netdev - Re: [virtio-dev] Re: [Qemu-devel] [PATCH v3 0/3] Use of unique identifier for pairing virtio and passthrough devices...

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Date:   Fri, 13 Jul 2018 11:15:17 +0200
From:   Cornelia Huck <cohuck@...hat.com>
To:     "Samudrala, Sridhar" <sridhar.samudrala@...el.com>
Cc:     Siwei Liu <loseweigh@...il.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        si-wei liu <si-wei.liu@...cle.com>,
        Roman Kagan <rkagan@...tuozzo.com>,
        Venu Busireddy <venu.busireddy@...cle.com>,
        Marcel Apfelbaum <marcel@...hat.com>,
        virtio-dev@...ts.oasis-open.org, qemu-devel@...gnu.org,
        Alexander Duyck <alexander.h.duyck@...el.com>,
        Netdev <netdev@...r.kernel.org>
Subject: Re: [virtio-dev] Re: [Qemu-devel] [PATCH v3 0/3] Use of unique
 identifier for pairing virtio and passthrough devices...

On Thu, 12 Jul 2018 21:20:41 -0400
"Samudrala, Sridhar" <sridhar.samudrala@...el.com> wrote:

> On 7/12/2018 6:19 PM, Siwei Liu wrote:
> > On Thu, Jul 12, 2018 at 2:00 PM, Michael S. Tsirkin <mst@...hat.com> wrote:  
> >> On Thu, Jul 12, 2018 at 01:52:53PM -0700, Siwei Liu wrote:  
> >>> The definition is incomplete due to lack of spec. There's no "host"
> >>> part defined yet in the host-guest interface. If match by MAC is an
> >>> interface, the same must be done on the host(device) side as well,
> >>> which has been agreed not the way to go. However, I don't think that's
> >>> what the author intends to do by interpreting his QEMU patch - it
> >>> missed the other parts as well, such as the feature negotiation and
> >>> how it interacts with the paired device.
> >>>
> >>> What I said is that match by MAC is just a guest implementation that
> >>> one can change at any time. We now have the group ID on QEMU, why
> >>> still sticking to matching by MAC? It shoulnd't be a host-guest
> >>> interface in the first place anyway.  
> >> I think that match by MAC is a simple portable way to match devices.
> >> E.g. it will work seamlessly with niche things like zPCI. However  
> > That's a good point. I'm not sure if it's a valid assumption that zPCI
> > should always use the same MAC address as that of virtio. Someone

I think we can mostly disregard the weirdness that is zPCI right now.
There should be no fundamental reasons that matching by MAC would not
work, though.

> > who's more familiar with the use case may decide and work on that. It
> > means VFIO device has to take in the MAC address as an identifier to
> > the "-device vfio-pci,.." QEMU option. I think there's no point to
> > match device using group ID in QEMU while using MAC in the guest.
> > Based on that assumption, I'd go with making VIRTIO_NET_F_STANDBY to
> > match device based on group ID, while someone may come up with another
> > feature bit later, say VIRTIO_NET_F_STANDBY_BY_MAC when its QEMU
> > support is available. Would it make sense?  
> 
> VIRTIO_NET_F_STANDBY as defined in the guest virtio_net driver supports match
> by MAC address. I think we should add support for this feature bit in QEMU.
> If submitting a patch to update the spec is a pre-requisite to add this
> feature bit to QEMU, i can do that.

Doing a spec patch and implementing matching by MAC in QEMU sounds like
a good plan to me.

> 
> As far as i understand, group id patches to QEMU are still under review.
> Matching by group ID can be another feature bit that could support matching
> by group id as well as MAC.

That plan sounds good to me as well.