tcp: add SYN/data info to TCP_INFO

Add a bit TCPI_OPT_SYN_DATA (32) to the socket option TCP_INFO:tcpi_options.
It's set if the data in SYN (sent or received) is acked by SYN-ACK. Server or
client application can use this information to check Fast Open success rate.

Signed-off-by: Yuchung Cheng <ycheng@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/tcp.h

@@ -191,7 +191,8 @@ struct tcp_sock {
 	u8	do_early_retrans:1,/* Enable RFC5827 early-retransmit  */
 		early_retrans_delayed:1, /* Delayed ER timer installed */
 		syn_data:1,	/* SYN includes data */
-		syn_fastopen:1;	/* SYN includes Fast Open option */
+		syn_fastopen:1,	/* SYN includes Fast Open option */
+		syn_data_acked:1;/* data in SYN is acked by SYN-ACK */
 
 /* RTT measurement */
 	u32	srtt;		/* smoothed round trip time << 3	*/

include/uapi/linux/tcp.h

@@ -130,6 +130,7 @@ enum {
 #define TCPI_OPT_WSCALE		4
 #define TCPI_OPT_ECN		8 /* ECN was negociated at TCP session init */
 #define TCPI_OPT_ECN_SEEN	16 /* we received at least one packet with ECT */
+#define TCPI_OPT_SYN_DATA	32 /* SYN-ACK acked data in SYN sent or rcvd */
 
 enum tcp_ca_state {
 	TCP_CA_Open = 0,

net/ipv4/tcp.c

@@ -2764,6 +2764,8 @@ void tcp_get_info(const struct sock *sk, struct tcp_info *info)
 		info->tcpi_options |= TCPI_OPT_ECN;
 	if (tp->ecn_flags & TCP_ECN_SEEN)
 		info->tcpi_options |= TCPI_OPT_ECN_SEEN;
+	if (tp->syn_data_acked)
+		info->tcpi_options |= TCPI_OPT_SYN_DATA;
 
 	info->tcpi_rto = jiffies_to_usecs(icsk->icsk_rto);
 	info->tcpi_ato = jiffies_to_usecs(icsk->icsk_ack.ato);

net/ipv4/tcp_input.c

@@ -5646,6 +5646,7 @@ static bool tcp_rcv_fastopen_synack(struct sock *sk, struct sk_buff *synack,
 		tcp_rearm_rto(sk);
 		return true;
 	}
+	tp->syn_data_acked = tp->syn_data;
 	return false;
 }
 

net/ipv4/tcp_ipv4.c

@@ -1461,6 +1461,7 @@ static int tcp_v4_conn_req_fastopen(struct sock *sk,
 		skb_set_owner_r(skb, child);
 		__skb_queue_tail(&child->sk_receive_queue, skb);
 		tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
+		tp->syn_data_acked = 1;
 	}
 	sk->sk_data_ready(sk, 0);
 	bh_unlock_sock(child);

net/ipv4/tcp_minisocks.c

@@ -510,6 +510,7 @@ struct sock *tcp_create_openreq_child(struct sock *sk, struct request_sock *req,
 		newtp->rx_opt.mss_clamp = req->mss;
 		TCP_ECN_openreq_child(newtp, req);
 		newtp->fastopen_rsk = NULL;
+		newtp->syn_data_acked = 0;
 
 		TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_PASSIVEOPENS);
 	}