On 10/30/25 3:34 PM, [email protected] wrote:
> From: Chia-Yu Chang <[email protected]>
>
> For Accurate ECN, the first SYN/ACK sent by the TCP server shall set the
> ACE flag (see Table 1 of RFC9768) and the AccECN option to complete the
> capability negotiation. However, if the TCP server needs to retransmit such
> a SYN/ACK (for example, because it did not receive an ACK acknowledging its
> SYN/ACK, or received a second SYN requesting AccECN support), the TCP server
> retransmits the SYN/ACK without the AccECN option. This is because the
> SYN/ACK may be lost due to congestion, or a middlebox may block the AccECN
> option. Furthermore, if this retransmission also times out, to expedite
> connection establishment, the TCP server should retransmit the SYN/ACK with
> (AE,CWR,ECE) = (0,0,0) and without the AccECN option, while maintaining
> AccECN feedback mode.
>
> This complies with Section 3.2.3.2.2 of the AccECN specification (RFC9768).
>
> Signed-off-by: Chia-Yu Chang <[email protected]>
> ---
> include/net/tcp_ecn.h | 14 ++++++++++----
> net/ipv4/tcp_output.c | 2 +-
> 2 files changed, 11 insertions(+), 5 deletions(-)
>
> diff --git a/include/net/tcp_ecn.h b/include/net/tcp_ecn.h
> index c66f0d944e1c..99d095ed01b3 100644
> --- a/include/net/tcp_ecn.h
> +++ b/include/net/tcp_ecn.h
> @@ -651,10 +651,16 @@ static inline void tcp_ecn_clear_syn(struct sock *sk,
> struct sk_buff *skb)
> static inline void
> tcp_ecn_make_synack(const struct request_sock *req, struct tcphdr *th)
> {
> - if (tcp_rsk(req)->accecn_ok)
> - tcp_accecn_echo_syn_ect(th, tcp_rsk(req)->syn_ect_rcv);
> - else if (inet_rsk(req)->ecn_ok)
> - th->ece = 1;
> + if (!req->num_retrans || !req->num_timeout) {
Why `if (!req->num_timeout)` is not a sufficient condition here?
Simplifying the above condition will make the TCP_SYNACK_RETRANS
alternative simpler, I think.
/P
