Re: [Qemu-devel] Re: [PATCH v2 3/9] provide in-kernel ioapic

[Jamie Lokier]

Glauber Costa wrote:
> On Thu, Oct 08, 2009 at 06:22:48PM +0200, Gleb Natapov wrote:
> > On Thu, Oct 08, 2009 at 06:17:57PM +0200, Avi Kivity wrote:
> > > On 10/08/2009 06:07 PM, Jamie Lokier wrote:
> > > >Haven't we already confirmed that it *isn't* just an ioapic accelerator
> > > >because you can't migrate between in-kernel iopic and qemu's ioapic?
> > > 
> > > We haven't confirmed it.  Both implement the same spec, and if you
> > > can't migrate between them, one of them has a bug (for example, qemu
> > > ioapic doesn't implement polarity - but it's still just a bug).
> > > 
> > Are you saying that HW spec (that only describes software visible behavior)
> > completely defines implementation? No other internal state is needed
> > that may be done differently by different implementations?
> Most specifications leaves a lot as implementation specific.
> 
> It's not hard to imagine a case in which both devices will follow
> the spec correctly, (no bugs involved), and yet differ in the
> implementation.

Avi's not saying the implementations won't differ.  I believe he's
saying that implementation-specific states don't need to be saved if
they have no effect on guest visible behaviour.

-- Jamie