net-tcp: Fast Open base

This patch impelements the common code for both the client and server.

1. TCP Fast Open option processing. Since Fast Open does not have an
   option number assigned by IANA yet, it shares the experiment option
   code 254 by implementing draft-ietf-tcpm-experimental-options
   with a 16 bits magic number 0xF989. This enables global experiments
   without clashing the scarce(2) experimental options available for TCP.

   When the draft status becomes standard (maybe), the client should
   switch to the new option number assigned while the server supports
   both numbers for transistion.

2. The new sysctl tcp_fastopen

3. A place holder init function

Signed-off-by: Yuchung Cheng <ycheng@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 21 insertions, 4 deletions

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 15a7c7bc3e58..4849be76ccd6 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -385,15 +385,17 @@ static inline bool tcp_urg_mode(const struct tcp_sock *tp)
 #define OPTION_MD5              (1 << 2)
 #define OPTION_WSCALE           (1 << 3)
 #define OPTION_COOKIE_EXTENSION (1 << 4)
+#define OPTION_FAST_OPEN_COOKIE (1 << 8)
 
 struct tcp_out_options {
-        u8 options;             /* bit field of OPTION_* */
+        u16 options;            /* bit field of OPTION_* */
+        u16 mss;                /* 0 to disable */
         u8 ws;                  /* window scale, 0 to disable */
         u8 num_sack_blocks;     /* number of SACK blocks to include */
         u8 hash_size;           /* bytes in hash_location */
-        u16 mss;                /* 0 to disable */
-        __u32 tsval, tsecr;     /* need to include OPTION_TS */
         __u8 *hash_location;    /* temporary pointer, overloaded */
+        __u32 tsval, tsecr;     /* need to include OPTION_TS */
+        struct tcp_fastopen_cookie *fastopen_cookie;    /* Fast open cookie */
 };
 
 /* The sysctl int routines are generic, so check consistency here.
@@ -442,7 +444,7 @@ static u8 tcp_cookie_size_check(u8 desired)
 static void tcp_options_write(__be32 *ptr, struct tcp_sock *tp,
                               struct tcp_out_options *opts)
 {
-        u8 options = opts->options;     /* mungable copy */
+        u16 options = opts->options;    /* mungable copy */
 
         /* Having both authentication and cookies for security is redundant,
          * and there's certainly not enough room.  Instead, the cookie-less
@@ -564,6 +566,21 @@ static void tcp_options_write(__be32 *ptr, struct tcp_sock *tp,
 
                 tp->rx_opt.dsack = 0;
         }
+
+        if (unlikely(OPTION_FAST_OPEN_COOKIE & options)) {
+                struct tcp_fastopen_cookie *foc = opts->fastopen_cookie;
+
+                *ptr++ = htonl((TCPOPT_EXP << 24) |
+                               ((TCPOLEN_EXP_FASTOPEN_BASE + foc->len) << 16) |
+                               TCPOPT_FASTOPEN_MAGIC);
+
+                memcpy(ptr, foc->val, foc->len);
+                if ((foc->len & 3) == 2) {
+                        u8 *align = ((u8 *)ptr) + foc->len;
+                        align[0] = align[1] = TCPOPT_NOP;
+                }
+                ptr += (foc->len + 3) >> 2;
+        }
 }
 
 /* Compute TCP options for SYN packets. This is not the final