Re: [Qemu-devel] seamless migration with spice

[Anthony Liguori <anthony@codemonkey.ws>]

On 03/11/2012 08:16 AM, Yonit Halperin wrote:
> Hi,
>
> We would like to implement seamless migration for Spice, i.e., keeping the
> currently opened spice client session valid after migration.
> Today, the spice client establishes the connection to the destination before
> migration starts, and when migration completes, the client's session is moved to
> the destination, but all the session data is being reset.
>
> We face 2 main challenges when coming to implement seamless migration:
>
> (1) Spice client must establish the connection to the destination before the
> spice password expires. However, during migration, qemu main loop is not
> processed, and when migration completes, the password might have already expired.
>
> Today we solve this by the async command client_migrate_info, which is expected
> to be called before migration starts. The command is completed
> once spice client has connected to the destination (or a timeout).
>
> Since async monitor commands are no longer supported, we are looking for a new
> solution.

We need to fix async monitor commands.  Luiz sent a note our to qemu-devel 
recently on this topic.

I'm not sure we'll get there for 1.1 but if we do a 3 month release cycle for 
1.2, then that's a pretty reasonable target IMHO.

Regards,

Anthony Liguori

> The straightforward solution would be to process the main loop on the
> destination side during migration.
>
> (2) In order to restore the source-client spice session in the destination, we
> need to pass data from the source to the destination.
> Example for such data: in flight copy paste data, in flight usb data
> We want to pass the data from the source spice server to the destination, via
> Spice client. This introduces a possible race: after migration completes, the
> source qemu can be killed before the spice-server completes transferring the
> migration data to the client.
>
> Possible solutions:
> - Have an async migration state notifiers. The migration state will change after
> all the notifiers complete callbacks are called.
> - libvirt will wait for qmp event corresponding to spice completing its
> migration, and only then will kill the source qemu process.
>
> Any thoughts?
>
> Thanks,
> Yonit.
>