is an X "soft" restart possible?

[Michael Pardee]

Lots of people these days are experimenting with multi-user
configurations where multiple X servers are running on different
cards.  Even though a lot of card combinations won't even initialize,
it is not too hard to get multiple nvidia cards up using either the nv
or nvidia driver.  However, it is a well known issue that nvidia cards
randomly crash when the X server re-inits during a logout/login cycle.
 This happens more frequently with the nvidia driver, but the nv
driver also has problems occasionally.  NVIDIA has a bug report filed
for why their driver can't re-initialize, but why re-initilize at all
if we dont' have to?

Most of us in this situation are using GDM and have
AlwaysRestartServer=false, but that still doesn't help all the time. 
Even when the X server is not being fully restarted, GDM sends a
SIGHUP to X to signal a re-init.  This signals a clean up of
authentication, etc., but what else is happenning?.  At that point,
there must be some video card re-initialization going on, since we see
the nv or nvidia drivers dying at that point and are unable to
restart.  So why does X have to do anything special with the video
card driver at that point?  If X could just leave the video card
hardware alone during a logout/login, we wouldn't have a problem.

So, here are the important questions:
1. Exactly what steps occur when X deals with one user logging out and
another logging in without a full server restart?
2. What would it take to prevent X from messing with the video card
during a logout/login cycle.  In other words, how could we do a truly
"soft" restart?

Thanks,
Michael Pardee
1-888-323-1742
Open Sense Solutions LLC
http://opensensesolutions.com