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Re: [libvirt] question about guest status



On Wed, 15 Feb 2012 11:00:25 +0000
"Daniel P. Berrange" <berrange redhat com> wrote:

> On Wed, Feb 15, 2012 at 02:44:18PM +0800, Wen Congyang wrote:
> > Hi all:
> > 
> > If the guest runs on xen, we can know the guest OS paniced, and the guest status
> > is paniced. But if the guest runs on qemu/kvm, we need the same feature. And the
> > feature to know guest-is-panic is a very very good feature for enterprise.
> > 
> > We have some ways to know that guest has paniced:
> > 1. watchdog timeouts
> >    It is not a good way, because we can not say "the guest is paniced" in 100% accuracy
> > 2. use a PV driver(like the XEN)
> >    The old RHELs do not have such driver...
> >    It can not work for the second kernel...
> > 3. Adding a function for console-logging (in ring buffer or some) and check messages
> >    given by guests. If we allow some filtering script or some, we can catch Linux's
> >    panic messages. We can say the guest paniced if we catch such messages. We may be
> >    able to catch other events by other script
> > 
> > I prefer to 3 now. Does anyone have a better idea?
> 
> I have discussed this with Anthony before and the thought was that QEMU/KVM
> should provide some kind of paravirtualized crash notification service to
> the guest. ie option 2.  such a device would likely be quite simple and
> thus possible to backport to older kernels as needed
> 
AFAIK, linux kernel has notifier at panic but it doesn't work if kdump is enabled.
And IIRC, There was a discussion in lkml that any modules should not be called when
crash_kexec() is called.  So, no chance to notify it from the module in the 1st kernel, now.
Calling it from 2nd kernel will work but the bahavior will be different from
non-kdump guest.

Can't we do notify by hypercall ? But this will require guest modification..

Thanks,
-Kame






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