tcp: Add TCP_USER_TIMEOUT socket option.

This patch provides a "user timeout" support as described in RFC793. The
socket option is also needed for the the local half of RFC5482 "TCP User
Timeout Option".

TCP_USER_TIMEOUT is a TCP level socket option that takes an unsigned int,
when > 0, to specify the maximum amount of time in ms that transmitted
data may remain unacknowledged before TCP will forcefully close the
corresponding connection and return ETIMEDOUT to the application. If
0 is given, TCP will continue to use the system default.

Increasing the user timeouts allows a TCP connection to survive extended
periods without end-to-end connectivity. Decreasing the user timeouts
allows applications to "fail fast" if so desired. Otherwise it may take
upto 20 minutes with the current system defaults in a normal WAN
environment.

The socket option can be made during any state of a TCP connection, but
is only effective during the synchronized states of a connection
(ESTABLISHED, FIN-WAIT-1, FIN-WAIT-2, CLOSE-WAIT, CLOSING, or LAST-ACK).
Moreover, when used with the TCP keepalive (SO_KEEPALIVE) option,
TCP_USER_TIMEOUT will overtake keepalive to determine when to close a
connection due to keepalive failure.

The option does not change in anyway when TCP retransmits a packet, nor
when a keepalive probe will be sent.

This option, like many others, will be inherited by an acceptor from its
listener.

Signed-off-by: H.K. Jerry Chu <hkchu@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 10 insertions, 1 deletions

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 176e11aaea77..cf3254528753 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2391,7 +2391,12 @@ static int do_tcp_setsockopt(struct sock *sk, int level,
                 err = tp->af_specific->md5_parse(sk, optval, optlen);
                 break;
 #endif
-
+        case TCP_USER_TIMEOUT:
+                /* Cap the max timeout in ms TCP will retry/retrans
+                 * before giving up and aborting (ETIMEDOUT) a connection.
+                 */
+                icsk->icsk_user_timeout = msecs_to_jiffies(val);
+                break;
         default:
                 err = -ENOPROTOOPT;
                 break;
@@ -2610,6 +2615,10 @@ static int do_tcp_getsockopt(struct sock *sk, int level,
         case TCP_THIN_DUPACK:
                 val = tp->thin_dupack;
                 break;
+
+        case TCP_USER_TIMEOUT:
+                val = jiffies_to_msecs(icsk->icsk_user_timeout);
+                break;
         default:
                 return -ENOPROTOOPT;
         }