[PATCH] tcp: Expose the initial RTO via a new sysctl.

[Benoit Sigoure <tsunanet@gmail.com>]

Instead of hardcoding the initial RTO to 3s and requiring
the kernel to be recompiled to change it, expose it as a
sysctl that can be tuned at runtime.  Leave the default
value unchanged.

Signed-off-by: Benoit Sigoure <tsunanet@gmail.com>
---
 Documentation/networking/ip-sysctl.txt |    6 ++++++
 include/linux/sysctl.h                 |    1 +
 include/net/tcp.h                      |    3 ++-
 kernel/sysctl_binary.c                 |    1 +
 net/ipv4/syncookies.c                  |    2 +-
 net/ipv4/sysctl_net_ipv4.c             |   11 +++++++++++
 net/ipv4/tcp.c                         |    4 ++--
 net/ipv4/tcp_input.c                   |    8 ++++----
 net/ipv4/tcp_ipv4.c                    |    6 +++---
 net/ipv4/tcp_minisocks.c               |    6 +++---
 net/ipv4/tcp_output.c                  |    2 +-
 net/ipv4/tcp_timer.c                   |    9 +++++----
 net/ipv6/syncookies.c                  |    2 +-
 net/ipv6/tcp_ipv6.c                    |    6 +++---
 14 files changed, 44 insertions(+), 23 deletions(-)

diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index d3d653a..c381c68 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -384,6 +384,12 @@ tcp_retries2 - INTEGER
 	RFC 1122 recommends at least 100 seconds for the timeout,
 	which corresponds to a value of at least 8.
 
+tcp_initial_rto - INTEGER
+	This value sets the initial retransmit timeout, that is how long
+	the kernel will wait before retransmitting the initial SYN packet.
+
+	RFC 1122 says that this SHOULD be 3 seconds, which is the default.
+
 tcp_rfc1337 - BOOLEAN
 	If set, the TCP stack behaves conforming to RFC1337. If unset,
 	we are not conforming to RFC, but prevent TCP TIME_WAIT
diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index 11684d9..96a9b41 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -425,6 +425,7 @@ enum
 	NET_TCP_ALLOWED_CONG_CONTROL=123,
 	NET_TCP_MAX_SSTHRESH=124,
 	NET_TCP_FRTO_RESPONSE=125,
+        NET_IPV4_TCP_INITIAL_RTO=126,
 };
 
 enum {
diff --git a/include/net/tcp.h b/include/net/tcp.h
index cda30ea..a2bb0f1 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -213,6 +213,7 @@ extern int sysctl_tcp_syn_retries;
 extern int sysctl_tcp_synack_retries;
 extern int sysctl_tcp_retries1;
 extern int sysctl_tcp_retries2;
+extern int sysctl_tcp_initial_rto;
 extern int sysctl_tcp_orphan_retries;
 extern int sysctl_tcp_syncookies;
 extern int sysctl_tcp_retrans_collapse;
@@ -295,7 +296,7 @@ static inline void tcp_synq_overflow(struct sock *sk)
 static inline int tcp_synq_no_recent_overflow(const struct sock *sk)
 {
 	unsigned long last_overflow = tcp_sk(sk)->rx_opt.ts_recent_stamp;
-	return time_after(jiffies, last_overflow + TCP_TIMEOUT_INIT);
+	return time_after(jiffies, last_overflow + sysctl_tcp_initial_rto);
 }
 
