netdev - [PATCH net-next 38/44] tcp: accecn: fallback outgoing half link to non-AccECN

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Message-Id: <20241015102940.26157-39-chia-yu.chang@nokia-bell-labs.com>
Date: Tue, 15 Oct 2024 12:29:34 +0200
From: chia-yu.chang@...ia-bell-labs.com
To: netdev@...r.kernel.org, ij@...nel.org, ncardwell@...gle.com,
        koen.de_schepper@...ia-bell-labs.com, g.white@...leLabs.com,
        ingemar.s.johansson@...csson.com, mirja.kuehlewind@...csson.com,
        cheshire@...le.com, rs.ietf@....at, Jason_Livingood@...cast.com,
        vidhi_goel@...le.com
Cc: Chia-Yu Chang <chia-yu.chang@...ia-bell-labs.com>
Subject: [PATCH net-next 38/44] tcp: accecn: fallback outgoing half link to non-AccECN

From: Chia-Yu Chang <chia-yu.chang@...ia-bell-labs.com>

Based on specification:
  https://tools.ietf.org/id/draft-ietf-tcpm-accurate-ecn-28.txt

3.2.2.1. ACE Field on the ACK of the SYN/ACK - If the Server is in
AccECN mode and in SYN-RCVD state, and if it receives a value of zero
on a pure ACK with SYN=0 and no SACK blocks, for the rest of the
connection the Server MUST NOT set ECT on outgoing packets and MUST
NOT respond to AccECN feedback. Nonetheless, as a Data Receiver it
MUST NOT disable AccECN feedback.

Signed-off-by: Chia-Yu Chang <chia-yu.chang@...ia-bell-labs.com>
---
 net/ipv4/tcp_minisocks.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 301606ff1708..ba7a3300ab9e 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -458,7 +458,10 @@ void tcp_accecn_third_ack(struct sock *sk, const struct sk_buff *skb,
 
 	switch (ace) {
 	case 0x0:
-		tcp_accecn_fail_mode_set(tp, TCP_ACCECN_ACE_FAIL_RECV);
+		if (!TCP_SKB_CB(skb)->sacked) {
+			tcp_accecn_fail_mode_set(tp, TCP_ACCECN_ACE_FAIL_RECV |
+						     TCP_ACCECN_OPT_FAIL_RECV);
+		}
 		break;
 	case 0x7:
 	case 0x5:
-- 
2.34.1