netdev - Re: [PATCH v4 2/2] virtio_net: Extend virtio to use VF datapath when available

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Date:   Fri, 2 Mar 2018 22:10:33 +0200
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     "Samudrala, Sridhar" <sridhar.samudrala@...el.com>
Cc:     Alexander Duyck <alexander.duyck@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Stephen Hemminger <stephen@...workplumber.org>,
        David Miller <davem@...emloft.net>,
        Netdev <netdev@...r.kernel.org>, virtio-dev@...ts.oasis-open.org,
        "Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
        "Duyck, Alexander H" <alexander.h.duyck@...el.com>,
        Jakub Kicinski <kubakici@...pl>
Subject: Re: [PATCH v4 2/2] virtio_net: Extend virtio to use VF datapath when
 available

On Fri, Mar 02, 2018 at 11:52:27AM -0800, Samudrala, Sridhar wrote:
> 
> 
> On 3/2/2018 11:41 AM, Michael S. Tsirkin wrote:
> > On Fri, Mar 02, 2018 at 07:26:25AM -0800, Alexander Duyck wrote:
> > > The design limits things to a 1:1 relationship since we just have the
> > > child and backup pointers, but I don't think I am seeing exception
> > > handling to prevent us from overwriting the child pointers so there
> > > may be a leak there.
> > > 
> > > Thanks.
> > > 
> > > - Alex
> > In fact maintaining a list in that case would be nicer, and
> > just use an arbitrary one.
> > E.g. one can see how a user wanting to swap device 1 for device 2
> > might first add device 2 with same MAC then drop device 1.
> 
> It should be possible to swap VF1 with VF2 by
> 1.- enabling virtio link
> 2.- unplugging VF1
> 3.- plugging VF2
> 4.- disabling virtio link
> 

True, but it isn't hard to avoid breakage if user
swapped steps 2 and 3. No need to make it more
fragile that it has to be.

-- 
MST