On 11/13/2011 09:08 PM, MATSUDA, Daiki wrote:
NACK. There is nothing inherently wrong with the source file not being a qcow2 file. The whole point of creating a runtime snapshot is that the original file (of _any_ format) becomes the backing file of a new qcow2 file, so that the original file now serves as the snapshot. Forbidding a live snapshot of a raw source file interferes with this intent.
I have some tested since you replied. Certainly other image file, e.g. raw type, has no problem after snapshot is taken in qcow2 format.
But in the case that direct disk block, e.g. /dev/sdc, is given for the guest OS, the same error occurs. It may not be accepted by qemu-kvm.
I'm not following you. As I already said, there's nothing wrong with a direct disk block as the backing file of a qcow2 image.
I do not understand which qemu-kvm or libvirt should be fixed. But at least libvirt should be stop to take snapshot for block device with following patch.
I still say NACK. Your patch is merely attempting to forbid a useful case, rather than fix a demonstrated problem. If I recall correctly, you started this thread when you used 'virsh snapshot-create --disk-only' without arguments, and thus fell victim to virsh picking the snapshot name for you, but trying to pick that name under /dev instead of a more typical location for a non-device file. But that's a usage error in you not taking time to provide virsh with the alternate name to use for the qcow2 file, and not a flaw that needs correcting in libvirt itself. Or even if there is a flaw in libvirt, the fix is not to forbid snapshots of a raw block device, but to be smarter about ensuring that any generated qcow2 file name is likely to be correct (a qcow2 file created under /dev probably only makes sense if the qcow2 data is being written atop a pre-existing block device, rather than trying to use open(O_CREAT) to create a regular file in /dev). -- Eric Blake eblake@redhat.com +1-919-301-3266 Libvirt virtualization library http://libvirt.org