Re: [Qemu-devel] [PATCH 1/3] balloon: drop old stats code & API

[Luiz Capitulino <lcapitulino@redhat.com>]

On Tue, 18 Dec 2012 14:34:16 -0700
Eric Blake <eblake@redhat.com> wrote:

> On 12/17/2012 03:13 AM, Dietmar Maurer wrote:
> >> Next commit will re-enable balloon stats with a different interface, but this
> >> old code conflicts with it. Let's drop it.
> > 
> > I don't really see any conflicts here?
> > 
> >> It's important to note that the QMP and HMP interfaces are also dropped by
> >> this commit. That shouldn't be a problem though, because:
> >>
> >>  1. All QMP fields are optional
> >>  2. This has never been really used
> 
> Libvirt has been using it when available (although reluctantly, as it
> risks hanging on an uncooperative guest);

This has always been disabled and qemu never returns the stats info.
I believe libvirt's code is rotting just like qemu's is.

> and while libvirt can be
> patched to call 6 QOM commands in a row to query six different QOM
> stats, I still think it would be nicer to add a command that provides
> all the stats at once.  In particular, when calling 6 commands in
> series, you no longer have an atomic picture of the guest (the polling
> interval could hit between two QOM queries, resulting in a combined set
> of statistics that has no counterpart to the transition of states that
> the guest actually went through). On the other hand, since the stats
> are already polling-based, and since it requires cooperation from the
> guest, not having a guarantee of an atomic set of stats is not really
> much of a loss.

Something I have been wondering if whether it's possible to have only
one property (say balloon-statistics) and return all properties in a
dict. QOM properties return a visitor, so maybe that's possible.

I'll check that.