Re: [Xen-devel] xl shutdown --wait "racy"

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

On 04/16/2014 04:02 PM, Ian Campbell wrote:
> On Wed, 2014-04-16 at 16:55 +0200, Sander Eikelenboom wrote:
> > Wednesday, April 16, 2014, 4:33:30 PM, you wrote:
> >
> > > On Wed, 2014-04-16 at 16:26 +0200, Sander Eikelenboom wrote:
> > > > Wednesday, April 16, 2014, 4:13:59 PM, you wrote:
> > > >
> > > > > On Wed, 2014-04-16 at 16:08 +0200, Sander Eikelenboom wrote:
> > > > > > Hi Ian (C|J) Konrad,
> > > > > >
> > > > > > I'm currently trying to workaround the pci-(detach|assignable-remove) issues i
> > > > > > reported earlier.
> > > > > >
> > > > > > The workaround i thought of was:
> > > > > > - shutting down the guest
> > > > > > - starting it without 1 of the original devices passed through
> > > > > > - use xl pci-assignable-remove and bind the device to the dom0 driver.
> > > > > >
> > > > > > But during this i noticed that a "xl shutdown --wait" does wait .. but returns:
> > > > > > - Before the domain is removed from for instance "xl list", it still listed 
> > > > > > there in
> > > > > > "--ps--" state.
> > > > > > - before pciback has done it's restore config space magic.
> > > > > >
> > > > > > So it seems the wait loop is exiting somewhat prematurely, is this expected ?
> > > > > It is waiting for the domain to be shutdown (state 's') not for the
> > > > > domain to be destroyed. So it's doing what it said it would (I
> > > > > appreciate you might not find this distinction helpful under the
> > > > > circumstances...)
> > > > It's at least not entirely what i expected ;-)
> > > >
> > > > Is it because there can be different "follow-up actions" due to the
> > > > "on_poweroff=" config option ?
> > > Not really, those are somewhat unrelated.
> > > shutdown and destroy are two distinct events. Once a domain has shutdown
> > > (called the shutdown hypercall etc) it goes into state "shutdown" and an
> > > event is generated from the hypervisor to the toolstack. The toolstack's
> > > response to this is to actually destroy the domain, that is to tear down
> > > the resources it is using etc.
> > > on_* only matter for the destroy phase since they tell the toolstack
> > > what it should do (restart, preserve, really destroy etc).
> > Hmm ok, it should be called "--wait_until_halfway" then ;-)
> ;-)
>
> > On the more serious side .. would patches be accepted that:
> >
> > a) differentiate when it returns from waiting based on the on_*
> >
> >          preserve: this could probably stay as is .. after the shutdown event
> >          destroy:
> >          restart:
> >          rename-restart:
> >          coredump-destroy:
> >          coredump-restart:
> >
> >          for the other ones .. i don't know if there actually are events in 
> > libxl
> >          that could be 'easily' coupled ?
> Might be tricky, since on_* is processed by the daemonised xl which is
> monitoring the domain, not the xl shutdown process.
Store it in xenstore somewhere?

> > b) make it possible for the xl commandline to overrule the on_* from the 
> > configfile
> I guess you mean the xl shutdown command. This will also be tricky, for
> the same reasons as a.
>
> > c) also introduce a -w/--wait for xl destroy
> Yes.
>
> I'll add:
>
> d) Make "xl shutdown --wait" actually wait for the domain to be
> destroyed.
This seems like the most reasonable thing to do.

 -George

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