linux-kernel - Re: Long file names in VFAT broken with iocharset=utf8

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Message-Id: <60F72760-C801-4F60-BF47-C661B4B5BE26@e18.physik.tu-muenchen.de>
Date:	Mon, 7 May 2007 20:07:26 +0200
From:	Roland Kuhn <rkuhn@....physik.tu-muenchen.de>
To:	Andrey Borzenkov <arvidjaar@...l.ru>
Cc:	hirofumi@...l.parknet.co.jp, linux-kernel@...r.kernel.org
Subject: Re: Long file names in VFAT broken with iocharset=utf8

Hi Andrey!

On 7 May 2007, at 19:51, Andrey Borzenkov wrote:

> This was posted in one of Russian forums. It was not possible to  
> archive
> (under Linux, using tar) vfat directory where files had long  
> Russian names
> (really long - over 150 - 170 characters) - tar returned stat  
> failure. When
> looking with plain ls, file names appeared truncated.
>
> Now looking at current (2.6.21) fat driver, __fat_readdir allocates  
> large
> enough buffer (PAGE_SIZE-522) for UTF-8 name; but for  
> iocharset=utf8 it calls
> uni16_to_x8() which artificially limits length of UTF-8 name to  
> 256 ... which
> is obviously not enough for long UTF-8 Russian string (2 bytes per  
> character)
> not to mention the - theoretical - general case of 6 bytes UTF-8  
> characters.
>
> Similar problem has apparently vfat_lookup()->...->fat_search_long 
> () call
> chain. Except this appears to be broken even in case of "utf8",  
> because
> fat_search_long allocates fixed 256 bytes buffer for UTF-8 name.
>
> Am I off track here?
>
PATH_MAX specifically counts _bytes_ not characters, so UTF-8 does  
not matter. ISTR that PATH_MAX was 256 at some point, but I just  
quickly grepped /usr/include and found various mention of 4096, so  
where's the central repository for this configuration item? A hard- 
coded value of 256 somewhere inside the kernel smells like a bug.

Ciao,
                     Roland

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