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[libvirt] Upgrade-problems from qemu-0.14.1 + libvirt-0.8.4 to qemu-0.15.1 + libvirt-0.9.6: Why I think multifunction=on is a bad idea...



Hello,

this mail is something between a bug report and a warning to other users of 
libvirt, before they also experience the problem I encountered today:

I just hat the painful experience of trying to install some newer versions of 
qemu(-kvm) and libvirt on a system with many managedsave-states and many 
snapshots. They are now all broken because
1. Newer qemu(-kvm) uses iPXE instead of etherboot, which have different ROM 
file sizes, which aborts loading the old VM state. So be careful to not 
delete your old PXE-ROM images.
2. libvirt defaults to add ',multifuntion=on' to the (in my case) rtl8139 
network card and balloon-driver, which produces the "really helpful" message 
of
	qemu: warning: error while loading state for instance 0x0 of 
device '0000:00:03.0/rtl8139'
or
	qemu: warning: error while loading state for instance 0x0 of device 'ram'

Nothing you can't fix with installing the old etherboot-qemu package and some 
dirty "dd"-hackery on your saved files and snapshot xml files to add an 
explicit 'multifunction=off', but hard to diagnose and annoying enough.

So even if the qemu people try to be backward compatible with their VMState 
format, libvirt doesn't seem to handle backward compatibility taht good at 
the moment.
Perhaps it would help to not (only) store the XML domain configuration for 
snapshots and managedsave-files, but the exact qemu-argv string to at least 
get libvirt out of any backward incompatible changes when re-constructing the 
qemu command line from the XML data.

Sincerely
Philipp

PS: I hope that info helps other people when getting those messages.
-- 
Philipp Hahn           Open Source Software Engineer      hahn univention de
Univention GmbH        Linux for Your Business        fon: +49 421 22 232- 0
Mary-Somerville-Str.1  D-28359 Bremen                 fax: +49 421 22 232-99
                                                   http://www.univention.de/

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