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net: explain __skb_checksum_complete() with comments

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Cc: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Cong Wang 2018-11-26 09:31:26 -08:00 committed by David S. Miller
parent 19bf62613a
commit 1464193107
2 changed files with 18 additions and 1 deletions
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1
net/core/dev.c
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@ -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)

18
net/core/skbuff.c
View File

@ -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)