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

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Date:   Fri, 22 Dec 2017 00:42:03 -0800
From:   Siwei Liu <loseweigh@...il.com>
To:     Jakub Kicinski <kubakici@...pl>
Cc:     Stephen Hemminger <stephen@...workplumber.org>,
        David Miller <davem@...emloft.net>,
        sridhar.samudrala@...el.com, mst@...hat.com,
        netdev@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        Alexander Duyck <alexander.duyck@...il.com>,
        jesse.brandeburg@...el.com
Subject: Re: [RFC PATCH] virtio_net: Extend virtio to use VF datapath when available

On Wed, Dec 20, 2017 at 8:52 PM, Jakub Kicinski <kubakici@...pl> wrote:
> On Wed, 20 Dec 2017 18:16:30 -0800, Siwei Liu wrote:
>> > The plan is to remove the delay and do the naming in the kernel.
>> > This was suggested by Lennart since udev is only doing naming policy
>> > because kernel names were not repeatable.
>> >
>> > This makes the VF show up as "ethN_vf" on Hyper-V which is user friendly.
>> >
>> > Patch is pending.
>>
>> While it's good to show VF with specific naming to indicate
>> enslavement, I wonder wouldn't it be better to hide this netdev at all
>> from the user space? IMHO this extra device is useless when being
>> enslaved and we may delegate controls (e.g. ethtool) over to the
>> para-virtual device instead? That way it's possible to eliminate the
>> possibility of additional udev setup or modification?
>>
>> I'm not sure if this  is consistent with Windows guest or not, but I
>> don't find it _Linux_ user friendly that ethtool doesn't work on the
>> composite interface any more, and I have to end up with finding out
>> the correct enslaved VF I must operate on.
>
> Hiding "low level" netdevs comes up from time to time, and is more
> widely applicable than just to VF bonds.  We should find a generic
> solution to that problem.

Wholeheartedly agreed.

Be it a generic virtual bond or virtio-net specific one, there should
be some common code between netvsc and virtio for this type of work.
For avoiding duplicated bugs, consistent (Linux) user experience,
future code refactoring/management, and whatever...

One thing worth to note is that, unlike the Hyper-V netvsc backend
there's currently no equivalent (fine-grained) Linux ndo_* driver
interface that is able to move around MAC address/VLAN filters at
run-time specifically. The OID_RECEIVE_FILTER_MOVE_FILTER request I
mean. That translates to one substantial difference in VF
plumbing/unplumbing sequence: you cannot move the MAC address around
to paravirt device until VF is fully unplugged out of the guest OS. I
don't know what backend changes to be proposed for virtio-net as
helper, but the common code needs to work with both flavors of data
path switching backends and do its job correctly.

Regards,
-Siwei