 extern struct proto tcp_prot;
diff --git a/kernel/sysctl_binary.c b/kernel/sysctl_binary.c
index 3b8e028..d608d84 100644
--- a/kernel/sysctl_binary.c
+++ b/kernel/sysctl_binary.c
@@ -354,6 +354,7 @@ static const struct bin_table bin_net_ipv4_table[] = {
 	{ CTL_INT,	NET_IPV4_TCP_KEEPALIVE_INTVL,		"tcp_keepalive_intvl" },
 	{ CTL_INT,	NET_IPV4_TCP_RETRIES1,			"tcp_retries1" },
 	{ CTL_INT,	NET_IPV4_TCP_RETRIES2,			"tcp_retries2" },
+	{ CTL_INT,	NET_IPV4_TCP_INITIAL_RTO,		"tcp_initial_rto" },
 	{ CTL_INT,	NET_IPV4_TCP_FIN_TIMEOUT,		"tcp_fin_timeout" },
 	{ CTL_INT,	NET_TCP_SYNCOOKIES,			"tcp_syncookies" },
 	{ CTL_INT,	NET_TCP_TW_RECYCLE,			"tcp_tw_recycle" },
diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index 8b44c6d..089bc92 100644
--- a/net/ipv4/syncookies.c
+++ b/net/ipv4/syncookies.c
@@ -186,7 +186,7 @@ __u32 cookie_v4_init_sequence(struct sock *sk, struct sk_buff *skb, __u16 *mssp)
  * sysctl_tcp_retries1. It's a rather complicated formula (exponential
  * backoff) to compute at runtime so it's currently hardcoded here.
  */
-#define COUNTER_TRIES 4
+#define COUNTER_TRIES (sysctl_tcp_initial_rto + 1)
 /*
  * Check if a ack sequence number is a valid syncookie.
  * Return the decoded mss if it is, or 0 if not.
diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index 321e6e8..24dc21d 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -30,6 +30,8 @@ static int tcp_adv_win_scale_min = -31;
 static int tcp_adv_win_scale_max = 31;
 static int ip_ttl_min = 1;
 static int ip_ttl_max = 255;
+static int tcp_initial_rto_min = TCP_RTO_MIN;
+static int tcp_initial_rto_max = TCP_RTO_MAX;
 
 /* Update system visible IP port range */
 static void set_local_port_range(int range[2])
@@ -246,6 +248,15 @@ static struct ctl_table ipv4_table[] = {
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec
 	},
+        {
+		.procname       = "tcp_initial_rto",
+		.data           = &sysctl_tcp_initial_rto,
+		.maxlen         = sizeof(int),
+		.mode           = 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= &tcp_initial_rto_min,
+		.extra2		= &tcp_initial_rto_max,
+	},
 	{
 		.procname	= "tcp_fin_timeout",
 		.data		= &sysctl_tcp_fin_timeout,
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index b22d450..e9e7c3f 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2352,7 +2352,7 @@ static int do_tcp_setsockopt(struct sock *sk, int level,
 	case TCP_DEFER_ACCEPT:
 		/* Translate value in seconds to number of retransmits */
 		icsk->icsk_accept_queue.rskq_defer_accept =
-			secs_to_retrans(val, TCP_TIMEOUT_INIT / HZ,
+			secs_to_retrans(val, sysctl_tcp_initial_rto / HZ,
 					TCP_RTO_MAX / HZ);
 		break;
 
@@ -2539,7 +2539,7 @@ static int do_tcp_getsockopt(struct sock *sk, int level,
 		break;
 	case TCP_DEFER_ACCEPT:
 		val = retrans_to_secs(icsk->icsk_accept_queue.rskq_defer_accept,
-				      TCP_TIMEOUT_INIT / HZ, TCP_RTO_MAX / HZ);
+				      sysctl_tcp_initial_rto / HZ, TCP_RTO_MAX / HZ);
 		break;
 	case TCP_WINDOW_CLAMP:
 		val = tp->window_clamp;
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index bef9f04..39f6c27 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -890,7 +890,7 @@ static void tcp_init_metrics(struct sock *sk)
 	if (dst_metric(dst, RTAX_RTT) == 0)
 		goto reset;
 
-	if (!tp->srtt && dst_metric_rtt(dst, RTAX_RTT) < (TCP_TIMEOUT_INIT << 3))
+	if (!tp->srtt && dst_metric_rtt(dst, RTAX_RTT) < (sysctl_tcp_initial_rto << 3))
 		goto reset;
 
