which instances are erroneously running
            3. reap - shutdown and cleanup any erroneously running instances
            4. shutdown - power off *and disable* any erroneously running
                          instances

        The use-case for this cleanup task is: for various reasons, it may be
        possible for the database to show an instance as deleted but for that
        instance to still be running on a host machine (see bug
        https://bugs.launchpad.net/nova/+bug/911366).

        This cleanup task is a cross-hypervisor utility for finding these
        zombied instances and either logging the discrepancy (likely what you
        should do in production), or automatically reaping the instances (more
        appropriate for dev environments).
        """
        action = CONF.running_deleted_instance_action

        if action == "noop":
            return

        # NOTE(sirp): admin contexts don't ordinarily return deleted records
        with utils.temporary_mutation(context, read_deleted="yes"):
            for instance in self._running_deleted_instances(context):
                if action == "log":
                    LOG.warning(_LW("Detected instance with name label "
                                    "'%s' which is marked as "
                                    "DELETED but still present on host."),
                                instance.name, instance=instance)

                elif action == 'shutdown':
                    LOG.info(_LI("Powering off instance with name label "
                                 "'%s' which is marked as "
                                 "DELETED but still present on host."),
                             instance.name, instance=instance)
                    try:
                        try:
                            # disable starting the instance
                            self.driver.set_bootable(instance, False)
                        except NotImplementedError:
                            LOG.warning(_LW("set_bootable is not implemented "
                                            "for the current driver"))
                        # and power it off
                        self.driver.power_off(instance)
                    except Exception:
                        msg = _LW("Failed to power off instance")
                        LOG.warn(msg, instance=instance, exc_info=True)

                elif action == 'reap':
                    LOG.info(_LI("Destroying instance with name label "
                                 "'%s' which is marked as "
                                 "DELETED but still present on host."),
                             instance.name, instance=instance)
                    bdms = objects.BlockDeviceMappingList.get_by_instance_uuid(
                        context, instance.uuid, use_slave=True)
                    self.instance_events.clear_events_for_instance(instance)
                    try:
                        self._shutdown_instance(context, instance, bdms,
                                                notify=False)
                        self._cleanup_volumes(context, instance.uuid, bdms)
                    except Exception as e:
                        LOG.warning(_LW("Periodic cleanup failed to delete "
                                        "instance: %s"),
                                    e, instance=instance)
                else:
                    raise Exception(_("Unrecognized value '%s'"
                                      " for CONF.running_deleted_"
                                      "instance_action") % action)

    def _running_deleted_instances(self, context):
        """Returns a list of instances nova thinks is deleted,
        but the hypervisor thinks is still running.
        """
        timeout = CONF.running_deleted_instance_timeout
        filters = {'deleted': True,
                   'soft_deleted': False,
                   'host': self.host}
        instances = self._get_instances_on_driver(context, filters)
        return [i for i in instances if self._deleted_old_enough(i, timeout)]

    def _deleted_old_enough(self, instance, timeout):
        deleted_at = instance.deleted_at
        if deleted_at:
            deleted_at = deleted_at.replace(tzinfo=None)
        return (not deleted_at or timeutils.is_older_than(deleted_at, timeout))

    @contextlib.contextmanager
    def _error_out_instance_on_exception(self, context, instance,
                                         quotas=None,
                                         instance_state=vm_states.ACTIVE):
        instance_uuid = instance.uuid
        try:
            yield
        except NotImplementedError as error:
            with excutils.save_and_reraise_exception():
                if quotas:
                    quotas.rollback()
                LOG.info(_LI("Setting instance back to %(state)s after: "
                             "%(error)s"),
                         {'state': instance_state, 'error': error},
                         instance_uuid=instance_uuid)
                self._instance_update(context, instance,
                                      vm_state=instance_state,
                                      task_state=None)
        except exception.InstanceFaultRollback as error:
            if quotas:
                quotas.rollback()
            LOG.info(_LI("Setting instance back to ACTIVE after: %s"),
                     error, instance_uuid=instance_uuid)
            self._instance_update(context, instance,
                                  vm_state=vm_states.ACTIVE,
                                  task_state=None)
            raise error.inner_exception
        except Exception:
            LOG.exception(_LE('Setting instance vm_state to ERROR'),
                          instance_uuid=instance_uuid)
            with excutils.save_and_reraise_exception():
                if quotas:
                    quotas.rollback()
                self._set_instance_obj_error_state(context, instance)

