[NETLINK]: Add nla_append()

Used to append data to a message without a header or padding.

Signed-off-by: Patrick McHardy <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/netlink.h

···
  *   nla_reserve_nohdr(skb, len)	reserve room for an attribute w/o hdr
  *   nla_put(skb, type, len, data)	add attribute to skb
  *   nla_put_nohdr(skb, len, data)	add attribute w/o hdr
+ *   nla_append(skb, len, data)		append data to skb
  *
  * Attribute Construction for Basic Types:
  *   nla_put_u8(skb, type, value)	add u8 attribute to skb
···
 				int attrlen, const void *data);
 extern int		nla_put_nohdr(struct sk_buff *skb, int attrlen,
 				      const void *data);
+extern int		nla_append(struct sk_buff *skb, int attrlen,
+				   const void *data);
 
 /**************************************************************************
  * Netlink Messages

net/netlink/attr.c

···
 	return 0;
 }
 
+/**
+ * nla_append - Add a netlink attribute without header or padding
+ * @skb: socket buffer to add attribute to
+ * @attrlen: length of attribute payload
+ * @data: head of attribute payload
+ *
+ * Returns -1 if the tailroom of the skb is insufficient to store
+ * the attribute payload.
+ */
+int nla_append(struct sk_buff *skb, int attrlen, const void *data)
+{
+	if (unlikely(skb_tailroom(skb) < NLA_ALIGN(attrlen)))
+		return -1;
+
+	memcpy(skb_put(skb, attrlen), data, attrlen);
+	return 0;
+}
+
 EXPORT_SYMBOL(nla_validate);
 EXPORT_SYMBOL(nla_parse);
 EXPORT_SYMBOL(nla_find);
···
 EXPORT_SYMBOL(nla_memcpy);
 EXPORT_SYMBOL(nla_memcmp);
 EXPORT_SYMBOL(nla_strcmp);
+EXPORT_SYMBOL(nla_append);