linux-kernel - Re: [RFC] Union Mount: Readdir approaches

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Message-ID: <20070907075855.GG1692@in.ibm.com>
Date:	Fri, 7 Sep 2007 13:28:55 +0530
From:	Bharata B Rao <bharata@...ux.vnet.ibm.com>
To:	hooanon05@...oo.co.jp
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	hch@...radead.org, Jan Blunck <jblunck@...e.de>,
	"Josef 'Jeff' Sipek" <jsipek@...sunysb.edu>
Subject: Re: [RFC] Union Mount: Readdir approaches

On Fri, Sep 07, 2007 at 04:31:26PM +0900, hooanon05@...oo.co.jp wrote:
> 
> When the first readdir is issued:
> - call vfs_readdir for every underlying opened dir (file) object.
> - store every entry to either the hash table for the result or the
>   whiteout, when the same-named entry didn't exist in the tables.
> - to improvement the performance, the allocated memory for the hash
>   tables are managed in a pointer array. and the elements are
>   concatinated logically by the pointer.
> - the pointer for the result-table, the version, and the currect jiffies
>   are set to vdir, which is a cache in an inode.
> - all cache are copied to a member in a file object.
> - the index of the cache memory block and the offset in an array is
>   handled as the seek position.

Ok, interesting approach. So you define the seek behaviour on your
directory cache rather than allowing the underlying filesystems to
interpret the seek. I guess we can do something similar with Union
Mounts also.

> If you are interested in this approach, please refer to
> http://aufs.sf.net. It is working and used by several people.

Will look at it. And thanks Junjiro for your detailed explanation of
the aufs approach.

Regards,
Bharata.
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