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

From: Jiri Pirko <[email-masked]>
Date: Fri, 2 Mar 2018 09:36:05 +0100

Thu, Mar 01, 2018 at 09:08:43PM CET, [email-masked] wrote:
>This patch enables virtio_net to switch over to a VF datapath when a VF
>netdev is present with the same MAC address. It allows live migration
>of a VM with a direct attached VF without the need to setup a bond/team
>between a VF and virtio net device in the guest.
>
>The hypervisor needs to enable only one datapath at any time so that
>packets don't get looped back to the VM over the other datapath. When a VF
>is plugged, the virtio datapath link state can be marked as down. The
>hypervisor needs to unplug the VF device from the guest on the source host
>and reset the MAC filter of the VF to initiate failover of datapath to
>virtio before starting the migration. After the migration is completed,
>the destination hypervisor sets the MAC filter on the VF and plugs it back
>to the guest to switch over to VF datapath.
>
>When BACKUP feature is enabled, an additional netdev(bypass netdev) is
>created that acts as a master device and tracks the state of the 2 lower
>netdevs. The original virtio_net netdev is marked as 'backup' netdev and a
>passthru device with the same MAC is registered as 'active' netdev.
>
>This patch is based on the discussion initiated by Jesse on this thread.
>https://marc.info/?l=linux-virtualization&m=151189725224231&w=2
>
>Signed-off-by: Sridhar Samudrala <[email-masked]>
>Signed-off-by: Alexander Duyck <[email-masked]>
>Reviewed-by: Jesse Brandeburg <[email-masked]>
>---
> drivers/net/virtio_net.c | 683 ++++++++++++++++++++++++++++++++++++++++++++++-

As I wrote to the discussion of the other version of this patchset,
I strongly believe you need to have a common part in net/core/ that will
be shared by both virtio_net and netvsc. There there should be explicit
limits for this in-driver bonding solution, like max 1 vf slave, etc.