src: add hash expression

This is special expression that transforms an input expression into a
32-bit unsigned integer. This expression takes a modulus parameter to
scale the result and the random seed so the hash result becomes harder
to predict.

You can use it to set the packet mark, eg.

 # nft add rule x y meta mark set jhash ip saddr . ip daddr mod 2 seed 0xdeadbeef

You can combine this with maps too, eg.

 # nft add rule x y dnat to jhash ip saddr mod 2 seed 0xdeadbeef map { \
	0 : 192.168.20.100, \
	1 : 192.168.30.100 \
   }

Currently, this expression implements the jenkins hash implementation
available in the Linux kernel:

 http://lxr.free-electrons.com/source/include/linux/jhash.h

But it should be possible to extend it to support any other hash
function type.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/src/Makefile.am b/src/Makefile.am
index 241a078b..63bbef2c 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -36,6 +36,7 @@ nft_SOURCES =	main.c				\
 		proto.c				\
 		payload.c			\
 		exthdr.c			\
+		hash.c				\
 		meta.c				\
 		numgen.c			\
 		ct.c				\