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

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Message-ID: <87mz10tyi1.fsf@duaron.myhome.or.jp>
Date:	Sun, 22 Apr 2007 20:55:02 +0900
From:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To:	DervishD <lkml@...vishd.net>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Juergen Beisert <juergen127@...uzholzen.de>,
	linux-kernel@...r.kernel.org
Subject: Re: Wrong free clusters count on FAT32

DervishD <lkml@...vishd.net> writes:

>     The problem is that if a program writes a file onto the filesystem
> without using statfs first to check for free space, the free_clusters
> entry won't have the real value and the driver may report "disk full" (I
> haven't read the code for the vfat driver, sorry, so I'm not sure about
> this) when really there are plenty of clusters to write the new file.

No need to worry about it. If we ignored the ->free_clusters in
FSINFO, the fat drivers counts the current free clusters by scaning
FAT entries if needed.

>     Probably it's stupid to update the free clusters count at mount time
> (sorry if so...) but it looks like a good idea to me. And of course, I
> don't mean to update the value _on disk_, but the kernel's idea of free
> clusters (so even FAT filesystems mounted R/O will report correct
> values).

It would add the limitation to following simple usage,

	# mount -t vfat /dev/sda1 /mnt
        # cp -a * /mnt
        # umount

if /dev/sda1 was the large and slow device, "mount" will need several
minutes to counts free clusters. I think the user will be hard to
accept the several minutes at "mount".

Thanks.
-- 
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
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