[NETLINK]: Add nla_append()

Used to append data to a message without a header or padding.
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/netlink.h

@@ -91,6 +91,7 @@
  *   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
@@ -254,6 +255,8 @@ extern int		nla_put(struct sk_buff *skb, int attrtype,
 				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

@@ -430,6 +430,24 @@ int nla_put_nohdr(struct sk_buff *skb, int attrlen, const void *data)
 	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);
@@ -445,3 +463,4 @@ EXPORT_SYMBOL(nla_put_nohdr);
 EXPORT_SYMBOL(nla_memcpy);
 EXPORT_SYMBOL(nla_memcmp);
 EXPORT_SYMBOL(nla_strcmp);
+EXPORT_SYMBOL(nla_append);