[Qemu-devel] Creating snapshots with specific runtime options

[Qemu-devel] Creating snapshots with specific runtime options

[Alberto Garcia]

As far as I can see there's no way to create a snapshot and either

  a) inherit the runtime options from the original image
  b) specify a new set of options

This comment in external_snapshot_prepare() before calling bdrv_open()
suggests that the problem is known but the discussion was postponed.

    /* TODO Inherit bs->options or only take explicit options with an
     * extended QMP command? */

I would like to retake this and make it possible. I discussed it
briefly with Stefan on IRC and he said that Kevin might have some
ideas.

In principle extending the QMP command sounds as simple as adding
'options': 'BlockdevOptions' to 'blockdev-snapshot-sync', but it's
surely more complicated than that :) Is the 'BlockdevOptions' API even
stable?

Berto

Re: [Qemu-devel] Creating snapshots with specific runtime options

[Stefan Hajnoczi]

On Tue, Aug 25, 2015 at 04:57:53PM +0300, Alberto Garcia wrote:
> As far as I can see there's no way to create a snapshot and either
> 
>   a) inherit the runtime options from the original image
>   b) specify a new set of options
> 
> This comment in external_snapshot_prepare() before calling bdrv_open()
> suggests that the problem is known but the discussion was postponed.
> 
>     /* TODO Inherit bs->options or only take explicit options with an
>      * extended QMP command? */
> 
> I would like to retake this and make it possible. I discussed it
> briefly with Stefan on IRC and he said that Kevin might have some
> ideas.
> 
> In principle extending the QMP command sounds as simple as adding
> 'options': 'BlockdevOptions' to 'blockdev-snapshot-sync', but it's
> surely more complicated than that :) Is the 'BlockdevOptions' API even
> stable?

Some block drivers don't have BlockdevOptions support yet.

I think that doesn't prevent us from passing BlockdevOptions to snapshot
creation though.

Re: [Qemu-devel] Creating snapshots with specific runtime options

[Alberto Garcia]

On Wed 26 Aug 2015 02:57:13 PM CEST, Stefan Hajnoczi wrote:

>> In principle extending the QMP command sounds as simple as adding
>> 'options': 'BlockdevOptions' to 'blockdev-snapshot-sync', but it's
>> surely more complicated than that :) Is the 'BlockdevOptions' API
>> even stable?
>
> Some block drivers don't have BlockdevOptions support yet.
>
> I think that doesn't prevent us from passing BlockdevOptions to
> snapshot creation though.

Hmmm, I see however that there's overlap between blockdev-snapshot-sync
and BlockdevOptions.

You must indicate the target file in both. Format and node name are also
present in both (these are optional however)... we can of course check
that the values match and/or ignore some of them but that's horrible.

Berto