tcp: ecn functions in separated include file

The following patches will modify ECN helpers and add AccECN herlpers,
and this patch moves the existing ones into a separated include file.

No functional changes.

Signed-off-by: Chia-Yu Chang <chia-yu.chang@nokia-bell-labs.com>
Acked-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20250911110642.87529-5-chia-yu.chang@nokia-bell-labs.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 116 insertions, 0 deletions

diff --git a/include/net/tcp_ecn.h b/include/net/tcp_ecn.h
new file mode 100644
index 000000000000..b3430557676b
--- /dev/null
+++ b/include/net/tcp_ecn.h
@@ -0,0 +1,116 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef _TCP_ECN_H
+#define _TCP_ECN_H
+
+#include <linux/tcp.h>
+#include <linux/skbuff.h>
+
+#include <net/inet_connection_sock.h>
+#include <net/sock.h>
+#include <net/tcp.h>
+#include <net/inet_ecn.h>
+
+static inline void tcp_ecn_queue_cwr(struct tcp_sock *tp)
+{
+	if (tcp_ecn_mode_rfc3168(tp))
+		tp->ecn_flags |= TCP_ECN_QUEUE_CWR;
+}
+
+static inline void tcp_ecn_accept_cwr(struct sock *sk,
+				      const struct sk_buff *skb)
+{
+	if (tcp_hdr(skb)->cwr) {
+		tcp_sk(sk)->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
+
+		/* If the sender is telling us it has entered CWR, then its
+		 * cwnd may be very low (even just 1 packet), so we should ACK
+		 * immediately.
+		 */
+		if (TCP_SKB_CB(skb)->seq != TCP_SKB_CB(skb)->end_seq)
+			inet_csk(sk)->icsk_ack.pending |= ICSK_ACK_NOW;
+	}
+}
+
+static inline void tcp_ecn_withdraw_cwr(struct tcp_sock *tp)
+{
+	tp->ecn_flags &= ~TCP_ECN_QUEUE_CWR;
+}
+
+static inline void tcp_ecn_rcv_synack(struct tcp_sock *tp,
+				      const struct tcphdr *th)
+{
+	if (tcp_ecn_mode_rfc3168(tp) && (!th->ece || th->cwr))
+		tcp_ecn_mode_set(tp, TCP_ECN_DISABLED);
+}
+
+static inline void tcp_ecn_rcv_syn(struct tcp_sock *tp,
+				   const struct tcphdr *th)
+{
+	if (tcp_ecn_mode_rfc3168(tp) && (!th->ece || !th->cwr))
+		tcp_ecn_mode_set(tp, TCP_ECN_DISABLED);
+}
+
+static inline bool tcp_ecn_rcv_ecn_echo(const struct tcp_sock *tp,
+					const struct tcphdr *th)
+{
+	if (th->ece && !th->syn && tcp_ecn_mode_rfc3168(tp))
+		return true;
+	return false;
+}
+
+/* Packet ECN state for a SYN-ACK */
+static inline void tcp_ecn_send_synack(struct sock *sk, struct sk_buff *skb)
+{
+	const struct tcp_sock *tp = tcp_sk(sk);
+
+	TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_CWR;
+	if (tcp_ecn_disabled(tp))
+		TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_ECE;
+	else if (tcp_ca_needs_ecn(sk) ||
+		 tcp_bpf_ca_needs_ecn(sk))
+		INET_ECN_xmit(sk);
+}
+
+/* Packet ECN state for a SYN.  */
+static inline void tcp_ecn_send_syn(struct sock *sk, struct sk_buff *skb)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	bool bpf_needs_ecn = tcp_bpf_ca_needs_ecn(sk);
+	bool use_ecn = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_ecn) == 1 ||
+		tcp_ca_needs_ecn(sk) || bpf_needs_ecn;
+
+	if (!use_ecn) {
+		const struct dst_entry *dst = __sk_dst_get(sk);
+
+		if (dst && dst_feature(dst, RTAX_FEATURE_ECN))
+			use_ecn = true;
+	}
+
+	tp->ecn_flags = 0;
+
+	if (use_ecn) {
+		if (tcp_ca_needs_ecn(sk) || bpf_needs_ecn)
+			INET_ECN_xmit(sk);
+
+		TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ECE | TCPHDR_CWR;
+		tcp_ecn_mode_set(tp, TCP_ECN_MODE_RFC3168);
+	}
+}
+
+static inline void tcp_ecn_clear_syn(struct sock *sk, struct sk_buff *skb)
+{
+	if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_ecn_fallback))
+		/* tp->ecn_flags are cleared at a later point in time when
+		 * SYN ACK is ultimatively being received.
+		 */
+		TCP_SKB_CB(skb)->tcp_flags &= ~(TCPHDR_ECE | TCPHDR_CWR);
+}
+
+static inline void
+tcp_ecn_make_synack(const struct request_sock *req, struct tcphdr *th)
+{
+	if (inet_rsk(req)->ecn_ok)
+		th->ece = 1;
+}
+
+#endif /* _LINUX_TCP_ECN_H */