linux-kernel - Re: Wrong free clusters count on FAT32

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Date:	Sun, 22 Apr 2007 22:11:15 +0200
From:	DervishD <lkml@...vishd.net>
To:	Bodo Eggert <7eggert@....de>
Cc:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
	Juergen Beisert <juergen127@...uzholzen.de>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: Wrong free clusters count on FAT32

    Hi Bodo :)

 * Bodo Eggert <7eggert@....de> dixit:
> OGAWA Hirofumi <hirofumi@...l.parknet.co.jp> wrote:
> >>  * Juergen Beisert <juergen127@...uzholzen.de> dixit:
> 
> >>> So the last free sector count is also stored. When mounting this
> >>> filesystem you don't need to walk through the whole FAT to calculate
> >>> the available space, you can use this "cached" value instead. And this
> >>> cached value seems not to be updated in your portable device.
> >>
> >>     It doesn't, certainly, but Windows doesn't care. Moreover, the
> >> device doesn't seem to recalculate the value on every run (unless it
> >> does it lightning fast!), so maybe the number is stored elsewhere (the
> >> count can be stored in many places as far as I've read, but I don't know
> >> the details).
> 
> AFAIR it's stored twice on FAT32, once in a backup sector and once in the
> superblock or extended superblock (don't remember, I think it was the
> extended ~). It's not stored on FAT{12,16}.

    I hadn't noticed the same problem with FAT16 pendrives, so I
suspected that. Thanks for confirming :)

    Raúl Núñez de Arenas Coronado

-- 
Linux Registered User 88736 | http://www.dervishd.net
It's my PC and I'll cry if I want to... RAmen!
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