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Subject: [Qemu-devel] Re: Should QMP be RPC to internal C interfaces?
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To: Anthony Liguori <anthony@codemonkey.ws>
Cc: qemu list <qemu-devel@nongnu.org>, Markus Armbruster <armbru@redhat.com>, agl@us.ibm.com, Amit Shah <amit.shah@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>

On Mon, 30 Aug 2010 10:38:45 -0500
Anthony Liguori <anthony@codemonkey.ws> wrote:

> On 08/30/2010 10:28 AM, Anthony Liguori wrote:
> > Having two interfaces guarantees failure.  What's the separation 
> > between internal and external?  Is qdev internal or external?
> 
> Let me put it another way, compatibility cannot be an after thought.
> 
> We need to think deeply about compatibility when we design our 
> interfaces and we're going to have to redesign interfaces with 
> compatibility in mind.  It's a hard problem but it's solvable.  Just 
> defaulting arguments in QMP doesn't do anything to improve compatibility.

The point is: C compat sucks, QMP's doesn't. QMP will suck too if we direct
map the two.

You seem to think it's worth it, we don't. How do we solve that?

> We cannot radically change our internal implementations and expect to 
> bridge it all in some special sauce code somewhere.
> 
> This also suggests that we're going to have to practice deprecation to 
> evolve our APIs in a reasonable fashion.

Deprecation should be mostly used for bad defined commands, not for simple
extensions.