From: Tan Xiaojun Subject: =?UTF-8?Q?Re:_IP_ID_check_=28flush=5fid=29_in_inet=5fgro=5freceive_?= =?UTF-8?Q?is_necessary_or_not=ef=bc=9f?= Date: Tue, 28 Jun 2016 15:44:00 +0800 Message-ID: <57722AC0.7090003@huawei.com> References: <5771FFA1.3050306@huawei.com> <1467089829.6850.181.camel@edumazet-glaptop3.roam.corp.google.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Cc: , , , , , , , , To: Eric Dumazet Return-path: In-Reply-To: <1467089829.6850.181.camel@edumazet-glaptop3.roam.corp.google.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On 2016/6/28 12:57, Eric Dumazet wrote: > On Tue, 2016-06-28 at 12:40 +0800, Tan Xiaojun wrote: >> Hi everyone, >> >> I'm sorry to bother you. But I was confused. >> >> The IP ID check (flush_id) in inet_gro_receive is only used by >> tcp_gro_receive, and in tcp_gro_receive we have tcphdr check to ensure >> the order of skbs, >> like below: >> >> flush |= (__force int)(th->ack_seq ^ th2->ack_seq); >> flush |= (ntohl(th2->seq) + skb_gro_len(p)) ^ ntohl(th->seq); >> >> So if I remove the IP ID check in inet_gro_receive, there will be a >> problem ? And under what circumstances ? > > You probably missed a recent patch ? > Thank you very much. Is this patch means forcing the IP ID to be incrementing by 1 is necessary in the case of using tunnel (if the IP_DF is not set in frag_off). I have not used the tunneled frames. Do you have some examples for that ? Xiaojun. > commit 1530545ed64b42e87acb43c0c16401bd1ebae6bf > Author: Alexander Duyck > Date: Sun Apr 10 21:44:57 2016 -0400 > > GRO: Add support for TCP with fixed IPv4 ID field, limit tunnel IP ID values > > This patch does two things. > > First it allows TCP to aggregate TCP frames with a fixed IPv4 ID field. As > a result we should now be able to aggregate flows that were converted from > IPv6 to IPv4. In addition this allows us more flexibility for future > implementations of segmentation as we may be able to use a fixed IP ID when > segmenting the flow. > > The second thing this does is that it places limitations on the outer IPv4 > ID header in the case of tunneled frames. Specifically it forces the IP ID > to be incrementing by 1 unless the DF bit is set in the outer IPv4 header. > This way we can avoid creating overlapping series of IP IDs that could > possibly be fragmented if the frame goes through GRO and is then > resegmented via GSO. > > Signed-off-by: Alexander Duyck > Signed-off-by: David S. Miller > > > > . >