tcp: TCP Fast Open Server - support TFO listeners

This patch builds on top of the previous patch to add the support
for TFO listeners. This includes -

1. allocating, properly initializing, and managing the per listener
fastopen_queue structure when TFO is enabled

2. changes to the inet_csk_accept code to support TFO. E.g., the
request_sock can no longer be freed upon accept(), not until 3WHS
finishes

3. allowing a TCP_SYN_RECV socket to properly poll() and sendmsg()
if it's a TFO socket

4. properly closing a TFO listener, and a TFO socket before 3WHS
finishes

5. supporting TCP_FASTOPEN socket option

6. modifying tcp_check_req() to use to check a TFO socket as well
as request_sock

7. supporting TCP's TFO cookie option

8. adding a new SYN-ACK retransmit handler to use the timer directly
off the TFO socket rather than the listener socket. Note that TFO
server side will not retransmit anything other than SYN-ACK until
the 3WHS is completed.

The patch also contains an important function
"reqsk_fastopen_remove()" to manage the somewhat complex relation
between a listener, its request_sock, and the corresponding child
socket. See the comment above the function for the detail.

Signed-off-by: H.K. Jerry Chu <hkchu@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 4 insertions, 15 deletions

diff --git a/include/net/request_sock.h b/include/net/request_sock.h
index c3cdd6c9f448..b01d8dd9ee7c 100644
--- a/include/net/request_sock.h
+++ b/include/net/request_sock.h
@@ -226,19 +226,6 @@ static inline struct request_sock *reqsk_queue_remove(struct request_sock_queue
         return req;
 }
 
-static inline struct sock *reqsk_queue_get_child(struct request_sock_queue *queue,
-                                                 struct sock *parent)
-{
-        struct request_sock *req = reqsk_queue_remove(queue);
-        struct sock *child = req->sk;
-
-        WARN_ON(child == NULL);
-
-        sk_acceptq_removed(parent);
-        __reqsk_free(req);
-        return child;
-}
-
 static inline int reqsk_queue_removed(struct request_sock_queue *queue,
                                       struct request_sock *req)
 {
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 9f8821e3293a..1421b02a7905 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -424,7 +424,8 @@ extern enum tcp_tw_status tcp_timewait_state_process(struct inet_timewait_sock *
                                                      const struct tcphdr *th);
 extern struct sock * tcp_check_req(struct sock *sk,struct sk_buff *skb,
                                    struct request_sock *req,
-                                   struct request_sock **prev);
+                                   struct request_sock **prev,
+                                   bool fastopen);
 extern int tcp_child_process(struct sock *parent, struct sock *child,
                              struct sk_buff *skb);
 extern bool tcp_use_frto(struct sock *sk);
@@ -478,7 +479,8 @@ extern int tcp_v4_connect(struct sock *sk, struct sockaddr *uaddr,
 extern int tcp_connect(struct sock *sk);
 extern struct sk_buff * tcp_make_synack(struct sock *sk, struct dst_entry *dst,
                                         struct request_sock *req,
-                                        struct request_values *rvp);
+                                        struct request_values *rvp,
+                                        struct tcp_fastopen_cookie *foc);
 extern int tcp_disconnect(struct sock *sk, int flags);
 
 void tcp_connect_init(struct sock *sk);