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

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Message-ID: <87fy685w0m.fsf@duaron.myhome.or.jp>
Date:	Tue, 08 May 2007 03:27:53 +0900
From:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To:	Roland Kuhn <rkuhn@....physik.tu-muenchen.de>
Cc:	Andrey Borzenkov <arvidjaar@...l.ru>, linux-kernel@...r.kernel.org
Subject: Re: Long file names in VFAT broken with iocharset=utf8

Hi,

Roland Kuhn <rkuhn@....physik.tu-muenchen.de> writes:

>> 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.

There is a nasty issue here. FAT is limited by 255 unicode chars or so.
So, we would need to count number of unicode chars of filename.

That's not implemented currently.
-- 
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
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