Subject: Re: [PATCH 00/10] Split UFO into v4 and v6 versions.

From: "Michael S. Tsirkin" <[email-masked]>
Date: Wed, 24 Dec 2014 20:59:22 +0200

On Wed, Dec 24, 2014 at 07:11:20PM +0100, Ben Hutchings wrote:
> On Thu, 2014-12-18 at 00:28 -0500, Jason Wang wrote:
> > 
> > ----- Original Message -----
> > > UFO support in the kernel applies to both IPv4 and IPv6 protocols
> > > with the same device feature.  However some devices may not be able
> > > to support one of the offloads.  For this we split the UFO offload
> > > feature into 2 pieces.  NETIF_F_UFO now controlls the IPv4 part and
> > > this series introduces NETIF_F_UFO6.
> > > 
> > > As a result of this work, we can now re-enable NETIF_F_UFO on
> > > virtio_net devices and restore UDP over IPv4 performance for guests.
> > > We also continue to support legacy guests that assume that UFO6
> > > support included into UFO(4).
> > > 
> > > Without this work, migrating a guest to a 3.18 kernel fails.
> > > 
> > 
> > This series eliminate the ambiguous NETIF_F_UFO.
> > 
> > But VIRTIO_NET_F_{HOST|GUEST}_UFO and VIRTIO_NET_F_HDR_GSO_UDP is still
> > ambigious. I know it was used to keep compatibility for legacy guest. But
> > what's the future plan? Differentiate UFOv4 and UFOv6 in virtio features and
> > gso type in vnet header looks sufficient?
> [...]
> 
> The IPv6 fragmentation ID needs to be added to the vnet header, to do
> UFOv6 properly.  If it wasn't for that lack, we wouldn't have to split
> the feature flag.
> 
> Ben.

Right.

I think a good plan is as follows:

1. add code generating IDs on rx path for virtio,
   and re-enable UFO (4+6).

2. Ben's patch doing similar things for tun/macvtap

3. similarly for packet sockets

above seem appropriate for stable

4. 4+6 split, to make it easier for drivers
   to identify when fragment ID is needed

5. extend vnet header, and add ways to enable it,
   when enabled, use that to pass
   fragment ID for tun/virtio/vhost/macvtap/packet socket

4 is what this patchset does.

> -- 
> Ben Hutchings
> If more than one person is responsible for a bug, no one is at fault.