tcp: add tcpi_min_rtt and tcpi_notsent_bytes to tcp_info

tcpi_min_rtt reports the minimal rtt observed by TCP stack for the flow,
in usec unit. Might be ~0U if not yet known.

tcpi_notsent_bytes reports the amount of bytes in the write queue that
were not yet sent.

This is done in a single patch to not add a temporary 32bit padding hole
in tcp_info.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/uapi/linux/tcp.h

@@ -196,6 +196,9 @@ struct tcp_info {
 	__u64	tcpi_bytes_received; /* RFC4898 tcpEStatsAppHCThruOctetsReceived */
 	__u32	tcpi_segs_out;	     /* RFC4898 tcpEStatsPerfSegsOut */
 	__u32	tcpi_segs_in;	     /* RFC4898 tcpEStatsPerfSegsIn */
+
+	__u32	tcpi_notsent_bytes;
+	__u32	tcpi_min_rtt;
 };
 
 /* for TCP_MD5SIG socket option */

net/ipv4/tcp.c

@@ -2642,6 +2642,7 @@ void tcp_get_info(struct sock *sk, struct tcp_info *info)
 	const struct inet_connection_sock *icsk = inet_csk(sk);
 	u32 now = tcp_time_stamp;
 	unsigned int start;
+	int notsent_bytes;
 	u64 rate64;
 	u32 rate;
 
@@ -2722,6 +2723,11 @@ void tcp_get_info(struct sock *sk, struct tcp_info *info)
 	} while (u64_stats_fetch_retry_irq(&tp->syncp, start));
 	info->tcpi_segs_out = tp->segs_out;
 	info->tcpi_segs_in = tp->segs_in;
+
+	notsent_bytes = READ_ONCE(tp->write_seq) - READ_ONCE(tp->snd_nxt);
+	info->tcpi_notsent_bytes = max(0, notsent_bytes);
+
+	info->tcpi_min_rtt = tcp_min_rtt(tp);
 }
 EXPORT_SYMBOL_GPL(tcp_get_info);