[libvirt] virsh domstate output when kvm killed vs guest OS panic

[Eric Blake]

On 09/05/2013 12:47 PM, Chris Friesen wrote:
> Hi,
> 
> If I kill a libvirt-managed kvm process with "kill -9", running "virsh
> domstate --reason <name>" gives
> 
> shut off (crashed)
> 
> Looking at the code, that corresponds to
> VIR_DOMAIN_SHUTOFF/VIR_DOMAIN_SHUTOFF_CRASHED.  The comment says that
> VIR_DOMAIN_SHUTOFF_CRASHED corresponds to "domain crashed".  Is this
> supposed to be a crash of the hypervisor, or of the guest OS?

Both.  Any case where a crash has transitioned the domain into a shutoff
state (no qemu process exists any more), in such a way that libvirt
knows that it is a crash.

> 
> If I trigger a panic in the guest, it sits there in the panicked state
> doing nothing and "virsh domstate" gives
> 
> running (booted)

Depending on what version of kernel you have and what version of qemu
you are using, you can set things up so that qemu exposes '-device
pvpanic' to the guest, and Linux guests can then write to that device on
kernel panic, so that qemu then forwards a crash event to libvirt.
(Theoretically, someone could write a windows driver so that Windows
guests could also trigger the qemu event, but to date, no one has done
that).  With that in place, a guest panic would no longer show up as
running(booted), but as crashed(panicked).

But right now, since qemu 1.6 botched the implementation of '-device
pvpanic', we are waiting for qemu 1.7 to stabilize the design, so there
is no easy way to pass -device pvpanic on the qemu command line except
using <qemu:commandline> XML extensions that take you into the realm of
unsupportedness.

> 
> So what's the point of VIR_DOMAIN_CRASHED/VIR_DOMAIN_CRASHED_PANICKED?

To differentiate between the qemu panic event (the qemu process still
exists) and the completely dead qemu (your kill -9 attempt), if you are
using the pvpanic device.

Trust me, this whole area is a big mess, that has been drawn out in
several long debates on both qemu and libvirt lists, for more than a
year now.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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