From 88078d98d1bb085d72af8437707279e203524fa5 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Wed, 18 Apr 2018 11:43:15 -0700 Subject: net: pskb_trim_rcsum() and CHECKSUM_COMPLETE are friends After working on IP defragmentation lately, I found that some large packets defeat CHECKSUM_COMPLETE optimization because of NIC adding zero paddings on the last (small) fragment. While removing the padding with pskb_trim_rcsum(), we set skb->ip_summed to CHECKSUM_NONE, forcing a full csum validation, even if all prior fragments had CHECKSUM_COMPLETE set. We can instead compute the checksum of the part we are trimming, usually smaller than the part we keep. Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller --- net/core/skbuff.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) (limited to 'net/core') diff --git a/net/core/skbuff.c b/net/core/skbuff.c index 345b51837ca8..ff49e352deea 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -1839,6 +1839,20 @@ done: } EXPORT_SYMBOL(___pskb_trim); +/* Note : use pskb_trim_rcsum() instead of calling this directly + */ +int pskb_trim_rcsum_slow(struct sk_buff *skb, unsigned int len) +{ + if (skb->ip_summed == CHECKSUM_COMPLETE) { + int delta = skb->len - len; + + skb->csum = csum_sub(skb->csum, + skb_checksum(skb, len, delta, 0)); + } + return __pskb_trim(skb, len); +} +EXPORT_SYMBOL(pskb_trim_rcsum_slow); + /** * __pskb_pull_tail - advance tail of skb header * @skb: buffer to reallocate -- cgit v1.2.1