[TCP]: Export accept queue len of a TCP listening socket via rx_queue

While debugging a TCP server hang issue, we noticed that currently there is
no way for a user to get the acceptq backlog value for a TCP listen socket.

All the standard networking utilities that display socket info like netstat,
ss and /proc/net/tcp have 2 fields called rx_queue and tx_queue. These
fields do not mean much for listening sockets. This patch uses one of these
unused fields(rx_queue) to export the accept queue len for listening sockets.

Signed-off-by: Sridhar Samudrala <sri@us.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 1 deletions

diff --git a/net/ipv4/tcp_diag.c b/net/ipv4/tcp_diag.c
index c148c1081880..b56399c7cc12 100644
--- a/net/ipv4/tcp_diag.c
+++ b/net/ipv4/tcp_diag.c
@@ -26,7 +26,10 @@ static void tcp_diag_get_info(struct sock *sk, struct inet_diag_msg *r,
         const struct tcp_sock *tp = tcp_sk(sk);
         struct tcp_info *info = _info;
 
-        r->idiag_rqueue = tp->rcv_nxt - tp->copied_seq;
+        if (sk->sk_state == TCP_LISTEN)
+                r->idiag_rqueue = sk->sk_ack_backlog;
+        else
+                r->idiag_rqueue = tp->rcv_nxt - tp->copied_seq;
         r->idiag_wqueue = tp->write_seq - tp->snd_una;
         if (info != NULL)
                 tcp_get_info(sk, info);