Bluetooth: L2CAP: add support for waiting disconnection resp

Whenever we disconnect a L2CAP connection, we would immediately
report a disconnection event (EPOLLHUP) to the upper layer, without
waiting for the response of the other device.

This patch offers an option to wait until we receive a disconnection
response before reporting disconnection event, by using the "how"
parameter in l2cap_sock_shutdown(). Therefore, upper layer can opt
to wait for disconnection response by shutdown(sock, SHUT_WR).

This can be used to enforce proper disconnection order in HID,
where the disconnection of the interrupt channel must be complete
before attempting to disconnect the control channel.
Signed-off-by: Archie Pusaka <apusaka@chromium.org>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

net/bluetooth/l2cap_sock.c

@@ -1271,14 +1271,21 @@ static int l2cap_sock_shutdown(struct socket *sock, int how)
 	struct l2cap_conn *conn;
 	int err = 0;
 
-	BT_DBG("sock %p, sk %p", sock, sk);
+	BT_DBG("sock %p, sk %p, how %d", sock, sk, how);
+
+	/* 'how' parameter is mapped to sk_shutdown as follows:
+	 * SHUT_RD   (0) --> RCV_SHUTDOWN  (1)
+	 * SHUT_WR   (1) --> SEND_SHUTDOWN (2)
+	 * SHUT_RDWR (2) --> SHUTDOWN_MASK (3)
+	 */
+	how++;
 
 	if (!sk)
 		return 0;
 
 	lock_sock(sk);
 
-	if (sk->sk_shutdown)
+	if ((sk->sk_shutdown & how) == how)
 		goto shutdown_already;
 
 	BT_DBG("Handling sock shutdown");
@@ -1301,11 +1308,20 @@ static int l2cap_sock_shutdown(struct socket *sock, int how)
 		 * has already been actioned to close the L2CAP
 		 * link such as by l2cap_disconnection_req().
 		 */
-		if (sk->sk_shutdown)
-			goto has_shutdown;
+		if ((sk->sk_shutdown & how) == how)
+			goto shutdown_matched;
 	}
 
-	sk->sk_shutdown = SHUTDOWN_MASK;
+	/* Try setting the RCV_SHUTDOWN bit, return early if SEND_SHUTDOWN
+	 * is already set
+	 */
+	if ((how & RCV_SHUTDOWN) && !(sk->sk_shutdown & RCV_SHUTDOWN)) {
+		sk->sk_shutdown |= RCV_SHUTDOWN;
+		if ((sk->sk_shutdown & how) == how)
+			goto shutdown_matched;
+	}
+
+	sk->sk_shutdown |= SEND_SHUTDOWN;
 	release_sock(sk);
 
 	l2cap_chan_lock(chan);
@@ -1335,7 +1351,7 @@ static int l2cap_sock_shutdown(struct socket *sock, int how)
 		err = bt_sock_wait_state(sk, BT_CLOSED,
 					 sk->sk_lingertime);
 
-has_shutdown:
+shutdown_matched:
 	l2cap_chan_put(chan);
 	sock_put(sk);
 
@@ -1363,7 +1379,7 @@ static int l2cap_sock_release(struct socket *sock)
 
 	bt_sock_unlink(&l2cap_sk_list, sk);
 
-	err = l2cap_sock_shutdown(sock, 2);
+	err = l2cap_sock_shutdown(sock, SHUT_RDWR);
 	chan = l2cap_pi(sk)->chan;
 
 	l2cap_chan_hold(chan);