netdev - Re: [PATCH v2] netfilter: save the hash of the tuple in the original direction for latter use

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Date:	Fri, 20 Aug 2010 09:43:14 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Changli Gao <xiaosuo@...il.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Patrick McHardy <kaber@...sh.net>,
	"David S. Miller" <davem@...emloft.net>,
	netfilter-devel@...r.kernel.org, netdev@...r.kernel.org,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] netfilter: save the hash of the tuple in the
	original direction for latter use

[ executive summary: trying to explain why static variable declarations
  within the body of functions is bad in kernel code. ]

* Changli Gao (xiaosuo@...il.com) wrote:
> On Fri, Aug 20, 2010 at 12:11 AM, Mathieu Desnoyers
> <mathieu.desnoyers@...ymtl.ca> wrote:
> >
> > Ah, I see. But I think the static variable should stay declared outside
> > of the function scope, with a nice comment explaining why it's not
> > initialized at init-time.
> >
> > Hiding global state in function code is usually frowned upon.
> >
> 
> I don't agree with you. We'd better not expose the variable which
> isn't expected to be used by others. If not, maybe someone will misuse
> it.

We are talking about a static variable usable only within a single file,
where is the problem ? A nice comment can have this effect.

> The user should only reply on the interface, but not the internal
> implementation.

I'm talking about good practice to help code review. This is way more
important than the potential "encapsulation" benefit of hiding global
state (a static variable) within the body of a function.

I remember that Andrew Morton has strong opinions about this, and I
remember being in complete agreement with him on the topic.

Thanks,

Mathieu

> 
> Thanks.
> 
> -- 
> Regards,
> Changli Gao(xiaosuo@...il.com)

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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