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

[Eric Blake]

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
> 
> 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.

> 
> HMP savevm:
>     - args_type = "force:-f,name:s?",
>     - if the name is not provided the HMP command will generates new
>       one for QMP command
>     - if there is already a snapshot with provided or generated name
>       it will fails
>     - there will be an optional -f parameter to force saving requested
>       snapshot and it will internally use vm-snapshot-delete and then
>       vm-snapshot-save
>     - all information about created snapshot will be printed
> 
> HMP loadvm:
>     - args_type = "name:s?,id:i?",
>     - follow the same behavior as the QMP command

Except that with HMP, arguments are positional.  You can't provide 'id'
in isolation; by listing id:i? second, the parser requires that the
first argument encountered is a name.

I think a better interface might be:

HMP loadvm:
    - args_type = "id:-i,name:s?'

If just name is given, first do a tag lookup; if that fails do an id
lookup.  If the -i flag is given, skip the tag lookup just do an id lookup.

> 
> HMP delvm:
>     - args_type = "name:s?,id:i?"
>     - same rules as loadvm

Same comment as for loadvm.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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