It seems that x11-drivers/nvidia-drivers-195.36.24 needs app-admin/eselect-opengl-1.1.1-r2 to install a libdri2.so symlink in /usr/lib/xorg/modules/extensions/, which it does not.
Hence the nvidia driver complains on Xorg startup:
[ 329.347] (II) Loading sub module "dri2"
[ 329.347] (II) LoadModule: "dri2"
[ 329.348] (WW) Warning, couldn't open module dri2
[ 329.348] (II) UnloadModule: "dri2"
[ 329.348] (EE) NVIDIA: Failed to load module "dri2" (module does not exist, 0)
[ 329.348] (II) NVIDIA(0): The X server will not be able to send the VDPAU driver name to
[ 329.348] (II) NVIDIA(0): libvdpau.
Manually symlinking /usr/lib/xorg/modules/extensions/libdri2.so -> ../../../opengl/xorg-x11/extensions/libdri2.so seems to silence the warning:
[ 968.780] (II) Loading sub module "dri2"
[ 968.780] (II) LoadModule: "dri2"
[ 968.780] (II) Reloading /usr/lib64/xorg/modules/extensions/libdri2.so
[ 968.780] (II) NVIDIA(0): [DRI2] Setup complete
[ 968.780] (II) NVIDIA(0): [DRI2] VDPAU driver: nvidia
This is a minor warning in the grand scheme, basically the dri2 module won't be able to send the driver name to VDPAU. But since nvidia-drivers don't use dri2, nvidia has provided a fall back in VDPAU to assume nvidia. So all is well in the end.
I can look at a work around within X to potentially clean up this warning.
I've brought this up with the eselect-opengl maintains and they're basically skipping creating the symlink for nvidia-drivers but shouldn't be.
Actually, I encountered this problem with xorg-server-1.11.3 and nvidia-290.10 on ~amd64 box.
It could be fixed either by symblink or adding module paths in xorg-server like
I've just unmasked eselect-opengl-1.3* and related packages, and I think they implicitly fix this issue. Could you upgrade @world and retry, please (removing any workarounds you have applied first)?