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 17:20:17 +0100

Fri, Mar 02, 2018 at 04:26:25PM CET, [email-masked] wrote:
>On Fri, Mar 2, 2018 at 12:36 AM, Jiri Pirko <[email-masked]> wrote:
>> 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.
>
>Yeah, this code essentially calls out the "shareable" code with a
>comment at the start and end of the section what defines the
>virtio_bypass functionality. It would just be a matter of mostly
>cutting and pasting to put it into a separate driver module.

Please put it there and unite the use of it with netvsc.

>
>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.

Ok.