From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757575Ab0I1IZf (ORCPT ); Tue, 28 Sep 2010 04:25:35 -0400 Received: from cantor.suse.de ([195.135.220.2]:57843 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751348Ab0I1IZd (ORCPT ); Tue, 28 Sep 2010 04:25:33 -0400 From: Andreas Gruenbacher Organization: SUSE Labs, Novell Inc. To: Valerie Aurora Subject: Re: [PATCH 6/7 v3] overlay: hybrid overlay filesystem prototype Date: Tue, 28 Sep 2010 10:24:59 +0200 User-Agent: KMail/1.13.5 (Linux/2.6.34-12-desktop; KDE/4.4.4; x86_64; ; ) Cc: Miklos Szeredi , linuxram@us.ibm.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, neilb@suse.de, viro@zeniv.linux.org.uk References: <20100920180404.939991832@szeredi.hu> <20100927184747.GC8089@shell> In-Reply-To: <20100927184747.GC8089@shell> MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <201009281025.00727.agruen@suse.de> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Monday 27 September 2010 20:47:47 Valerie Aurora wrote: > Maybe I don't understand. It seems like directories created when the > file system is *not* union mounted should definitely be merged with > matching directories on the lower layer. > > Take the case of /etc/fstab. The first union mount never touches /etc > and it doesn't exist on the topmost layer. Then we unmount the upper > layer, mount it somewhere else as a plain mount, and create /etc/ and > /etc/fstab. When we union mount it back over the lower layer again, > we still want the lower layer /etc/ to be merged with the topmost > /etc/, or else init.d will disappear. I can't think of a reason why the upper layer would really *need* to be modified separately as in this example though, and I'm sure that examples for opaqueness by default can be constructed as well. Transparency comes at a cost though (lookup, readdir, whiteouts), and defaulting to opaque directories will be more efficient in some cases. This is why I think that opaqueness by default is preferable. > Again, maybe I'm misunderstanding, but this doesn't make much sense to > me. Say I create: > > /upper/a_dir/upper_file > /lower/a_dir/lower_file > > Then when I union mount them, I want a_dir/ to be transparent > automatically and show both upper_file and lower_file, without marking > it manually. Why? Thanks, Andreas