linux-kernel - Re: [PATCH 1/9] Squashfs: move zlib decompression wrapper code into a separate file

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Message-ID: <4B217421.5000802@openwrt.org>
Date:	Thu, 10 Dec 2009 23:20:17 +0100
From:	Felix Fietkau <nbd@...nwrt.org>
To:	Phillip Lougher <phillip@...gher.demon.co.uk>
CC:	Geert Uytterhoeven <geert@...ux-m68k.org>, dedekind1@...il.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-embedded@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, phillip.lougher@...il.com,
	Tim Bird <tim.bird@...sony.com>,
	Geert Uytterhoeven <Geert.Uytterhoeven@...ycom.com>
Subject: Re: [PATCH 1/9] Squashfs: move zlib decompression wrapper code into
 a 	separate file

On 2009-12-10 10:17 PM, Phillip Lougher wrote:
> Geert Uytterhoeven wrote:
>> 
>>> Yes I did consider using the cryptoapi, but this doesn't have support for
>>> lzma in mainline.
>> 
>> IIRC, Felix Fietkau added support for that for OpenWRT...
>> 
> 
> Yes, but it isn't in mainline, and OpenWRT don't appear to have tried to submit
> it.  IMHO the major problem with their patch is it uses a second private copy
> of lzma, rather than being a wrapper around the pre-existing lzma implementation.
> I don't think it's going to be easy to get a second lzma implementation accepted
> into mainline, when it took so long to get one accepted.  I have nothing against
> the cryptoapi, but it doesn't seem likely to be getting lzma support anytime soon.
> 
> As I previously said my aim is to use the pre-existing lzma implementation.  Unless
> it is stupendously bad (which it isn't), that seems to be the quickest, easiest and
> best way to get lzma support into Squashfs.
The main reason why my implementation couldn't be done as a simple
wrapper around the existing implementation is that it reuses the
caller's split output buffers instead wasting precious RAM by allocating
a contiguous buffer big enough to cover the entire block.
Especially at bigger block sizes (which provide better compression),
this probably has noticeable effects on tiny embedded systems with
little RAM.

- Felix
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