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

[Colin Guthrie]

'Twas brillig, and Colin Guthrie at 27/08/11 00:46 did gyre and gimble:
> 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

OK, sussed it out eventually (I was looking in fedora's "master" branch
rather than "f16" branch so missed some patches :()

gdm patched to make it all work now. I'm not really sure how kdm will
behave but I wouldn't be surprised if it's broken.

Col



-- 

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

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