proto_ops: Add locked held versions of sendmsg and sendpage

Add new proto_ops sendmsg_locked and sendpage_locked that can be
called when the socket lock is already held. Correspondingly, add
kernel_sendmsg_locked and kernel_sendpage_locked as front end
functions.

These functions will be used in zero proxy so that we can take
the socket lock in a ULP sendmsg/sendpage and then directly call the
backend transport proto_ops functions.

Signed-off-by: Tom Herbert <tom@quantonium.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/af_inet.c

@@ -944,6 +944,8 @@ const struct proto_ops inet_stream_ops = {
 	.sendpage	   = inet_sendpage,
 	.splice_read	   = tcp_splice_read,
 	.read_sock	   = tcp_read_sock,
+	.sendmsg_locked    = tcp_sendmsg_locked,
+	.sendpage_locked   = tcp_sendpage_locked,
 	.peek_len	   = tcp_peek_len,
 #ifdef CONFIG_COMPAT
 	.compat_setsockopt = compat_sock_common_setsockopt,

net/ipv4/tcp.c

@@ -1046,23 +1046,29 @@ out_err:
 }
 EXPORT_SYMBOL_GPL(do_tcp_sendpages);
 
-int tcp_sendpage(struct sock *sk, struct page *page, int offset,
-		 size_t size, int flags)
+int tcp_sendpage_locked(struct sock *sk, struct page *page, int offset,
+			size_t size, int flags)
 {
-	ssize_t res;
-
 	if (!(sk->sk_route_caps & NETIF_F_SG) ||
 	    !sk_check_csum_caps(sk))
 		return sock_no_sendpage(sk->sk_socket, page, offset, size,
 					flags);
 
-	lock_sock(sk);
-
 	tcp_rate_check_app_limited(sk);  /* is sending application-limited? */
 
-	res = do_tcp_sendpages(sk, page, offset, size, flags);
+	return do_tcp_sendpages(sk, page, offset, size, flags);
+}
+
+int tcp_sendpage(struct sock *sk, struct page *page, int offset,
+		 size_t size, int flags)
+{
+	int ret;
+
+	lock_sock(sk);
+	ret = tcp_sendpage_locked(sk, page, offset, size, flags);
 	release_sock(sk);
-	return res;
+
+	return ret;
 }
 EXPORT_SYMBOL(tcp_sendpage);
 
@@ -1156,7 +1162,7 @@ static int tcp_sendmsg_fastopen(struct sock *sk, struct msghdr *msg,
 	return err;
 }
 
-int tcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
+int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 	struct sk_buff *skb;
@@ -1167,8 +1173,6 @@ int tcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
 	bool sg;
 	long timeo;
 
-	lock_sock(sk);
-
 	flags = msg->msg_flags;
 	if (unlikely(flags & MSG_FASTOPEN || inet_sk(sk)->defer_connect)) {
 		err = tcp_sendmsg_fastopen(sk, msg, &copied_syn, size);
@@ -1377,7 +1381,6 @@ out:
 		tcp_push(sk, flags, mss_now, tp->nonagle, size_goal);
 	}
 out_nopush:
-	release_sock(sk);
 	return copied + copied_syn;
 
 do_fault:
@@ -1401,9 +1404,19 @@ out_err:
 		sk->sk_write_space(sk);
 		tcp_chrono_stop(sk, TCP_CHRONO_SNDBUF_LIMITED);
 	}
-	release_sock(sk);
 	return err;
 }
+
+int tcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
+{
+	int ret;
+
+	lock_sock(sk);
+	ret = tcp_sendmsg_locked(sk, msg, size);
+	release_sock(sk);
+
+	return ret;
+}
 EXPORT_SYMBOL(tcp_sendmsg);
 
 /*