On Mon, May 10, 2021 at 9:19 AM Willem de Bruijn <willemdebruijn.kernel@xxxxxxxxx> wrote: > > > > That generates TCP packets with different MSS within the same stream. > > > > > > My suggestion remains to just not change MSS at all. But this has to > > > be a new flag to avoid changing established behavior. > > > > I don't understand why the mss size should be kept in GSO step. Will > > there be any issue with different mss? > > This issue has come up before and that has been the feedback from > TCP experts at one point. > > > In general, upgrading mss make sense when 6 to 4. The new flag would be > > set by user to not change mss. What happened if user does not set the > > flag? I still think we should fix the issue with a general approach. Or > > can we remove the skb_increase_gso_size line? > > Admins that insert such BPF packets should be aware of these issues. > And likely be using clamping. This is a known issue. > > We arrived that the flag approach in bpf_skb_net_shrink. Extending > that to bpf_skb_change_proto would be consistent. As for more generic approach: does downgrading to non-TSO by clearing gso_size work for this edge case?
