netdev - Re: [PATCH] xfrm: xfrm hash to use Jenkins' hash

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Date:	Thu, 6 Aug 2009 11:58:55 +0300 (EEST)
From:	Jussi Maki <jmaki@...apiiri.net.net>
To:	Jussi Maki <joamaki@...il.com>
cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH] xfrm: xfrm hash to use Jenkins' hash


Hi,

Did some testing and one possible fix to this problem
would be to change the xor to addition. Would this be OK?

---
 net/xfrm/xfrm_hash.h |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/net/xfrm/xfrm_hash.h b/net/xfrm/xfrm_hash.h
index d401dc8..e5195c9 100644
--- a/net/xfrm/xfrm_hash.h
+++ b/net/xfrm/xfrm_hash.h
@@ -16,7 +16,7 @@ static inline unsigned int __xfrm6_addr_hash(xfrm_address_t *addr)
 
 static inline unsigned int __xfrm4_daddr_saddr_hash(xfrm_address_t *daddr, xfrm_address_t *saddr)
 {
-	return ntohl(daddr->a4 ^ saddr->a4);
+	return ntohl(daddr->a4 + saddr->a4);
 }
 
 static inline unsigned int __xfrm6_daddr_saddr_hash(xfrm_address_t *daddr, xfrm_address_t *saddr)
-- 
1.5.6.5

On Thu, 6 Aug 2009, Jussi Maki wrote:

> Hi David,
> 
> Changing the (h >> 16) to ((h >> 16) ^ (h >> 24)) still has the same
> problem as given in the example,
> that is if you have a set of transports with incrementing addresses
> (192.168.0.1-172.16.0.1, 192.168.0.2-172.16.0.2,..) they
> still hash to the same value. The reason to this is that it's doing
> src^dst in __xfrm4_daddr_saddr_hash.
> 
> Should I pursue with fixing the inlining issue in my patch or would
> you have any suggestions how I could
> fix this by perhaps modifying __xfrm4_daddr_saddr_hash?
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