Starting DBus from gnome-session instead of Xsession

Loïc · External Since: Nov 11, 2004 Posts: 475

Hi,

The session DBus in Debian Xsessions is currently started by
/etc/X11/Xsession.d/75dbus_dbus-launch if the use-session-dbus option
is set.

Newer gnome-session will spawn a session DBus automatically if none has
been started.

If gnome-session launches DBus, DBus will inherit env from
gnome-session which is handy for gnome-keyring for example.

I suspect we wouldn't suffer from the sound issues (the desktop sounds
are not working bugs) would we be moving to launch DBus from
gnome-session, and I think this is what we should aim to do.

I personally think it makes a lot of sense to launch DBus from
gnome-session; what I wonder about is how we're going to switch to this
setup.
Ubuntu plans to fix this via a patch to the dbus Xsession snippet to
avoid starting DBus when running GNOME session; see Ubuntu #62163 and
<http://librarian.launchpad.net/7170382/dbus_1.0.2-1ubuntu34.patch>.
It's not trivial to know whether we're really in a GNOME session
because:
- from the PoV of gdm, there are a couple of GNOME sessions, and the
"Default" session, which will launch x-session-manager which might or
might not gnome-session
- sessions can be started via startx and/or various other ways

Note: there's currently an upstream bug that gnome-session does not
wait on DBus enough; see GNOME bug #395488.

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Alan Baghumian · External Since: Oct 20, 2006 Posts: 17

Hi,

Does d-i install dbus service as a standard part of the system?

Alan

> Hi,
>
> The session DBus in Debian Xsessions is currently started by
> /etc/X11/Xsession.d/75dbus_dbus-launch if the use-session-dbus option
> is set.
>
> Newer gnome-session will spawn a session DBus automatically if none has
> been started.
>
> If gnome-session launches DBus, DBus will inherit env from
> gnome-session which is handy for gnome-keyring for example.
>
> I suspect we wouldn't suffer from the sound issues (the desktop sounds
> are not working bugs) would we be moving to launch DBus from
> gnome-session, and I think this is what we should aim to do.
>
>
> I personally think it makes a lot of sense to launch DBus from
> gnome-session; what I wonder about is how we're going to switch to this
> setup.
> Ubuntu plans to fix this via a patch to the dbus Xsession snippet to
> avoid starting DBus when running GNOME session; see Ubuntu #62163 and
> <http://librarian.launchpad.net/7170382/dbus_1.0.2-1ubuntu34.patch>.
> It's not trivial to know whether we're really in a GNOME session
> because:
> - from the PoV of gdm, there are a couple of GNOME sessions, and the
> "Default" session, which will launch x-session-manager which might or
> might not gnome-session
> - sessions can be started via startx and/or various other ways
>
>
> Note: there's currently an upstream bug that gnome-session does not
> wait on DBus enough; see GNOME bug #395488.
>
> --
> Loï¿½c Minier
>
>
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Alan Baghumian · External Since: Oct 20, 2006 Posts: 17

Oh GOD,

As I understand, if we prevent /etc/X11/Xsession.d/75dbus_dbus-launch to
be executed, gnome-session will start dbus and it's what we need exactly.
But that #395488 bug complicates the situation... the risk of killing
dbus-daemon at all...

Alan

> Hi,
>
> Does d-i install dbus service as a standard part of the system?
>
> Alan
>
>> Hi,
>>
>> The session DBus in Debian Xsessions is currently started by
>> /etc/X11/Xsession.d/75dbus_dbus-launch if the use-session-dbus option
>> is set.
>>
>> Newer gnome-session will spawn a session DBus automatically if none has
>> been started.
>>
>> If gnome-session launches DBus, DBus will inherit env from
>> gnome-session which is handy for gnome-keyring for example.
>>
>> I suspect we wouldn't suffer from the sound issues (the desktop sounds
>> are not working bugs) would we be moving to launch DBus from
>> gnome-session, and I think this is what we should aim to do.
>>
>>
>> I personally think it makes a lot of sense to launch DBus from
>> gnome-session; what I wonder about is how we're going to switch to this
>> setup.
>> Ubuntu plans to fix this via a patch to the dbus Xsession snippet to
>> avoid starting DBus when running GNOME session; see Ubuntu #62163 and
>> <http://librarian.launchpad.net/7170382/dbus_1.0.2-1ubuntu34.patch>.
>> It's not trivial to know whether we're really in a GNOME session
>> because:
>> - from the PoV of gdm, there are a couple of GNOME sessions, and the
>> "Default" session, which will launch x-session-manager which might or
>> might not gnome-session
>> - sessions can be started via startx and/or various other ways
>>
>>
>> Note: there's currently an upstream bug that gnome-session does not
>> wait on DBus enough; see GNOME bug #395488.
>>
>> --
>> Loï¿½c Minier
>>
>>
>> --
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>> with a subject of "unsubscribe". Trouble? Contact
>> listmaster.TakeThisOut@lists.debian.org
>>
>>
>
>
>
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Loïc · External Since: Nov 11, 2004 Posts: 475

