linux-kernel - Re: Linux & FAT32 label

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Message-ID: <20171216224510.cepzvrctqypp2s25@pali>
Date:   Sat, 16 Dec 2017 23:45:10 +0100
From:   Pali Rohár <pali.rohar@...il.com>
To:     Andreas Bombe <aeb@...ian.org>
Cc:     util-linux@...r.kernel.org, linux-kernel@...r.kernel.org,
        Karel Zak <kzak@...hat.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Pavel Machek <pavel@....cz>
Subject: Re: Linux & FAT32 label

On Thursday 09 November 2017 22:21:31 Pali Rohár wrote:
> So from all tests and discussion I would propose new unification:
> 
> 1. Read label only from the root directory. If label in root directory
>    is missing then disk would be treated as without label. Label from
>    boot sector would not be read.
> 
>    --> Reason: Windows XP and mlabel ignores what is written in boot
>        sector. Windows XP even do not update boot sector, so label
>        stored in boot sector is incorrect after any change done by
>        Windows XP.
> 
>        This logic is used by all tested MS-DOS and Windows versions,
>        plus also by mtools on Linux.
> 
> 2. Write label to to both location, boot sector and root directory.
> 
>    --> Reason: MS-DOS 6.22, MS-DOS 7.10, Windows 98 and also mtools on
>        Linux do this. This is also what is written in FAT specification.
> 
>        It also provides backward compatibility with old dosfslabel
>        versions which read label only from boot sector.
> 
> 2. Process 'NO NAME    ' label in root directory as 'NO NAME' name. Not
>    as empty label.
> 
>    --> Reason: 'NO NAME    ' is regular entry in root directory and both
>        Windows XP and mlabel handle it in this way.
> 
> 3. Process 'NO NAME    ' label in boot directory as empty label. Not as
>    label with name 'NO NAME'.
> 
>    --> Reason: On Windows XP when formatting empty disk and label is not
>        specified then 'NO NAME    ' is stored to boot sector.
> 
>        Also in FAT specification is written that empty label is stored
>        as 'NO NAME    '.
> 
> With this change we would get compatibility with MS-DOS, Windows (both
> DOS-based and NT-based) and also with Linux mtools, modulo problems DOS
> code page.
> 
> There are just two negatives:
> 
> 1) Labels set by old dosfslabel versions (which stored them only to boot
>    sector) would not be visible. But they are already not visible on
>    MS-DOS or Windows machines, and also via mlabel (from mtools).
> 
> 2) Behavior of blkid and fatlabel would be changed as both tools have
>    different as proposed above, and based on tests they also differ each
>    from other.
> 
> Andreas, Karel, what do you think about it?

Andreas, any comments? It is OK?

More then month passed... and I would like to move forward.

-- 
Pali Rohár
pali.rohar@...il.com