[libvirt] Re: [PATCH] Hardware watchdog patch, version 6 (was: Re: [Qemu-devel] [PATCH] Hardware watchdog patch, version 5)

[Daniel P. Berrange]

On Tue, Apr 07, 2009 at 04:19:42PM -0500, Hollis Blanchard wrote:
> Hi Rich, your watchdog qemu patch is working fine for me (i6300esb,
> default reset behavior), but I was wondering... how should libvirt find
> out about the watchdog firing?

This falls into the general problem space of how does QEMU notify its
management app  of interesting events. We already really want the
ability to be notify of ENOSPC errors in disks, and also would like
to know if the VM is paused for any reason outside our control.
There have been proposals to just print an async message to the 
monitor upon events, that mgmt app could then parse. This is a little
fragile though, so for a long term solutiuon we really need the generic
libqemumonitor.so type API with formal async notification support.

For notification of the watchdog firing, I guess the answer depends
on what sort of action you've told QEMU todo. If the action is a
'shutdown', then there won't be much opportunity to notify the mgmt
app before QEMU exits. We could define a watchdog action of 'pause'
which just pauses the VM CPUs, and then notifies via the monitor
that the watchdog fired. The mgmt app could receive this, and then
destroy the VM if desired.

> At that point, I think the next step from libvirt is to send a
> VIR_DOMAIN_EVENT_STOPPED_CRASHED domain event, correct?

That would be the ideal event to emit if we could get a notification of
the fact that watchdog fired. If QEMU does the shutdown itself, then we
won't be able to distinguish this from a regular graceful VM shutdown
and so would just end up with VIR_DOMAIN_EVENT_STOPPED_SHUTDOWN event
being emitted when we see QEMU exit.


Daniel
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