linux-ext4 - Re: ext5

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Message-ID: <20100211175557.GA27418@atrey.karlin.mff.cuni.cz>
Date:	Thu, 11 Feb 2010 18:55:58 +0100
From:	Jan Kara <jack@...e.cz>
To:	tytso@....edu
Cc:	Manish Katiyar <mkatiyar@...il.com>,
	"Anonymous Remailer (austria)" <mixmaster@...ailer.privacy.at>,
	linux-ext4@...r.kernel.org
Subject: Re: ext5

> On Thu, Feb 11, 2010 at 09:08:36AM +0530, Manish Katiyar wrote:
> > 
> > Is this design somewhere on net so that we can read/lookup it up ?
> 
> Not yet, but the basic idea is to do the compression in userspace,
> using libz with regular resync points every 64k or 128k of
> uncompressed data.  An array, indexed by each fixed-block of
> uncompressed data, is located at the beginning of the file indicating
> where each compressed block begins.  The file is stored on-disk
> written by the installer in a compressed format, and then the
> installer flips an attribute bit which marks the file as containing
> compressed data, and which also makes the file immutable.  (Any
> attempt to open the file read/write will result in an error.)
  From the first reading, this sounds like what zisofs is doing.
The reading part is already implemented in kernel in fs/isofs/compress.c
so that might be lifted to a generic level and used for ext4 as well..

								Honza
-- 
Jan Kara <jack@...e.cz>
SuSE CR Labs
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