libvirt users - Jul 2013 - How to trigger a script in a guest after resume? (aka guest system clock incorrect after host reboot with suspended guest)

Hi

Is there a way i can trigger a script within a libvirt guest immediately
after resume? E.g. i don't see any log message that indicates to a guest
that it had been paused and was just woken up.


The problem that i am trying to solve is that when i reboot the host
(pausing all guests), the guests' system clocks are a few minutes late
after resume. The guests RTC (current_clocksource
= kvm-clock) are correct though, so a "hwclock --hctosys" fixed the
offset. I only need to find out how to call hwclock right after resume!


Right now i call hwclock every few minutes, but i'd like to shorten the
window of wrong time. OTOH i'd like to avoid installing ntpd into all
guests, given their perfectly fine RTCs.


On the host i am using CentOS 6.4 with all patches and the packaged
libvirt-0.10.2 and qemu-kvm-0.12.1.2. All guests are Ubuntu 12.04.


/nils.

On 07/24/2013 08:07 AM, Nils Toedtmann wrote:
> Hi
> 
> Is there a way i can trigger a script within a libvirt guest immediately
> after resume? E.g. i don't see any log message that indicates to a
guest
> that it had been paused and was just woken up.
Upstream qemu has added the guest-set-time command to qemu-ga as of qemu
1.5; if you have the qemu-ga daemon running in your guest (available at
least for Linux and Windows guests), then triggering this guest-agent
command would do what you want.

It might be nice to expose an API in libvirt for poking the guest-agent
command on demand, and/or adding some XML configuration to a guest that
requests that libvirt will automatically send the guest-agent command
every time the guest is resumed.  But for now, you're stuck using the
unsupported 'virsh qemu-agent-command' option for triggering the command
manually.

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