[libvirt] [PATCH 3/3] qemu_domain: use correct default USB controller on ppc64

Andrea Bolognani abologna at redhat.com
Tue Mar 7 13:55:43 UTC 2017


On Tue, 2017-03-07 at 09:19 +0100, Pavel Hrdina wrote:
> > However, after migration is complete, the <controller>
> > element has model='nec-xhci' instead of model='pci-ohci',
> > which means that power cycling the guest results in
> > breaking the guest ABI.
> 
> I'm not so sure that this is an ABI change.  The guest ABI is to ensure
> that the same guest XML will always start the same QEMU guest.  However
> the PERSISTENT migration can make ABI changes because it is the same as
> virsh dumpxml $domain > $domain.xml && copy the XML onto remote host
> and virsh define $domain.xml.  This would also change the *model*.
> 
> If this would be considered to be guest ABI stable it would mean that
> other changes done by using this flag would be wrong because they also
> modifies the persistent XML during migration.

I assume there are very good reasons for persistent
migration to behave differently, but as a user I find
it extremely surprising. Do you have any insight on the
rationale behind allowing ABI changes when performing
persistent migration?

The only other example I could find of ABI update being
used is in virDomainDefPostParseMemory(), and AFAIU adding
or removing memory from a guest is not an ABI change. Did
I miss other uses?

-- 
Andrea Bolognani / Red Hat / Virtualization




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