Re: [Qemu-devel] [PATCH V4 0/3] Block migration if any of the block device is busy

[Kevin Wolf]

Am 24.07.2012 12:04, schrieb Stefan Hajnoczi:
> On Tue, Jul 24, 2012 at 10:52 AM, Kevin Wolf <address@hidden> wrote:
>> Am 23.07.2012 16:22, schrieb address@hidden:
>>> From: Benoît Canet <address@hidden>
>>>
>>> This patchset is designed to avoid starting a live migration while any of
>>> the block device is busy.
>>>
>>> Tested with the following sequence:
>>>
>>> QEMU 1.1.50 monitor - type 'help' for more information
>>> (qemu) block_stream virtio0 1k
>>> (qemu) migrate tcp:localhost:4444
>>> migrate: Migration is blocked by streaming
>>> (qemu)  block_job_cancel virtio0
>>> (qemu)  migrate tcp:localhost:4444
>>> migrate: Connection can not be completed immediately
>>> (qemu)
>>> => migration then succeed
>>
>> Maybe I'm missing the obvious, but why? Migration will stop the
>> streaming if it isn't restarted explicitly on the destination, but I
>> think that's expected.
> 
> Hmm...maybe this is a policy decision.  I figure if you are running
> image streaming and try to migrate, chances are you're migration will
> break on the destination host because you were trying to do pre-copy
> storage migration and never finished.

Sure, if you're migrating without shared storage, you always need to
know what you're doing.

But you could be doing a post-copy storage migration and migrate to the
next host before it has completed. I think this is a completely
legitimate action that shouldn't be blocked.

Kevin