netdev - Re: [PATCH] netfilter: xt

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Message-ID: <20120514190211.GC14897@1984>
Date:	Mon, 14 May 2012 21:02:11 +0200
From:	Pablo Neira Ayuso <pablo@...filter.org>
To:	Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>
Cc:	Hans Schillstrom <hans.schillstrom@...csson.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Jan Engelhardt <jengelh@...i.de>,
	"kaber@...sh.net" <kaber@...sh.net>,
	"jengelh@...ozas.de" <jengelh@...ozas.de>,
	"netfilter-devel@...r.kernel.org" <netfilter-devel@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"dan.carpenter@...cle.com" <dan.carpenter@...cle.com>,
	"hans@...illstrom.com" <hans@...illstrom.com>
Subject: Re: [PATCH] netfilter: xt_HMARK: endian bugs

On Mon, May 14, 2012 at 08:35:26PM +0200, Jozsef Kadlecsik wrote:
> On Mon, 14 May 2012, Hans Schillstrom wrote:
> 
> > On Monday 14 May 2012 18:24:34 Eric Dumazet wrote:
> > > On Mon, 2012-05-14 at 18:09 +0200, Hans Schillstrom wrote:
> > > 
> > > > This context can contain both le & be machines,
> > > > so at least in hmark it make sense
> > > 
> > > Before jhash() and its shuffle ? What do you mean ?
> > 
> > I want that a Big endian machine should produce the same
> > hash value independent of flow direction as a Little endian.
> > 
> > OK, I missed ntohl() before calling jhash_3words()
> > 
> > Correct me if I'm wrong here (have no big endian machine available for test)
> > jhash_3words() and __jhash_final() seems to be "endian" safe.
> 
> No, but as Eric wrote: what is the point in forcing the same hash value 
> for the same input on big endian and little endian machines? Are you going 
> to transfer the hash value between machines?

IIRC, Hans wants that, in case you have a cluster composed of system
with different endianess, the hash mark calculated will be the same
in both systems. To ensure that the distribution is consistent with
independency of the endianess.
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