Re: [Qemu-devel] [PATCH 1/2] virtio-balloon: export all balloon statistics

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Feb 23, 2016 at 06:29:33PM +0300, Denis V. Lunev wrote:
> On 02/23/2016 06:24 PM, Michael S. Tsirkin wrote:
> >On Tue, Feb 23, 2016 at 05:59:44PM +0300, Denis V. Lunev wrote:
> >>From: Igor Redko <redkoi@virtuozzo.com>
> >>
> >>We are making experiments with different autoballooning strategies
> >>based on the guest behavior. Thus we need to experiment with different
> >>guest statistics. For now every counter change requires QEMU recompilation
> >>and dances with Libvirt.
> >>
> >>This patch introduces transport for unrecognized counters in virtio-balloon.
> >>This transport can be used for measuring benefits from using new
> >>balloon counters, before submitting any patches. Current alternative
> >>is 'guest-exec' transport which isn't made for such delicate matters
> >>and can influence test results.
> >>
> >>Originally all counters with tag >= VIRTIO_BALLOON_S_NR were ignored.
> >>Instead of this we keep first (VIRTIO_BALLOON_S_NR + 32) counters from the
> >>queue and pass unrecognized ones with the following names: 'x-stat-XXXX',
> >>where XXXX is a tag number in hex. Defined counters are reported with their
> >>regular names.
> >>
> >>Signed-off-by: Igor Redko <redkoi@virtuozzo.com>
> >>Signed-off-by: Denis V. Lunev <den@openvz.org>
> >>CC: Michael S. Tsirkin <mst@redhat.com>
> >This seems to open the ABI to abuse.
> >Seems like a reasonable way to experiment though.
> >How about adding this within #if 0 statements?
> >You can uncomment them for debugging ...
> I'd prefer to have this enabled.
> 
> Why do you think that it opens "abuse" way?

Because people will use this to hack drivers and management tools
bypassing qemu.

> Actually the amount of host data is limited. If the guest
> will send fake stats before real ones - this guest is
> not cooperative and in this case the guest can
> hust ignore any balloon change requests.