explain_getgrouplist(3)

NAME
explain_getgrouplist - explain getgrouplist(3) errors

SYNOPSIS
#include <libexplain/getgrouplist.h>

const char *explain_getgrouplist(const char *user, gid_t group, gid_t *groups, int *ngroups);
const char *explain_errno_getgrouplist(int errnum, const char *user, gid_t group, gid_t *groups, int *ngroups);
void explain_message_getgrouplist(char *message, int message_size, const char *user, gid_t group, gid_t *groups, int *ngroups);
void explain_message_errno_getgrouplist(char *message, int message_size, int errnum, const char *user, gid_t group, gid_t *groups, int *ngroups);

DESCRIPTION
These functions may be used to obtain explanations for errors returned by the getgrouplist(3) system call.

  explain_getgrouplist
const char *explain_getgrouplist(const char *user, gid_t group, gid_t *groups, int *ngroups);

The explain_getgrouplist function is used to obtain an explanation of an error returned by the getgrouplist(3) system call. The least the message will contain is the value of strerror(errno), but usually it will do much better, and indicate the underlying cause in more detail.

The errno global variable will be used to obtain the error value to be decoded.

user
    The original user, exactly as passed to the getgrouplist(3) system call.

group
    The original group, exactly as passed to the getgrouplist(3) system call.

groups
    The original groups, exactly as passed to the getgrouplist(3) system call.

ngroups
    The original ngroups, exactly as passed to the getgrouplist(3) system call.

Returns:
    The message explaining the error. This message buffer is shared by all libexplain functions which do not supply a buffer in their argument list. This will be overwritten by the next call to any libexplain function which shares this buffer, including other threads.

Note: This function is not thread safe, because it shares a return buffer across all threads, and many other functions in this library.

Example: This function is intended to be used in a fashion similar to the following example:
    errno = 0;
    if (getgrouplist(user, group, groups, ngroups) < 0 && errno != 0)
    {
    fprintf(stderr, "%s\n", explain_getgrouplist(user, group, groups, ngroups));
        exit(EXIT_FAILURE);
    }

The above code example is available pre-packaged as the explain_getgrouplist_or_die(3) function.

  explain_errno_getgrouplist
const char *explain_errno_getgrouplist(int errnum, const char *user, gid_t group, gid_t *groups, int *ngroups);

The explain_errno_getgrouplist function is used to obtain an explanation of an error returned by the getgrouplist(3) system call. The least the message will contain is the value of strerror(errno), but usually it will do much better, and indicate the underlying cause in more detail.

errnum
    The error value to be decoded, usually obtained from the errno global variable just before this function is called. This is necessary if you need to call any code between the system call to be explained and this function, because many libc functions will alter the value of errno.

user
    The original user, exactly as passed to the getgrouplist(3) system call.

group
    The original group, exactly as passed to the getgrouplist(3) system call.

groups
    The original groups, exactly as passed to the getgrouplist(3) system call.

ngroups
    The original ngroups, exactly as passed to the getgrouplist(3) system call.

Returns:
    The message explaining the error. This message buffer is shared by all libexplain functions which do not supply a buffer in their argument list. This will be overwritten by the next call to any libexplain function which shares this buffer, including other threads.

Note: This function is not thread safe, because it shares a return buffer across all threads, and many other functions in this library.

Example: This function is intended to be used in a fashion similar to the following example:
    errno = 0;
    if (getgrouplist(user, group, groups, ngroups) < 0 && errno != 0)
    {
        int err = errno;
    fprintf(stderr, "%s\n", explain_errno_getgrouplist(err, user, group, groups, ngroups));
        exit(EXIT_FAILURE);
    }

The above code example is available pre-packaged as the explain_getgrouplist_or_die(3) function.

  explain_message_getgrouplist
void explain_message_getgrouplist(char *message, int message_size, const char *user, gid_t group, gid_t *groups, int *ngroups);

The explain_message_getgrouplist function is used to obtain an explanation of an error returned by the getgrouplist(3) system call. The least the message will contain is the value of strerror(errno), but usually it will do much better, and indicate the underlying cause in more detail.

The errno global variable will be used to obtain the error value to be decoded.

message
    The location in which to store the returned message. If a suitable message return buffer is supplied, this function is thread safe.

message_size
    The size in bytes of the location in which to store the returned message.

user
    The original user, exactly as passed to the getgrouplist(3) system call.

group
    The original group, exactly as passed to the getgrouplist(3) system call.

groups
    The original groups, exactly as passed to the getgrouplist(3) system call.

ngroups
    The original ngroups, exactly as passed to the getgrouplist(3) system call.

Example: This function is intended to be used in a fashion similar to the following example:
    errno = 0;
    if (getgrouplist(user, group, groups, ngroups) < 0 && errno != 0)
    {
        char message[3000];
    explain_message_getgrouplist(message, sizeof(message), user, group, groups, ngroups);
        fprintf(stderr, "%s\n", message);
        exit(EXIT_FAILURE);
    }

The above code example is available pre-packaged as the explain_getgrouplist_or_die(3) function.

  explain_message_errno_getgrouplist
void explain_message_errno_getgrouplist(char *message, int message_size, int errnum, const char *user, gid_t group, gid_t *groups, int *ngroups);

The explain_message_errno_getgrouplist function is used to obtain an explanation of an error returned by the getgrouplist(3) system call. The least the message will contain is the value of strerror(errno), but usually it will do much better, and indicate the underlying cause in more detail.

message
    The location in which to store the returned message. If a suitable message return buffer is supplied, this function is thread safe.

message_size
    The size in bytes of the location in which to store the returned message.

errnum
    The error value to be decoded, usually obtained from the errno global variable just before this function is called. This is necessary if you need to call any code between the system call to be explained and this function, because many libc functions will alter the value of errno.

user
    The original user, exactly as passed to the getgrouplist(3) system call.

group
    The original group, exactly as passed to the getgrouplist(3) system call.

groups
    The original groups, exactly as passed to the getgrouplist(3) system call.

ngroups
    The original ngroups, exactly as passed to the getgrouplist(3) system call.

Example: This function is intended to be used in a fashion similar to the following example:
    errno = 0;
    if (getgrouplist(user, group, groups, ngroups) < 0 && errno != 0)
    {
        int err = errno;
        char message[3000];
    explain_message_errno_getgrouplist(message, sizeof(message), err, user, group, groups, ngroups);
        fprintf(stderr, "%s\n", message);
        exit(EXIT_FAILURE);
    }

The above code example is available pre-packaged as the explain_getgrouplist_or_die(3) function.

SEE ALSO

getgrouplist(3)
    get list of groups to which a user belongs

explain_getgrouplist_or_die(3)
    get list of groups to which a user belongs and report errors

COPYRIGHT
libexplain version
Copyright (C) 2013 Peter Miller