Re: [Qemu-devel] [PATCH 5/7] QMP: Update spec file

[Luiz Capitulino <lcapitulino@redhat.com>]

On Fri, 18 Dec 2009 18:20:52 +0100
Markus Armbruster <armbru@redhat.com> wrote:

> Luiz Capitulino <lcapitulino@redhat.com> writes:
> 
> [...]
> > -4. Notes to Client implementors
> > --------------------------------
> > +4. Compatibility Considerations
> > +--------------------------------
> >  
> > -4.1 It is recommended to always start the Server in pause mode, thus the
> > -    Client is able to perform any setup procedure without the risk of
> > -    race conditions and related problems
> > +In order to achieve maximum compatibility between versions, the following
> > +changes are forbidden in newer versions of the Server:
> >  
> > -4.2 It is recommended to always check the capabilities json-array, issued
> > -    with the greeting message, at connection time
> > +- Removal of commands
> > +- Removal of command arguments
> > +- Addition of extra mandatory arguments for commands
> > +- Modification of arguments types
> > +- Modification of arguments, commands, events or error names
> > +- Modification of arguments in replies, events or errors
> 
> While I think these promises are appropriate for a mature version of the
> protocol, I do not think we should make them for 0.12.
> 
> We've just dreamed up version 0.1 of the protocol.  It hasn't been used
> in anger.  Yes, we put some serious thought in it, and we even have
> prototype code using it in libvirt, but let's face it, we're not
> infallible: we *will* have to evolve stuff.

 While I agree with your arguments, I think this will happen to any
QMP version or any stable protocol/API.

 You have the point that QMP is immature at this point, but:

1. Given the current Monitor design, if you want QMP to be perfect to be
useful then we're going to have it around QEMU version 10.0

2. I don't think we're going to get any serious user until we
declare it stable