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

[Sander Eikelenboom <linux@xxxxxxxxxxxxxx>]

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 ?

b) make it possible for the xl commandline to overrule the on_* from the 
configfile
c) also introduce a -w/--wait for xl destroy

(with b and c, i could emulate "a" by doing a "xl shutdown -w preserve" 
followed 
by a "xl destroy -w".

>> I can see the shutdown state would be the thing to wait for if it's 
>> configured 
>> with "preserve", but if it's configured with the default "destroy" i would 
>> expect it to wait until the guest is actually destroyed. The "restart" is 
>> perhaps 
>> somewhat more difficult, same goes for the coredump variants.




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