kern/50001: drmkms does not work with VT switching

[dholland%NetBSD.org@localhost]

>Number:         50001
>Category:       kern
>Synopsis:       drmkms does not work with VT switching
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Jun 26 05:05:00 +0000 2015
>Originator:     David A. Holland
>Release:        NetBSD 7.99.17 (20150519)
>Organization:
>Environment:
System: NetBSD macaran 7.99.17 NetBSD 7.99.17 (MACARAN) #26: Fri May 22 18:22:29 EDT 2015  dholland@macaran:/usr/src/sys/arch/amd64/compile/MACARAN amd64
Architecture: x86_64
Machine: amd64
>Description:

drmkms (or at least radeondrmkms) does not work with VT switching and
two (or more) X servers. If you start a second X server on screen :1
(or whatever) and try to run glxgears you get

  libGL error: failed to open drm device: Permission denied
  libGL error: failed to load driver: r600

and then it runs... but slowly.

(On the plus side, though, the X server does run, glxgears does run,
and nothing seems prone to explode in this configuration.)

In an ideal world there would be one drm device per vt, or something
like that. Or it would be tied to the existing vt switching logic,
although that perhaps isn't the best possible alternative as the vt
switching logic has always looked kinda grotty to me.

Or something.

If trying to design something, take note of what's in
   http://wiki.netbsd.org/projects/project/user-switching/
as that's where the related long-term goals are currently
accumulating.

>How-To-Repeat:

   startx
   ctrl-alt-f2
   startx -- :1
   glxgears

>Fix: