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net/tcp-fastopen: Add new API support
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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>
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tracywwnj authored and davem330 committed Jan 25, 2017
1 parent 25776aa commit 19f6d3f
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Showing 9 changed files with 111 additions and 11 deletions.
3 changes: 2 additions & 1 deletion include/linux/tcp.h
Original file line number Diff line number Diff line change
Expand Up @@ -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,
Expand Down
6 changes: 5 additions & 1 deletion include/net/inet_sock.h
Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand Down
1 change: 1 addition & 0 deletions include/net/tcp.h
Original file line number Diff line number Diff line change
Expand Up @@ -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 */
Expand Down
1 change: 1 addition & 0 deletions include/uapi/linux/tcp.h
Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand Down
31 changes: 24 additions & 7 deletions net/ipv4/af_inet.c
Original file line number Diff line number Diff line change
Expand Up @@ -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) {
Expand All @@ -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:
Expand All @@ -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.
Expand Down
35 changes: 34 additions & 1 deletion net/ipv4/tcp.c
Original file line number Diff line number Diff line change
Expand Up @@ -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();
Expand Down Expand Up @@ -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))
Expand All @@ -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;
Expand All @@ -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;
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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;
Expand Down
33 changes: 33 additions & 0 deletions net/ipv4/tcp_fastopen.c
Original file line number Diff line number Diff line change
Expand Up @@ -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);
7 changes: 6 additions & 1 deletion net/ipv4/tcp_ipv4.c
Original file line number Diff line number Diff line change
Expand Up @@ -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,
Expand All @@ -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;

Expand Down
5 changes: 5 additions & 0 deletions net/ipv6/tcp_ipv6.c
Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand Down

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