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>

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 5371b3d70cfe7c10d8fce6eb4006898ef1e4f948..f88f4649ba6f8a9a19578f55272533a12e5c9680 100644 (file)
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -222,7 +222,8 @@ struct tcp_sock {
        u32     chrono_stat[3]; /* Time in jiffies for chrono_stat stats */
        u8      chrono_type:2,  /* current chronograph type */
                rate_app_limited:1,  /* rate_{delivered,interval_us} limited? */
-               unused:5;
+               fastopen_connect:1, /* FASTOPEN_CONNECT sockopt */
+               unused:4;
        u8      nonagle     : 4,/* Disable Nagle algorithm?             */
                thin_lto    : 1,/* Use linear timeouts for thin streams */
                unused1     : 1,

diff --git a/include/net/inet_sock.h b/include/net/inet_sock.h
index c9cff977a7fb2cc9d8446715cc09a51e5090aff9..aa95053dfc78d35d04aef276e2a5dce7343f72a0 100644 (file)
--- a/include/net/inet_sock.h
+++ b/include/net/inet_sock.h
@@ -206,7 +206,11 @@ struct inet_sock {
                                transparent:1,
                                mc_all:1,
                                nodefrag:1;
-       __u8                    bind_address_no_port:1;
+       __u8                    bind_address_no_port:1,
+                               defer_connect:1; /* Indicates that fastopen_connect is set
+                                                 * and cookie exists so we defer connect
+                                                 * until first data frame is written
+                                                 */
        __u8                    rcv_tos;
        __u8                    convert_csum;
        int                     uc_index;

diff --git a/include/net/tcp.h b/include/net/tcp.h
index de67541d7adfc76e7ae83780777d660ecb9b483c..6ec4ea652f3f55e53675dbe09f29599af179c41a 100644 (file)
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1495,6 +1495,7 @@ struct sock *tcp_try_fastopen(struct sock *sk, struct sk_buff *skb,
 void tcp_fastopen_init_key_once(bool publish);
 bool tcp_fastopen_cookie_check(struct sock *sk, u16 *mss,
                             struct tcp_fastopen_cookie *cookie);
+bool tcp_fastopen_defer_connect(struct sock *sk, int *err);
 #define TCP_FASTOPEN_KEY_LENGTH 16
 
 /* Fastopen key context */

diff --git a/include/uapi/linux/tcp.h b/include/uapi/linux/tcp.h
index c53de2691cecec43f4dbde55dd69da3c07da719f..6ff35eb48d104c4128e13b41d772a09178a95bac 100644 (file)
--- a/include/uapi/linux/tcp.h
+++ b/include/uapi/linux/tcp.h
@@ -116,6 +116,7 @@ enum {
 #define TCP_SAVE_SYN           27      /* Record SYN headers for new connections */
 #define TCP_SAVED_SYN          28      /* Get SYN headers recorded for connection */
 #define TCP_REPAIR_WINDOW      29      /* Get/set window parameters */
+#define TCP_FASTOPEN_CONNECT   30      /* Attempt FastOpen with connect */
 
 struct tcp_repair_opt {
        __u32   opt_code;

diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index 28fe8da4e1ac6230b5ddab88be9a0b9dcb8ad800..92e7f3e957fafd837ad50b7b7e3e20a8817b41a9 100644 (file)
--- 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.

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index c43eb1a831d7a0a36b447421908a149b1808590b..d9735b76d0730600e35259e824ada9c1396a6ab3 100644 (file)
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -533,6 +533,12 @@ unsigned int tcp_poll(struct file *file, struct socket *sock, poll_table *wait)
 
                if (tp->urg_data & TCP_URG_VALID)
                        mask |= POLLPRI;
+       } else if (sk->sk_state == TCP_SYN_SENT && inet_sk(sk)->defer_connect) {
+               /* Active TCP fastopen socket with defer_connect
+                * Return POLLOUT so application can call write()
+                * in order for kernel to generate SYN+data
+                */
+               mask |= POLLOUT | POLLWRNORM;
        }
        /* This barrier is coupled with smp_wmb() in tcp_reset() */
        smp_rmb();
@@ -1071,6 +1077,7 @@ static int tcp_sendmsg_fastopen(struct sock *sk, struct msghdr *msg,
                                int *copied, size_t size)
 {
        struct tcp_sock *tp = tcp_sk(sk);
+       struct inet_sock *inet = inet_sk(sk);
        int err, flags;
 
        if (!(sysctl_tcp_fastopen & TFO_CLIENT_ENABLE))
@@ -1085,9 +1092,19 @@ static int tcp_sendmsg_fastopen(struct sock *sk, struct msghdr *msg,
        tp->fastopen_req->data = msg;
        tp->fastopen_req->size = size;
 
