netdev - Re: [virtio-dev] Re: [Qemu-devel] [PATCH] qemu: Introduce VIRTIO_NET_F_STANDBY feature bit to virtio

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Date:   Thu, 21 Jun 2018 18:21:55 -0700
From:   Siwei Liu <loseweigh@...il.com>
To:     Cornelia Huck <cohuck@...hat.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        "Samudrala, Sridhar" <sridhar.samudrala@...el.com>,
        Alexander Duyck <alexander.h.duyck@...el.com>,
        virtio-dev@...ts.oasis-open.org, aaron.f.brown@...el.com,
        Jiri Pirko <jiri@...nulli.us>, Jakub Kicinski <kubakici@...pl>,
        Netdev <netdev@...r.kernel.org>, qemu-devel@...gnu.org,
        virtualization@...ts.linux-foundation.org, konrad.wilk@...cle.com,
        boris.ostrovsky@...cle.com,
        Joao Martins <joao.m.martins@...cle.com>,
        Venu Busireddy <venu.busireddy@...cle.com>,
        vijay.balakrishna@...cle.com
Subject: Re: [virtio-dev] Re: [Qemu-devel] [PATCH] qemu: Introduce
 VIRTIO_NET_F_STANDBY feature bit to virtio_net

On Thu, Jun 21, 2018 at 7:59 AM, Cornelia Huck <cohuck@...hat.com> wrote:
> On Wed, 20 Jun 2018 22:48:58 +0300
> "Michael S. Tsirkin" <mst@...hat.com> wrote:
>
>> On Wed, Jun 20, 2018 at 06:06:19PM +0200, Cornelia Huck wrote:
>> > In any case, I'm not sure anymore why we'd want the extra uuid.
>>
>> It's mostly so we can have e.g. multiple devices with same MAC
>> (which some people seem to want in order to then use
>> then with different containers).
>>
>> But it is also handy for when you assign a PF, since then you
>> can't set the MAC.
>>
>
> OK, so what about the following:
>
> - introduce a new feature bit, VIRTIO_NET_F_STANDBY_UUID that indicates
>   that we have a new uuid field in the virtio-net config space
> - in QEMU, add a property for virtio-net that allows to specify a uuid,
>   offer VIRTIO_NET_F_STANDBY_UUID if set
> - when configuring, set the property to the group UUID of the vfio-pci
>   device

If feature negotiation fails on VIRTIO_NET_F_STANDBY_UUID, is it safe
to still expose UUID in the config space on virtio-pci?

I'm not even sure if it's sane to expose group UUID on the PCI bridge
where the corresponding vfio-pci device attached to for a guest which
doesn't support the feature (legacy).

-Siwei


> - in the guest, use the uuid from the virtio-net device's config space
>   if applicable; else, fall back to matching by MAC as done today
>
> That should work for all virtio transports.