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

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Message-Id: <BD281C0E-5278-4944-ABF0-AF692325945C@e18.physik.tu-muenchen.de>
Date:	Mon, 7 May 2007 21:59:15 +0200
From:	Roland Kuhn <rkuhn@....physik.tu-muenchen.de>
To:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Cc:	Andrey Borzenkov <arvidjaar@...l.ru>, linux-kernel@...r.kernel.org
Subject: Re: Long file names in VFAT broken with iocharset=utf8

Hi!

On 7 May 2007, at 20:27, OGAWA Hirofumi wrote:

> 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 NUL"? Adding unicode parsing to the kernel is completely  
useless _and_ a big trouble maker.

Ciao,
                     Roland

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