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[NET]: Avoid copying TCP packets unnecessarily

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TCP packets all have writable heads, that is, even though it's cloned, it is
writable up to the end of the TCP header.  This patch makes skb_checksum_help
aware of this fact by using skb_clone_writable and avoiding a copy for TCP.

I've also modified the BUG_ON tests to be unsigned.  The only case where this
makes a difference is if csum_start points to a location before skb->data.
Since skb->data should always include the header where the checksum field
is (and all currently callers adhere to that), this change is safe and may
uncover bugs later.

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 2007-10-15 01:47:15 -07:00 committed by David S. Miller
parent 172a863f2b
commit a030847e9f
1 changed files with 10 additions and 11 deletions
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21
net/core/dev.c
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@ -1362,22 +1362,21 @@ int skb_checksum_help(struct sk_buff *skb)
goto out_set_summed;
}
if (skb_cloned(skb)) {
offset = skb->csum_start - skb_headroom(skb);
BUG_ON(offset >= skb_headlen(skb));
csum = skb_checksum(skb, offset, skb->len - offset, 0);
offset += skb->csum_offset;
BUG_ON(offset + sizeof(__sum16) > skb_headlen(skb));
if (skb_cloned(skb) &&
!skb_clone_writable(skb, offset + sizeof(__sum16))) {
ret = pskb_expand_head(skb, 0, 0, GFP_ATOMIC);
if (ret)
goto out;
}
offset = skb->csum_start - skb_headroom(skb);
BUG_ON(offset > (int)skb->len);
csum = skb_checksum(skb, offset, skb->len-offset, 0);
offset = skb_headlen(skb) - offset;
BUG_ON(offset <= 0);
BUG_ON(skb->csum_offset + 2 > offset);
*(__sum16 *)(skb->head + skb->csum_start + skb->csum_offset) =
csum_fold(csum);
*(__sum16 *)(skb->data + offset) = csum_fold(csum);
out_set_summed:
skb->ip_summed = CHECKSUM_NONE;
out: