[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>

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 625d73b07ab79c7925865a36e0d7fbcf3abb7805..9391e4a4c3447d53b73dba487255cab67ef24b6e 100644 (file)
--- 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
  */