Re: [Xen-devel] libxl: error when destroying domain on NetBSD

[Roger Pau Monnà <roger.pau@xxxxxxxxxxxxx>]

2011/12/2 Ian Campbell <Ian.Campbell@xxxxxxxxxx>:
> On Fri, 2011-12-02 at 10:29 +0000, Roger Pau Monnà wrote:
>> 2011/12/2 Ian Campbell <Ian.Campbell@xxxxxxxxxx>:
>> > libxl_destroy_domain should be called with force = 1 in the main_destroy
>> > case, I suspect. Does that cause the scripts to be run?
>>
>> Well, with force = 1 hotplug scripts are executed, but devices are
>> still busy and they cannot be disconnected (mainly vnd). Also crashed
>> the server, but that's NetBSD buggy vnd driver problem. Seeing the
>> execution order in libxl_domain_destroy, shouldn't we first destroy
>> the domain (xc_domain_destroy) and then remove the devices?
>
> In the force case, yes, I expect so.
>
> In the non-force case you want to let the guest shutdown its devices
> gracefully so you would do devices first.
>
> However I'm not entirely sure that a non-forced libxl_domain_destroy
> makes much sense. The callsites are:
>
> Â Â Â* handle_domain_death: The guest has already shutdown at this
> Â Â Â Âpoint. Nothing graceful can happen.
> Â Â Â* create_domain: We have failed to start the guest, no chance of
> Â Â Â Âgraceful shutdown.
> Â Â Â* destroy_domain: Semantics are explicitly the force case.
> Â Â Â* save_domain: Domain has already suspended. There's nothing which
> Â Â Â Âcan be done gracefully.
> Â Â Â* migrate_domain: Already forced, domain is gone already, no
> Â Â Â Âchance of a graceful shutdown.
> Â Â Â* migrate_receive: Already forced, we have failed to receive the
> Â Â Â Âdomain, no possibility of a graceful shutdown.
> Â Â Â* libxl_domain_create, on the failure path so no need for a
> Â Â Â Âgraceful option.
> Â Â Â* libxl__destroy_device_model. Maybe this should be doing a
> Â Â Â Âgraceful shutdown but in that case it should either be calling
> Â Â Â Âlibxl_domain_shutdown or writing the qemu-dm control node and
> Â Â Â Âwaiting, at which point after some timeout perhaps a forced
> Â Â Â Âshutdown would be appropriate.
>
> So it seems to me that the non-forced option in libxl_domain_destroy can
> be removed and we should just shoot the domain and then forcibly
> teardown the backends, running script as necessary.
>
> The only wrinkle is the stub device-model case but really that's already
> a special domain and should be treated as such.
>
> Does that make sense to anyone else?
>
> Ian.
>

Well, I think I found the underlying problem that was preventing
NetBSD from correctly detaching vnd devices when destroying a domain,
the frontend state needs to be manually set to 6
(/local/domain/<domid>/device/vbd/<devid>/state and the same for vif
to be more "correct") so the kernel closes the device and it can then
be correctly unmounted.


I will prepare a patch (or a series) to adress this, and change
libxl_domain_destroy to use the force when called.

Thanks, Roger.

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