linux-kernel - Re: [PATCH 01/27] nilfs2: add document

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Message-ID: <20080917145437.GE8750@logfs.org>
Date:	Wed, 17 Sep 2008 16:54:38 +0200
From:	Jörn Engel <joern@...fs.org>
To:	Ryusuke Konishi <konishi.ryusuke@....ntt.co.jp>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 01/27] nilfs2: add document

On Mon, 15 September 2008 04:07:58 +0900, Ryusuke Konishi wrote:
> +
> +The logs include regular files, directory files, symbolic link files
> +and several meta data files.  The mata data files are the files used
> +to maintain file system meta data.  The current version of NILFS2 uses
> +the following meta data files:
> +
> + 1) Inode file (ifile)             -- Stores on-disk inodes
> + 2) Checkpoint file (cpfile)       -- Stores checkpoints
> + 3) Segment usage file (sufile)    -- Stores allocation state of segments
> + 4) Data address translation file  -- Maps virtual block numbers to usual
> +    (DAT)                             block numbers.  This file serves to
> +                                      make on-disk blocks relocatable.
> + 5) Sketch file (sketch)           -- Keeps read-only data which can be
> +                                      associated with checkpoints (optional)

How are the sufile and the DAT written?  If you naively stick to the
log-structured approach, their contents will reflect a filesystem state
prior to writing them and be outdated by the time they hit the medium.
So either you bend the rules here and update those files in-place or you
do something tricky.  Can you explain your solution?

Jörn

-- 
Write programs that do one thing and do it well. Write programs to work
together. Write programs to handle text streams, because that is a
universal interface.
-- Doug MacIlroy
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