Re: [Xen-devel] PCI hotplug related issues

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2012-06-05 at 09:42 +0100, Jan Beulich wrote:
> >>> On 04.06.12 at 21:00, Anil Rao <anil.rao@xxxxxxxxxxxx> wrote:
> > A) Does Xen support case 1 (hotplugging a PCI device to a running VM that 
> > was powered-on before the device was added to
> >     the host)?
> 
> As far as I'm aware, only hotplug from the perspective of the guest
> is really supported/tested.
> 
> But the issue here really seems less Xen related, but more towards
> libpci behavior (as according to qemu this is where the device isn't
> known). As that's a component Xen/qemu-dm simply builds upon,
> failure there (e.g. lack of hotplug awareness) would surface as a
> Xen misbehavior. Quickly going through the list of provided symbols
> of libpci.so doesn't show anything that looks hotplug related (e.g.
> some sort of notification registration). But of course it's possible
> that I'm overlooking something here, and that in fact qemu-dm's
> interaction with libpci is simply incomplete.

Your theory tallies with what I remember from looking at PCI hotplug
using a stub qemu -- IIRC libpci scans the bus at start of day and has
no capability to refresh the list of known devices after that. This
means that on host hotplug (actually mini-os hotplug in the case I was
looking at) the device doesn't become known to qemu.

Anyway the upshot is that AFAIK even for non-stub qemu either (or both)
qemu and libpci need to be taught about host PCI hotplug somehow.

Ian.


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