Re: gnome-Session

[Lanoxx <lanoxx gmx net>]

On 27/01/13 14:38, Vincent Untz wrote:
> Le dimanche 27 janvier 2013, à 14:10 +0100, Lanoxx a écrit :
> > On 27/01/13 09:02, Vincent Untz wrote:
> > > Le dimanche 27 janvier 2013, à 00:30 +0100, Lanoxx a écrit :
> > > > DesktopName
> > > This is not used, not sure where you saw that.
> > On Ubuntu all the session files have such a line.
> Then it's an Ubuntu-specific thing.
>
> > > > Additionally the man page mentions TASK in the context of required
> > > > and default providers, but does not explain that in more detail.
> > > >
> > > > Where do get more information about what these tasks and providers
> > > > are and what they reference? For example in one of my session files
> > > > I find these lines:
> > > >
> > > > RequiredProviders=windowmanager;
> > > > DefaultProvider-windowmanager=gnome-wm
> > > > DefaultProvider-notifications=notify-osd
> > > >
> > > > Who do I know what the TASKs windowmanager and notification are?
> > > > Under which circumstances could I add another line with some other
> > > > TASK and why would I want to do that?
> > > You can define anything as a task.
> > So what is a task used for and why whom? Does gnome-session just
> > simply run any of the specified TASKs?
> The idea behind this is to allow alternative software to be used instead
> of some default part of GNOME. To be honest, it doesn't make much sense
> in GNOME 3 anymore, and it's more of a GNOME 2 thing.
Well I still use it to run gnome-panel. And I find it rather convinient 
to be able to swap metacity, mutter or compitz that way.
> For instance, you could replace notification-daemon with notify-osd this way. Or metacity
> with compiz. The example you gave with anjuta doesn't make much sense,
> though, as it's more about some parts needed for the desktop shell, not
> about applications.
>
> And the only use of this is the RequiredProviders line of the .session
> files. gnome-session will start the components providing those
> providers.
So I understand that the first two lines are related to each other. 
First its defined that there should be a required provider TASK named 
'windowmanager' and then we specify that the default provider for this 
task is gnome-wm. I also found the .desktop file in 
/usr/share/applications. So far so good.

RequiredProviders=windowmanager;
DefaultProvider-windowmanager=gnome-wm

But this line here is where I get confused:

DefaultProvider-notifications=notify-osd

There seems to be no other line that references a TASK named 
notifications and there is also no corresponding .desktop file in 
/usr/share/applications. What I do not understand is, how do I know what 
is a valid provider? Does gnome-session hard code the valid provider 
names somewhere in its soure, or is this some kind of interface that is 
known by the TASKS?

What would happen if I just remove that line, would the notification 
system stop working?

I admit the anjuta example was not very good, but would that make more 
sense:

DefaultProvider-network=nm-applet
or:
DefaultProvider-sound=indicator-sound-service

Maybe I am just lacking some important background knowledge to 
understand whats going on here? If so, where should I start reading?
> > > The providers for a task are found in
> > > the .desktop files, thanks to the X-GNOME-Provides key. These .desktop
> > > files must either be in the autostart paths, or explicitly mentioned in
> > > DefaultProvider-TASK.
> > So there should exist a gnome-wm.desktop and notify-osd.desktop file
> > somewhere, yes? Could you give me the exact path where I can find
> > it?
> Most likely /usr/share/applications/.
>
> > Could I put a new line there and point it to any application's
> > desktop file and it would get started, say for example anjuta?
> Yes, but as I said, it doesn't make much sense because this is not a
> part of the shell, but an app that you want to automatically start. It
> makes more sense to use the autostart spec for this:
> http://specifications.freedesktop.org/autostart-spec/autostart-spec-latest.html
> (ie: simply drop a .desktop file in /etc/xdg/autostart/)
>
> Vincent
Lanoxx