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

[Eric Blake <eblake@redhat.com>]

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On 04/10/2013 06:40 AM, Luiz Capitulino wrote:
> On Wed, 10 Apr 2013 06:24:11 -0600
> Eric Blake <eblake@redhat.com> wrote:
> 
>>>   - If you want to overwrite an existing snapshot, you could specify
>>>     the 'id' or the 'name' argument or both of them and also you will
>>>     have to use the 'force' argument
>>
>> But the argument made in this thread is that QMP should _not_ have a
>> force argument.  It should be a flat-out error in QMP to try to create a
>> snapshot with a conflicting name or tag; preferably with a distinct
>> error type.  Higher-level apps (HMP savevm -f) would try to create; if
>> -f is not specified, the error is good enough; if -f is specified and
>> that particular error is returned, then HMP calls delete and then
>> re-tries the create.  No 'force' argument needed at the QMP layer.
> 
> To avoid adding a new error class, the HMP command could query for the
> snapshot name and delete it if it exists before creating the snapshot.

Atomic collision detection is nicer than having to pre-query - fewer QMP
calls in the common case.  But you're right that none of the existing
ErrorClass categories fit the idea of "creation refused because name
would collide".

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


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