tcp: TCP Fast Open Server - header & support functions

This patch adds all the necessary data structure and support
functions to implement TFO server side. It also documents a number
of flags for the sysctl_tcp_fastopen knob, and adds a few Linux
extension MIBs.

In addition, it includes the following:

1. a new TCP_FASTOPEN socket option an application must call to
supply a max backlog allowed in order to enable TFO on its listener.

2. A number of key data structures:
"fastopen_rsk" in tcp_sock - for a big socket to access its
request_sock for retransmission and ack processing purpose. It is
non-NULL iff 3WHS not completed.

"fastopenq" in request_sock_queue - points to a per Fast Open
listener data structure "fastopen_queue" to keep track of qlen (# of
outstanding Fast Open requests) and max_qlen, among other things.

"listener" in tcp_request_sock - to point to the original listener
for book-keeping purpose, i.e., to maintain qlen against max_qlen
as part of defense against IP spoofing attack.

3. various data structure and functions, many in tcp_fastopen.c, to
support server side Fast Open cookie operations, including
/proc/sys/net/ipv4/tcp_fastopen_key to allow manual rekeying.

Signed-off-by: H.K. Jerry Chu <hkchu@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 22 insertions, 7 deletions

diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index d64e53124b8c..c7fc10724948 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -467,16 +467,31 @@ tcp_syncookies - BOOLEAN
 tcp_fastopen - INTEGER
         Enable TCP Fast Open feature (draft-ietf-tcpm-fastopen) to send data
         in the opening SYN packet. To use this feature, the client application
-        must not use connect(). Instead, it should use sendmsg() or sendto()
-        with MSG_FASTOPEN flag which performs a TCP handshake automatically.
-
-        The values (bitmap) are:
-        1: Enables sending data in the opening SYN on the client
-        5: Enables sending data in the opening SYN on the client regardless
-           of cookie availability.
+        must use sendmsg() or sendto() with MSG_FASTOPEN flag rather than
+        connect() to perform a TCP handshake automatically.
+
+        The values (bitmap) are
+        1: Enables sending data in the opening SYN on the client.
+        2: Enables TCP Fast Open on the server side, i.e., allowing data in
+           a SYN packet to be accepted and passed to the application before
+           3-way hand shake finishes.
+        4: Send data in the opening SYN regardless of cookie availability and
+           without a cookie option.
+        0x100: Accept SYN data w/o validating the cookie.
+        0x200: Accept data-in-SYN w/o any cookie option present.
+        0x400/0x800: Enable Fast Open on all listeners regardless of the
+           TCP_FASTOPEN socket option. The two different flags designate two
+           different ways of setting max_qlen without the TCP_FASTOPEN socket
+           option.
 
         Default: 0
 
+        Note that the client & server side Fast Open flags (1 and 2
+        respectively) must be also enabled before the rest of flags can take
+        effect.
+
+        See include/net/tcp.h and the code for more details.
+
 tcp_syn_retries - INTEGER
         Number of times initial SYNs for an active TCP connection attempt
         will be retransmitted. Should not be higher than 255. Default value