Re: [Qemu-devel] [PATCH V2 09/12] qmp: add interface blockdev-snapshot-delete-internal-sync

[Stefan Hajnoczi]

On Wed, Jun 19, 2013 at 02:18:48PM +0800, Wenchao Xia wrote:
> 于 2013-6-18 22:20, Stefan Hajnoczi 写道:
> >On Mon, Jun 17, 2013 at 11:25:26AM +0800, Wenchao Xia wrote:
> >>于 2013-6-15 17:55, Eric Blake 写道:
> >>>Should this command be made available via 'transaction'?  That is, if I
> >>>have a two-disk VM, and use 'transaction' to take a snapshot of both
> >>>disks at once, shouldn't I also have a way to delete the snapshots of
> >>>both at once, or gracefully fail without data loss if the second one has
> >>>problems?
> >>
> >>   I think adding it in transaction is not very useful but brings more
> >>complexity. Transcation is used to guareentee all operations are taken
> >>in one time point, for example, snapshot creation use it to make sure
> >>all are consistent to VM. But for deletion, this requirement do not
> >>exist.
> >
> >I guess the problem is: can we make internal snapshot deletion
> >transactional?  It's hard to do rollback for snapshot deletion.
> >
>   Several deletion in transaction equals to several calls of
> 'blockdev-snapshot-delete-internal-sync', unlike creation, so I hope
> not add it which have rollback issue.
> 
> 
> >But batching is definitely useful for doing 'delvm' in QMP.  I just
> >don't think transactions help.  We just need a 'delvm' equivalent in
> >QMP.
> >
>   Maybe the caller can encapsulate a batch interface at its level.

'delvm' is a batch interface - it deletes internal snapshots that have
the same name across multiple devices.

It's not as flexible as:
blkdev-internal-snapshot-delete drive0 drive2 drive4

Because that would allow you to specify specific drives.

Stefan