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

[Benoit Rousselle]

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 ;) )
2) can i just change it in all xmls ? ( i have plenty of linux/windows 
flavors running in my vms)
3) is it possible to put a more generic value? So we don't have the same 
issue on next upgrade.
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 ?

Thanks for the feedback !
Benoit.

-- 
Benoit Rousselle