[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PATCH V5 0/8] add internal snapshot support at block d
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [PATCH V5 0/8] add internal snapshot support at block device level |
Date: |
Fri, 19 Jul 2013 13:32:00 +0800 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Thu, Jul 18, 2013 at 02:34:52PM +0200, Kevin Wolf wrote:
> Am 11.07.2013 um 07:46 hat Wenchao Xia geschrieben:
> > This series brings internal snapshot support at block devices level, now
> > we
> > have two three methods to do block snapshot lively: 1) backing chain,
> > 2) internal one and 3) drive-back up approach.
> >
> > Comparation:
> > Advantages: Disadvantages:
> > 1) delta data, taken fast, export, size performance, delete slow.
> > 2) taken fast, delete fast, performance, size delta data, format
> > 3) performance, export, format taken slow, delta data,
> > size
> >
> > I think in most case, saving vmstate in an standalone file is better than
> > saving it inside qcow2, So suggest treat internal snapshot as block level
> > methods and not encourage user to savevm in qcow2 any more.
> >
> > Implemention details:
> > To avoid trouble, this serial have hide ID in create interfaces, this make
> > sure no chaos of ID and name will be introduced by these interfaces.
> > There is one patch may be common to Pavel's savvm transaction, patch 1/11,
> > others are not quite related. Patch 1/11 will not set errp when no snapshot
> > find, since patch 3/11 need to distinguish real error case.
> >
> > Next steps to better full VM snapshot:
> > Improve internal snapshot's export capability.
> > Better vmstate saving.
> >
> > Thanks Kevin to give advisement about how add it in qmp_transaction,
> > oldest
> > version comes drom Dietmar Maurer.
> >
> > v3:
> > General:
> > Rebased after Stenfan's driver-backup patch V6.
> >
> > Address Eric's comments:
> > 4/9: grammar fix and better doc.
> > 5/9: parameter name is mandatory now. grammar fix.
> > 6/9: redesiged interface: take both id and name as optional parameter,
> > return
> > the deleted snapshot's info.
> >
> > Address Stefan's comments:
> > 4/9: add '' around %s in message. drop code comments about vm_clock.
> > 9/9: better doc, refined the code and add more test case.
> >
> > v4:
> > Address Stefan's comments:
> > 4/9: use error_setg_errno() to show error reason for
> > bdrv_snapshot_create(),
> > spell fix and better doc.
> > 5/9: better doc.
> > 6/9: remove spurious ';' in code, spell fix and better doc.
> >
> > v5:
> > Address Kevin's comments:
> > 3/8, 4/8, 8/8: remove the limit of numeric snapshot name.
> > General change:
> > 4/8: use existing type as parameter in qapi schema.
> >
> > Wenchao Xia (8):
> > 1 snapshot: new function bdrv_snapshot_find_by_id_and_name()
> > 2 snapshot: distinguish id and name in snapshot delete
> > 3 qmp: add internal snapshot support in qmp_transaction
> > 4 qmp: add interface blockdev-snapshot-internal-sync
> > 5 qmp: add interface blockdev-snapshot-delete-internal-sync
> > 6 hmp: add interface hmp_snapshot_blkdev_internal
> > 7 hmp: add interface hmp_snapshot_delete_blkdev_internal
> > 8 qemu-iotests: add 056 internal snapshot for block device test case
>
> Okay, reviewed the whole series. I had some comments on two or three
> patches.
>
> One thing that I want to add is that in order to provide transactional
> behaviour (i.e. snapshotting multiple device in one transaction should
> result in a consistent snapshot), I think we may in fact need to stop
> the VM while taking the snapshots.
If we are doing guest memory snapshots we definitely need to stop vcpus.
For disk-only snapshots I do not think it's necessary to stop the guest
because:
1. Guest I/O can only be processed from the QEMU global mutex. But we
currently hold it so no one else can make progress.
2. In the dataplane case the drain callback that I added stops the
dataplane thread temporarily. It cannot be restarted until the main
loop iterates again (see #1).
Therefore I think stopping vcpus is not necessary for disk-only
snapshots.
Stefan
- Re: [Qemu-devel] [PATCH V5 2/8] snapshot: distinguish id and name in snapshot delete, (continued)
- [Qemu-devel] [PATCH V5 3/8] qmp: add internal snapshot support in qmp_transaction, Wenchao Xia, 2013/07/11
- [Qemu-devel] [PATCH V5 4/8] qmp: add interface blockdev-snapshot-internal-sync, Wenchao Xia, 2013/07/11
- [Qemu-devel] [PATCH V5 5/8] qmp: add interface blockdev-snapshot-delete-internal-sync, Wenchao Xia, 2013/07/11
- [Qemu-devel] [PATCH V5 6/8] hmp: add interface hmp_snapshot_blkdev_internal, Wenchao Xia, 2013/07/11
- [Qemu-devel] [PATCH V5 7/8] hmp: add interface hmp_snapshot_delete_blkdev_internal, Wenchao Xia, 2013/07/11
- [Qemu-devel] [PATCH V5 8/8] qemu-iotests: add 056 internal snapshot for block device test case, Wenchao Xia, 2013/07/11
- Re: [Qemu-devel] [PATCH V5 0/8] add internal snapshot support at block device level, Stefan Hajnoczi, 2013/07/18
- Re: [Qemu-devel] [PATCH V5 0/8] add internal snapshot support at block device level, Kevin Wolf, 2013/07/18
- Re: [Qemu-devel] [PATCH V5 0/8] add internal snapshot support at block device level,
Stefan Hajnoczi <=