Re: [PATCH 0/3][RFC] PV Passthrough PCI Device Hotplug Support

[Yosuke Iwamatsu <y-iwamatsu@ab.jp.nec.com>]

Keir Fraser wrote:
> On 21/2/08 11:00, "Yosuke Iwamatsu" <y-iwamatsu@ab.jp.nec.com> wrote:
> 
>> - Interface changes
>>   New xenbus states "Reconfiguring" and "Reconfigured" are introduced.
> 
> Not sure about this. If this is just to flag changes to individual devices,
> could pcifront watch individual device nodes? Or at least I think a separate
> configuration xenstore node would be sensible, with its own state-machine
> enumeration. I'm reluctant to mess with the main state node as we currently
> have something that works!

PCI device attach/detach may result in changing several nodes such as
"num_devs", "root-#" and "root_num". So I thought switching the main
state might be suitable here.

If you are unwilling to change the main state node,
watching individual device nodes may be a possible solution.
In that case, we prepare pci slots for hotplug and make pciback/pcifront
watch all the states of these slots. But I wonder if it is acceptable
that pv drivers watch lots of xenstore nodes.

I'm not sure about the idea to have a separate configuration node
per device. Does that mean having pv drivers for each pci device?

> 
>> - Xenstore changes
>>   Substates(state-#) and virtual pci slots(vdev-#) entries are added
>>   for pciback driver. For example, when PCI devices 00:1d.0 and 00:1d.1
>>   are connected, xenstore-ls will show information like this.
> 
> Why vdev-#? Aren't the dev-# names already the virtual names (mapped to
> physical slots transparently by pciback)?

dev-# names are the physical names.
vdev-# becomes the same as dev-# when compiled with PCIDEV_BACKEND_PASS,
but different when compiled with other options (VPCI, SLOT).
vdev-# names are necessary for pcifront to recognize which devices are
to be detached.

Thanks,
   Yosuke

> 
>  -- Keir
>