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

When connection is initialized after ECN negotiation, this patch
enables CA to control whether ECT(0) or ECT(1) should be used.
A new identiifer (TCP_CONG_ECT_1_ESTABLISH) defines the expected
ECT value in the IP header.

Signed-off-by: Chia-Yu Chang <chia-yu.chang@nokia-bell-labs.com>
---
 include/net/tcp.h     | 1 +
 include/net/tcp_ecn.h | 6 ++++++
 net/ipv4/tcp_cong.c   | 4 +++-
 net/ipv4/tcp_output.c | 2 +-
 4 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index aa5d779b99d7..e8090f542f7c 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -428,6 +428,7 @@ static inline void tcp_dec_quickack_mode(struct sock *sk)
 #define	TCP_ECN_DEMAND_CWR	BIT(2)
 #define	TCP_ECN_SEEN		BIT(3)
 #define	TCP_ECN_MODE_ACCECN	BIT(4)
+#define	TCP_ECN_ECT_1_ESTABLISH	BIT(5)
 
 #define	TCP_ECN_DISABLED	0
 #define	TCP_ECN_MODE_PENDING	(TCP_ECN_MODE_RFC3168 | TCP_ECN_MODE_ACCECN)
diff --git a/include/net/tcp_ecn.h b/include/net/tcp_ecn.h
index 865d5c5a7718..210ec63538f8 100644
--- a/include/net/tcp_ecn.h
+++ b/include/net/tcp_ecn.h
@@ -38,6 +38,12 @@ static inline void INET_ECN_xmit_ect_1_negotiation(struct sock *sk)
 	__INET_ECN_xmit(sk, tcp_ca_ect_1_negotiation(sk));
 }
 
+/* Apply either ECT(0) or ECT(1) based on TCP_CONG_ECT_1_ESTABLISH flag */
+static inline void INET_ECN_xmit_ect_1_establish(struct sock *sk)
+{
+	__INET_ECN_xmit(sk, tcp_sk(sk)->ecn_flags & TCP_ECN_ECT_1_ESTABLISH);
+}
+
 static inline void tcp_ecn_queue_cwr(struct tcp_sock *tp)
 {
 	/* Do not set CWR if in AccECN mode! */
diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c
index e9f6c77e0631..7ebf033f87d2 100644
--- a/net/ipv4/tcp_cong.c
+++ b/net/ipv4/tcp_cong.c
@@ -240,7 +240,9 @@ void tcp_init_congestion_control(struct sock *sk)
 	tcp_sk(sk)->prior_ssthresh = 0;
 	if (icsk->icsk_ca_ops->init)
 		icsk->icsk_ca_ops->init(sk);
-	if (tcp_ca_needs_ecn(sk))
+	if (tcp_ca_needs_accecn(sk))
+		INET_ECN_xmit_ect_1_establish(sk);
+	else if (tcp_ca_needs_ecn(sk))
 		INET_ECN_xmit(sk);
 	else
 		INET_ECN_dontxmit(sk);
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index d3b8e61d3c5e..fe725d94a225 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -350,7 +350,7 @@ static void tcp_ecn_send(struct sock *sk, struct sk_buff *skb,
 	if (tcp_ecn_mode_accecn(tp)) {
 		if (!tcp_accecn_ace_fail_recv(tp) &&
 		    !tcp_accecn_ace_fail_send(tp))
-			INET_ECN_xmit(sk);
+			INET_ECN_xmit_ect_1_establish(sk);
 		else
 			INET_ECN_dontxmit(sk);
 		tcp_accecn_set_ace(tp, skb, th);
-- 
2.34.1