On Tue, Jan 28, 2014 at 08:57:11AM -0800, Ian Main wrote: > On Tue, Jan 28, 2014 at 03:31:36PM +0100, Stefan Hajnoczi wrote: > > On Mon, Jan 27, 2014 at 11:48:06AM +0800, Fam Zheng wrote: > > > This series adds for point-in-time snapshot NBD exporting based on > > > blockdev-backup (variant of drive-backup with existing device as target). > > > > > > We get a thin point-in-time snapshot by COW mechanism of drive-backup, and > > > export it through built in NBD server. The steps are as below: > > > > > > 1. (SHELL) qemu-img create -f qcow2 BACKUP.qcow2 <source size here> > > > > > > (Alternatively we can use -o backing_file=RUNNING-VM.img to omit > > > explicitly > > > providing the size by ourselves, but it's risky because > > > RUNNING-VM.qcow2 is > > > used r/w by guest. Whether or not setting backing file in the image > > > file > > > doesn't matter, as we are going to override the backing hd in the next > > > step) > > > > > > 2. (QMP) blockdev-add backing=source-drive file.driver=file > > > file.filename=BACKUP.qcow2 id=target0 if=none driver=qcow2 > > > > > > (where source-drive is the running BlockDriverState name for > > > RUNNING-VM.img. This patch implements "backing=" option to override > > > backing_hd for added drive) > > > > > > 3. (QMP) blockdev-backup device=source-drive sync=none target=target0 > > > > > > (this is the QMP command introduced by this series, which use a named > > > device as target of drive-backup) > > > > > > 4. (QMP) nbd-server-add device=target0 > > > > > > When image fleecing done: > > > > > > 1. (QMP) block-job-cancel device=source-drive > > > > > > 2. (HMP) drive_del target0 > > > > > > 3. (SHELL) rm BACKUP.qcow2 > > > > Seems to work as advertized but do you have qemu-iotests for > > blockdev-backup and image fleecing in particular? > > We have them for drive-backup but not blockdev-backup afaik. Mostly the > same code but certainly a different API. > > It shouldn't be too hard to duplicate the 055 drive-backup code and make > it a blockdev-backup test. Testing nbd export would be difficult > however.
A Python NBD client is pretty easy to implement. Here is a *server* I wrote for testing a while back: https://lists.gnu.org/archive/html/qemu-devel/2013-03/msg01535.html Stefan
