linux-kernel - Re: [PATCH] Check for Null return of function of affs_bread in function affs

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Date:	Fri, 20 Jun 2014 20:09:18 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Nick Krause <xerofoify@...il.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Dan Carpenter <dan.carpenter@...cle.com>,
	viro@...iv.linux.org.uk, fabf@...net.be,
	kirill.shutemov@...ux.intel.com, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Check for Null return of function of affs_bread in
 function affs_truncate

On Fri, 20 Jun 2014 22:55:07 -0400 Nick Krause <xerofoify@...il.com> wrote:

> On Fri, Jun 20, 2014 at 10:38 PM, Andrew Morton
> <akpm@...ux-foundation.org> wrote:
> > On Fri, 20 Jun 2014 22:25:47 -0400 Nick Krause <xerofoify@...il.com> wrote:
> >
> >> If you have any ideas about what is better
> >> please let me known.
> >
> > I think the proposed patch was not a good one - it will cause truncate
> > to silently return, probably leaving the fs in an inconsistent state.
> > Neither the user nor the running application know this happened so they
> > will just keep on modifying the filesystem, possibly mangling it
> > further.
> >
> > The code as it stands at present is better - if bread() fails we'll get
> > a nice solid oops and the current app will be terminated (at least).
> > As we're in truncate it's quite possible that the entire fs will get
> > wedged up due to now-permanently-held i_mutex, which is even better.
> >
> >
> > As for the best fix, umm, hard.  We're pretty screwed if we cannot read
> > that block at this code site.  Perhaps emit loud printks, forcibly turn
> > the fs read-only then return -EIO/-ENOMEM/etc from the truncate.  Such
> > a change would require runtime testing, with some form of developer fault
> > injection.
>
> Fair enough if somebody is running this file system I would be
> happy to have someone test my code in order to fix this.

(top-posting repaired - please don't top-post!)

It's going to be hard to find such a person.  As mkfs.affs doesn't
appear to exist (?) your best bet would be to find someone who has an
Amiga, get them to create a new fs for you (via loopback-on-file) then
gzip the underlying file and send it to you.  You can then use that fs
image file as many times as you want via loopback or straight onto a
disk.  Make sure the image file is zeroed out first so it compresses
well.

Or something like that.
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