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

[Alexander Duyck <alexander.duyck@gmail.com>]

On Fri, Mar 2, 2018 at 12:36 AM, Jiri Pirko <jiri@resnulli.us> wrote:
> Thu, Mar 01, 2018 at 09:08:43PM CET, sridhar.samudrala@intel.com 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 <sridhar.samudrala@intel.com>
>>Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
>>Reviewed-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
>>---
>> 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.

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.

Thanks.

- Alex