netdev - [RFC PATCH net] tcp: allow to use TCP Fastopen with MSG

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Date:   Tue,  3 Apr 2018 15:43:19 +0300
From:   Alexey Kodanev <alexey.kodanev@...cle.com>
To:     netdev@...r.kernel.org
Cc:     Willem de Bruijn <willemb@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        David Miller <davem@...emloft.net>,
        Alexey Kodanev <alexey.kodanev@...cle.com>
Subject: [RFC PATCH net] tcp: allow to use TCP Fastopen with MSG_ZEROCOPY

With TCP Fastopen we can have the following cases, which could also
use MSG_ZEROCOPY flag with send() and sendto():

* sendto() + MSG_FASTOPEN flag, sk state can be in TCP_CLOSE at
  the start of tcp_sendmsg()

* set socket option TCP_FASTOPEN_CONNECT, then connect()
  and send(), sk state in TCP_SYN_SENT

Currently, both cases with tcp_sendmsg() and MSG_ZEROCOPY flag results
to EINVAL error, because of the check for TCP_ESTABLISHED sk state in
the beginning of tcp_sendmsg().

Both conditions require two more checks there: !tp->fastopen_connect
and !(flags & MSG_FASTOPEN). It looks like we could remove the original
check altogether for this unlikely event instead. That way tcp_sendmsg()
without TFO should fail with EPIPE on sk_stream_wait_connect(), as
before the introduction of MSG_ZEROCOPY there. And work smoothly for
the TFO cases.

Fixes: f214f915e7db ("tcp: enable MSG_ZEROCOPY")
Signed-off-by: Alexey Kodanev <alexey.kodanev@...cle.com>
---

Is there something that I've overlooked and we can't use it here, and
we should handle this type of error, while using sendto() + TFO,
in userspace?

 net/ipv4/tcp.c | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 9225610..768f02c 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1193,11 +1193,6 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
 	flags = msg->msg_flags;

 	if (flags & MSG_ZEROCOPY && size) {
-		if (sk->sk_state != TCP_ESTABLISHED) {
-			err = -EINVAL;
-			goto out_err;
-		}
-
 		skb = tcp_write_queue_tail(sk);
 		uarg = sock_zerocopy_realloc(sk, size, skb_zcopy(skb));
 		if (!uarg) {
-- 
1.8.3.1