Re: [Xen-devel] [PATCH 12 of 14 v4] libxl: set frontend status to 6 on domain destroy

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2011-12-14 at 11:12 +0000, Roger Pau Monnà wrote:
> 2011/12/14 Ian Campbell <Ian.Campbell@xxxxxxxxxx>:
> > So if you rm the backend directory the NetBSD does not take that as a
> > sign to tear down the device? That sounds like a bug in the NetBSD
> > backend -- it should treat deletion of the backend state dir as if it
> > were reading state = "6" and shut everything down.
> 
> Yes, if I delete the frontend from xenstore, the devices are detached.
> Anyway, doing it one way or another (deletion or setting state to 6)
> doesn't really make a difference, you still have to wait for the
> backend to be disconnected (detached) before executing hotplug
> scripts.

Right. This might actually be tricky in the case where the backend dir
has been removed since I expect there will be nowhere else which
indicates this.

> > Or is the issue only in the userspace portions?
> >
> >>  I've added some libxl__wait_for_device_state logic here, to
> >> assure the backend state is set to 6 before trying to execute hotplug
> >> scripts.
> >
> > But that will always be true with this patch since you set it that way
> > just before, right?
> 
> I set frontend status to 6, and I suggest to wait for backend status
> to be 6 also, then execute hotplug scripts. It won't be true, because
> frontend and backend status are not tied (in the NetBSD case backend
> status is set by the Dom0 kernel or hotplug scripts, while frontend
> status is set by the DomU).

I think (but I'm not sure) that it is not permissible for the toolstack
to mess with the frontend state like that.

> > If you go down this path then I think you need to set the state to
> > "5" (Closing) in order to prompt the backend to transition to
> > "6" (Closed) itself. However you need to be careful about adding a
> > synchronous wait to the device destroy function. This should eventually
> > work even if the frontend and backend are not co-operating. That starts
> > to look a bit like calling libxl__device_remove instead.
> 
> Do you mean to set backend status to 5 instead of setting frontend to
> 6, and then wait for the kernel to do the transition from 5 to 6,
> instead of setting the frontend to 6?

Yes.

Ian.



_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel