[virt-tools-list] Obtaining usable output from virDomainMemoryStats()

[Daniel P. Berrange]

On Mon, May 13, 2013 at 11:09:04AM -0600, Eric Blake wrote:
> On 05/11/2013 10:19 AM, Tadej Janež wrote:
> > On Sat, 2013-05-11 at 11:50 -0400, Cole Robinson wrote: 
> >>>
> >>
> >> Hmm, qemu doesn't seem to be reporting this info? I'm on F19 with latest
> >> libvirt and qemu 1.4.1
> > 
> >> sudo virsh qemu-monitor-command --hmp f18 "info balloon"
> >> balloon: actual=2048
> > 
> > I get a similar output for this command on my machine:
> > balloon: actual=1024
> > 
> > The version of qemu that I'm using is qemu-kvm-1.2.2-11.fc18.x86_64.
> > 
> >> Not sure what the problem is...
> > 
> > Me neither. Maybe someone else on the list has some clues?
> 
> qemu can't provide guest stats without guest interaction, but waiting
> for guest interaction is a security hole (a non-cooperative guest can
> refuse to acknowledge the request, and thus block qemu and libvirt from
> doing useful work on other guests).  Therefore, ever since qemu 0.15 or
> so, the 'info balloon' command was intentionally crippled so as to plug
> the security hole, so that the information it reports is now only what
> qemu can report without guest interaction.
> 
> There is work underway to switch to an event-based solution - where qemu
> periodically asks the guest but without blocking, the guest informs qemu
> when it wants, and where libvirt can then query the most recent guest
> information (if any) without blocking, which works to remove the hole of
> a non-cooperative guest stopping progress.  But until libvirt been has
> wired up to use the new QMP querying commands for those properties (and
> for that matter, until you are using a qemu new enough), there's no way
> for libvirt to report a stat that qemu doesn't provide.
> 
> https://lists.gnu.org/archive/html/qemu-devel/2013-01/msg04832.html
> 
> I couldn't (quickly) find an open bugzilla against libvirt requesting
> that it start using the qom-get command on new-enough qemu, in order to
> get guest memory stat reporting back operational.

Oh, I thought we had already updated to use the new command for
this. I should have checked more closely

Daniel
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