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

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Date:   Mon, 22 Jan 2018 17:34:37 -0800
From:   "Samudrala, Sridhar" <sridhar.samudrala@...el.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     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>,
        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 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
>
>> As we are using virtio_net to control and manage the VF data path, it is not
>> clear to me
>> what is the advantage of creating a new device rather than extending
>> virtio_net to manage
>> the VF datapath via transparent bond mechanism.
>>
>> Thanks
>> Sridhar
> So that XDP redirect actions can differentiate between virtio, PT
> device and the bond. Without it there's no way to redirect
> to virtio specifically.
I guess this usecase is for a guest admin to add bpf programs to VF 
netdev and
redirect frames to virtio.  How does bond enable this feature?


Thanks
Sridhar