On Thu, Nov 04, 2021 at 09:58:11AM +0100, Markus Armbruster wrote: > From: Vladimir Sementsov-Ogievskiy <vsementsov@xxxxxxxxxxxxx> > > Modern way is using blockdev-add + blockdev-backup, which provides a > lot more control on how target is opened. > > As example of drive-backup problems consider the following: > > User of drive-backup expects that target will be opened in the same > cache and aio mode as source. Corresponding logic is in > drive_backup_prepare(), where we take bs->open_flags of source. > > It works rather bad if source was added by blockdev-add. Assume source > is qcow2 image. On blockdev-add we should specify aio and cache options > for file child of qcow2 node. What happens next: > > drive_backup_prepare() looks at bs->open_flags of qcow2 source node. > But there no BDRV_O_NOCAHE neither BDRV_O_NATIVE_AIO: BDRV_O_NOCAHE is > places in bs->file->bs->open_flags, and BDRV_O_NATIVE_AIO is nowhere, > as file-posix parse options and simply set s->use_linux_aio. > > The documentation is updated in a minimal way, so that drive-backup is > noted only as a deprecated command, and blockdev-backup used in most of > places. > > Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@xxxxxxxxxxxxx> > Reviewed-by: Kashyap Chamarthy <kchamart@xxxxxxxxxx> > Signed-off-by: Markus Armbruster <armbru@xxxxxxxxxx> > --- Reviewed-by: Eric Blake <eblake@xxxxxxxxxx> I think this is appropriate for inclusion in 6.2, even if it did not quite make soft freeze, so that we aren't delaying the deprecation for an entire cycle. > docs/about/deprecated.rst | 11 ++++++ > docs/interop/live-block-operations.rst | 47 +++++++++++++++++--------- > qapi/block-core.json | 5 ++- > qapi/transaction.json | 6 +++- > 4 files changed, 51 insertions(+), 18 deletions(-) > -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org
