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

[Daniel P. Berrange]

On Tue, Apr 12, 2011 at 05:12:18PM -0600, Eric Blake wrote:
> On 02/09/2011 09:58 AM, Daniel P. Berrange wrote:
> > This patch attempts to introduce a version 3 that uses the
> > improved 5 step sequence
> > 
> >  *  Src: Begin
> >           - Generate XML to pass to dst
> >           - Generate optional cookie to pass to dst
> > 
> >  *  Dst: Prepare
> >           - Get ready to accept incoming VM
> >           - Generate optional cookie to pass to src
> > 
> >  *  Src: Perform
> >           - Start migration and wait for send completion
> >           - Generate optional cookie to pass to dst
> > 
> >  *  Dst: Finish
> >           - Wait for recv completion and check status
> >           - Kill off VM if failed, resume if success
> >           - Generate optional cookie to pass to src
> > 
> >  *  Src: Confirm
> >           - Kill off VM if success, resume if failed
> 
> I've been thinking about this a bit more, and have a question.  What
> happens when the source side decides to abort the migration?  For
> example, if libvirtd on the source gets a SIGHUP or SIGINT, it would be
> nice to have the cleanup code abort any in-flight migrations so that
> when libvirtd is restarted, the guest is still operational on the
> source, and the guest does not have to wait for a full TCP timeout cycle
> to realize that the source is not going to complete the migration.
> 
> Does this call for additional internal points in the RPC implementation
> of v3 migration?

The source can already abort migration, even in the v2 protocol, using
the virDomainJobAbort() API (or  virsh domjobabort).  This issues a
'migrate_cancel' monitor command to QEMU, which in turns causes the
'perform' step to return failure, which is passed to the 'finish'
step which tears down the destination VM

Regards,
Daniel
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