On Fri, 27 Aug 2010 15:59:21 +0200 Markus Armbruster <arm...@redhat.com> wrote:
> "Daniel P. Berrange" <berra...@redhat.com> writes: > > > On Fri, Aug 27, 2010 at 07:39:37AM -0500, Anthony Liguori wrote: > >> On 08/27/2010 04:29 AM, Daniel P. Berrange wrote: > >> >On Fri, Aug 27, 2010 at 10:57:10AM +0530, Amit Shah wrote: > >> > > >> >>This error message denotes some command was not successful in completing > >> >>as the guest was unresponsive. > >> >> > >> >>Use it in the virtio-balloon code when showing older, cached data. > >> >> > >> >>Signed-off-by: Amit Shah<amit.s...@redhat.com> > >> >>--- > >> >> hw/virtio-balloon.c | 1 + > >> >> qerror.c | 4 ++++ > >> >> qerror.h | 3 +++ > >> >> 3 files changed, 8 insertions(+), 0 deletions(-) > >> >> > >> >>diff --git a/hw/virtio-balloon.c b/hw/virtio-balloon.c > >> >>index d6c66cf..309c343 100644 > >> >>--- a/hw/virtio-balloon.c > >> >>+++ b/hw/virtio-balloon.c > >> >>@@ -140,6 +140,7 @@ static void complete_stats_request(VirtIOBalloon *vb) > >> >> > >> >> static void show_old_stats(void *opaque) > >> >> { > >> >>+ qerror_report(QERR_MACHINE_STOPPED); > >> >> complete_stats_request(opaque); > >> >> } > >> >> > >> > > >> >NACK. It has always been allowed& valid to call query-balloon > >> >to get the current balloon level. We must not throw an error > >> >just because the recently added mem stats can't be refreshed. > >> > >> I think that's a fair comment but why even bother fixing the command. > >> Let's introduce a new command that just gets a single piece of > >> information instead of having a command return lots of information. > > > > The existing query-balloon command that has been around for years & > > is used by all current apps has a significant regression since we added > > the memstats code to it: a guest can now trivially inflict a DOS on the > > mgmt app if it crashes or is malicious. IMHO we need to fix that regression > > for 0.13 so that existing apps don't suffer[1]. Adding a timeout to silently > > skip the stats refresh if the guest doesn't respond, but without raising > > an error seems the best tradeoff we can do here. > > I agree. > > Adding a roundtrip through the guest to an existing command was a > mistake. 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. > > > 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. >