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Date:   Wed, 16 Oct 2019 09:50:01 -0700
From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     Pali =?iso-8859-1?Q?Roh=E1r?= <pali.rohar@gmail.com>
Cc:     Sasha Levin <sashal@kernel.org>, devel@driverdev.osuosl.org,
        Valdis =?utf-8?Q?Kl=C4=93tnieks?= <valdis.kletnieks@vt.edu>,
        Christoph Hellwig <hch@infradead.org>,
        linux-kernel@vger.kernel.org,
        Sasha Levin <alexander.levin@microsoft.com>,
        linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH] staging: exfat: add exfat filesystem code to staging
Message-ID: <20191016165001.GA639209@kroah.com>
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On Wed, Oct 16, 2019 at 06:32:31PM +0200, Pali Roh?r wrote:
> On Wednesday 16 October 2019 09:22:11 Greg Kroah-Hartman wrote:
> > On Wed, Oct 16, 2019 at 06:03:49PM +0200, Pali Roh?r wrote:
> > > > Can I assume you will be implementing TexFAT support once the spec is
> > > > available?
> > > 
> > > I cannot promise that I would implement something which I do not know
> > > how is working... It depends on how complicated TexFAT is and also how
> > > future exfat support in kernel would look like.
> > > 
> > > But I'm interesting in implementing it.
> > 
> > What devices need TexFAT?  I thought it the old devices that used it are
> > long obsolete and gone.  How is this feature going to be tested/used?
> 
> Hi Greg! Per 3.1.16 of exFAT specification [1], TexFAT extension is the
> only way how to use more FAT tables, like in FAT32 (where you normally
> have two FATs). Secondary FAT table can be used e.g. for redundancy or
> data recovery. For FAT32 volumes, e.g. fsck.fat uses secondary FAT table
> when first one is corrupted.
> 
> Usage of just one FAT table in exFAT is just step backward from FAT32 as
> secondary FAT table is sometimes the only way how to recover broken FAT
> fs. So I do not think that exFAT is for old devices, but rather
> non-exFAT is for old devices. Modern filesystems have journal or other
> technique to do (fast|some) recovery, exFAT has nothing.
> 
> And how is this feature going to be used? That depends on specification.
> 
> [1] - https://docs.microsoft.com/en-us/windows/win32/fileio/exfat-specification#3116-numberoffats-field

Ok, but given that the "only" os that can read/write the TexFAT
extension is WinCE, and that os is obsolete these days, it might be hard
to find images to test/validate against :)

But hey, I'll take the patch if you write it, no objection!

thanks,

greg k-h