Subject: Re: End of FAT directories
From: Michael Karcher <kernel@mkarcher.dialup.fu-berlin.de>
To: Pavel Machek <pavel@ucw.cz>
Cc: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>,
        dosfstools <daniel@debian.org>, mtools <Alain@linux.lu>,
        linux-kernel@vger.kernel.org
In-Reply-To: <20110428132551.GA5701@ucw.cz>
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Date: Thu, 28 Apr 2011 15:43:05 +0200
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Am Donnerstag, den 28.04.2011, 15:25 +0200 schrieb Pavel Machek:
> > >  For overwriting the
> > > zeroed entry, why we have to check all entries until see next zeroed
> > > (yeah, now, we allowed the crappy data after zeroed)?
> > My point was not about checking all entries until the next zeroed entry,
> > which is overcomplicating stuff. I meant that if we hit the end (i.e.
> > the first zeroed entry) when searching for free slots, in that case we
> > just clear the one entry directly following the inserted entries. This
> > makes sure that no files magically appear. I *do* understand that
> This sounds like a good idea, and costs nothing. I hope we can
> convince Ogawa...

I am going to implement that and publish a patch. If the patch is clean
enough, maybe we can convince him. But the freedom of open source can't
prevent me from using a patch like that, of course. And maybe it also
helps when the patch gets some testing.

> > I think the *most* important fact is to have at least dosfsck and linux
> > consistent about directories with trailing garbage. So I won't even try
> > to submit a patch to the Linux kernel that stops reading at the first
> > unused directory entry if dosfsck will not accept to stop reading at the
> > first unused directory entry.
> They should *not* be consistent.
> 
> Kernel should stop at zero invalid entry.
> 
> fsck should consider any garbage past zero entry as an error, and zero
> it out. (Complaining about duplicate blocks is unhelpful but better
> than nothing.  It should really zero the garbage out.)

In fact, what you describe is something I would call "consistent". I was
not implying that kernel and dosfsck should do exactly the same thing,
but I was implying that the kernel and dosfsck should either both or
none consider entries past the gap as existing file. Current state is:
both consider past-gap entries valid. Your described state will be: none
consider past-gap entries valid. The behaviour you describe is exactly
what I would imagine as best way to go. Maybe fsck should ask for "shift
post-gap entries/create a dummy deleted entry" vs. "clear post-gap
entries".

Regards,
  Michael Karcher


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