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Re: [Qemu-devel] [PATCH] savevm: create snapshot failed when id_str alre


From: Stefan Hajnoczi
Subject: Re: [Qemu-devel] [PATCH] savevm: create snapshot failed when id_str already exits
Date: Wed, 11 Mar 2015 12:57:50 +0000
User-agent: Mutt/1.5.23 (2014-03-12)

On Tue, Mar 10, 2015 at 02:48:46PM +0100, Kevin Wolf wrote:
> Am 10.03.2015 um 14:28 hat Stefan Hajnoczi geschrieben:
> > On Mon, Mar 09, 2015 at 09:32:47PM +0800, Yi Wang wrote:
> > > This will trigger the problem: vda has snapshot s1 with id "1", vdb
> > > doesn't have s1 but has snapshot s2 with id "1"。When we want to run
> > > command "virsh create s1", del_existing_snapshots() only deletes s1 in
> > > vda, and bdrv_snapshot_create() tries to create vdb's snapshot s1 with
> > > id "1", but id "1" alreay exists in vdb with name "s2"!
> > > 
> > > This shows the condition:
> > > # qemu-img snapshot -l win7.img.1
> > > Snapshot list:
> > > ID TAG VM SIZE DATE VM CLOCK
> > > 1 s1 534M 2015-03-09 10:28:54 00:03:54.504
> > > 
> > > # qemu-img snapshot -l win7.append
> > > Snapshot list:
> > > ID TAG VM SIZE DATE VM CLOCK
> > > 1 s2 0 2015-03-05 10:29:21 00:00:00.000
> > > 
> > > # virsh snapshot-create-as win7 s1
> > > error: operation failed: Failed to take snapshot: Error while creating
> > > snapshot on 'drive-virtio-disk1'
> > 
> > Then we've arrived at changing the behavior of 'savevm' so it always
> > generates IDs.
> > 
> > Kevin: What do you think about changing savevm semantics to always
> > generate IDs?
> 
> Sounds reasonable. We're free to set whatever ID we want.
> 
> However, I wouldn't set id_str = "" like in the patch below, but remove
> the check qcow2_snapshot_create() and call find_new_snapshot_id()
> unconditionally.

Good idea!

Yi: If you are happy with the approach Kevin suggested, please send a
patch.

Stefan

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