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Date: Fri, 28 Mar 2008 14:07:34 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Sam Ravnborg <sam@ravnborg.org>
CC: LKML <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@elte.hu>
Subject: Re: use of volatile in iounmap()?
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Sam Ravnborg wrote:
>>>
>> Yes.  The use of volatile in a function prototype like this means that 
>> it is valid to pass a volatile pointer to that function -- in other 
>> words, we're telling gcc that we're not going to do anything with the 
>> pointer that is invalid for a volatile pointer.

> If I understand you correct then it is then not wrong to say
> that we have the argument volatile to avoid warnings from gcc
> when we pass a volatile pointer.
> 
> And then having the pointer marked volatile put a few restrictions
> on iounmap().

Correct.

>> A lot of the "volatile considered harmful" stuff that has been bandied 
>> about is explicitly about marking *data* items volatile (it does have 
>> its uses, but it's easy to get wrong); Linus has explicitly made the 
>> distinction between volatile *data* and volatile *operations*.
> 
> Yes - but unfortunately the volatile-considered-harmful.txt
> does many deal with the data part.

Yes, it does.

	-hpa