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SubjectRe: [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prior to writing them and be outdated by the time they hit the medium.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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