[libvirt] [PATCH v5 0/2] qemu: Support for QXL heads

[Martin Kletzander]

On Fri, May 06, 2016 at 12:30:27PM +0100, Daniel P. Berrange wrote:
>On Fri, May 06, 2016 at 01:27:15PM +0200, Pavel Hrdina wrote:
>> On Thu, May 05, 2016 at 07:18:51PM -0400, John Ferlan wrote:
>>
>> [...]
>>
>> > Been sitting on list for a while ....
>> >
>> > Obviously I think you know you have to update to top of tree
>> >
>> > Would be nice to perhaps add a few intro comments to
>> > qemuMigratePrepareDomain at least with respect to what the purpose is
>> > and what "could" be done in the future in the code.  Looks like to me
>> > it's now a shim to qemuProcessPrepareDomain to take care of any of those
>> > "inconsistencies" between what can be supported in/on the new system
>> > (perhaps could work in the opposite direction too ;-))... When I'm
>> > reading code, I'm not necessarily looking at the commit message that
>> > added which may have that information.
>> >
>> > I think you could also update the commit message to point at the
>> > previous code that was reverted to help understand the history.
>> >
>> > ACK for the concept - looks like things are OK to me.
>> >
>> > John
>>
>> The only issue with this patch is that it breaks migration back to older
>> libvirt.  We generally try to not break migration to old libvirt if you migrate
>> from new libvirt to old libvirt with the same XML that would be also valid for
>> the old libvirt.  Since there is no change in the XML and we start using the
>> 'heads' attribute and we now pass that value to qemu you cannot migrate back to
>> some older libvirt.
>>
>> NACK, we need to figure this out.
>
>Yep, the major use of QXL is RHEV/oVirt and they explicitly require libvirt
>to support migration to old versions. So we need to figure this out.
>

So I should basically revert the difference between v1 and v2 and send a
v6 with that?  The discussion in v1 [1] didn't reach any conclusion so I
believe we can safely do that.

Martin

[1] https://www.redhat.com/archives/libvir-list/2016-March/msg00418.html



>Regards,
>Daniel
>--
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