Messages in this thread | | | Date | Fri, 1 Jun 2007 22:54:26 +0530 | From | "Satyam Sharma" <> | Subject | Re: JFFS2 using 'private' zlib header (was [RFC] LZO de/compression support - take 6) |
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Hi Daniel,
On 6/1/07, Daniel Hazelton <dhazelton@enter.net> wrote: > 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.
Right, s/PRESET_DICT/0x20/ would have the least fall-out / unknown side-effects.
> > 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.
David would have to comment on that, but you could simultaneously make and submit the patch as suggested by Mark with both your signed-offs-by. That'll naturally need to go through David's tree, so we'll know if he likes/accepts the suggested modifications ... - 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/
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