tcp: Add a TCP_FASTOPEN socket option to get a max backlog on its listner

This patch adds a TCP_FASTOPEN socket option to get a max backlog on its
listener to getsockopt().

Signed-off-by: Kenjiro Nakayama <nakayamakenjiro@gmail.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 8 insertions, 0 deletions

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 4bd6d52eeffb..eb1dde37e678 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2916,6 +2916,14 @@ static int do_tcp_getsockopt(struct sock *sk, int level,
         case TCP_USER_TIMEOUT:
                 val = jiffies_to_msecs(icsk->icsk_user_timeout);
                 break;
+
+        case TCP_FASTOPEN:
+                if (icsk->icsk_accept_queue.fastopenq != NULL)
+                        val = icsk->icsk_accept_queue.fastopenq->max_qlen;
+                else
+                        val = 0;
+                break;
+
         case TCP_TIMESTAMP:
                 val = tcp_time_stamp + tp->tsoffset;
                 break;