DRM SMPng locking for review

[Eric Anholt]

I've been working on locking of the DRM, based off of the work that was
already done for linux and ported to BSD.  I think the current locking
was wrong, including that it used lockmgr and simplelocks on -stable
when as far as I know it was unnecessary.  Also, I had marked the IRQ
handlers MPSAFE without understanding the issue really, so IRQs could
get missed.  Here's a patch, which I hope someone can review because I
don't trust myself at all.
http://people.freebsd.org/~anholt/dri/files/drm-locking-2.diff

It's against DRI CVS, as I haven't merged to FreeBSD in a while.  You
can get it using the instructions at:
http://dri.sourceforge.net/cgi-bin/moin.cgi/CVS
If you don't want to build the whole tree, you can just:

cd xc
patch -p0 < ~/drm-locking-2.diff
cd programs/Xserver/hw/xfree86/os-support/bsd/drm/kernel
ln -s ../../../shared/drm/kernel/*.[ch] ./

Quick question: If open returns an error, close doesn't get called, does
it?

-- 
Eric Anholt                                eta at lclark.edu          
http://people.freebsd.org/~anholt/         anholt at FreeBSD.org