netdev - [PATCH v9 net-next 13/15] tcp: accecn: add tcpi_ecn_mode and tcpi_option2 in tcp

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Message-Id: <20260119185852.11168-14-chia-yu.chang@nokia-bell-labs.com>
Date: Mon, 19 Jan 2026 19:58:50 +0100
From: chia-yu.chang@...ia-bell-labs.com
To: pabeni@...hat.com,
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Cc: Chia-Yu Chang <chia-yu.chang@...ia-bell-labs.com>
Subject: [PATCH v9 net-next 13/15] tcp: accecn: add tcpi_ecn_mode and tcpi_option2 in tcp_info

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

Add 2-bit tcpi_ecn_mode feild within tcp_info to indicate which ECN
mode is negotiated: ECN_MODE_DISABLED, ECN_MODE_RFC3168, ECN_MODE_ACCECN,
or ECN_MODE_PENDING. This is done by utilizing available bits from
tcpi_accecn_opt_seen (reduced from 16 bits to 2 bits) and
tcpi_accecn_fail_mode (reduced from 16 bits to 4 bits).

Also, an extra 24-bit tcpi_options2 field is identified to represent
newer options and connection features, as all 8 bits of tcpi_options
field have been used.

Signed-off-by: Chia-Yu Chang <chia-yu.chang@...ia-bell-labs.com>
Co-developed-by: Neal Cardwell <ncardwell@...gle.com>
Signed-off-by: Neal Cardwell <ncardwell@...gle.com>
---
 include/net/tcp_ecn.h    | 11 -----------
 include/uapi/linux/tcp.h | 26 +++++++++++++++++++++++---
 net/ipv4/tcp.c           |  8 ++++++++
 3 files changed, 31 insertions(+), 14 deletions(-)

diff --git a/include/net/tcp_ecn.h b/include/net/tcp_ecn.h
index 41b593ece1dd..a31ba18b10d8 100644
--- a/include/net/tcp_ecn.h
+++ b/include/net/tcp_ecn.h
@@ -67,12 +67,6 @@ static inline void tcp_ecn_withdraw_cwr(struct tcp_sock *tp)
 	tp->ecn_flags &= ~TCP_ECN_QUEUE_CWR;
 }
 
-/* tp->accecn_fail_mode */
-#define TCP_ACCECN_ACE_FAIL_SEND	BIT(0)
-#define TCP_ACCECN_ACE_FAIL_RECV	BIT(1)
-#define TCP_ACCECN_OPT_FAIL_SEND	BIT(2)
-#define TCP_ACCECN_OPT_FAIL_RECV	BIT(3)
-
 static inline bool tcp_accecn_ace_fail_send(const struct tcp_sock *tp)
 {
 	return tp->accecn_fail_mode & TCP_ACCECN_ACE_FAIL_SEND;
@@ -105,11 +99,6 @@ static inline void tcp_accecn_ace_fail_send_set_retrans(struct request_sock *req
 		tcp_accecn_fail_mode_set(tp, TCP_ACCECN_ACE_FAIL_SEND);
 }
 
-#define TCP_ACCECN_OPT_NOT_SEEN		0x0
-#define TCP_ACCECN_OPT_EMPTY_SEEN	0x1
-#define TCP_ACCECN_OPT_COUNTER_SEEN	0x2
-#define TCP_ACCECN_OPT_FAIL_SEEN	0x3
-
 static inline u8 tcp_accecn_ace(const struct tcphdr *th)
 {
 	return (th->ae << 2) | (th->cwr << 1) | th->ece;
diff --git a/include/uapi/linux/tcp.h b/include/uapi/linux/tcp.h
index dce3113787a7..7be9044c5af3 100644
--- a/include/uapi/linux/tcp.h
+++ b/include/uapi/linux/tcp.h
@@ -226,6 +226,24 @@ enum tcp_ca_state {
 #define TCPF_CA_Loss	(1<<TCP_CA_Loss)
 };
 
+/* Values for tcpi_ecn_mode after negotiation */
+#define TCPI_ECN_MODE_DISABLED		0x0
+#define TCPI_ECN_MODE_RFC3168		0x1
+#define TCPI_ECN_MODE_ACCECN		0x2
+#define TCPI_ECN_MODE_PENDING		0x3
+
+/* Values for accecn_opt_seen */
+#define TCP_ACCECN_OPT_NOT_SEEN		0x0
+#define TCP_ACCECN_OPT_EMPTY_SEEN	0x1
+#define TCP_ACCECN_OPT_COUNTER_SEEN	0x2
+#define TCP_ACCECN_OPT_FAIL_SEEN	0x3
+
+/* Values for accecn_fail_mode */
+#define TCP_ACCECN_ACE_FAIL_SEND	BIT(0)
+#define TCP_ACCECN_ACE_FAIL_RECV	BIT(1)
+#define TCP_ACCECN_OPT_FAIL_SEND	BIT(2)
+#define TCP_ACCECN_OPT_FAIL_RECV	BIT(3)
+
 struct tcp_info {
 	__u8	tcpi_state;
 	__u8	tcpi_ca_state;
@@ -316,15 +334,17 @@ struct tcp_info {
 					 * in milliseconds, including any
 					 * unfinished recovery.
 					 */
-	__u32	tcpi_received_ce;    /* # of CE marks received */
+	__u32	tcpi_ecn_mode:2,
+		tcpi_accecn_opt_seen:2,
+		tcpi_accecn_fail_mode:4,
+		tcpi_options2:24;
+	__u32	tcpi_received_ce;    /* # of CE marked segments received */
 	__u32	tcpi_delivered_e1_bytes;  /* Accurate ECN byte counters */
 	__u32	tcpi_delivered_e0_bytes;
 	__u32	tcpi_delivered_ce_bytes;
 	__u32	tcpi_received_e1_bytes;
 	__u32	tcpi_received_e0_bytes;
 	__u32	tcpi_received_ce_bytes;
-	__u16	tcpi_accecn_fail_mode;
-	__u16	tcpi_accecn_opt_seen;
 };
 
 /* netlink attributes types for SCM_TIMESTAMPING_OPT_STATS */
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 37a6e0aa9176..f9e61e49f811 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -4321,6 +4321,14 @@ void tcp_get_info(struct sock *sk, struct tcp_info *info)
 	if (tp->rto_stamp)
 		info->tcpi_total_rto_time += tcp_clock_ms() - tp->rto_stamp;
 
+	if (tcp_ecn_disabled(tp))
+		info->tcpi_ecn_mode = TCPI_ECN_MODE_DISABLED;
+	else if (tcp_ecn_mode_rfc3168(tp))
+		info->tcpi_ecn_mode = TCPI_ECN_MODE_RFC3168;
+	else if (tcp_ecn_mode_accecn(tp))
+		info->tcpi_ecn_mode = TCPI_ECN_MODE_ACCECN;
+	else if (tcp_ecn_mode_pending(tp))
+		info->tcpi_ecn_mode = TCPI_ECN_MODE_PENDING;
 	info->tcpi_accecn_fail_mode = tp->accecn_fail_mode;
 	info->tcpi_accecn_opt_seen = tp->saw_accecn_opt;
 	info->tcpi_received_ce = tp->received_ce;
-- 
2.34.1