Re: [OSSTEST PATCH 01/38] ts-logs-capture: Cope if xl shutdown leaves domain running for a bit

[Jason Andryuk <jandryuk@xxxxxxxxx>]

On Tue, May 19, 2020 at 3:03 PM Ian Jackson <ian.jackson@xxxxxxxxxxxxx> wrote:
>
> This seems mostly to affect buster but it could in principle affect
> earlier releases too I think.
>
> In principle it would be nice to fix this bug, and to have a proper
> test for it, but a reliable test is hard and an unreliable one is not
> useful.  So I guess we are going to have this workaround
> indefinitely...

`xl shutdown -w` waits for either domain shutdown or destruction in
wait_for_domain_deaths()
https://github.com/xen-project/xen/blob/master/tools/xl/xl_vmcontrol.c#L183

My understanding is shutdown happens first when the guest stops and
destruction happens afterward when all the resources are cleaned up.
So your race is that the domain shutdown, but it still shows up in `xl
list` since it hasn't been destroyed.

OpenXT has a hack to only wait for destruction
https://github.com/OpenXT/xenclient-oe/blob/master/recipes-extended/xen/files/xl-shutdown-wait-for-domain-death.patch.
I didn't write it, and the explanation isn't specific, but I think the
purpose is to all resources are released before the OpenXT toolstack
proceeds with (blktap) cleanup.

Maybe a new `xl shutdown` flag to wait for domain destruction would be
worthwhile?

Regards,
Jason