Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759438AbXHBRyS (ORCPT ); Thu, 2 Aug 2007 13:54:18 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755443AbXHBRyF (ORCPT ); Thu, 2 Aug 2007 13:54:05 -0400 Received: from lazybastard.de ([212.112.238.170]:41325 "EHLO longford.lazybastard.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752757AbXHBRyD (ORCPT ); Thu, 2 Aug 2007 13:54:03 -0400 Date: Thu, 2 Aug 2007 19:50:09 +0200 From: =?utf-8?B?SsO2cm4=?= Engel To: Josef Sipek Cc: Dave Kleikamp , Jan Blunck , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Bharata B Rao , hch@infradead.org Subject: Re: [RFC 12/26] ext2 white-out support Message-ID: <20070802175008.GA12627@lazybastard.org> References: <20070730161323.100048969@weierstrass.suse.de> <20070730161324.261652101@weierstrass.suse.de> <20070731163656.GC22350@filer.fsl.cs.sunysb.edu> <20070731170012.GN5101@hasse.suse.de> <20070731171159.GA27234@filer.fsl.cs.sunysb.edu> <1185981810.18007.14.camel@kleikamp.austin.ibm.com> <20070801184405.GA18405@filer.fsl.cs.sunysb.edu> <1185995431.18007.24.camel@kleikamp.austin.ibm.com> <20070801193330.GA20928@filer.fsl.cs.sunysb.edu> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20070801193330.GA20928@filer.fsl.cs.sunysb.edu> User-Agent: Mutt/1.5.9i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1458 Lines: 36 On Wed, 1 August 2007 15:33:30 -0400, Josef Sipek wrote: > > This brings up an very interesting (but painful) question...which makes more > sense? Allowing the modifications in only the top-most branch, or any branch > (given the user allows it at mount-time)? > > This is really question to the community at large, not just you, Dave :) Only write to top-most layer. There are two reasons for this. First it allows users to create a union mount, test something (e.g. update the distribution) and remove every trace from the test by umounting the top-most layer. Such a thing can be quite valuable. The second reason is simplicity. I personally couldn't even start to describe the semantics. If the user does a rename, which layer will the change end up in? What if source or target exist in multiple layers? How to rename a directory in a lower layer containing a new file in an upper layer? Finding new and interesting corner cases for such a beast can be quite entertaining. And until someone has properly documented the semantics for _all_ the corner cases, my enthusiasm is below freezing point. Does such a documentation exist? Jörn -- A surrounded army must be given a way out. -- Sun Tzu - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/