Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753687AbXFADG2 (ORCPT ); Thu, 31 May 2007 23:06:28 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752461AbXFADGU (ORCPT ); Thu, 31 May 2007 23:06:20 -0400 Received: from keil-draco.com ([216.193.185.50]:50088 "EHLO mail.keil-draco.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752369AbXFADGT (ORCPT ); Thu, 31 May 2007 23:06:19 -0400 From: Daniel Hazelton To: Mark Adler Subject: Re: JFFS2 using 'private' zlib header (was [RFC] LZO de/compression support - take 6) Date: Thu, 31 May 2007 23:06:12 -0400 User-Agent: KMail/1.9.6 Cc: Satyam Sharma , "Michael-Luke Jones" , lkml , dwmw2@infradead.org, jloup@gzip.org References: <4cefeab80705280734i37df1742k6738cd4200813684@mail.gmail.com> <1084DBE5-D72F-4403-B231-66DA8FE6AC73@alumni.caltech.edu> In-Reply-To: <1084DBE5-D72F-4403-B231-66DA8FE6AC73@alumni.caltech.edu> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200705312306.12626.dhazelton@enter.net> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2032 Lines: 44 On Wednesday 30 May 2007 19:02:28 Mark Adler wrote: > On May 30, 2007, at 6:30 AM, Satyam Sharma wrote: > > [1] For your reference, here is the user code in question: > > ... > > > if (srclen > 2 && !(data_in[1] & PRESET_DICT) && > > ((data_in[0] & 0x0f) == Z_DEFLATED) && > > !(((data_in[0]<<8) + data_in[1]) % 31)) { > > The funny thing here is that the author felt compelled to use a > #defined constant for the dictionary bit (PRESET_DICT), but had no > problem with a numeric constant to isolate the compression method > (0x0f), or for that matter extracting the window bits from the > header. The easy way to avoid the use of an internal zlib header > file here is to simply replace PRESET_DICT with 0x20. That constant > will never change -- it is part of the definition of the zlib header > in RFC 1950. If there is no objection, I'll put together a patch that changes the use in JFFS2 into a "magic number", complete with documentation on it, and also moves all of the zlib stuff into a single directory. > The slightly more involved patch to avoid the problem is to let > inflate() do all that work for you, including the integrity check on > the zlib header (% 31). Also this corrects an error in the original > code, which is that it continues to try to decompress after finding > that a dictionary is needed or that the zlib header is invalid. In > this version, a bad header simply returns an error: > Does anyone know if doing as Mark suggests would negatively impact the performance of JFFS2 to such a degree that it could be considered a regression? I, unfortunately, don't have the hardware to properly test the code. And, at this point in time, I also don't have enough familiarity with the JFFS2 code to make such a change myself. DRH - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/