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, 3 insertions, 0 deletions

diff --git a/src/scanner.l b/src/scanner.l
index cff375f3..8b5a383b 100644
--- a/src/scanner.l
+++ b/src/scanner.l
@@ -471,6 +471,9 @@ addrstring	({macaddr}|{ip4addr}|{ip6addr})
 "inc"			{ return INC; }
 "mod"			{ return MOD; }
 
+"jhash"			{ return JHASH; }
+"seed"			{ return SEED; }
+
 "dup"			{ return DUP; }
 "fwd"			{ return FWD; }