Re: [Qemu-devel] Re: [PATCH v3 2/3] qerror: Add a new MACHINE_STOPPED error message

[Anthony Liguori]

On 08/27/2010 09:15 AM, Luiz Capitulino wrote:
> I wondered if we could drop it for now to make it right in 0.14, but I
> believe it's already part of the user monitor for some time and libvirt
> uses the stats, right?
>
> I think we need testing/unstable namespace in QMP, where commands can be
> tested for while so that we reduce the risk of nasty surprises like this one.
>    

It's trying to plug a sieve with a band-aid.  It's certainly an 
"improvement" but it's of question utility looking at the bigger picture.

Balloon is a perfect example of where what we really need to do is build 
interface interfaces that make sense, and then expose them in QMP.

What's a reasonable C-level API to query statistics that potentially may 
never return?  Building in a timeout is something of a crappy API 
because it puts policy deep in the API that is trivial to implement 
elsewhere.  What you'd probably do is something like:

BalloonStatsRequest *query_guest_balloon_stats(CompletionCallback *cb, 
void *opaque);
int cancel_guest_balloon_stats(BalloonStatsRequest *req);
void release_guest_balloon_stats(BalloonStatsRequest *req);

Regards,

Anthony Liguori

> >      
> > > Beyond fixing that regression, I agree that this command is terminally
> > > flawed&  we need to deprecate it&  provide better specified new
> > > replacement(s). This seems like 0.14 work to me though.
> > >        
> > Yup.
> >
> >      
> > > Regards,
> > > Daniel
> > >
> > > [1] I know that they could already suffer if there was a bug in qemu
> > >      that prevented it responding, even if the guest was not being
> > >      malicious/crashed.
> > >        
> >      
>