[PATCH v1 bpf-next 4/8] tcp: Split out __tcp_set_rcvlowat().

[Kuniyuki Iwashima <kuniyu@google.com>]

We will add a kfunc for BPF_SOCK_OPS_RCVLOWAT_CB hooks to
adjust sk->sk_rcvlowat.

These hooks will be triggered when:

  1. TCP stack enqueues skb to sk->sk_receive_queue
  2. TCP recvmsg() completes

In the enqueue path, tcp_data_ready() is always called
after the hooks in tcp_queue_rcv() and tcp_ofo_queue().

If tcp_set_rcvlowat() were used as is, tcp_data_ready()
could be called twice for the same skb, which is redundant
and also confusing.

Let's split out __tcp_set_rcvlowat() and add a flag to
control wakeup behaviour.

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
---
 include/net/tcp.h |  1 +
 net/ipv4/tcp.c    | 12 +++++++++---
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index dfa52ceefd23..4e9e634e276b 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -515,6 +515,7 @@ void tcp_set_keepalive(struct sock *sk, int val);
 void tcp_syn_ack_timeout(const struct request_sock *req);
 int tcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
 		int flags);
+int __tcp_set_rcvlowat(struct sock *sk, int val, bool wakeup);
 int tcp_set_rcvlowat(struct sock *sk, int val);
 void tcp_set_rcvbuf(struct sock *sk, int val);
 int tcp_set_window_clamp(struct sock *sk, int val);
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 2014a6408e93..1d9e52fc454f 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1829,8 +1829,7 @@ int tcp_peek_len(struct socket *sock)
 	return tcp_inq(sock->sk);
 }
 
-/* Make sure sk_rcvbuf is big enough to satisfy SO_RCVLOWAT hint */
-int tcp_set_rcvlowat(struct sock *sk, int val)
+int __tcp_set_rcvlowat(struct sock *sk, int val, bool wakeup)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 	int space, cap;
@@ -1843,7 +1842,8 @@ int tcp_set_rcvlowat(struct sock *sk, int val)
 	WRITE_ONCE(sk->sk_rcvlowat, val ? : 1);
 
 	/* Check if we need to signal EPOLLIN right now */
-	tcp_data_ready(sk);
+	if (wakeup)
+		tcp_data_ready(sk);
 
 	if (sk->sk_userlocks & SOCK_RCVBUF_LOCK)
 		return 0;
@@ -1858,6 +1858,12 @@ int tcp_set_rcvlowat(struct sock *sk, int val)
 	return 0;
 }
 
+/* Make sure sk_rcvbuf is big enough to satisfy SO_RCVLOWAT hint */
+int tcp_set_rcvlowat(struct sock *sk, int val)
+{
+	return __tcp_set_rcvlowat(sk, val, true);
+}
+
 void tcp_set_rcvbuf(struct sock *sk, int val)
 {
 	tcp_set_window_clamp(sk, tcp_win_from_space(sk, val));
-- 
2.54.0.563.g4f69b47b94-goog