Re: [Xen-devel] Processed: Re: [HVM} xen_platform_pci=0 doesn't prevent platform device creation and disk and nic take over by PV drivers.

[George Dunlap <dunlapg@xxxxxxxxx>]

On Fri, Oct 11, 2013 at 5:53 PM, Anthony PERARD
<anthony.perard@xxxxxxxxxx> wrote:
> On Fri, Oct 11, 2013 at 05:22:47PM +0200, Sander Eikelenboom wrote:
>> > The original message was simply:
>> >> While trying to get to the bottom of my passthrough problem with the rom 
>> >> bar,
>> >> i noticed that specifiying "xen_platform_pci=0" in the config file does 
>> >> not prevent
>> >> the platform device to appear in my HVM guest and consequently the disk 
>> >> and nic are taken over.
>> >>
>> >> Running latest xen-unstable, together with upstream qemu and upstream 
>> >> seabios.
>
> I've start looking at this, and the fix would be easy: removing the
> creation of the xen-platform from QEMU, and let xl ask QEMU to create
> it.
>
> But if one uses an older version of one project (qemu/xl) and a newer
> version of the other, then we can end-up with no xen-platform or two
> xen-platform ...

So what's the plan for compatibility here -- full forward and backward
compatibily on both sides?  (i.e., newer qemu works with older Xen,
newer Xen works with older qemu)?

> So should we try to be clever about this, or just backport patchs for
> both qemu and xl?
>
> "Clever" option: There is a recent patch for xl that make use of
> the -nodefault QEMU's command line option. So if it's present, we could
> ask QEMU to not add xen-platform, and xl can decide.

I wouldn't mind doing something like this; but would it make more
sense to have some kind of a "capability" or "version" interface, like
we have between Xen and Linux, rather than relying on other quirks
like the presence of "-nodefault"?

 -George

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