[NET]: Avoid allocating skb in skb_pad
First of all it is unnecessary to allocate a new skb in skb_pad since
the existing one is not shared. More importantly, our hard_start_xmit
interface does not allow a new skb to be allocated since that breaks
requeueing.
This patch uses pskb_expand_head to expand the existing skb and linearize
it if needed. Actually, someone should sift through every instance of
skb_pad on a non-linear skb as they do not fit the reasons why this was
originally created.
Incidentally, this fixes a minor bug when the skb is cloned (tcpdump,
TCP, etc.). As it is skb_pad will simply write over a cloned skb. Because
of the position of the write it is unlikely to cause problems but still
it's best if we don't do it.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 66f8819..f8c7eb7 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -345,7 +345,7 @@
extern struct sk_buff *skb_copy_expand(const struct sk_buff *skb,
int newheadroom, int newtailroom,
gfp_t priority);
-extern struct sk_buff * skb_pad(struct sk_buff *skb, int pad);
+extern int skb_pad(struct sk_buff *skb, int pad);
#define dev_kfree_skb(a) kfree_skb(a)
extern void skb_over_panic(struct sk_buff *skb, int len,
void *here);
@@ -1122,16 +1122,15 @@
*
* Pads up a buffer to ensure the trailing bytes exist and are
* blanked. If the buffer already contains sufficient data it
- * is untouched. Returns the buffer, which may be a replacement
- * for the original, or NULL for out of memory - in which case
- * the original buffer is still freed.
+ * is untouched. Otherwise it is extended. Returns zero on
+ * success. The skb is freed on error.
*/
-static inline struct sk_buff *skb_padto(struct sk_buff *skb, unsigned int len)
+static inline int skb_padto(struct sk_buff *skb, unsigned int len)
{
unsigned int size = skb->len;
if (likely(size >= len))
- return skb;
+ return 0;
return skb_pad(skb, len-size);
}