Bluetooth: Add support for per socket msg_name callback

This allows to add a per socket msg_name callback that can be used
for updating the msg_name information for recvmsg() system calls.

This feature is used by another patch to support address information
on L2CAP connectionless channels.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>

include/net/bluetooth/bluetooth.h

@@ -221,6 +221,7 @@ struct bt_sock {
 	struct list_head accept_q;
 	struct sock *parent;
 	unsigned long flags;
+	void (*skb_msg_name)(struct sk_buff *, void *, int *);
 };
 
 enum {

net/bluetooth/af_bluetooth.c

@@ -221,12 +221,12 @@ int bt_sock_recvmsg(struct kiocb *iocb, struct socket *sock,
 	if (flags & (MSG_OOB))
 		return -EOPNOTSUPP;
 
-	msg->msg_namelen = 0;
-
 	skb = skb_recv_datagram(sk, flags, noblock, &err);
 	if (!skb) {
-		if (sk->sk_shutdown & RCV_SHUTDOWN)
+		if (sk->sk_shutdown & RCV_SHUTDOWN) {
+			msg->msg_namelen = 0;
 			return 0;
+		}
 		return err;
 	}
 
@@ -238,9 +238,16 @@ int bt_sock_recvmsg(struct kiocb *iocb, struct socket *sock,
 
 	skb_reset_transport_header(skb);
 	err = skb_copy_datagram_iovec(skb, 0, msg->msg_iov, copied);
-	if (err == 0)
+	if (err == 0) {
 		sock_recv_ts_and_drops(msg, sk, skb);
 
+		if (bt_sk(sk)->skb_msg_name)
+			bt_sk(sk)->skb_msg_name(skb, msg->msg_name,
+						&msg->msg_namelen);
+		else
+			msg->msg_namelen = 0;
+	}
+
 	skb_free_datagram(sk, skb);
 
 	return err ? : copied;