[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, 2 insertions, 1 deletions

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 25ecc6e2478b..4c6ef47eb1c3 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1726,7 +1726,8 @@ static void get_tcp4_sock(struct sock *sp, char *tmpbuf, int i)
         sprintf(tmpbuf, "%4d: %08X:%04X %08X:%04X %02X %08X:%08X %02X:%08lX "
                         "%08X %5d %8d %lu %d %p %u %u %u %u %d",
                 i, src, srcp, dest, destp, sp->sk_state,
-                tp->write_seq - tp->snd_una, tp->rcv_nxt - tp->copied_seq,
+                tp->write_seq - tp->snd_una,
+                (sp->sk_state == TCP_LISTEN) ? sp->sk_ack_backlog : (tp->rcv_nxt - tp->copied_seq),
                 timer_active,
                 jiffies_to_clock_t(timer_expires - jiffies),
                 icsk->icsk_retransmits,