 	/* Initial rtt is determined from SYN,SYN-ACK.
@@ -916,7 +916,7 @@ static void tcp_init_metrics(struct sock *sk)
 		tp->mdev_max = tp->rttvar = max(tp->mdev, tcp_rto_min(sk));
 	}
 	tcp_set_rto(sk);
-	if (inet_csk(sk)->icsk_rto < TCP_TIMEOUT_INIT && !tp->rx_opt.saw_tstamp) {
+	if (inet_csk(sk)->icsk_rto < sysctl_tcp_initial_rto && !tp->rx_opt.saw_tstamp) {
 reset:
 		/* Play conservative. If timestamps are not
 		 * supported, TCP will fail to recalculate correct
@@ -924,8 +924,8 @@ reset:
 		 */
 		if (!tp->rx_opt.saw_tstamp && tp->srtt) {
 			tp->srtt = 0;
-			tp->mdev = tp->mdev_max = tp->rttvar = TCP_TIMEOUT_INIT;
-			inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
+			tp->mdev = tp->mdev_max = tp->rttvar = sysctl_tcp_initial_rto;
+			inet_csk(sk)->icsk_rto = sysctl_tcp_initial_rto;
 		}
 	}
 	tp->snd_cwnd = tcp_init_cwnd(tp, dst);
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index f7e6c2c..21920e6 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1383,7 +1383,7 @@ int tcp_v4_conn_request(struct sock *sk, struct sk_buff *skb)
 	    want_cookie)
 		goto drop_and_free;
 
-	inet_csk_reqsk_queue_hash_add(sk, req, TCP_TIMEOUT_INIT);
+	inet_csk_reqsk_queue_hash_add(sk, req, sysctl_tcp_initial_rto);
 	return 0;
 
 drop_and_release:
@@ -1834,8 +1834,8 @@ static int tcp_v4_init_sock(struct sock *sk)
 	tcp_init_xmit_timers(sk);
 	tcp_prequeue_init(tp);
 
-	icsk->icsk_rto = TCP_TIMEOUT_INIT;
-	tp->mdev = TCP_TIMEOUT_INIT;
+	icsk->icsk_rto = sysctl_tcp_initial_rto;
+	tp->mdev = sysctl_tcp_initial_rto;
 
 	/* So many TCP implementations out there (incorrectly) count the
 	 * initial SYN frame in their delayed-ACK and congestion control
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 80b1f80..c63ffa0 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -472,8 +472,8 @@ struct sock *tcp_create_openreq_child(struct sock *sk, struct request_sock *req,
 		tcp_init_wl(newtp, treq->rcv_isn);
 
 		newtp->srtt = 0;
-		newtp->mdev = TCP_TIMEOUT_INIT;
-		newicsk->icsk_rto = TCP_TIMEOUT_INIT;
+		newtp->mdev = sysctl_tcp_initial_rto;
+		newicsk->icsk_rto = sysctl_tcp_initial_rto;
 
 		newtp->packets_out = 0;
 		newtp->retrans_out = 0;
@@ -582,7 +582,7 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
 			 * it can be estimated (approximately)
 			 * from another data.
 			 */
-			tmp_opt.ts_recent_stamp = get_seconds() - ((TCP_TIMEOUT_INIT/HZ)<<req->retrans);
+			tmp_opt.ts_recent_stamp = get_seconds() - ((sysctl_tcp_initial_rto/HZ)<<req->retrans);
 			paws_reject = tcp_paws_reject(&tmp_opt, th->rst);
 		}
 	}
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 17388c7..e34b0f6 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2599,7 +2599,7 @@ static void tcp_connect_init(struct sock *sk)
 	tp->rcv_wup = 0;
 	tp->copied_seq = 0;
 
