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>

1 files changed, 8 insertions, 2 deletions

diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index 07a02f6e9696..edc414625be2 100644
--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -556,11 +556,12 @@ int inet_dgram_connect(struct socket *sock, struct sockaddr *uaddr,
 }
 EXPORT_SYMBOL(inet_dgram_connect);
 
-static long inet_wait_for_connect(struct sock *sk, long timeo)
+static long inet_wait_for_connect(struct sock *sk, long timeo, int writebias)
 {
         DEFINE_WAIT(wait);
 
         prepare_to_wait(sk_sleep(sk), &wait, TASK_INTERRUPTIBLE);
+        sk->sk_write_pending += writebias;
 
         /* Basic assumption: if someone sets sk->sk_err, he _must_
          * change state of the socket from TCP_SYN_*.
@@ -576,6 +577,7 @@ static long inet_wait_for_connect(struct sock *sk, long timeo)
                 prepare_to_wait(sk_sleep(sk), &wait, TASK_INTERRUPTIBLE);
         }
         finish_wait(sk_sleep(sk), &wait);
+        sk->sk_write_pending -= writebias;
         return timeo;
 }
 
@@ -634,8 +636,12 @@ int inet_stream_connect(struct socket *sock, struct sockaddr *uaddr,
         timeo = sock_sndtimeo(sk, flags & O_NONBLOCK);
 
         if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
+                int writebias = (sk->sk_protocol == IPPROTO_TCP) &&
+                                tcp_sk(sk)->fastopen_req &&
+                                tcp_sk(sk)->fastopen_req->data ? 1 : 0;
+
                 /* Error code is set above */
-                if (!timeo || !inet_wait_for_connect(sk, timeo))
+                if (!timeo || !inet_wait_for_connect(sk, timeo, writebias))
                         goto out;
 
                 err = sock_intr_errno(timeo);