Re: [Qemu-devel] [PATCH 0/3] client_migrate_switch and auto_switch (RHBZ 725009)

[Daniel P. Berrange]

On Fri, Aug 26, 2011 at 02:39:59PM +0200, Gerd Hoffmann wrote:
> >>   (1) libvirt sets spice ticket at dst (stage 2)
> >>   (2) migration src->dst (stage 3)
> >>   (3) spice client switches connection to dst
> >
> >This is actually what we have already. The problem is that
> >the 'migration src->dst' here can take an arbitrary amount
> >of time. So by the time the spice client switchs to dst,
> >the ticket will likely have already expired.
> 
> Ah, *that* is the bug.
> 
> >The only way to fix this AFAICT is to ensure the SPICE
> >client connects to dst before migration starts, but delays
> >display switch until the end. eg
> >
> >     (1) libvirt sets spice ticket at dst (libvirt stage 2)
> >     (2) spice client connects to dst (start of libvirt stage 3)
> 
> That must be in stage 2.  Once the migration started qemu will not
> accept new connections and thus the client would not be able to
> connect.

NB, I said "start of libvirt stage 3" which has multi-steps:

  3. Perform(src)
      - Issue migrate_client_info
      - Issue migrate_set_speed
      - Issue migrate
      - Loop
          - Issue query-migrate
          - Break if finished/failed

ie, before step 3.3

> Can qemu handle async monitor commands now?  We would need to wait
> until the client has actually connected, but without blocking the
> iothread because it can take a while.

Not sure about that


Daniel
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