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

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Date:	Tue, 08 May 2007 06:01:07 +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

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

>> Roland Kuhn <rkuhn@....physik.tu-muenchen.de> writes:
>>> 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.
>>
> No, we don't. At least not when looking at the POSIX spec, which  
> explicitly mentions _bytes_ and _not_ unicode characters. So, to be  
> on the safe side, FAT filesystems would need to support a NAME_MAX of  
> roughly 6*255+3=1533 bytes (not to mention the hassles of forbidden  
> sequences, etc.; do we need to count zero-width characters?) and  
> report it through pathconf() to userspace, then userspace could do  
> with that whatever it liked.
>
> What happened to: "file names are just sequences of octets, excluding  
> '/' and UL"? Adding unicode parsing to the kernel is completely  
> useless _and_ a big trouble maker.

The UCS2 in FAT is just on-disk format of the filename. So...
-- 
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
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