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Re: [Qemu-devel] [PATCH v4 0/7] Drop in_use from BlockDriverState and en
From: |
Kevin Wolf |
Subject: |
Re: [Qemu-devel] [PATCH v4 0/7] Drop in_use from BlockDriverState and enable point-in-time snapshot exporting over NBD |
Date: |
Mon, 25 Nov 2013 10:29:44 +0100 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
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
- [Qemu-devel] [PATCH v4 4/7] block: Add checks of blocker in block operations, (continued)
- [Qemu-devel] [PATCH v4 4/7] block: Add checks of blocker in block operations, Fam Zheng, 2013/11/22
- [Qemu-devel] [PATCH v4 5/7] block: Parse "backing" option to reference existing BDS, Fam Zheng, 2013/11/22
- [Qemu-devel] [PATCH v4 6/7] qmp: add command 'blockdev-backup', Fam Zheng, 2013/11/22
- [Qemu-devel] [PATCH v4 7/7] block: Allow backup on referenced named BlockDriverState, Fam Zheng, 2013/11/22
- Re: [Qemu-devel] [PATCH v4 0/7] Drop in_use from BlockDriverState and enable point-in-time snapshot exporting over NBD, Stefan Hajnoczi, 2013/11/22