[NET]: Update comments for skb checksums

Rusty (whose comments we should all study and emulate :) pointed
out that our comments for skb checksums are no longer up-to-date.
So here is a patch to

1) add the case of partial checksums on input;
2) update partial checksum case to mention csum_start/csum_offset;
3) mention the new IPv6 feature bit.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 10 insertions, 2 deletions

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 625d73b07ab7..9391e4a4c344 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -65,13 +65,20 @@
  *          is able to produce some skb->csum, it MUST use COMPLETE,
  *          not UNNECESSARY.
  *
+ *      PARTIAL: identical to the case for output below.  This may occur
+ *          on a packet received directly from another Linux OS, e.g.,
+ *          a virtualised Linux kernel on the same host.  The packet can
+ *          be treated in the same way as UNNECESSARY except that on
+ *          output (i.e., forwarding) the checksum must be filled in
+ *          by the OS or the hardware.
+ *
  * B. Checksumming on output.
  *
  *      NONE: skb is checksummed by protocol or csum is not required.
  *
  *      PARTIAL: device is required to csum packet as seen by hard_start_xmit
- *      from skb->transport_header to the end and to record the checksum
- *      at skb->transport_header + skb->csum.
+ *      from skb->csum_start to the end and to record the checksum
+ *      at skb->csum_start + skb->csum_offset.
  *
  *      Device must show its capabilities in dev->features, set
  *      at device setup time.
@@ -82,6 +89,7 @@
  *                        TCP/UDP over IPv4. Sigh. Vendors like this
  *                        way by an unknown reason. Though, see comment above
  *                        about CHECKSUM_UNNECESSARY. 8)
+ *      NETIF_F_IPV6_CSUM about as dumb as the last one but does IPv6 instead.
  *
  *      Any questions? No questions, good.              --ANK
  */