[NET]: Add skb_header_pointer, and use it where possible.

This greatly improves netfilter performance where
the wanted header area is in the linear SKB data
area, therefore no copy into the temporary buffer
is needed.

Signed-off-by: David S. Miller <davem@redhat.com>

1 files changed, 14 insertions, 0 deletions

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 354f1ff564bb..256c05c11298 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -1107,6 +1107,20 @@ extern void	       skb_copy_and_csum_dev(const struct sk_buff *skb, u8 *to);
 extern void	       skb_split(struct sk_buff *skb,
 				 struct sk_buff *skb1, const u32 len);
 
+static inline void *skb_header_pointer(const struct sk_buff *skb, int offset,
+				       int len, void *buffer)
+{
+	int hlen = skb_headlen(skb);
+
+	if (offset + len <= hlen)
+		return skb->data + offset;
+
+	if (skb_copy_bits(skb, offset, buffer, len) < 0)
+		return NULL;
+
+	return buffer;
+}
+
 extern void skb_init(void);
 extern void skb_add_mtu(int mtu);