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 <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit 88078d98d1bb085d72af8437707279e203524fa5)
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 4e545e4..038ec74 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -1578,6 +1578,20 @@
}
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