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

[Kevin Wolf <kwolf@redhat.com>]

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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.

Kevin

> diff --git a/savevm.c b/savevm.c
> index ce2b6a2..bee2143 100644
> --- a/savevm.c
> +++ b/savevm.c
> @@ -1141,7 +1141,6 @@ void hmp_savevm(Monitor *mon, const QDict *qdict)
>          ret = bdrv_snapshot_find(bs, old_sn, name);
>          if (ret >= 0) {
>              pstrcpy(sn->name, sizeof(sn->name), old_sn->name);
> -            pstrcpy(sn->id_str, sizeof(sn->id_str), old_sn->id_str);
>          } else {
>              pstrcpy(sn->name, sizeof(sn->name), name);
>          }
> @@ -1178,6 +1177,12 @@ void hmp_savevm(Monitor *mon, const QDict *qdict)
>          if (bdrv_can_snapshot(bs1)) {
>              /* Write VM state size only to the image that contains the state */
>              sn->vm_state_size = (bs == bs1 ? vm_state_size : 0);
> +
> +            /* Force ID generation for each image since there could be naming
> +             * collisions.
> +             */
> +            sn->id_str[0] = '\0';
> +
>              ret = bdrv_snapshot_create(bs1, sn);
>              if (ret < 0) {
>                  monitor_printf(mon, "Error while creating snapshot on '%s'\n",



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