    @wrap_exception()
    def add_aggregate_host(self, context, aggregate, host, slave_info):
        """Notify hypervisor of change (for hypervisor pools)."""
        try:
            self.driver.add_to_aggregate(context, aggregate, host,
                                         slave_info=slave_info)
        except NotImplementedError:
            LOG.debug('Hypervisor driver does not support '
                      'add_aggregate_host')
        except exception.AggregateError:
            with excutils.save_and_reraise_exception():
                self.driver.undo_aggregate_operation(
                                    context,
                                    aggregate.delete_host,
                                    aggregate, host)

    @wrap_exception()
    def remove_aggregate_host(self, context, host, slave_info, aggregate):
        """Removes a host from a physical hypervisor pool."""
        try:
            self.driver.remove_from_aggregate(context, aggregate, host,
                                              slave_info=slave_info)
        except NotImplementedError:
            LOG.debug('Hypervisor driver does not support '
                      'remove_aggregate_host')
        except (exception.AggregateError,
                exception.InvalidAggregateAction) as e:
            with excutils.save_and_reraise_exception():
                self.driver.undo_aggregate_operation(
                                    context,
                                    aggregate.add_host,
                                    aggregate, host,
                                    isinstance(e, exception.AggregateError))

    def _process_instance_event(self, instance, event):
        _event = self.instance_events.pop_instance_event(instance, event)
        if _event:
            LOG.debug('Processing event %(event)s',
                      {'event': event.key}, instance=instance)
            _event.send(event)

    def _process_instance_vif_deleted_event(self, context, instance,
                                            deleted_vif_id):
        # If an attached port is deleted by neutron, it needs to
        # be detached from the instance.
        # And info cache needs to be updated.
        network_info = instance.info_cache.network_info
        for index, vif in enumerate(network_info):
            if vif['id'] == deleted_vif_id:
                LOG.info(_LI('Neutron deleted interface %(intf)s; '
                             'detaching it from the instance and '
                             'deleting it from the info cache'),
                         {'intf': vif['id']},
                         instance=instance)
                del network_info[index]
                base_net_api.update_instance_cache_with_nw_info(
                                 self.network_api, context,
                                 instance,
                                 nw_info=network_info)
                try:
                    self.driver.detach_interface(instance, vif)
                except exception.NovaException as ex:
                    LOG.warning(_LW("Detach interface failed, "
                                    "port_id=%(port_id)s, reason: %(msg)s"),
                                {'port_id': deleted_vif_id, 'msg': ex},
                                instance=instance)
                break

    @wrap_exception()
    def external_instance_event(self, context, instances, events):
        # NOTE(danms): Some event types are handled by the manager, such
        # as when we're asked to update the instance's info_cache. If it's
        # not one of those, look for some thread(s) waiting for the event and
        # unblock them if so.
        for event in events:
            instance = [inst for inst in instances
                        if inst.uuid == event.instance_uuid][0]
            LOG.debug('Received event %(event)s',
                      {'event': event.key},
                      instance=instance)
            if event.name == 'network-changed':
                try:
                    self.network_api.get_instance_nw_info(context, instance)
                except exception.NotFound as e:
                    LOG.info(_LI('Failed to process external instance event '
                                 '%(event)s due to: %(error)s'),
                             {'event': event.key, 'error': six.text_type(e)},
                             instance=instance)
            elif event.name == 'network-vif-deleted':
                self._process_instance_vif_deleted_event(context,
                                                         instance,
                                                         event.tag)
            else:
                self._process_instance_event(instance, event)

    @periodic_task.periodic_task(spacing=CONF.image_cache_manager_interval,
                                 external_process_ok=True)
    def _run_image_cache_manager_pass(self, context):
        """Run a single pass of the image cache manager."""

        if not self.driver.capabilities["has_imagecache"]:
            return

        # Determine what other nodes use this storage
        storage_users.register_storage_use(CONF.instances_path, CONF.host)
        nodes = storage_users.get_storage_users(CONF.instances_path)

        # Filter all_instances to only include those nodes which share this
        # storage path.
        # TODO(mikal): this should be further refactored so that the cache
        # cleanup code doesn't know what those instances are, just a remote
        # count, and then this logic should be pushed up the stack.
        filters = {'deleted': False,
                   'soft_deleted': True,
                   'host': nodes}
        filtered_instances = objects.InstanceList.get_by_filters(context,
                                 filters, expected_attrs=[], use_slave=True)

        self.driver.manage_image_cache(context, filtered_instances)

