net-tcp: Fast Open client - sending SYN-data

This patch implements sending SYN-data in tcp_connect(). The data is
from tcp_sendmsg() with flag MSG_FASTOPEN (implemented in a later patch).

The length of the cookie in tcp_fastopen_req, init'd to 0, controls the
type of the SYN. If the cookie is not cached (len==0), the host sends
data-less SYN with Fast Open cookie request option to solicit a cookie
from the remote. If cookie is not available (len > 0), the host sends
a SYN-data with Fast Open cookie option. If cookie length is negative,
  the SYN will not include any Fast Open option (for fall back operations).

To deal with middleboxes that may drop SYN with data or experimental TCP
option, the SYN-data is only sent once. SYN retransmits do not include
data or Fast Open options. The connection will fall back to regular TCP
handshake.

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

3 files changed, 15 insertions, 1 deletions

diff --git a/include/linux/snmp.h b/include/linux/snmp.h
index e5fcbd079e4a..00bc189cb395 100644
--- a/include/linux/snmp.h
+++ b/include/linux/snmp.h
@@ -238,6 +238,7 @@ enum
         LINUX_MIB_TCPOFOMERGE,                  /* TCPOFOMerge */
         LINUX_MIB_TCPCHALLENGEACK,              /* TCPChallengeACK */
         LINUX_MIB_TCPSYNCHALLENGE,              /* TCPSYNChallenge */
+        LINUX_MIB_TCPFASTOPENACTIVE,            /* TCPFastOpenActive */
         __LINUX_MIB_MAX
 };
 
diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 12948f543839..1edf96afab44 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -386,7 +386,8 @@ struct tcp_sock {
                 unused      : 1;
         u8      repair_queue;
         u8      do_early_retrans:1,/* Enable RFC5827 early-retransmit  */
-                early_retrans_delayed:1; /* Delayed ER timer installed */
+                early_retrans_delayed:1, /* Delayed ER timer installed */
+                syn_fastopen:1; /* SYN includes Fast Open option */
 
 /* RTT measurement */
         u32     srtt;           /* smoothed round trip time << 3        */
@@ -500,6 +501,9 @@ struct tcp_sock {
         struct tcp_md5sig_info  __rcu *md5sig_info;
 #endif
 
+/* TCP fastopen related information */
+        struct tcp_fastopen_request *fastopen_req;
+
         /* When the cookie options are generated and exchanged, then this
          * object holds a reference to them (cookie_values->kref).  Also
          * contains related tcp_cookie_transactions fields.
diff --git a/include/net/tcp.h b/include/net/tcp.h
index e601da197361..867557b4244a 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1289,6 +1289,15 @@ extern int tcp_md5_hash_skb_data(struct tcp_md5sig_pool *, const struct sk_buff
 extern int tcp_md5_hash_key(struct tcp_md5sig_pool *hp,
                             const struct tcp_md5sig_key *key);
 
+struct tcp_fastopen_request {
+        /* Fast Open cookie. Size 0 means a cookie request */
+        struct tcp_fastopen_cookie      cookie;
+        struct msghdr                   *data;  /* data in MSG_FASTOPEN */
+        u16                             copied; /* queued in tcp_connect() */
+};
+
+void tcp_free_fastopen_req(struct tcp_sock *tp);
+
 /* write queue abstraction */
 static inline void tcp_write_queue_purge(struct sock *sk)
 {