inet: split inet_csk_get_port into two functions

inet_csk_get_port does two different things, it either scans for an open port,
or it tries to see if the specified port is available for use.  Since these two
operations have different rules and are basically independent lets split them
into two different functions to make them both more readable.

Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/inet_connection_sock.c

@@ -156,33 +156,21 @@ static int inet_csk_bind_conflict(const struct sock *sk,
 	return sk2 != NULL;
 }
 
-/* Obtain a reference to a local port for the given sock,
- * if snum is zero it means select any available local port.
- * We try to allocate an odd port (and leave even ports for connect())
+/*
+ * Find an open port number for the socket.  Returns with the
+ * inet_bind_hashbucket lock held.
  */
-int inet_csk_get_port(struct sock *sk, unsigned short snum)
+static struct inet_bind_hashbucket *
+inet_csk_find_open_port(struct sock *sk, struct inet_bind_bucket **tb_ret, int *port_ret)
 {
-	bool reuse = sk->sk_reuse && sk->sk_state != TCP_LISTEN;
 	struct inet_hashinfo *hinfo = sk->sk_prot->h.hashinfo;
-	int ret = 1, port = snum;
+	int port = 0;
 	struct inet_bind_hashbucket *head;
 	struct net *net = sock_net(sk);
 	int i, low, high, attempt_half;
 	struct inet_bind_bucket *tb;
-	kuid_t uid = sock_i_uid(sk);
 	u32 remaining, offset;
-	bool reuseport_ok = !!snum;
 
-	if (port) {
-		head = &hinfo->bhash[inet_bhashfn(net, port,
-						  hinfo->bhash_size)];
-		spin_lock_bh(&head->lock);
-		inet_bind_bucket_for_each(tb, &head->chain)
-			if (net_eq(ib_net(tb), net) && tb->port == port)
-				goto tb_found;
-
-		goto tb_not_found;
-	}
 	attempt_half = (sk->sk_reuse == SK_CAN_REUSE) ? 1 : 0;
 other_half_scan:
 	inet_get_local_port_range(net, &low, &high);
@@ -219,11 +207,12 @@ other_parity_scan:
 		spin_lock_bh(&head->lock);
 		inet_bind_bucket_for_each(tb, &head->chain)
 			if (net_eq(ib_net(tb), net) && tb->port == port) {
-				if (!inet_csk_bind_conflict(sk, tb, false, reuseport_ok))
+				if (!inet_csk_bind_conflict(sk, tb, false, false))
 					goto success;
 				goto next_port;
 			}
-		goto tb_not_found;
+		tb = NULL;
+		goto success;
 next_port:
 		spin_unlock_bh(&head->lock);
 		cond_resched();
@@ -238,8 +227,41 @@ next_port:
 		attempt_half = 2;
 		goto other_half_scan;
 	}
-	return ret;
+	return NULL;
+success:
+	*port_ret = port;
+	*tb_ret = tb;
+	return head;
+}
+
+/* Obtain a reference to a local port for the given sock,
+ * if snum is zero it means select any available local port.
+ * We try to allocate an odd port (and leave even ports for connect())
+ */
+int inet_csk_get_port(struct sock *sk, unsigned short snum)
+{
+	bool reuse = sk->sk_reuse && sk->sk_state != TCP_LISTEN;
+	struct inet_hashinfo *hinfo = sk->sk_prot->h.hashinfo;
+	int ret = 1, port = snum;
+	struct inet_bind_hashbucket *head;
+	struct net *net = sock_net(sk);
+	struct inet_bind_bucket *tb = NULL;
+	kuid_t uid = sock_i_uid(sk);
 
+	if (!port) {
+		head = inet_csk_find_open_port(sk, &tb, &port);
+		if (!head)
+			return ret;
+		if (!tb)
+			goto tb_not_found;
+		goto success;
+	}
+	head = &hinfo->bhash[inet_bhashfn(net, port,
+					  hinfo->bhash_size)];
+	spin_lock_bh(&head->lock);
+	inet_bind_bucket_for_each(tb, &head->chain)
+		if (net_eq(ib_net(tb), net) && tb->port == port)
+			goto tb_found;
 tb_not_found:
 	tb = inet_bind_bucket_create(hinfo->bind_bucket_cachep,
 				     net, head, port);
@@ -255,7 +277,7 @@ tb_found:
 		      !rcu_access_pointer(sk->sk_reuseport_cb) &&
 		      sk->sk_reuseport && uid_eq(tb->fastuid, uid)))
 			goto success;
-		if (inet_csk_bind_conflict(sk, tb, true, reuseport_ok))
+		if (inet_csk_bind_conflict(sk, tb, true, true))
 			goto fail_unlock;
 	}
 success: