On Mon, Dec 07, 2009 at 07:39:11AM -0600, Anthony Liguori wrote: > Richard W.M. Jones wrote: >> Also if we only acquire the lock during the commit operation then >> we'll end up with disk corruption. > > Why do we end up with disk corruption?
Forget about locking for a minute, I don't think this is safe currently. If you have two VMs set up like: qemu-img create -b backing.img foo.img qemu-img create -b backing.img bar.img qemu -drive file=foo.img # VM1 qemu -drive file=bar.img # VM2 If VM1 does a commit to the backing image, then VM2 may be caching (in its kernel memory) bits of the old backing image, and will subsequently fetch bits of the new backing image, so it'll see a mixture of old and new data. How is VM2 supposed to cope with this? It sounds like massive disk corruption to me ... Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones virt-p2v converts physical machines to virtual machines. Boot with a live CD or over the network (PXE) and turn machines into Xen guests. http://et.redhat.com/~rjones/virt-p2v
