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Commit 791521e2 authored by Eric Dumazet's avatar Eric Dumazet Committed by Greg Kroah-Hartman
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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: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
(cherry picked from commit 88078d98d1bb085d72af8437707279e203524fa5)
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent a8444b1c

include/linux/skbuff.h

+2 −3
Original line number Diff line number Diff line
@@ -2954,6 +2954,7 @@ static inline unsigned char *skb_push_rcsum(struct sk_buff *skb, 
	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
@@ -2967,9 +2968,7 @@ 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)

net/core/skbuff.c

+14 −0
Original line number Diff line number Diff line
@@ -1578,6 +1578,20 @@ 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