Bluetooth: Add bt_skb_sendmsg helper

bt_skb_sendmsg helps takes care of allocation the skb and copying the
the contents of msg over to the skb while checking for possible errors
so it should be safe to call it without holding lock_sock.

Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

include/net/bluetooth/bluetooth.h

@@ -444,6 +444,34 @@ out:
 	return NULL;
 }
 
+/* Shall not be called with lock_sock held */
+static inline struct sk_buff *bt_skb_sendmsg(struct sock *sk,
+					     struct msghdr *msg,
+					     size_t len, size_t mtu,
+					     size_t headroom, size_t tailroom)
+{
+	struct sk_buff *skb;
+	size_t size = min_t(size_t, len, mtu);
+	int err;
+
+	skb = bt_skb_send_alloc(sk, size + headroom + tailroom,
+				msg->msg_flags & MSG_DONTWAIT, &err);
+	if (!skb)
+		return ERR_PTR(err);
+
+	skb_reserve(skb, headroom);
+	skb_tailroom_reserve(skb, mtu, tailroom);
+
+	if (!copy_from_iter_full(skb_put(skb, size), size, &msg->msg_iter)) {
+		kfree_skb(skb);
+		return ERR_PTR(-EFAULT);
+	}
+
+	skb->priority = sk->sk_priority;
+
+	return skb;
+}
+
 int bt_to_errno(u16 code);
 
 void hci_sock_set_flag(struct sock *sk, int nr);