[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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