On Wed, May 4, 2016 at 8:26 PM, Alexander Duyck <alexander.du...@gmail.com> wrote: > On Wed, May 4, 2016 at 6:20 PM, Eric Dumazet <eric.duma...@gmail.com> wrote: >> On Wed, 2016-05-04 at 18:02 -0700, Tom Herbert wrote: >>> Signed-off-by: Tom Herbert <t...@herbertland.com> >>> --- >>> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h >>> index 928b456..6a811fa 100644 >>> --- a/include/linux/skbuff.h >>> +++ b/include/linux/skbuff.h >>> @@ -484,6 +484,8 @@ enum { >>> SKB_GSO_TUNNEL_REMCSUM = 1 << 14, >>> >>> SKB_GSO_IP6IP6 = 1 << 15, >>> + >>> + SKB_GSO_IP4IP6 = 1 << 16, >>> }; >>> >> >> Houston, we have a problem. >> >> gso_type is 16bit (unsigned short), or maybe I missed something ? >> >> struct skb_shared_info { >> unsigned char nr_frags; >> __u8 tx_flags; >> unsigned short gso_size; >> unsigned short gso_segs; >> unsigned short gso_type; <<-->> > > No, I am pretty sure you have it right. We are out of bits. > > Also it seems like we are generating a number of duplicate entries. > What is the difference between IP6IP6 and SIT over IPv6? I'm not > really seeing the difference. > > I'm wondering if maybe we shouldn't look at the possibly using the > IPIP and SIT bits to instead indicate that the frame is encapsulated > in an outer IPv4 or outer IPv6 header since we already have TCPV4 and > TCPV6 to indicate if the inner network type is a V4 or V6. Then there > is no need for this patch set to introduce any new tunnel types to be > segmented since all cases should be covered. As far as I can tell > SKB_GSO_IPIP/SIT were never really being tested against anyway so we > might want to go the IPIPV4 IPIPV6 route instead as that is probably > closer to what most device limitations would be. > My worry is that the current public interface means IPIP is IPv4 over IPv4, and SIT means IPv6 over IPv4. There are some drivers advertising offload support for these so I don't think we safely redefine SKB_GSO_IPIP/SIT.
For finding more bits in gso_type there are some SKB_GOS_* that are not really types at all but more flags. I'm going try to turn SKB_GSO_DODGY into a skbuff for the purposes here. We'll still have the problem of running out bits next time a new type is added (maybe SKB_GSO_SCTP?) but can probably make room for one or two more. Longer term I think the the solution is too eliminate gso_type altogether as we are once again running into the problem of trying to indicate a combinatorial set of constraints and complex layering in a just few flag bits. Tom > - Alex