Re: [Qemu-devel] [PATCH 2/2] QMP: Require 'use_unstable' arg for capabilities negotiation

[Markus Armbruster]

Luiz Capitulino <address@hidden> writes:

> On Fri, 09 Jul 2010 10:44:32 +0200
> Markus Armbruster <address@hidden> wrote:
>
>> Luiz Capitulino <address@hidden> writes:
>> 
>> > This helps ensuring two things:
>> >
>> > 1. An initial warning on client writers playing with current QMP
>> > 2. Clients using unstable QMP will break when we declare QMP stable and
>> >    drop that argument
[...]
>> Is it really necessary to break all existing users of QMP?
>
> The protocol is going to change, they will break anyway.

Then why break them now in addition to then?

>> What are we trying to accomplish by that?
>
> QMP in 0.13 is in usable state. I fear that people will start using it
> without noting/caring the protocol is going to be different in 0.14.
>
> The removal of this flag in 0.14 (assuming we'll have a stable QMP by then),
> makes clients break right away, instead of unexpected breaking in subtle ways.
>
> This makes it easy to identify what's wrong and the message will be: you
> should review your QMP usage, because the protocol has changed.
>
> That said, I'm not that strong about this particular solution. What I really
> would like to have is an easy way to identify old clients using a now
> stable version of QMP.

If we want obsolete clients to break when we release 0.14, then let's
break them then.  No need to break not-yet-obsolete clients now.
Especially not in a way that unbreaks them in 0.14, when they are
*really* obsolete.

[...]