A mechanism to set defaults

The new gdm uses a number of regular desktop components on the login screen.
As a consequence, setting system-wide gconf defaults is the way to
configure many
aspects of the login screen, e.g. the background, or the power
management settings.

Currently GConf lacks an adaequate way of setting system-wide defaults
from within
a session, short of running gconftool-2 as root.  We can do a lot
better nowadays,
with tools such as dbus system-bus activation and PolicyKit.

This is what the patch in bug http://bugzilla.gnome.org/show_bug.cgi?id=531169
is about. It adds a dbus service which can be called by session
programs, e.g. capplets,
to transfer gconf values from the session to the system-wide defaults.
 The mechanism
uses PolicyKit to control access to this functionality, in a clever
way that allows
to control different parts of the gconf settings tree by different privileges.

An example of how this mechanism is used from the session can be found in
http://bugzilla.gnome.org/show_bug.cgi?id=536531.

I talked about this with Havoc earlier, and he was in favour of adding
this functionality
to GConf. So, if nobody objects, I'd like to merge this into GConf before 2.24.
Before doing so, I will make this conditional depending on the
availability of PolicyKit
and add some documentation.


Matthias