Am 22.11.2013 um 17:58 hat Stefan Hajnoczi geschrieben: > On Fri, Nov 22, 2013 at 01:24:47PM +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 ide0-hd0 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-complete device=ide0-hd0 > > > > 2. (HMP) drive_del target0 > > > > 3. (SHELL) rm BACKUP.qcow2
I haven't looked at the code yet, but the interface looks right. > Interesting implementation, it looks pretty good. I'll need to review > it a second time to track all the operation block/unblocks. It wasn't > immediately clear to me whether these patches will restrict something > that used to work. We still have a lot of time for 1.8, so I think we can be radical here: If something doesn't have a test case and we don't catch it during the normal review, then let's just break it. Someone will find it and then we'll get a test case for it, so that it doesn't happen again. Kevin
