Re: [Qemu-devel] [PULL 5/5] hw/arm/virt: Support legacy -nic command line syntax

[Peter Maydell]

On 18 January 2016 at 13:57, Eric Auger <address@hidden> wrote:
> Hi Peter,
> On 01/18/2016 02:34 PM, Peter Maydell wrote:
>> Hmm, I guess this is changing things in that we now will have a
>> virtio PCI device appearing if you use the default (-net nic -net user)
>> settings. But I don't see why that would particularly interfere
>> with VFIO passthrough, except in as much as the guest now has
>> two network cards in it and might be preferring one as eth0
>> rather than the other...
> Yes that's what currently happens I think. I get the slirp thing on eth0
> and my passthrough'ed device on eth1. That's not very straightforward
> for the end-user to get those 2 NIC's now. In case I passthrough some
> NIC's I would have expected this default NIC not be instantiated?

The QEMU networking layer only knows about networking controlled
by the -net or -netdev options (and in those cases it does disable
the default network device). Because the back-end for passthrough
NICs is completely unknown to QEMU (it is all done in hardware),
I'm not sure we have any way to know that the thing you've passed through
is a NIC and not some other random PCI device...

> Alex, how do you manage on x86 platforms with VFIO-PCI NIC?

...but presumably the x86 folks have been here before us
and know how this should work :-)

thanks
-- PMM