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

[Luiz Capitulino <lcapitulino@redhat.com>]

On Fri, 27 Aug 2010 09:59:55 -0500
Anthony Liguori <anthony@codemonkey.ws> wrote:

> 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.

Are you talking about the testing namespace idea? It doesn't have anything
to do with balloon or how our interfaces are built. It would be just a way
to play with commands that has been converted to QMP but are not available
because they're not stable yet (eg. Jan's device_show).

> 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.

Main question is: can we drop the stats the way they are today to do the
Right Thing for 0.14 or not?

I think we have agreed on the internal interfaces approach. My only
concern is whether this will conflict when extending the wire protocol
(eg. adding new arguments to existing commands). Not a problem if the
C API is not stable, of course.

> 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);

Shouldn't the API provide a general cancel method? All functions that
talk to the guest will need one.

> 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.
> >>>        
> >>      
> >    
>