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>
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index b774a03..fc04711 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -305,6 +305,35 @@
}
/*
+ * Timer for Fast Open socket to retransmit SYNACK. Note that the
+ * sk here is the child socket, not the parent (listener) socket.
+ */
+static void tcp_fastopen_synack_timer(struct sock *sk)
+{
+ struct inet_connection_sock *icsk = inet_csk(sk);
+ int max_retries = icsk->icsk_syn_retries ? :
+ sysctl_tcp_synack_retries + 1; /* add one more retry for fastopen */
+ struct request_sock *req;
+
+ req = tcp_sk(sk)->fastopen_rsk;
+ req->rsk_ops->syn_ack_timeout(sk, req);
+
+ if (req->retrans >= max_retries) {
+ tcp_write_err(sk);
+ return;
+ }
+ /* XXX (TFO) - Unlike regular SYN-ACK retransmit, we ignore error
+ * returned from rtx_syn_ack() to make it more persistent like
+ * regular retransmit because if the child socket has been accepted
+ * it's not good to give up too easily.
+ */
+ req->rsk_ops->rtx_syn_ack(sk, req, NULL);
+ req->retrans++;
+ inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
+ TCP_TIMEOUT_INIT << req->retrans, TCP_RTO_MAX);
+}
+
+/*
* The TCP retransmit timer.
*/
@@ -317,7 +346,15 @@
tcp_resume_early_retransmit(sk);
return;
}
-
+ if (tp->fastopen_rsk) {
+ BUG_ON(sk->sk_state != TCP_SYN_RECV &&
+ sk->sk_state != TCP_FIN_WAIT1);
+ tcp_fastopen_synack_timer(sk);
+ /* Before we receive ACK to our SYN-ACK don't retransmit
+ * anything else (e.g., data or FIN segments).
+ */
+ return;
+ }
if (!tp->packets_out)
goto out;
