Re: [Qemu-devel] [PATCH 1/3] block: Additional info string in ImageInfo and BDI

[Max Reitz <mreitz@redhat.com>]

On 2013-09-05 14:25, Eric Blake wrote:
> On 09/05/2013 06:05 AM, Max Reitz wrote:
>> Add a string for additional information to ImageInfo and
>> BlockDriverInfo. Also, use this string to emit the compatibility level
>> and lazy_refcount value (on compat=1.1) for qcow2.
>>
>> Signed-off-by: Max Reitz <mreitz@redhat.com>
>> ---
>> +++ b/qapi-schema.json
>> @@ -238,6 +238,9 @@
>>   #
>>   # @backing-image: #optional info of the backing image (since 1.6)
>>   #
>> +# @info-string: #optional string supplying additional format-specific
>> +# information (since 1.7)
>> +#
>>   # Since: 1.3
>>   #
>>   ##
>> @@ -248,7 +251,7 @@
>>              '*cluster-size': 'int', '*encrypted': 'bool',
>>              '*backing-filename': 'str', '*full-backing-filename': 'str',
>>              '*backing-filename-format': 'str', '*snapshots': ['SnapshotInfo'],
>> -           '*backing-image': 'ImageInfo' } }
>> +           '*backing-image': 'ImageInfo', '*info-string': 'str' } }
> This may work for HMP, but is LOUSY for use by QMP clients.  If you are
> passing back more than a single piece of information, you are now
> requiring the QMP client to do a parse of a free-form string to learn
> those pieces of information.  I'd much rather see a full JSON schema
> where EVERY piece of information passed back gets its own optional
> field, or even where the additional information is a union type
> discriminated by the image, so that we have full structure of the
> information being returned rather than just an ad-hoc blobbed string.
>
> Please rework this so that QMP clients like libvirt can easily probe
> what compat mode a qcow2 image uses, without having to parse a free-form
> string.
>
Seems very reasonable; I'll do my best.

Max