From mboxrd@z Thu Jan  1 00:00:00 1970
From: Rusty Russell <rusty@rustcorp.com.au>
Subject: Re: [PATCH RFC] virtio-pci: new config layout: using memory BAR
Date: Fri, 07 Jun 2013 11:28:04 +0930
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Cc: Peter Maydell <peter.maydell@linaro.org>, kvm@vger.kernel.org,
	virtualization@lists.linux-foundation.org,
	Stefan Hajnoczi <stefanha@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>,
	KONRAD Frederic <fred.konrad@greensocs.com>
To: Anthony Liguori <aliguori@us.ibm.com>,
	"Michael S. Tsirkin" <mst@redhat.com>
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Anthony Liguori <aliguori@us.ibm.com> writes:
> Hi Rusty,
>
> Rusty Russell <rusty@rustcorp.com.au> writes:
>
>> Anthony Liguori <aliguori@us.ibm.com> writes:
>>> 4) Do virtio-pcie, make it PCI-e friendly (drop the IO BAR completely), give
>>>    it a new device/vendor ID.   Continue to use virtio-pci for existing
>>>    devices potentially adding virtio-{net,blk,...}-pcie variants for
>>>    people that care to use them.
>>
>> Now you have a different compatibility problem; how do you know the
>> guest supports the new virtio-pcie net?
>
> We don't care.
>
> We would still use virtio-pci for existing devices.  Only new devices
> would use virtio-pcie.

My concern is that new features make the virtio-pcie driver so desirable
that libvirt is pressured to use it ASAP.  Have we just punted the
problem upstream?

(Of course, feature bits were supposed to avoid such a transition issue,
but mistakes accumulate).

Cheers,
Rusty.