KVM (or qemu for that matter) does not care about concurrent access to disk images it opens. So it's possible to mount the same guest block device on more than one guest, resulting in a badly broken filesystem. I wonder if the right way is to open all the devices in exclusive mode (O_EXCL). At least for real block devices. On linux this ensures there's no other holders of that device, open() errors out with -EBUSY if it's not the case. With an option to stop adding such a flag, in order to be able to use some cluster-aware filesystem or read-only device. Dunno how it applies to files (qcow etc), but it *seems* here the situation is even worse, because not only the filesystem (meta)data might be damaged, but qcow structure too, and there's no fsck.qcow program available to repair it. So I think kvm should ensure exclusive access to the files it opens (except of cd-rom images and the like), using either O_EXCL for block devices or locking for qcow/raw files, and have an option to stop that (e.g. exclusive=0). Comments? Thanks! /mjt -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
