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| author | Cong Wang <xiyou.wangcong@gmail.com> | 2018-11-26 09:31:26 -0800 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2018-11-29 13:47:16 -0800 |
| commit | 1464193107da8041e05341388964733bbba3be27 (patch) | |
| tree | 4cb7f9a9342d0a532d10965098faee255632efe4 /net/core/skbuff.c | |
| parent | 19bf62613a800ef4ffa26cbae6b723d9f46740ed (diff) | |
| download | linux-1464193107da8041e05341388964733bbba3be27.tar.bz2 | |
net: explain __skb_checksum_complete() with comments
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>
Diffstat (limited to 'net/core/skbuff.c')
| -rw-r--r-- | net/core/skbuff.c | 18 |
1 files changed, 17 insertions, 1 deletions
diff --git a/net/core/skbuff.c b/net/core/skbuff.c index 02cd7ae3d0fb..3c814565ed7c 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -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) |