[Mageia-dev] systemd + udev 173 + gnome-shell

[Colin Guthrie]

Hi,

OK, so this combo is currently broken!

Here is the explanation.

With udev 172, udev-acl would apply ACLs to devices (such as the DRI
device) when console-kit registers a new session.

This included the gdm user at the login manager.

systemd is gradually taking over the job of consolekit. This means that
systemd now handles the ACL writing and login sessions should be
visiible via systemctl-loginctl (as opposed to ck-list-sessions).


With udev 172, both systemd and console-kit would trigger ACL writes.
Normally this is fine, they both ultimately do the same thing.

But, it seems that in actual fact, systemctl-logind wasn't ever
registering the gdm session. Thankfully console-kit did, and thus gdm
user got the ACLs it needed.


Now this is where the problem arises. With udev 173, udev-acl knows
whether or not systemd is running and if it is, it it won't write the
ACLs. This means that even tho' gdm is still registered with
console-kit, this will never actually trigger an ACL write.

This means that gdm does not have access to /dev/dri/card0 and thus
cannot determine if the device is capable of 3D accel. This then sets an
atom on the root window which the gnome-session-check-accelerated binary
looks for. This atom acts as a little cache. If it doesn't exist, it
does a full probe and then writes the atom. The next time it runs it
finds the atom and skips the actual checks. But as the atom was written
by gdm when it couldn't access dri, it says no accel is available, even
although the user can actually access it.


I've not yet sussed out gdm is not registering with systemd... it should
all be automatic via pam... but something somewhere is failing :s


Col


-- 

Colin Guthrie
mageia(at)colin.guthr.ie
http://colin.guthr.ie/

Day Job:
  Tribalogic Limited [http://www.tribalogic.net/]
Open Source:
  Mageia Contributor [http://www.mageia.org/]
  PulseAudio Hacker [http://www.pulseaudio.org/]
  Trac Hacker [http://trac.edgewall.org/]