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From: Juan Quintela <quintela@redhat.com>
In-Reply-To: <4BF00592.5040403@redhat.com> (Avi Kivity's message of "Sun, 16
	May 2010 17:47:46 +0300")
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Date: Sun, 16 May 2010 22:04:08 +0200
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Subject: [Qemu-devel] Re: Qemu-KVM Livate Migration 0.12.2 -> 0.12.3/4
	broken?
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To: Avi Kivity <avi@redhat.com>
Cc: Peter Lieven <pl@dlh.net>, qemu-devel@nongnu.org, kvm@vger.kernel.org

Avi Kivity <avi@redhat.com> wrote:
> On 05/16/2010 05:42 PM, Juan Quintela wrote:
>>
>>> Any idea why it fails?  And how to fix it?
>>>      
>> Lack of "proper" subsections.  IDE is something like:
>>
>> const VMStateDescription vmstate_ide_drive = {
>>      .version_id = 4,
>> ....
>> }
>>
>> static const VMStateDescription vmstate_bmdma = {
>>      .name = "ide bmdma",
>>      .version_id = 4,
>> ...
>> }
>>
>> const VMStateDescription vmstate_ide_pci = {
>>      .name = "ide",
>>      .version_id = 4,
>> ....
>>          VMSTATE_STRUCT_ARRAY(bmdma, PCIIDEState, 2, 0,
>>                       vmstate_bmdma, BMDMAState),
>>          VMSTATE_IDE_DRIVES(bus[0].ifs, PCIIDEState),
>>          VMSTATE_IDE_DRIVES(bus[1].ifs, PCIIDEState),
>> ....
>> }
>>
>>
>> Notice that everything is at version 4.  It used to be everything at
>> version 3.  Now the problem is that when migrating from v3 ->  v4.  We
>> put in one place v3, But we only have a version number at the toplevel,
>> rest of "subsections" don't sent a version number.  There is no way to
>> fix it in the general case.  We can hack something around for ide, but
>> that will just be a hack, or we can backport marcelo change and port it
>> as a proper subsection (that is my plan).  I expect to have time at the
>> end of next time to work on this.
>>    
>
> end of next week?

Humm, for Spaniards weeks start on Monday :)  (Monday is holiday here).

I mean here Friday 21.

>> So, to make the story short: I know what is happening, and I know how to
>> fix it, just that fix is not trivial.  I just need time.
>>    
>
> Meanwhile, we have a broken 0.12.4.  Is there a quick'n'dirty
> workaround that will be forward compatible with the real fix that we
> can push out?

revert the patch.  It almost never happen (being in the middle of one
IO) while migrating.

> We've regressed from failing some migrations to failing all migrations.

Humm, 0.12.4 -> 0.12.4 should work.  My advise is just revert the patch
and live with it for another week, what do you think?

Later, Juan.