TCPCT part 1c: sysctl_tcp_cookie_size, socket option TCP_COOKIE_TRANSACTIONS

Define sysctl (tcp_cookie_size) to turn on and off the cookie option
default globally, instead of a compiled configuration option.

Define per socket option (TCP_COOKIE_TRANSACTIONS) for setting constant
data values, retrieving variable cookie values, and other facilities.

Move inline tcp_clear_options() unchanged from net/tcp.h to linux/tcp.h,
near its corresponding struct tcp_options_received (prior to changes).

This is a straightforward re-implementation of an earlier (year-old)
patch that no longer applies cleanly, with permission of the original
author (Adam Langley):

    http://thread.gmane.org/gmane.linux.network/102586

These functions will also be used in subsequent patches that implement
additional features.

Requires:
   net: TCP_MSS_DEFAULT, TCP_MSS_DESIRED

Signed-off-by: William.Allen.Simpson@gmail.com
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 8 insertions, 0 deletions

diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index 554440af675..989f5538b8d 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -164,6 +164,14 @@ tcp_congestion_control - STRING
 	additional choices may be available based on kernel configuration.
 	Default is set as part of kernel configuration.
 
+tcp_cookie_size - INTEGER
+	Default size of TCP Cookie Transactions (TCPCT) option, that may be
+	overridden on a per socket basis by the TCPCT socket option.
+	Values greater than the maximum (16) are interpreted as the maximum.
+	Values greater than zero and less than the minimum (8) are interpreted
+	as the minimum.  Odd values are interpreted as the next even value.
+	Default: 0 (off).
+
 tcp_dsack - BOOLEAN
 	Allows TCP to send "duplicate" SACKs.