Bug#798207: nvidia-legacy-340xx-driver: Wrong module loaded, X fails to start when legacy installed alongside mainline driver

[Luca Boccassi]

On Sat, 2015-09-19 at 02:45 +0200, Andreas Beckmann wrote:
> On 2015-09-19 00:05, Luca Boccassi wrote:
> >> In the next round you could try to add this to
> >> /etc/nvidia/nvidia-modprobe.conf:
> >>
> >> alias	pci:v000010DEd00000E00sv*sd*bc04sc80i00*	nvidia
> >> alias	pci:v000010DEd00000AA3sv*sd*bc0Bsc40i00*	nvidia
> >> alias	pci:v000010DEd*sv*sd*bc03sc02i00*		nvidia
> >> alias	pci:v000010DEd*sv*sd*bc03sc00i00*		nvidia
> > 
> > This works and the right module is loaded, but then Gnome crashes
> > because of the error below :-( Still, progress is progress.
> if gdm crashes, try e.g. kdm/xdm/...

As mentioned in #799948, adding Debian-gdm to the "video" group fixes
the problem. From that bug report, it also looks like the crash is not
related to the co-existence of nvidia-current and nvidia-legacy-340xx.
After that workaround, everything works great now with both drivers
installed!

Another bug report, against gdm3, reports the same problem: #800327

> I did some debugging, and found out that /usr/lib/gnome-session/gnome-session-
> check-accelerated-helper fails. I ran the program under strace as user Debian-
> gdm and noticed the following :
> 
> stat("/dev/nvidiactl", {st_mode=S_IFCHR|0660, st_rdev=makedev(195, 255), ...})
> = 0
> open("/dev/nvidiactl", O_RDWR)          = -1 EACCES (Permission denied)

I guess this is due to the new functionality of auto-loading when X
starts?

If so, should we make the xserver-xorg-video-nvidia package add the
various desktop-manager users to the "video" group in the postinst?
I guess the gdm3/ssdm/etc packages should do the same, to avoid ordering
issues.

Kind regards,
Luca Boccassi