Re: [Qemu-devel] [PATCH 01/11] QMP: Introduce specification file

[Avi Kivity <avi@redhat.com>]

On 06/28/2009 08:23 PM, Anthony Liguori wrote:
>> It's important to allow clients to use json emitters so they can 
>> construct a dict and throw it at qemu, similarly to parse qemu results.
>>
>>> arg_list: value arg_list?
>>>
>>> command: symbol arg_list? '\n'
>>
>> Better to use a dictionary for the argument list (more 
>> self-documenting, easier expansion).
>
> Verses a list?  I'm not sure a dict fits the current QEMU model very 
> well.  How would you propose fitting it into the current monitor 
> infrastructure?

First, I would like to consider the protocol mostly from the point of 
view of clients, not qemu, and certainly not current qemu code.  There 
is only one qemu, but many clients.  Code problems can be solved 
tomorrow, but interface problems remain forever.

Second, I think it fits quite nicely.  Positional arguments are nasty 
when you have many of them, especially when some are optional.  And we 
already support dictionaries: -drive file=blah,cache=none.  We make a 
dictionary interface, and have both the command line parser and the 
monitor json thing implement it.

(note: it would be nice to have this interface detect unused arguments 
so we can flag typos in keywords).

>> Similarly, return a value that contains message type, id, and return 
>> value.
>
> I think command outputs are basically return values.  What's nice 
> about the current QMP proposal is that we're basically returning tuples.

Yes, I meant { 'type': 'respose', 'id': 'foo', 'return': value }.  
'type' is the new =, and 'id' is the tag.  If multiple return values are 
needed, value can be a list or dictionary.

>> I think it's fine to drop jsonrpc as the standard (but retain its 
>> features) and just adopt json for encoding.
>
> Yeah, I think if we focus on defining a grammar and semantics, if it 
> happens to look like JSON, I don't really care.  I just don't want to 
> adopt the baggage of json and particularly json-rpc.

If 'looks like' == 'compatible with', I agree.

-- 
error compiling committee.c: too many arguments to function