cdebconf plugins (custom widgets)
---------------------------------

cdebconf has the facility to load custom implementations for template types
at run-time. This may be used to provide more sophisticated user interfaces
than can be achieved using the standard generic template types. Naturally,
these implementations are per-frontend.

The CAPB command may be used to query the existence of a given plugin for
the current frontend. If the type "foo" is supported by a plugin, CAPB will
return the capability "plugin-foo".

Plugins are dynamically-loaded libraries. The library must be in the
following location:

  <frontend_path>/<frontend>/plugin-<type>.so

(The initial "plugin-" is to allow for more convenient testing within the
cdebconf source tree.)

In the default cdebconf.conf, <frontend_path> is /usr/lib/cdebconf/frontend.
Thus, an implementation of the "detect-keyboard" type for the newt frontend
would be stored in:

  /usr/lib/cdebconf/frontend/newt/plugin-detect-keyboard.so

The library must provide a function with the following name:

  cdebconf_<frontend>_handler_<type>

Any hyphens in <type> here are substituted with underscores, so:

  cdebconf_newt_handler_detect_keyboard

The required prototype for this function depends on the frontend. For newt
and text, it is (again with hyphens in <type> substituted with underscores):

  int cdebconf_<frontend>_handler_<type>(struct frontend *obj, struct question *q)

For gtk, it is:

  int cdebconf_<frontend>_handler_<type>(struct frontend *obj, struct question *q, GtkWidget *questionbox);

The handler should return DC_OK (defined in common.h) if all went well,
DC_GOBACK if the user wants to back up to the previous question, or DC_NOTOK
if an error occurred.

Plugins should generally use exported functions instead of dereferencing 
structs directly where possible. You can find the exported functions in 
the headers in /usr/include/cdebconf

You might want to look at existing plugins to see how things are done:
  cdebconf-keystep 
    (http://archive.ubuntu.com/ubuntu/pool/main/c/cdebconf-keystep/)
  cdebconf-entropy 
    (http://ftp.debian.org/debian/pool/main/c/cdebconf-entropy/)
