[Spice-devel] changing the timing of spice client linking in migration (RHBZ #725009)

[Yonit Halperin]

On 08/25/2011 02:15 PM, Daniel P. Berrange wrote:
> On Thu, Aug 25, 2011 at 02:13:01PM +0300, Yonit Halperin wrote:
>> On 08/25/2011 01:53 PM, Gerd Hoffmann wrote:
>>> I've played with a approach simliar to (2) long ago.  Actually did it by
>>> registering a "live" migration handler.  Didn't work that well too.
>>> spice client will stay connected to both source and target for a long
>>> time, and the spice code base simply couldn't handle that very well. One
>>> problem was a timeout somewhere which was *way* to short.  Second was
>>> that some stuff such as new connects are blocked in that "migration"
>>> state.  Doesn't hurt much if that lasts a second or two, but for a few
>>> minutes it isn't acceptable.  Maybe there was more which I don't remember.
>>
>> If we can't connect to the target during migration, this means the
>> "not seamless" solution is problematic as well, and we may need ==>
>> a libvirt change<== :
>> We need to connect to the target before migration starts. We can
>> either do it upon client_migrate_info, under the assumption that the
>> target is already up and that it is called just before migration.
>> Or otherwise, we need to introduce a new command from libvirt, just
>> before migration, with the same assumptions.
>
> Yes, the target QEMU is neccessarily up by the time client_migrate_info
> is run, because we need to know the SPICE port number for the running
> target QEMU. We run client_migrate_info, immediately before running
> migrate monitor command.
>
> If you're wanting to ensure the client connects to target QEMU before
> migrate starts, then this implies that the libspice-server.so would
> block in client_migrate_info, until it knows the client has succesfully
> connected to the target ?
>
Yes, but with a reasonable timeout. But this is for seamless. And I'm 
not sure we want the seamless solution for 6.3

Thanks,
Yonit.

> Daniel