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

From: Jason Wang <[email-masked]>
Date: Thu, 25 Dec 2014 09:58:25 +0008

On Thu, Dec 25, 2014 at 3:14 PM, Michael S. Tsirkin <[email-masked]> 
wrote:
> On Thu, Dec 25, 2014 at 03:10:01AM +0008, Jason Wang wrote:
>>  
>>  
>>  On Thu, Dec 25, 2014 at 2:59 AM, Michael S. Tsirkin 
>> <[email-masked]> wrote:
>>  >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
>>  
>>  I wonder whether or not we can do this lazily.
>>  
>>  E.g during UFO6 software segment for dodgy packets?
>>  
>>  And this can eliminate the effort of duplicating it in all untrusted
>>  sources?
> 
> But then we'll need to then change it again in step 5,
> probably by setting some flag?

The idea is if no segmentation (either software or hardware), no need 
for an id.
 
So looks like dodgy is sufficient since we are sure kernel should set 
id in all other cases. And we can add the id only when we see it was 
not set for the ufo packet(legacy guest). This seems not conflict with 
step 5.
> 
> Might as well do it directly.
> 
>>  >
>>  >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.
>>  >
>>  >
>>  >--
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