linux-kernel - Re: [PATCH] Added CONFIG_VFAT_FS

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Message-ID: <20090701151727.38928bd9@lxorguk.ukuu.org.uk>
Date:	Wed, 1 Jul 2009 15:17:27 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Theodore Tso <tytso@....edu>
Cc:	Rusty Russell <rusty@...tcorp.com.au>, Pavel Machek <pavel@....cz>,
	tridge@...ba.org, OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
	john.lanza@...ux.com, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	Dave Kleikamp <shaggy@...ux.vnet.ibm.com>,
	Steve French <sfrench@...ibm.com>,
	Mingming Cao <cmm@...ibm.com>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH] Added CONFIG_VFAT_FS_DUALNAMES option

> > shouldn't accidentally be able to specify -o vfat and get non-vfat. Thats
> > asking for incompatibility, data loss and unpleasant unwarned of suprises.
> 
> There really was no such thing as "vfat" anyway.  VFAT in the Windows

In the eyes of the end user there is such a thing as vfat. This is about
expectations not technical issues.
 
> Arguably what we should have done is kept it as a single filesystem,
> with a mount options "lfn" and "nolfn", but that's water under the
> bridge now.

Well we didn't so now we need to add "lfat" or similar for our fat style.
Doesn't need new code just making sure that USSA_COMPLIANCE_MODE=y
causes mount -o lfat to work and without it both lfat and vfat work.

> The other big user I can think of are digital cameras, but (a)
> normally most users read from them and then delete the pictures, and
> rarely write to media meant for a digital camera, and (b) the DCIM

Except when they hit save instead of "save as" and they get a long file
name and invisible loss of space on the camera.

> standard for digital cameras explicitly only supports 8.3 filenames
> and so digital camera manufacturers explicitly don't need to deal with
> Long File Names at all.  (Hmm.... I wonder why....)  

Can't think - but HAL should clearly mount those 8.3 to avoid the
problem. It seems to use the dcim to find them.

> This suggests that some userspace mechanism for detecting media cards
> used for cameras and explicitly mounting them with FAT might be useful

HAL is very good at that already.

> Ultimately, though, requiring that every single possible device be
> tested is probably not reasonable, so the best way to do this testing
> is the way do most of our testing; we do basic due diligence, but then
> we merge it into mainline and let our huge user community try it out.
> If there are regressions we can work through those issues if and when
> they arise.

>From the funnies we've had in the past with FAT my gut impression is
there are only a few implementations out there. Psion seems to have their
own but most of the rest behave remarkably similarly which makes me
suspect they all licensed a tiny number of implementations (DRDOS one
perhaps ?). If we can keep most of those devices mounted 8.3 we nicely
sidestep the issue anyway.

Alan
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