linux-ext4 - Re: Random corruption test for e2fsck

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Message-ID: <20070712222426.GB1011@one.firstfloor.org>
Date:	Fri, 13 Jul 2007 00:24:26 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Andreas Dilger <adilger@...sterfs.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Kalpak Shah <kalpak@...sterfs.com>,
	linux-ext4 <linux-ext4@...r.kernel.org>,
	TheodoreTso <tytso@....edu>
Subject: Re: Random corruption test for e2fsck

On Thu, Jul 12, 2007 at 04:16:24PM -0600, Andreas Dilger wrote:
> On Jul 12, 2007  13:09 +0200, Andi Kleen wrote:
> > > "dd if=/dev/urandom bs=1k ..." than to spin in a loop getting 16-bit
> > > random numbers from bash.  We would also be at the mercy of the shell
> > > being identical on the user and debugger's systems.
> > 
> > With /dev/urandom you have the guarantee you'll never ever reproduce
> > it again. 
> 
> That is kind of the point of this testing - getting new test images for
> each user that runs "make check" or "make rpm".  I'm We also save the
> generated image before e2fsck touches it so that it can be used for
> debugging if needed.

If you seed a good pseudo RNG with the time (or even a few bytes from 
/dev/urandom; although the time tends to work as well) you'll also effectively 
get a new image every time.

But the advantage is if you print out the seed the image
can be easily recreated just by re-running the fuzzer
with the same seed. No need to ship potentially huge images
around.

You can essentially compress your whole image into a single
number this way.

-Andi
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