Re: [Xen-devel] question about migration

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Andrew Cooper writes ("Re: [Xen-devel] question about migration"):
> On 04/01/16 17:46, Ian Jackson wrote:
> > Suppose a domain goes into SHUTDOWN with reason code SUSPEND.  Then
> > later it is resumed again (perhaps the migration failed).  And later
> > it shuts down cleanly.
> >
> > Will this generate a second @releaseDomain ?  How is a toolstack
> > supposed to discover this situation ?
> 
> By the looks of it in Xen, domain_resume() sets d->is_shut_down = 0,
> which means a subsequent domain_shutdown() will generate a new VIRQ.
> 
> Therefore, a new @releaseDomain will arrive at a later point.

Well, jolly good.

> > Should libxl simply treat domains in state SHUTDOWN/SUSPEND as if they
> > were running, and not issue a notification to anyone ?
> 
> As far as libxl_evenable_domain_death() is concerned, yes.

Would you like to prepare a patch ?

> In general however, no.  Consider a libxl user (such as a snapshotting
> utility) which asks a domain to suspend to quiesce the disks and then
> intends to resume the domain.

Currently such a utility would have to use
libxl_evenable_domain_death to discover when the domain suspends, but
that would cause breakage as discussed in this thread.  So I think
such a utility would need a new libxl evenable interface.  Do you
agree ?

Ian.

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