kvm incompatible with xfs

Just found this out by way of an experiment for a partner. Cool partner, cool product, running on our fast hardware for SC13. Problem is that I was seeing some very odd error messages when I tried to mount a volume stored in a file on an xfs based LUN. I could dd to the file. I could mkfs.ext* the /dev/vda. But the moment I tried to mount it, block errors.
This was true with both the virtio and the IDE driver.
Then I tried several different kernel versions from 2.6.32-* through 3.10.*. Still no joy.
Then while I was out at a family function, I got the idea to try ext4 rather than xfs as the base. There is no reason this should work. Really, none at all.
And yet, when I tried it, this was the one thing that did work.
I’ll gather more info and toss it up to both lists, but this is very annoying. We use lots of xfs, and I seem to remember a number of our kvm units are using NFS exported xfs. It just doesn’t like the local version.

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