From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tomas M Subject: Re: [RFC 2/8] Aufs2: structure Date: Mon, 23 Feb 2009 10:22:20 +0100 Message-ID: <49A26ACC.90804@slax.org> References: <7558.1235374266@jrobl> <7769.1235374482@jrobl> <49A268A7.1010708@slax.org> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit To: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Return-path: Received: from cuda1.bluetone.cz ([212.158.128.5]:45803 "EHLO mail.bluetone.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752125AbZBWJWE (ORCPT ); Mon, 23 Feb 2009 04:22:04 -0500 In-Reply-To: <49A268A7.1010708@slax.org> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: > The struct of a xino file is simple, just a sequence of aufs inode > numbers which is indexed by the lower inode number. > In the above sample, assume the inode number of /ro/fileA is i111 and > aufs assigns the inode number i999 for fileA. Then aufs writes 999 as > 4(8) bytes at 111 * 4(8) bytes offset in the xino file. I think it is worth mentioning that the xino file, if I understand it correctly, is a 'sparse file', that means it is full of 'holes' and doesn't consume as much disk space as it might appear. In my opinion, the current xino-file approach is not much usable on filesystems which do not support sparse files (for example, if you wish to union two vfats), since some 'seeks' would probably write a lot of nulls. But I am not any kernel developer so I don't even know if there exists any filesystem which would be unable to support sparse files (except the mentioned VFAT, of course). Tomas M slax.org