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 <[e-mail]>
Signed-off-by: Miao Xu <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Martin KaFai Lau <[e-mail]>

include/net/tcp.h

···
 	/* 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

···
 	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

···
 	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

···
 	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

···
 #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;
···
 }
 
 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")