From: Andi Kleen Subject: Re: Random corruption test for e2fsck Date: Fri, 13 Jul 2007 00:24:26 +0200 Message-ID: <20070712222426.GB1011@one.firstfloor.org> References: <1184072860.4440.39.camel@garfield.linsyssoft.com> <20070712051938.GD5586@schatzie.adilger.int> <20070712110923.GA500@one.firstfloor.org> <20070712221624.GA5880@schatzie.adilger.int> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Andi Kleen , Kalpak Shah , linux-ext4 , TheodoreTso To: Andreas Dilger Return-path: Received: from one.firstfloor.org ([213.235.205.2]:33171 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754778AbXGLWY1 (ORCPT ); Thu, 12 Jul 2007 18:24:27 -0400 Content-Disposition: inline In-Reply-To: <20070712221624.GA5880@schatzie.adilger.int> Sender: linux-ext4-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org 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