-	inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
+	inet_csk(sk)->icsk_rto = sysctl_tcp_initial_rto;
 	inet_csk(sk)->icsk_retransmits = 0;
 	tcp_clear_retrans(tp);
 }
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index ecd44b0..b9da62b 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -29,6 +29,7 @@ int sysctl_tcp_keepalive_probes __read_mostly = TCP_KEEPALIVE_PROBES;
 int sysctl_tcp_keepalive_intvl __read_mostly = TCP_KEEPALIVE_INTVL;
 int sysctl_tcp_retries1 __read_mostly = TCP_RETR1;
 int sysctl_tcp_retries2 __read_mostly = TCP_RETR2;
+int sysctl_tcp_initial_rto __read_mostly = TCP_TIMEOUT_INIT;
 int sysctl_tcp_orphan_retries __read_mostly;
 int sysctl_tcp_thin_linear_timeouts __read_mostly;
 
@@ -135,8 +136,8 @@ static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk)
 
 /* This function calculates a "timeout" which is equivalent to the timeout of a
  * TCP connection after "boundary" unsuccessful, exponentially backed-off
- * retransmissions with an initial RTO of TCP_RTO_MIN or TCP_TIMEOUT_INIT if
- * syn_set flag is set.
+ * retransmissions with an initial RTO of TCP_RTO_MIN or
+ * sysctl_tcp_initial_rto if syn_set flag is set.
  */
 static bool retransmits_timed_out(struct sock *sk,
 				  unsigned int boundary,
@@ -144,7 +145,7 @@ static bool retransmits_timed_out(struct sock *sk,
 				  bool syn_set)
 {
 	unsigned int linear_backoff_thresh, start_ts;
-	unsigned int rto_base = syn_set ? TCP_TIMEOUT_INIT : TCP_RTO_MIN;
+	unsigned int rto_base = syn_set ? sysctl_tcp_initial_rto : TCP_RTO_MIN;
 
 	if (!inet_csk(sk)->icsk_retransmits)
 		return false;
@@ -495,7 +496,7 @@ out_unlock:
 static void tcp_synack_timer(struct sock *sk)
 {
 	inet_csk_reqsk_queue_prune(sk, TCP_SYNQ_INTERVAL,
-				   TCP_TIMEOUT_INIT, TCP_RTO_MAX);
+				   sysctl_tcp_initial_rto, TCP_RTO_MAX);
 }
 
 void tcp_syn_ack_timeout(struct sock *sk, struct request_sock *req)
diff --git a/net/ipv6/syncookies.c b/net/ipv6/syncookies.c
index 352c260..50baaec 100644
--- a/net/ipv6/syncookies.c
+++ b/net/ipv6/syncookies.c
@@ -45,7 +45,7 @@ static __u16 const msstab[] = {
  * sysctl_tcp_retries1. It's a rather complicated formula (exponential
  * backoff) to compute at runtime so it's currently hardcoded here.
  */
-#define COUNTER_TRIES 4
+#define COUNTER_TRIES (sysctl_tcp_initial_rto + 1)
 
 static inline struct sock *get_cookie_sock(struct sock *sk, struct sk_buff *skb,
 					   struct request_sock *req,
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 4f49e5d..7e791e6 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -1349,7 +1349,7 @@ have_isn:
 	    want_cookie)
 		goto drop_and_free;
 
-	inet6_csk_reqsk_queue_hash_add(sk, req, TCP_TIMEOUT_INIT);
+	inet6_csk_reqsk_queue_hash_add(sk, req, sysctl_tcp_initial_rto);
 	return 0;
 
 drop_and_release:
@@ -1957,8 +1957,8 @@ static int tcp_v6_init_sock(struct sock *sk)
 	tcp_init_xmit_timers(sk);
 	tcp_prequeue_init(tp);
 
-	icsk->icsk_rto = TCP_TIMEOUT_INIT;
-	tp->mdev = TCP_TIMEOUT_INIT;
+	icsk->icsk_rto = sysctl_tcp_initial_rto;
+	tp->mdev = sysctl_tcp_initial_rto;
 
 	/* So many TCP implementations out there (incorrectly) count the
 	 * initial SYN frame in their delayed-ACK and congestion control
-- 
1.7.0.4