Bluetooth: Add bt_skb_sendmmsg helper

This works similarly to bt_skb_sendmsg but can split the msg into
multiple skb fragments which is useful for stream sockets.
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

@@ -472,6 +472,44 @@ static inline struct sk_buff *bt_skb_sendmsg(struct sock *sk,
 	return skb;
 }
 
+/* Similar to bt_skb_sendmsg but can split the msg into multiple fragments
+ * accourding to the MTU.
+ */
+static inline struct sk_buff *bt_skb_sendmmsg(struct sock *sk,
+					      struct msghdr *msg,
+					      size_t len, size_t mtu,
+					      size_t headroom, size_t tailroom)
+{
+	struct sk_buff *skb, **frag;
+
+	skb = bt_skb_sendmsg(sk, msg, len, mtu, headroom, tailroom);
+	if (IS_ERR_OR_NULL(skb))
+		return skb;
+
+	len -= skb->len;
+	if (!len)
+		return skb;
+
+	/* Add remaining data over MTU as continuation fragments */
+	frag = &skb_shinfo(skb)->frag_list;
+	while (len) {
+		struct sk_buff *tmp;
+
+		tmp = bt_skb_sendmsg(sk, msg, len, mtu, headroom, tailroom);
+		if (IS_ERR_OR_NULL(tmp)) {
+			kfree_skb(skb);
+			return tmp;
+		}
+
+		len -= tmp->len;
+
+		*frag = tmp;
+		frag = &(*frag)->next;
+	}
+
+	return skb;
+}
+
 int bt_to_errno(u16 code);
 
 void hci_sock_set_flag(struct sock *sk, int nr);