On Sun, May 06, 2007, Josselin Mouette wrote:
> > - from the PoV of gdm, there are a couple of GNOME sessions, and the
> > "Default" session, which will launch x-session-manager which might or
> > might not gnome-session
>
> See the gnomerc snippet which already does this detection:
>
> BASESTARTUP=`basename "$STARTUP" | cut -d\ -f1`
> if [ "$BASESTARTUP" = gnome-session -o \
> $ "$BASESTARTUP" = x-session-manager -a \
> "`readlink /etc/alternatives/x-session-manager`" = \
> /usr/bin/gnome-session $ ]; then
> blabla
> fi

Yes, I know, this is exactly what the patch I pointed at does ... and
it's very fragile. It would also be quite ugly to encode GNOME
awareness in dbus stuff.

I think there might be better ways to be more robust, cleaner, while
still offering more control to the end-user/end-administrator. For
example:
1) we could force all GDM sessions to be based on a .desktop file, pass
this .desktop file to the whole session via an env var or another
convention (~/.gdm-session-$DISPLAY.desktop could be a symlink to
this desktop file); options would be encoded in X- fields of this
file
2) we could pass various information directly via environment, such as
X_SESSION_OPTIONS="nodbus" and X_SESSION_TYPE="gnome" and use this as
a base to decide to parse .gnomerc and to disable dbus (a Xsession.d
script would add "nodbus" to X_SESSION_OPTIONS if X_SESSION_TYPE is
gnome)

I think both of the above options could be more robust than the current
check for the value of "STARTUP", while still giving end-user control
over what the session should or should not do.

> > - sessions can be started via startx and/or various other ways
>
> AFAIK startx also uses Xsession.

Yes, startx does, but by various other ways I meant:
- .xsession or .Xsession (Xsession.d/* are still read, but STARTUP wont
match this)
- overrides files of various dms, or session .desktop files
- custom manual calls to /etc/X11/Xsession

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Loïc · External Since: Nov 11, 2004 Posts: 475

On Sun, May 06, 2007, Tim Dijkstra wrote:
> For me it doesn't make sense. DBus aims to be more generic than just
> for gnome. You didn't make really clear why it should be started from
> gnome-session instead of during the X start-up. If you try to sneak in
> extra information into DBus' environment, that could be annoying for
> people who use an occasional gnome program, but do not use
> gnome-session.

gnome-session is the canonical way to properly start a GNOME session,
with a working GNOME stack. If a normal GNOME session needs dbus, then
I find it quite normal that gnome-session spawns it instead of relying
on the distributor to integrate dbus in the startup before
gnome-session.
In fact, you can go even farther and say that each individual
application needing the session dbus should arrange for it being
present, which is the case with recent DBus: but this is already solved
by newer DBus which will spawn a session dbus if any app needs to
access it.

Yes, starting dbus from gnome-session is a broken design, but it will
work in more cases than the current way of starting it, and it will
more consistent across distributions; I think we would benefit from
switching to this startup style.

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Sjoerd Simons · External Since: Nov 10, 2004 Posts: 203

On Mon, May 07, 2007 at 10:41:54AM +0200, Loïc Minier wrote:
> Yes, starting dbus from gnome-session is a broken design, but it will
> work in more cases than the current way of starting it, and it will
> more consistent across distributions; I think we would benefit from
> switching to this startup style.

Your obviously correct in this, we should care about our users Smile

. But before
switching to this style i'd like to take some time to find out what exactly
breaks when gnome-session _doesn't_ start dbus. So we can raise our concerns
nicely with upstream and tell them what to fix Smile

The upstream bug reports the gnome-keyring socket env var as one
of the reasons, but currently gnome-keyring supports socket discovering magic
though dbus.. So that should be fine.

The other thing is that the SESSION_MANAGER env var isn't set. And there seems
to be an issue with system sounds through esd (although it's unclear if it's
related).

Sjoerd
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