Re: [Qemu-devel] QMP forward compatibility support

[Anthony Liguori]

On 01/11/2010 12:34 PM, Luiz Capitulino wrote:
>   Hi.
>
>   We (Markus and I) are working on getting QMP forward compatibility support,
> supported. :)
>
>   We have a plan for it and I'd like to ask the CC'ed people to review it.
>
>   Needless to say, but the objective here is to add new commands, arguments,
> async messages and protocol features w/o breaking existing clients.
>
> General Plan
> ------------
>
> 1. QMP should describe itself, ie. it should dump all accepted commands,
> their replies and arguments, async messages and protocol features. All in
> JSON format
>
> 2. Protocol features are advertised by the (already existent) capabilities
> array, but are _disabled_ by default. The exception is async messages,
> which are _enabled_ by default
>    

Any reason to have an exception like this?

> 3. We should add command(s) to enable/disable protocol features
>
> 4. Proper feature negotiation is done in pause mode. That's, clients
> interested in enabling new protocol features should start QEMU in
> pause mode and enable the features they are interested in using
>    

Why does this matter?

We should be careful to support connecting to a VM long after it's been 
started so any requirement like this is likely to cause trouble.

Regards,

Anthony Liguori