Code review comment for lp:~cemil-azizoglu/mir/MesaBufferAllocatorTest-failure-under-sbuild

@"A better solution would be to use shm with a O_TMPFILE which is what this proposal is doing." - if only that were true. ;)

I don't like fallbacks in production code to cover situations that should only occur in tests. They tend to obscure problems in live running. (We don't want to use /tmp in a real system.)

An alternative solution be to set $XDG_RUNTIME_DIR to "/tmp" in MesaBufferAllocatorTest?

However, we already use "/tmp" if $XDG_RUNTIME_DIR isn't set, so it isn't introducing any new issue.