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

Signed-off-by: Benoit Sigoure <redacted>
---
 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))