net: explain __skb_checksum_complete() with comments (14641931) · Commits · 戴 / test

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)

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