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

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Date:   Wed, 24 Jan 2018 01:01:03 +0200
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Alexander Duyck <alexander.duyck@...il.com>
Cc:     "Samudrala, Sridhar" <sridhar.samudrala@...el.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>,
        Jakub Kicinski <kubakici@...pl>,
        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 Mon, Jan 22, 2018 at 07:36:32PM -0800, Alexander Duyck wrote:
> On Mon, Jan 22, 2018 at 6:04 PM, Michael S. Tsirkin <mst@...hat.com> wrote:
> > On Mon, Jan 22, 2018 at 05:34:37PM -0800, Samudrala, Sridhar wrote:
> >> On 1/22/2018 4:05 PM, Michael S. Tsirkin wrote:
> >> > On Mon, Jan 22, 2018 at 03:27:40PM -0800, Samudrala, Sridhar wrote:
> >> > > > > You could probably
> >> > > > > even handle the Tx queue selection via a simple eBPF program and map
> >> > > > > since the input for whatever is used to select Tx should be pretty
> >> > > > > simple, destination MAC, source NUMA node, etc, and the data-set
> >> > > > > shouldn't be too large.
> >> > > > That sounds interesting. A separate device might make this kind of setup
> >> > > > a bit easier.  Sridhar, did you look into creating a separate device for
> >> > > > the virtual bond device at all?  It does not have to be in a separate
> >> > > > module, that kind of refactoring can come later, but once we commit to
> >> > > > using the same single device as virtio, we can't change that.
> >> > > No. I haven't looked into creating a separate device. If we are going to
> >> > > create a new
> >> > > device, i guess it has to be of a new device type with its own driver.
> >> > Well not necessarily - just a separate netdev ops.
> >> > Kind of like e.g. vlans share a driver with the main driver.
> >>
> >> Not sure what you meant by vlans sharing a driver with the main driver.
> >> IIUC, vlans are supported via 802.1q driver and  creates a netdev of type
> >> 'vlan'
> >> with vlan_netdev_ops
> >
> > But nothing prevents a single module from registering
> > multiple ops.
> 
> Just to clarify, it seems like what you are suggesting is just adding
> the "master" as a separate set of netdev ops or netdevice and to have
> virtio spawn two network devices, one slave and one master, if the
> BACKUP bit is set. Do I have that right?

Yes, that was my idea.

> I am good with the code still living in the virtio driver and
> consolidation with other similar implementations and further
> improvement could probably happen later as part of some refactor.
> 
> Thanks.
> 
> - Alex