[Qemu-devel] Re: [PATCH 3/8] Add QBuffer

[Jan Kiszka]

Avi Kivity wrote:
> On 05/16/2010 12:37 PM, Paolo Bonzini wrote:
>> On 05/15/2010 07:31 PM, Avi Kivity wrote:
>>> On 05/15/2010 11:59 AM, Jan Kiszka wrote:
>>>>
>>>>> Is this __class__ stuff documented anywhere?
>>>>>
>>>> Not yet. Also, we should clarify the proposed private extension section
>>>> that only "__some_key" is reserved for downstream, not
>>>> '__some_other_key__' (i.e. downstream names must not end with '__').
>>>>
>>>
>>> Why use such weird names at all? What's wrong with 'class'?
>>
>> That it conflicts with e.g. PCI classes?
> 
> Won't the context tell it apart?  When you expect a pci function,
> 'class': 'video' means one thing, when you read a buffer it means another.

The point is to make this notation context-independent so that you can do

    def __json_obj_hook(self, dct):
        if '__class__' in dct:
            if dct['__class__'] == 'buffer':
                return base64.b64decode(dct['data'])
            else:
                return
        return dct

and

        line = json.loads(self.sockfile.readline(),
                          object_hook=self.__json_obj_hook)

i.e. parse the QMP stream into a proper representation without known QMP
at all.

> 
> The only reason to use a special name is if it's a protocol level
> feature that can happen in all contexts.  But in that case we're better
> off with a schema, we don't want to push class descriptors everywhere.
> 

Not everywhere, just into those nodes that aren't expressible with
native JSON types.

Jan

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