tcp: Add new args for cong_control in tcp_congestion_ops

This patch adds two new arguments for cong_control of struct
tcp_congestion_ops:
 - ack
 - flag
These two arguments are inherited from the caller tcp_cong_control in
tcp_intput.c. One use case of them is to update cwnd and pacing rate
inside cong_control based on the info they provide. For example, the
flag can be used to decide if it is the right time to raise or reduce a
sender's cwnd.
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Miao Xu <miaxu@meta.com>
Link: https://lore.kernel.org/r/20240502042318.801932-2-miaxu@meta.comSigned-off-by: Martin KaFai Lau <martin.lau@kernel.org>

include/net/tcp.h

@@ -1172,7 +1172,7 @@ struct tcp_congestion_ops {
 	/* call when packets are delivered to update cwnd and pacing rate,
 	 * after all the ca_state processing. (optional)
 	 */
-	void (*cong_control)(struct sock *sk, const struct rate_sample *rs);
+	void (*cong_control)(struct sock *sk, u32 ack, int flag, const struct rate_sample *rs);
 
 
 	/* new value of cwnd after loss (required) */

net/ipv4/bpf_tcp_ca.c

@@ -307,7 +307,8 @@ static u32 bpf_tcp_ca_min_tso_segs(struct sock *sk)
 	return 0;
 }
 
-static void bpf_tcp_ca_cong_control(struct sock *sk, const struct rate_sample *rs)
+static void bpf_tcp_ca_cong_control(struct sock *sk, u32 ack, int flag,
+				    const struct rate_sample *rs)
 {
 }
 

net/ipv4/tcp_bbr.c

@@ -1024,7 +1024,7 @@ static void bbr_update_model(struct sock *sk, const struct rate_sample *rs)
 	bbr_update_gains(sk);
 }
 
-__bpf_kfunc static void bbr_main(struct sock *sk, const struct rate_sample *rs)
+__bpf_kfunc static void bbr_main(struct sock *sk, u32 ack, int flag, const struct rate_sample *rs)
 {
 	struct bbr *bbr = inet_csk_ca(sk);
 	u32 bw;

net/ipv4/tcp_input.c

@@ -3541,7 +3541,7 @@ static void tcp_cong_control(struct sock *sk, u32 ack, u32 acked_sacked,
 	const struct inet_connection_sock *icsk = inet_csk(sk);
 
 	if (icsk->icsk_ca_ops->cong_control) {
-		icsk->icsk_ca_ops->cong_control(sk, rs);
+		icsk->icsk_ca_ops->cong_control(sk, ack, flag, rs);
 		return;
 	}
 

tools/testing/selftests/bpf/progs/tcp_ca_kfunc.c

@@ -5,7 +5,7 @@
 #include <bpf/bpf_tracing.h>
 
 extern void bbr_init(struct sock *sk) __ksym;
-extern void bbr_main(struct sock *sk, const struct rate_sample *rs) __ksym;
+extern void bbr_main(struct sock *sk, u32 ack, int flag, const struct rate_sample *rs) __ksym;
 extern u32 bbr_sndbuf_expand(struct sock *sk) __ksym;
 extern u32 bbr_undo_cwnd(struct sock *sk) __ksym;
 extern void bbr_cwnd_event(struct sock *sk, enum tcp_ca_event event) __ksym;
@@ -42,9 +42,9 @@ void BPF_PROG(in_ack_event, struct sock *sk, u32 flags)
 }
 
 SEC("struct_ops/cong_control")
-void BPF_PROG(cong_control, struct sock *sk, const struct rate_sample *rs)
+void BPF_PROG(cong_control, struct sock *sk, u32 ack, int flag, const struct rate_sample *rs)
 {
-	bbr_main(sk, rs);
+	bbr_main(sk, ack, flag, rs);
 }
 
 SEC("struct_ops/cong_avoid")