+       if (inet->defer_connect) {
+               err = tcp_connect(sk);
+               /* Same failure procedure as in tcp_v4/6_connect */
+               if (err) {
+                       tcp_set_state(sk, TCP_CLOSE);
+                       inet->inet_dport = 0;
+                       sk->sk_route_caps = 0;
+               }
+       }
        flags = (msg->msg_flags & MSG_DONTWAIT) ? O_NONBLOCK : 0;
        err = __inet_stream_connect(sk->sk_socket, msg->msg_name,
                                    msg->msg_namelen, flags);
+       inet->defer_connect = 0;
        *copied = tp->fastopen_req->copied;
        tcp_free_fastopen_req(tp);
        return err;
@@ -1107,7 +1124,7 @@ int tcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
        lock_sock(sk);
 
        flags = msg->msg_flags;
-       if (flags & MSG_FASTOPEN) {
+       if (unlikely(flags & MSG_FASTOPEN || inet_sk(sk)->defer_connect)) {
                err = tcp_sendmsg_fastopen(sk, msg, &copied_syn, size);
                if (err == -EINPROGRESS && copied_syn > 0)
                        goto out;
@@ -2656,6 +2673,18 @@ static int do_tcp_setsockopt(struct sock *sk, int level,
                        err = -EINVAL;
                }
                break;
+       case TCP_FASTOPEN_CONNECT:
+               if (val > 1 || val < 0) {
+                       err = -EINVAL;
+               } else if (sysctl_tcp_fastopen & TFO_CLIENT_ENABLE) {
+                       if (sk->sk_state == TCP_CLOSE)
+                               tp->fastopen_connect = val;
+                       else
+                               err = -EINVAL;
+               } else {
+                       err = -EOPNOTSUPP;
+               }
+               break;
        case TCP_TIMESTAMP:
                if (!tp->repair)
                        err = -EPERM;
@@ -3016,6 +3045,10 @@ static int do_tcp_getsockopt(struct sock *sk, int level,
                val = icsk->icsk_accept_queue.fastopenq.max_qlen;
                break;
 
+       case TCP_FASTOPEN_CONNECT:
+               val = tp->fastopen_connect;
+               break;
+
        case TCP_TIMESTAMP:
                val = tcp_time_stamp + tp->tsoffset;
                break;

diff --git a/net/ipv4/tcp_fastopen.c b/net/ipv4/tcp_fastopen.c
index f90e09e1ff4c8014e257ebe157f0bf44c5733975..9674bec4a0f8109f22c1db7eb931b4d99fe9cd20 100644 (file)
--- a/net/ipv4/tcp_fastopen.c
+++ b/net/ipv4/tcp_fastopen.c
@@ -346,3 +346,36 @@ bool tcp_fastopen_cookie_check(struct sock *sk, u16 *mss,
        }
        return cookie->len > 0;
 }
+
+/* This function checks if we want to defer sending SYN until the first
+ * write().  We defer under the following conditions:
+ * 1. fastopen_connect sockopt is set
+ * 2. we have a valid cookie
+ * Return value: return true if we want to defer until application writes data
+ *               return false if we want to send out SYN immediately
+ */
+bool tcp_fastopen_defer_connect(struct sock *sk, int *err)
+{
+       struct tcp_fastopen_cookie cookie = { .len = 0 };
+       struct tcp_sock *tp = tcp_sk(sk);
+       u16 mss;
+
+       if (tp->fastopen_connect && !tp->fastopen_req) {
+               if (tcp_fastopen_cookie_check(sk, &mss, &cookie)) {
+                       inet_sk(sk)->defer_connect = 1;
+                       return true;
+               }
+
+               /* Alloc fastopen_req in order for FO option to be included
+                * in SYN
+                */
+               tp->fastopen_req = kzalloc(sizeof(*tp->fastopen_req),
+                                          sk->sk_allocation);
+               if (tp->fastopen_req)
+                       tp->fastopen_req->cookie = cookie;
+               else
+                       *err = -ENOBUFS;
+       }
+       return false;
+}
+EXPORT_SYMBOL(tcp_fastopen_defer_connect);

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index a90b4540c11eca6ed5b374ec69c8ced2ff180727..8c9e9aa17d660d7e92bdced72ace0c8644621371 100644 (file)
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -232,6 +232,7 @@ int tcp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
        /* OK, now commit destination to socket.  */
        sk->sk_gso_type = SKB_GSO_TCPV4;
        sk_setup_caps(sk, &rt->dst);
+       rt = NULL;
 
        if (!tp->write_seq && likely(!tp->repair))
                tp->write_seq = secure_tcp_sequence_number(inet->inet_saddr,
@@ -242,9 +243,13 @@ int tcp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
 
        inet->inet_id = tp->write_seq ^ jiffies;
 
+       if (tcp_fastopen_defer_connect(sk, &err))
+               return err;
+       if (err)
+               goto failure;
+
        err = tcp_connect(sk);
 
-       rt = NULL;
        if (err)
                goto failure;
 

diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 0b7cd3d009b653c5b4ee3929f48c1594f2a7764f..95c05e5293b1889bebe97e896c8b61a1e9a3812c 100644 (file)
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -287,6 +287,11 @@ static int tcp_v6_connect(struct sock *sk, struct sockaddr *uaddr,
                                                             inet->inet_dport,
                                                             &tp->tsoffset);
 
+       if (tcp_fastopen_defer_connect(sk, &err))
+               return err;
+       if (err)
+               goto late_failure;
+
        err = tcp_connect(sk);
        if (err)
                goto late_failure;