Here are some hints for ~amd64 users who are about to have trouble with gnome3-session failing to start:
After updating today to mesa-10.4.2 and xorg-server-1.16.3-r1, gnome3 failed to start, complaining that 3d acceleration was not available. This was true, unfortunately, and the reason is that xorg-server is looking for the nvidia glx module in the wrong directory, i.e. /usr/lib64/xorg/modules/extensions/libglx.so. The correct path is /usr/lib64/opengl/nvidia/extensions/libglx.so. Normally, 'eselect opengl' sets this path correctly, but not today, apparently. I finally worked around this problem by creating an appropriate symlink to the nvidia libglx.so file in the correct location. Another recent problem is that xorg-server is honoring *only* the first path listed in /etc/X11/xorg.conf.d/20opengl, and fails if the appropriate file isn't there: i.e. it looks in /usr/lib32/ as the first default path (even on a 64-bit machine) and fails to look in /usr/lib64/ even though that path is correctly included in the list of places to look. I think the devs are already aware of these bugs and are working on the problem. (Obviously not fixed yet :) BTW, some good news: mesa-10.4.2 fixes a problem with running gnome3 as virtualbox guest: The software rasterizer in the new mesa is now fast enough to satisfy /usr/libexec/gnome-session- check-accelerated, so gnome-session no longer craps out when starting in virtualbox :)
