tree 9c3251d5226c75826a19f10d33e3b7279d6f0969
parent e51271d4ce7b229f5c02903e3c44bf92c0dbef6b
author Edward Cree <ecree@solarflare.com> 1455223684 +0000
committer David S. Miller <davem@davemloft.net> 1455274335 -0500

net: local checksum offload for encapsulation

The arithmetic properties of the ones-complement checksum mean that a
 correctly checksummed inner packet, including its checksum, has a ones
 complement sum depending only on whatever value was used to initialise
 the checksum field before checksumming (in the case of TCP and UDP,
 this is the ones complement sum of the pseudo header, complemented).
Consequently, if we are going to offload the inner checksum with
 CHECKSUM_PARTIAL, we can compute the outer checksum based only on the
 packed data not covered by the inner checksum, and the initial value of
 the inner checksum field.

Signed-off-by: Edward Cree <ecree@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>