[libvirt] [PATCH 3/6] Introduce yet another migration version in API.

[Christian Benvenuti (benve)]

> -----Original Message-----
> From: Stefan Berger [mailto:stefanb at linux.vnet.ibm.com]
> Sent: Thursday, April 21, 2011 6:34 AM
> To: Daniel P. Berrange
> Cc: Christian Benvenuti (benve); eblake at redhat.com; laine at laine.org;
> chrisw at redhat.com; libvir-list at redhat.com; David Wang (dwang2); Roopa
> Prabhu (roprabhu); Gerhard Stenzel; Jens Osterkamp; Anthony Liguori
> Subject: Re: [libvirt] [PATCH 3/6] Introduce yet another migration
> version in API.
> 
> On 04/21/2011 07:43 AM, Daniel P. Berrange wrote:
> > On Thu, Apr 21, 2011 at 07:37:30AM -0400, Stefan Berger wrote:
> >>
> >> and simply doesn't start the VM. After this function is called all
> >> sockets are closed and the communication with the source host is
> >> cut. I don't think it allows for fall-back at this point.
> > Sure it does. As long as the destination QEMU CPUs have not been
> > started, you can fallback by simply killing the dest QEMU and
> > restarting CPUs on the src QEMU.
> >
> FWIW, I did a test and disabled the starting of the CPUs on the
> destination side and
> did a sleep() instead. Before the sleep() was over the Qemu on the
> source side had already disappeared.

Did you test this with migration V2 or migration V3?
I think what you describe is V2 (V3 now is different):

- Migration V2


 SRC HOST                         DST HOST
  |
  |- dump XML
  |
  |                               (PREPARE)
  +------------------------------>Start empty VM
  |
  |(PERFORM)
  |- migrate cmd to monitor
  |- kill VM
  |
  |                                (FINISH)
  +------------------------------->Start CPU


- Migration V3


 SRC HOST                         DST HOST
  |
  |(BEGIN)
  |- dumpxml
  |                              (PREPARE)
  +------------------------------>Start empty VM
  |
  |(PERFORM)
  |- migrate cmd to monitor
  |  (src CPU is now paused)
  |
  |                                (FINISH)
  +------------------------------->Start CPU
  |
  |(CONFIRM)
  |- if FINISH succeeded: Kill src VM
  |- if FINISH failed   : Run  src VM



/Christian