net/tcp-fastopen: Add new API support

This patch adds a new socket option, TCP_FASTOPEN_CONNECT, as an
alternative way to perform Fast Open on the active side (client). Prior
to this patch, a client needs to replace the connect() call with
sendto(MSG_FASTOPEN). This can be cumbersome for applications who want
to use Fast Open: these socket operations are often done in lower layer
libraries used by many other applications. Changing these libraries
and/or the socket call sequences are not trivial. A more convenient
approach is to perform Fast Open by simply enabling a socket option when
the socket is created w/o changing other socket calls sequence:
  s = socket()
    create a new socket
  setsockopt(s, IPPROTO_TCP, TCP_FASTOPEN_CONNECT …);
    newly introduced sockopt
    If set, new functionality described below will be used.
    Return ENOTSUPP if TFO is not supported or not enabled in the
    kernel.

  connect()
    With cookie present, return 0 immediately.
    With no cookie, initiate 3WHS with TFO cookie-request option and
    return -1 with errno = EINPROGRESS.

  write()/sendmsg()
    With cookie present, send out SYN with data and return the number of
    bytes buffered.
    With no cookie, and 3WHS not yet completed, return -1 with errno =
    EINPROGRESS.
    No MSG_FASTOPEN flag is needed.

  read()
    Return -1 with errno = EWOULDBLOCK/EAGAIN if connect() is called but
    write() is not called yet.
    Return -1 with errno = EWOULDBLOCK/EAGAIN if connection is
    established but no msg is received yet.
    Return number of bytes read if socket is established and there is
    msg received.

The new API simplifies life for applications that always perform a write()
immediately after a successful connect(). Such applications can now take
advantage of Fast Open by merely making one new setsockopt() call at the time
of creating the socket. Nothing else about the application's socket call
sequence needs to change.

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

1 files changed, 24 insertions, 7 deletions

diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index 28fe8da4e1ac..92e7f3e957fa 100644
--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -576,13 +576,24 @@ int __inet_stream_connect(struct socket *sock, struct sockaddr *uaddr,
 	int err;
 	long timeo;
 
-	if (addr_len < sizeof(uaddr->sa_family))
-		return -EINVAL;
+	/*
+	 * uaddr can be NULL and addr_len can be 0 if:
+	 * sk is a TCP fastopen active socket and
+	 * TCP_FASTOPEN_CONNECT sockopt is set and
+	 * we already have a valid cookie for this socket.
+	 * In this case, user can call write() after connect().
+	 * write() will invoke tcp_sendmsg_fastopen() which calls
+	 * __inet_stream_connect().
+	 */
+	if (uaddr) {
+		if (addr_len < sizeof(uaddr->sa_family))
+			return -EINVAL;
 
-	if (uaddr->sa_family == AF_UNSPEC) {
-		err = sk->sk_prot->disconnect(sk, flags);
-		sock->state = err ? SS_DISCONNECTING : SS_UNCONNECTED;
-		goto out;
+		if (uaddr->sa_family == AF_UNSPEC) {
+			err = sk->sk_prot->disconnect(sk, flags);
+			sock->state = err ? SS_DISCONNECTING : SS_UNCONNECTED;
+			goto out;
+		}
 	}
 
 	switch (sock->state) {
@@ -593,7 +604,10 @@ int __inet_stream_connect(struct socket *sock, struct sockaddr *uaddr,
 		err = -EISCONN;
 		goto out;
 	case SS_CONNECTING:
-		err = -EALREADY;
+		if (inet_sk(sk)->defer_connect)
+			err = -EINPROGRESS;
+		else
+			err = -EALREADY;
 		/* Fall out of switch with err, set for this state */
 		break;
 	case SS_UNCONNECTED:
@@ -607,6 +621,9 @@ int __inet_stream_connect(struct socket *sock, struct sockaddr *uaddr,
 
 		sock->state = SS_CONNECTING;
 
+		if (!err && inet_sk(sk)->defer_connect)
+			goto out;
+
 		/* Just entered SS_CONNECTING state; the only
 		 * difference is that return value in non-blocking
 		 * case is EINPROGRESS, rather than EALREADY.