linux-kernel - Re: [RFC/PATCH] doc: volatile considered evil

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Message-ID: <20070509094305.GC28774@linuxtv.org>
Date:	Wed, 9 May 2007 11:43:05 +0200
From:	Johannes Stezenbach <js@...uxtv.org>
To:	Jonathan Corbet <corbet@....net>
Cc:	Randy Dunlap <randy.dunlap@...cle.com>,
	Paul Sokolovsky <pmiscml@...il.com>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC/PATCH] doc: volatile considered evil

On Tue, May 08, 2007, Jonathan Corbet wrote:
> 
> I just took a shot at turning this into something more like a normal
> document:
> 
> 	http://lwn.net/Articles/233479/

I think the "jiffies variable is special" part misses the
"for stupid legacy reasons" explanation.

According to the other volatile rules one should use
something like that:

extern unsigned long __jiffies;
static inline unsigned long read_ulong(unsigned long *addr)
{
	return *(volatile unsigned long *)addr;
}
static inline unsigned long get_jiffies(void)
{
	return read_ulong(&__jiffies);
}

But of course changing all references to jiffies in the kernel would
be insane, thus jiffies is special "for stupid legacy reasons".

Right?


Johannes
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