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Re: [Qemu-devel] [PATCH V5 0/8] add internal snapshot support at block d

From: Kevin Wolf
Subject: Re: [Qemu-devel] [PATCH V5 0/8] add internal snapshot support at block device level
Date: Thu, 18 Jul 2013 14:34:52 +0200
User-agent: Mutt/1.5.21 (2010-09-15)

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

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.


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