When TCP_FASTOPEN_CONNECT has been set on the socket before a connect,
the defer flag is set and must be handled when sendmsg is called.

This is similar to what is done in tcp_sendmsg_locked().

Signed-off-by: Benjamin Hesmans <benjamin.hesmans@tessares.net>
---

Notes:
    v1:
    - error case use latest patch from Paolo (propagate fastclose error)
    - I believe the use __mptcp_nmpc_socket(msk); is correct here (instead of
      msk->first but would be nice is someone can confirm
    - add unlikely for the TFO check
    - propagate the ssk state to the msk (Paolo)

 net/mptcp/protocol.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 7d4e197ec567..f5f20910cd83 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -1668,6 +1668,7 @@ static int mptcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 {
 	struct mptcp_sock *msk = mptcp_sk(sk);
 	struct page_frag *pfrag;
+	struct socket *ssock;
 	size_t copied = 0;
 	int ret = 0;
 	long timeo;
@@ -1681,6 +1682,27 @@ static int mptcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 
 	lock_sock(sk);
 
+	ssock = __mptcp_nmpc_socket(msk);
+	if (unlikely(ssock && inet_sk(ssock->sk)->defer_connect)) {
+		struct sock *ssk = ssock->sk;
+		int copied_syn = 0;
+
+		lock_sock(ssk);
+
+		ret = tcp_sendmsg_fastopen(ssk, msg, &copied_syn, len, NULL);
+		copied += copied_syn;
+		if (ret == -EINPROGRESS && copied_syn > 0) {
+			/* reflect the new state on the MPTCP socket */
+			inet_sk_state_store(sk, inet_sk_state_load(ssk));
+			release_sock(ssk);
+			goto out;
+		} else if (ret) {
+			release_sock(ssk);
+			goto do_error;
+		}
+		release_sock(ssk);
+	}
+
 	timeo = sock_sndtimeo(sk, msg->msg_flags & MSG_DONTWAIT);
 
 	if ((1 << sk->sk_state) & ~(TCPF_ESTABLISHED | TCPF_CLOSE_WAIT)) {
-- 
2.25.1


-- 


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Hello,

On Wed, 2022-09-21 at 17:25 +0200, Benjamin Hesmans wrote:
> When TCP_FASTOPEN_CONNECT has been set on the socket before a connect,
> the defer flag is set and must be handled when sendmsg is called.
> 
> This is similar to what is done in tcp_sendmsg_locked().
> 
> Signed-off-by: Benjamin Hesmans <benjamin.hesmans@tessares.net>
> ---
> 
> Notes:
>     v1:
>     - error case use latest patch from Paolo (propagate fastclose error)
>     - I believe the use __mptcp_nmpc_socket(msk); is correct here (instead of
>       msk->first but would be nice is someone can confirm

Yep, AFAICS it's correct. 

And patch LGTM.

Cheers,

Paolo