OLPC and .service files in a users home directory

[John (J5) Palmieri]

An issue arose within OLPC dealing with activating activities.  In
OLPC's sugar environment we use D-Bus extensively for activating what we
call activities.  Activities are just apps that integrate with the sugar
environment.  We are moving away from the traditional install everything
in system directories to what we call bundles which are a lot like the
MacOSX app bundles in that they are self contained and installing them
is a matter of copying to the correct directory.  

This presents a problem to D-Bus activation in that we do not have
access to write to the /usr/share/dbus-1/service directory.  What we
want the ability to do is have sugar generate the .service files from
the activity bundles and place them in a directory in the users home.  I
think this should also be in the default system.conf.  We already have
an xdg autostart directory in the users home so this does not present
any security issues but it would allow the user to override default
handlers for a specific service if they wanted to (say the notification
daemon for instance).

There are a couple of ways we can go about this.  We can expand
variables in the path that start with the dollar sign (e.g.
<servicedir>$HOME/.dbus/service</service>) or add a special tag (e.g.
<servicedir><homedir />/.dbus/service</service>).

The former is more flexible but would require a separate config file in
windows. The latter allows us to hide platform specifics in the conf
file but breaks the dtd and isn't nice to look at.  I think the real
question is do we want to allow random env variable or just restrict it
to the users home directory?

-- 
John (J5) Palmieri <johnp at redhat.com>