From: Eric Dumazet edumazet@google.com
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 edumazet@google.com Signed-off-by: David S. Miller davem@davemloft.net (cherry picked from commit 88078d98d1bb085d72af8437707279e203524fa5) --- include/linux/skbuff.h | 5 ++--- net/core/skbuff.c | 14 ++++++++++++++ 2 files changed, 16 insertions(+), 3 deletions(-)
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index 9c8457375aee..758084b434c8 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -3135,6 +3135,7 @@ static inline void *skb_push_rcsum(struct sk_buff *skb, unsigned int len) return skb->data; }
+int pskb_trim_rcsum_slow(struct sk_buff *skb, unsigned int len); /** * pskb_trim_rcsum - trim received skb and update checksum * @skb: buffer to trim @@ -3148,9 +3149,7 @@ static inline int pskb_trim_rcsum(struct sk_buff *skb, unsigned int len) { if (likely(len >= skb->len)) return 0; - if (skb->ip_summed == CHECKSUM_COMPLETE) - skb->ip_summed = CHECKSUM_NONE; - return __pskb_trim(skb, len); + return pskb_trim_rcsum_slow(skb, len); }
static inline int __skb_trim_rcsum(struct sk_buff *skb, unsigned int len) diff --git a/net/core/skbuff.c b/net/core/skbuff.c index 8fd690def5c1..168a3e8883d4 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -1839,6 +1839,20 @@ int ___pskb_trim(struct sk_buff *skb, unsigned int len) } 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