    @periodic_task.periodic_task(spacing=CONF.instance_delete_interval)
    def _run_pending_deletes(self, context):
        """Retry any pending instance file deletes."""
        LOG.debug('Cleaning up deleted instances')
        filters = {'deleted': True,
                   'soft_deleted': False,
                   'host': CONF.host,
                   'cleaned': False}
        attrs = ['info_cache', 'security_groups', 'system_metadata']
        with utils.temporary_mutation(context, read_deleted='yes'):
            instances = objects.InstanceList.get_by_filters(
                context, filters, expected_attrs=attrs, use_slave=True)
        LOG.debug('There are %d instances to clean', len(instances))

        for instance in instances:
            attempts = int(instance.system_metadata.get('clean_attempts', '0'))
            LOG.debug('Instance has had %(attempts)s of %(max)s '
                      'cleanup attempts',
                      {'attempts': attempts,
                       'max': CONF.maximum_instance_delete_attempts},
                      instance=instance)
            if attempts < CONF.maximum_instance_delete_attempts:
                success = self.driver.delete_instance_files(instance)

                instance.system_metadata['clean_attempts'] = str(attempts + 1)
                if success:
                    instance.cleaned = True
                with utils.temporary_mutation(context, read_deleted='yes'):
                    instance.save()

    @periodic_task.periodic_task(spacing=CONF.instance_delete_interval)
    def _cleanup_incomplete_migrations(self, context):
        """Delete instance files on failed resize/revert-resize operation

        During resize/revert-resize operation, if that instance gets deleted
        in-between then instance files might remain either on source or
        destination compute node because of race condition.
        """
        LOG.debug('Cleaning up deleted instances with incomplete migration ')
        migration_filters = {'host': CONF.host,
                             'status': 'error'}
        migrations = objects.MigrationList.get_by_filters(context,
                                                          migration_filters)

        if not migrations:
            return

        inst_uuid_from_migrations = set([migration.instance_uuid for migration
                                         in migrations])

        inst_filters = {'deleted': True, 'soft_deleted': False,
                        'uuid': inst_uuid_from_migrations}
        attrs = ['info_cache', 'security_groups', 'system_metadata']
        with utils.temporary_mutation(context, read_deleted='yes'):
            instances = objects.InstanceList.get_by_filters(
                context, inst_filters, expected_attrs=attrs, use_slave=True)

        for instance in instances:
            if instance.host != CONF.host:
                for migration in migrations:
                    if instance.uuid == migration.instance_uuid:
                        # Delete instance files if not cleanup properly either
                        # from the source or destination compute nodes when
                        # the instance is deleted during resizing.
                        self.driver.delete_instance_files(instance)
                        try:
                            migration.status = 'failed'
                            with migration.obj_as_admin():
                                migration.save()
                        except exception.MigrationNotFound:
                            LOG.warning(_LW("Migration %s is not found."),
                                        migration.id, context=context,
                                        instance=instance)
                        break

    @messaging.expected_exceptions(exception.InstanceQuiesceNotSupported,
                                   exception.QemuGuestAgentNotEnabled,
                                   exception.NovaException,
                                   NotImplementedError)
    @wrap_exception()
    def quiesce_instance(self, context, instance):
        """Quiesce an instance on this host."""
        context = context.elevated()
        image_meta = utils.get_image_from_system_metadata(
            instance.system_metadata)
        self.driver.quiesce(context, instance, image_meta)

    def _wait_for_snapshots_completion(self, context, mapping):
        for mapping_dict in mapping:
            if mapping_dict.get('source_type') == 'snapshot':

                def _wait_snapshot():
                    snapshot = self.volume_api.get_snapshot(
                        context, mapping_dict['snapshot_id'])
                    if snapshot.get('status') != 'creating':
                        raise loopingcall.LoopingCallDone()

                timer = loopingcall.FixedIntervalLoopingCall(_wait_snapshot)
                timer.start(interval=0.5).wait()

    @messaging.expected_exceptions(exception.InstanceQuiesceNotSupported,
                                   exception.QemuGuestAgentNotEnabled,
                                   exception.NovaException,
                                   NotImplementedError)
    @wrap_exception()
    def unquiesce_instance(self, context, instance, mapping=None):
        """Unquiesce an instance on this host.

        If snapshots' image mapping is provided, it waits until snapshots are
        completed before unqueiscing.
        """
        context = context.elevated()
        if mapping:
            try:
                self._wait_for_snapshots_completion(context, mapping)
            except Exception as error:
                LOG.exception(_LE("Exception while waiting completion of "
                                  "volume snapshots: %s"),
                              error, instance=instance)
        image_meta = utils.get_image_from_system_metadata(
            instance.system_metadata)
        self.driver.unquiesce(context, instance, image_meta)
