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[NET]: Avoid allocating skb in skb_pad

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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>
This commit is contained in:
Herbert Xu
2006-06-23 02:06:41 -07:00
committed by David S. Miller
parent 5fa21d821f
commit 5b057c6b1a
36 changed files with 74 additions and 103 deletions
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11
include/linux/skbuff.h
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@@ -345,7 +345,7 @@ extern struct sk_buff *skb_realloc_headroom(struct sk_buff *skb,
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 @@ static inline int skb_cow(struct sk_buff *skb, unsigned int headroom)
*
* 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);
}