Re: [Qemu-devel] [PATCH v4 00/11] convert savevm to use qapi and introduce qmp command

[Kevin Wolf]

Am 11.04.2013 um 11:20 hat Markus Armbruster geschrieben:
> [Cc: Wenchao Xia because of overlap with his work]
> 
> Eric Blake <address@hidden> writes:
> 
> > On 04/10/2013 08:05 AM, Pavel Hrdina wrote:
> >> Here is another proposal how to handle vm snapshots:
> >> 
> >> QMP vm-snapshot-save:
> >>     - { 'command': 'vm-snapshot-save',
> >>         'data': { 'name': 'str' },
> >>         'returns': 'SnapshotInfo' }
> >>     - vm-snapshot-save returns an error if there is an existing
> >>       snapshot with the same name
> >>     - you cannot provide an id for a new snapshot
> >>     - on success all information about created snapshot will be returned

Would it make sense to (optionally) let the caller specify in which
image the VM state will be stored, or whether it should be stored at
all?

> >> QMP vm-snapshot-load
> >>     - { 'command': 'vm-snapshot-load',
> >>         'data': { '*name': 'str', '*id': 'int' },
> >>         'returns': 'SnapshotInfo' }
> >>     - one of the name or id must be provided
> >>     - if both are provided they will match only the snapshot with the
> >>       same name and id
> >>     - returns SnapshotInfo only if the snapshot exists.
> >> 
> >> QMP vm-snapshot-delete:
> >>     - { 'command': 'vm-snapshot-delete',
> >>         'data': { '*name': 'str', '*id': 'int' },
> >>         'returns': 'SnapshotInfo' }
> >>     - same rules as vm-snapshot-load
> >
> > Missing some form of query-snapshots to list all consistent snapshots
> > that can be loaded or deleted (or is that another series?)
> >
> > Also, while load can only take a consistent snapshot, it might make
> > sense to expose two levels of delete - one that deletes consistent
> > snapshots, and one that deletes a snapshot for a given block device
> > regardless of whether it is consistent across all devices in use by the VM.
> 
> I agree distinguishing between two levels (vm and device) make sense.
> 
> On the vm level, we consider only "consistent" snapshots, i.e. ones that
> cover all devices and the VM state.  Semantics of save, load, delete and
> query should all be obvious.
> 
> On the device level, query and delete make obvious sense.  Save and load
> still have perfectly well-defined semantics (they apply just to the
> device, and never include VM state), but may not be terribly useful in
> practice.  Include them or not?  Not sure.

We have a command for disk-only external snapshots of single disks, so
it would only be consistent to have the same for internal snapshots.

Kevin