[libvirt-users] os/type/machine/pc-xxxx meaning ? following live migration issue after an upgrade

[Daniel P. Berrange]

On Fri, Jul 04, 2014 at 11:04:53AM +0200, Benoit Rousselle wrote:
> Dear All,
> 
> I have upgrade my hypervisors:
> qemu-kvm                            0.12.5   =>  1.1.2
> libvirt-bin                         0.8.3-5  =>  0.9.12.3
> (debian6 to debian7)
> 
> After that upgrade, i noticed that live migration was most of the time
> failing (freeze) (not always)
> I also noticed that creating a machine with the updated hypervisor was
> always working.
> 
> After some days of investigation mainly on network side, i found this
> setting that seems to fix the issue in the xml:
> 
>   <os>
>     <type arch='x86_64' machine='pc-0.12'>hvm</type>
>     <boot dev='hd'/>
>   </os>
> 
> replacing pc-0.12 with pc-1.1 seems to fix the issue.
> 
> Here are my questions :
> 1) what is the meaning/purpose of that setting ? (i guess it is somehow
> linked to the version of kvm ;) )

It encodes a specific guest machine ABI.

> 2) can i just change it in all xmls ? ( i have plenty of linux/windows
> flavors running in my vms)

If you change it, the guest machine ABI will have changes. Usually fairly
minor, but changes none the less. This is not a problem for most guest
OS. Sometimes though, a change will be enough to cause Windows to want
todo license re-activation.

> 3) is it possible to put a more generic value? So we don't have the same
> issue on next upgrade.

We use a fixed version in an attempt to prevent windows re-activation.

> 4) Is there a script/doc that explains what needs to be done on the vm
> itself (xml or other) when we upgrade libvirt/kvm ?

Not really. If you don't mind the risk of Windows re-activation then
just delete the machine attribute and libvirt will re-add it using the
newest machine type version.

Regards,
Daniel
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