From: Herbert Xu Date: Mon, 15 Oct 2007 08:47:15 +0000 (-0700) Subject: [NET]: Avoid copying TCP packets unnecessarily X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=a030847e9f0eed2a080f6114381c649a7aa43d25;p=linux-beck.git [NET]: Avoid copying TCP packets unnecessarily 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 Signed-off-by: David S. Miller --- diff --git a/net/core/dev.c b/net/core/dev.c index 39aba4862f21..38b03da5c1ca 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -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: