netdev - Re: [virtio-dev] [RFC PATCH net-next v2 1/2] virtio_net: Introduce VIRTIO_NET_F

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Date:   Tue, 23 Jan 2018 11:21:33 -0800
From:   Jakub Kicinski <kubakici@...pl>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     "Samudrala, Sridhar" <sridhar.samudrala@...el.com>,
        Alexander Duyck <alexander.duyck@...il.com>,
        Stephen Hemminger <stephen@...workplumber.org>,
        David Miller <davem@...emloft.net>,
        Netdev <netdev@...r.kernel.org>,
        virtualization@...ts.linux-foundation.org,
        virtio-dev@...ts.oasis-open.org,
        "Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
        "Duyck, Alexander H" <alexander.h.duyck@...el.com>,
        achiad shochat <achiad.mellanox@...il.com>,
        Achiad Shochat <achiad@...lanox.com>
Subject: Re: [virtio-dev] [RFC PATCH net-next v2 1/2] virtio_net: Introduce
 VIRTIO_NET_F_BACKUP feature bit

On Tue, 23 Jan 2018 03:23:57 +0200, Michael S. Tsirkin wrote:
> > > > b. next-gen silicon may be able to disguise as virtio device, and the
> > > >    loop check in virtio driver will prevent the legitimate bond it such
> > > >    case.  AFAIU that's one of the goals of next-gen virtio spec as well.    
> > > 
> > > In fact we have a virtio feature bit for the fallback.
> > > So this part does not depend on how software in guest works
> > > and does not need software solutions.  
> > 
> > You mean in the new spec?  Nice.  Still I think people will try to
> > implement the old one too given sufficiently capable HW.  
> 
> Existing HW won't have the BACKUP feature so the new functionality
> won't be activated. So no problem I think.

I meant code that compares of netdev_ops, e.g.:

+	/* Skip our own events */
+	if (event_dev->netdev_ops == &virtnet_netdev)
+		return NOTIFY_DONE;

Would be an obstacle to bonding virtio_nets.  But that's just one of
the thoughts, perhaps of disputable value.  Anyway, separate netdev and
netdev_ops will solve this, and I think we agree that's preferable :)