On 1/9/20 12:21 PM, Peter Krempa wrote:
Posted as RFC because qemu probably doesn't reopen backing images for bitmap operations resulting in: $ virsh checkpoint-delete vm --checkpointname a error: Failed to delete checkpoint a error: internal error: unable to execute QEMU command 'transaction': Bitmap 'a' is readonly and cannot be modified Unfortunately this can't be done manually because 'blockdev-reopen' is still experimental.
In the meantime, with existing qemu, can we still at least teach libvirt to delete its metadata, and ignore unknown bitmaps leftover in qcow2 images that we were unable to delete because of the qemu limitation on read-only backing files? Yes, your qcow2 files will get bloated with dead bitmaps, but that's not going to interfere with guest operations or with future backups that use the bitmaps still tracked by libvirt. And it matches the failure scenario where an attempt at an incremental backup fails due to qemu crashing: the active bitmap is corrupt, so all older bitmaps are no longer usable, and your only recourse is to resort to full backup instead of incremental backup; but full backup is still worthwhile, and ignoring the now-useless bitmaps from the earlier backup points doesn't interfere with that.
-- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org
