[DCCP]: Add sysctls to control retransmission behaviour

This adds 3 sysctls which govern the retransmission behaviour of DCCP control
packets (3way handshake, feature negotiation).

It removes 4 FIXMEs from the code.

The close resemblance of sysctl variables to their TCP analogues is emphasised
not only by their name, but also by giving them the same initial values.
This is useful since there is not much practical experience with DCCP yet.

Furthermore, with regard to the previous patch, it is now possible to limit
the number of keepalive-Responses by setting net.dccp.default.request_retries
(also a bit like in TCP).

Lastly, added documentation of all existing DCCP sysctls.

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
diff --git a/net/dccp/dccp.h b/net/dccp/dccp.h
index d5c414b..e7b96074 100644
--- a/net/dccp/dccp.h
+++ b/net/dccp/dccp.h
@@ -64,6 +64,17 @@
 
 #define DCCP_XMIT_TIMEO 30000 /* Time/msecs for blocking transmit per packet */
 
+/* sysctl variables for DCCP */
+extern int  sysctl_dccp_request_retries;
+extern int  sysctl_dccp_retries1;
+extern int  sysctl_dccp_retries2;
+extern int  dccp_feat_default_sequence_window;
+extern int  dccp_feat_default_rx_ccid;
+extern int  dccp_feat_default_tx_ccid;
+extern int  dccp_feat_default_ack_ratio;
+extern int  dccp_feat_default_send_ack_vector;
+extern int  dccp_feat_default_send_ndp_count;
+
 /* is seq1 < seq2 ? */
 static inline int before48(const u64 seq1, const u64 seq2)
 {
diff --git a/net/dccp/feat.h b/net/dccp/feat.h
index cee553d..6048373 100644
--- a/net/dccp/feat.h
+++ b/net/dccp/feat.h
@@ -26,11 +26,4 @@
 extern int  dccp_feat_clone(struct sock *oldsk, struct sock *newsk);
 extern int  dccp_feat_init(struct dccp_minisock *dmsk);
 
-extern int  dccp_feat_default_sequence_window;
-extern int  dccp_feat_default_rx_ccid;
-extern int  dccp_feat_default_tx_ccid;
-extern int  dccp_feat_default_ack_ratio;
-extern int  dccp_feat_default_send_ack_vector;
-extern int  dccp_feat_default_send_ndp_count;
-
 #endif /* _DCCP_FEAT_H */
diff --git a/net/dccp/proto.c b/net/dccp/proto.c
index db54e55..9c9c08c 100644
--- a/net/dccp/proto.c
+++ b/net/dccp/proto.c
@@ -212,6 +212,7 @@
 
 	dccp_init_xmit_timers(sk);
 	icsk->icsk_rto		= DCCP_TIMEOUT_INIT;
+	icsk->icsk_syn_retries	= sysctl_dccp_request_retries;
 	sk->sk_state		= DCCP_CLOSED;
 	sk->sk_write_space	= dccp_write_space;
 	icsk->icsk_sync_mss	= dccp_sync_mss;
diff --git a/net/dccp/sysctl.c b/net/dccp/sysctl.c
index 38bc157..7b09f21 100644
--- a/net/dccp/sysctl.c
+++ b/net/dccp/sysctl.c
@@ -11,6 +11,7 @@
 
 #include <linux/mm.h>
 #include <linux/sysctl.h>
+#include "dccp.h"
 #include "feat.h"
 
 #ifndef CONFIG_SYSCTL
@@ -66,6 +67,30 @@
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec,
 	},
+	{
+		.ctl_name	= NET_DCCP_DEFAULT_REQ_RETRIES,
+		.procname	= "request_retries",
+		.data		= &sysctl_dccp_request_retries,
+		.maxlen		= sizeof(sysctl_dccp_request_retries),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec,
+	},
+	{
+		.ctl_name	= NET_DCCP_DEFAULT_RETRIES1,
+		.procname	= "retries1",
+		.data		= &sysctl_dccp_retries1,
+		.maxlen		= sizeof(sysctl_dccp_retries1),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec,
+	},
+	{
+		.ctl_name	= NET_DCCP_DEFAULT_RETRIES2,
+		.procname	= "retries2",
+		.data		= &sysctl_dccp_retries2,
+		.maxlen		= sizeof(sysctl_dccp_retries2),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec,
+	},
 	{ .ctl_name = 0, }
 };
 
diff --git a/net/dccp/timer.c b/net/dccp/timer.c
index bda0af6..7b3f16e 100644
--- a/net/dccp/timer.c
+++ b/net/dccp/timer.c
@@ -15,6 +15,11 @@
 
 #include "dccp.h"
 
+/* sysctl variables governing numbers of retransmission attempts */
+int  sysctl_dccp_request_retries	__read_mostly = TCP_SYN_RETRIES;
+int  sysctl_dccp_retries1		__read_mostly = TCP_RETR1;
+int  sysctl_dccp_retries2		__read_mostly = TCP_RETR2;
+
 static void dccp_write_timer(unsigned long data);
 static void dccp_keepalive_timer(unsigned long data);
 static void dccp_delack_timer(unsigned long data);
@@ -44,11 +49,10 @@
 	if (sk->sk_state == DCCP_REQUESTING || sk->sk_state == DCCP_PARTOPEN) {
 		if (icsk->icsk_retransmits != 0)
 			dst_negative_advice(&sk->sk_dst_cache);
-		retry_until = icsk->icsk_syn_retries ? :
-			    /* FIXME! */ 3 /* FIXME! sysctl_tcp_syn_retries */;
+		retry_until = icsk->icsk_syn_retries ?
+			    : sysctl_dccp_request_retries;
 	} else {
-		if (icsk->icsk_retransmits >=
-		     /* FIXME! sysctl_tcp_retries1 */ 5 /* FIXME! */) {
+		if (icsk->icsk_retransmits >= sysctl_dccp_retries1) {
 			/* NOTE. draft-ietf-tcpimpl-pmtud-01.txt requires pmtu
 			   black hole detection. :-(
 
@@ -72,7 +76,7 @@
 			dst_negative_advice(&sk->sk_dst_cache);
 		}
 
-		retry_until = /* FIXME! */ 15 /* FIXME! sysctl_tcp_retries2 */;
+		retry_until = sysctl_dccp_retries2;
 		/*
 		 * FIXME: see tcp_write_timout and tcp_out_of_resources
 		 */
@@ -196,7 +200,7 @@
 	icsk->icsk_rto = min(icsk->icsk_rto << 1, DCCP_RTO_MAX);
 	inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto,
 				  DCCP_RTO_MAX);
-	if (icsk->icsk_retransmits > 3 /* FIXME: sysctl_dccp_retries1 */)
+	if (icsk->icsk_retransmits > sysctl_dccp_retries1)
 		__sk_dst_reset(sk);
 out:;
 }