Re: [Qemu-devel] seamless migration with spice

[Alon Levy <alevy@redhat.com>]

On Sun, Mar 11, 2012 at 09:18:17AM -0500, Anthony Liguori wrote:
> 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.

What about the second part? it's independant of the async issue.

> 
> 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.
> >
> 
>