OK, I believe the case that's causing it to go down this route is a perms screw
up somewhere; I was running this test in a separate X session (just logging as
a normal user on the console and running X :2 )

But with a bit of debug I'm seeing:

libGL: OpenDriver: trying /usr/lib64/dri/tls/r600_dri.so
libGL: OpenDriver: trying /usr/lib64/dri/r600_dri.so
libGL error: failed to open drm device: Permission denied
libGL error: failed to load driver: r600

[dg@major ~]$ ls -lZ /dev/dri/card0
crw-rw----+ root video system_u:object_r:dri_device_t:s0 /dev/dri/card0
[dg@major ~]$ id -Z
unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023

So I'm not quite sure what the perm screw up is, but that's separate - this
will seg in glxgears or anything if the drm device won't open.

Dave