[Mesa-dev] [RFC] Disable virgl driver when no 3D for virtio.

[Lepton Wu]

I know this looks like a hack. But just want to send this out for comments
to see how can I address this issue in mesa:
virgl driver enabled image can't work on legacy qemu or GL disabled qemu.

It seems another choice could be playing with MESA_LOADER_DRIVER_OVERRIDE to
override driver name, but that means everybody have to do something similar.
It should be better to fix this in mesa. Another possible solution
could be to add detection in virgl driver and let virgl handle the fallback
itself. Then it seems we have to duplicate code from kms_swrast or do some
non trivial refactoring?

Any thoughts? Thanks!