[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>

1 files changed, 41 insertions, 0 deletions

diff --git a/Documentation/networking/dccp.txt b/Documentation/networking/dccp.txt
index a8142a81038..c2328c862e9 100644
--- a/Documentation/networking/dccp.txt
+++ b/Documentation/networking/dccp.txt
@@ -63,6 +63,47 @@ DCCP_SOCKOPT_SEND_CSCOV is for the receiver and has a different meaning: it
         coverage value are also acceptable. The higher the number, the more
         restrictive this setting (see [RFC 4340, sec. 9.2.1]).
 
+Sysctl variables
+================
+Several DCCP default parameters can be managed by the following sysctls
+(sysctl net.dccp.default or /proc/sys/net/dccp/default):
+
+request_retries
+        The number of active connection initiation retries (the number of
+        Requests minus one) before timing out. In addition, it also governs
+        the behaviour of the other, passive side: this variable also sets
+        the number of times DCCP repeats sending a Response when the initial
+        handshake does not progress from RESPOND to OPEN (i.e. when no Ack
+        is received after the initial Request).  This value should be greater
+        than 0, suggested is less than 10. Analogue of tcp_syn_retries.
+
+retries1
+        How often a DCCP Response is retransmitted until the listening DCCP
+        side considers its connecting peer dead. Analogue of tcp_retries1.
+
+retries2
+        The number of times a general DCCP packet is retransmitted. This has
+        importance for retransmitted acknowledgments and feature negotiation,
+        data packets are never retransmitted. Analogue of tcp_retries2.
+
+send_ndp = 1
+        Whether or not to send NDP count options (sec. 7.7.2).
+
+send_ackvec = 1
+        Whether or not to send Ack Vector options (sec. 11.5).
+
+ack_ratio = 2
+        The default Ack Ratio (sec. 11.3) to use.
+
+tx_ccid = 2
+        Default CCID for the sender-receiver half-connection.
+
+rx_ccid = 2
+        Default CCID for the receiver-sender half-connection.
+
+seq_window = 100
+        The initial sequence window (sec. 7.5.2).
+
 Notes
 =====