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Date: Wed, 23 Mar 2011 23:08:43 +0000
From: Stuart Swales <stuart.swales.croftnuisk@gmail.com>
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To: Andrew Morton <akpm@linux-foundation.org>
CC: Geert Uytterhoeven <geert@linux-m68k.org>,
        Russell King <rmk+kernel@arm.linux.org.uk>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] adfs: add hexadecimal filetype suffix option
References: <4D2DEDDB.1070605@gmail.com>	<20110119154915.a0bb2878.akpm@linux-foundation.org>	<AANLkTimpYyErnvEjSCevMCcKTW5ffyi9V5EB3U8RwuBG@mail.gmail.com> <20110323135835.0c2e296c.akpm@linux-foundation.org>
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The file typing code is using -1 (truncated to __u16) to represent the 
case when no explicit 12-bit file type was set on the file, such as is 
the case where the file has explicit 32-bit load and execute addresses 
(Acorn specific legacy stuff, started with the BBC Micro).  It would 
seem to be best if the -1 were replaced by 0xffffu.

Stuart

On 23/03/2011 20:58, Andrew Morton wrote:
> On Wed, 23 Mar 2011 21:36:48 +0100
> Geert Uytterhoeven<geert@linux-m68k.org>  wrote:
>
>> On Thu, Jan 20, 2011 at 00:49, Andrew Morton<akpm@linux-foundation.org>  wrote:
>>> On Wed, 12 Jan 2011 18:07:23 +0000
>>> Stuart Swales<stuart.swales.croftnuisk@gmail.com>  wrote:
>>>> From: Stuart Swales<stuart.swales.croftnuisk@gmail.com>
>>
>>>> +static inline int append_filetype_suffix(char *buf, __u16 filetype)
>>>> +{
>>>> + __ __ if ((__u16) -1 == filetype)
>>>
>>> unneeded cast.
>>
>> My compiler tends to disagree. On current mainline, it says:
>>
>> fs/adfs/adfs.h: In function ___append_filetype_suffix___:
>> fs/adfs/adfs.h:115: warning: comparison is always false due to limited
>> range of data type
>>
>
> hm, OK, I'll add a cast.
>
> The code seems a bit fishy - it wants 0xffff but the comment says it's
> handling a 12-bit quantity.  Obviously the all-ones pattern has some
> magical out-of-band meaning here, but it is not explained what that
> meaning *is*.  Perhaps that is described elsewhere.
>


-- 
Stuart Swales