Commit 14641931 authored by Cong Wang's avatar Cong Wang Committed by David S. Miller
Browse files

net: explain __skb_checksum_complete() with comments 



Cc: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: default avatarCong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 19bf6261

net/core/dev.c

+1 −0
Original line number Diff line number Diff line
@@ -5791,6 +5791,7 @@ __sum16 __skb_gro_checksum_complete(struct sk_buff *skb) 


	/* NAPI_GRO_CB(skb)->csum holds pseudo checksum */

	sum = csum_fold(csum_add(NAPI_GRO_CB(skb)->csum, wsum));

	/* See comments in __skb_checksum_complete(). */

	if (likely(!sum)) {

		if (unlikely(skb->ip_summed == CHECKSUM_COMPLETE) &&

		    !skb->csum_complete_sw)

net/core/skbuff.c

+17 −1
Original line number Diff line number Diff line
@@ -2635,6 +2635,7 @@ __sum16 __skb_checksum_complete_head(struct sk_buff *skb, int len) 
	__sum16 sum;



	sum = csum_fold(skb_checksum(skb, 0, len, skb->csum));

	/* See comments in __skb_checksum_complete(). */

	if (likely(!sum)) {

		if (unlikely(skb->ip_summed == CHECKSUM_COMPLETE) &&

		    !skb->csum_complete_sw)
@@ -2646,6 +2647,15 @@ __sum16 __skb_checksum_complete_head(struct sk_buff *skb, int len) 
}

EXPORT_SYMBOL(__skb_checksum_complete_head);



/* This function assumes skb->csum already holds pseudo header's checksum,

 * which has been changed from the hardware checksum, for example, by

 * __skb_checksum_validate_complete(). And, the original skb->csum must

 * have been validated unsuccessfully for CHECKSUM_COMPLETE case.

 *

 * It returns non-zero if the recomputed checksum is still invalid, otherwise

 * zero. The new checksum is stored back into skb->csum unless the skb is

 * shared.

 */

__sum16 __skb_checksum_complete(struct sk_buff *skb)

{

	__wsum csum;
@@ -2653,8 +2663,14 @@ __sum16 __skb_checksum_complete(struct sk_buff *skb) 


	csum = skb_checksum(skb, 0, skb->len, 0);



	/* skb->csum holds pseudo checksum */

	sum = csum_fold(csum_add(skb->csum, csum));

	/* This check is inverted, because we already knew the hardware

	 * checksum is invalid before calling this function. So, if the

	 * re-computed checksum is valid instead, then we have a mismatch

	 * between the original skb->csum and skb_checksum(). This means either

	 * the original hardware checksum is incorrect or we screw up skb->csum

	 * when moving skb->data around.

	 */

	if (likely(!sum)) {

		if (unlikely(skb->ip_summed == CHECKSUM_COMPLETE) &&

		    !skb->csum_complete_sw)