From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030484AbWGIMtj (ORCPT ); Sun, 9 Jul 2006 08:49:39 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1030481AbWGIMtj (ORCPT ); Sun, 9 Jul 2006 08:49:39 -0400 Received: from [212.76.87.152] ([212.76.87.152]:19473 "EHLO raad.intranet") by vger.kernel.org with ESMTP id S1030479AbWGIMti (ORCPT ); Sun, 9 Jul 2006 08:49:38 -0400 From: Al Boldi To: "Eric Van Hensbergen" Subject: Re: [RFC] VFS: FS CoW using redirection Date: Sun, 9 Jul 2006 15:50:36 +0300 User-Agent: KMail/1.5 Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org References: <200607082041.54489.a1426z@gawab.com> In-Reply-To: MIME-Version: 1.0 Content-Disposition: inline Content-Type: text/plain; charset="windows-1256" Content-Transfer-Encoding: 7bit Message-Id: <200607091550.36407.a1426z@gawab.com> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Eric Van Hensbergen wrote: > On 7/8/06, Al Boldi wrote: > > Copy on Write is a neat way to quickly achieve a semi-clustered system, > > by mounting any shared FS read-only and redirecting writes to some > > perClient FS. > > > > Would this redirection be easy to implement into the VFS? > > There are a variety of solutions that have been proposed or are > available to do this sort of thing. You may want to start by looking > at unionfs and mapfs. There are also folks looking at doing this from > the block layer (look at the dm-userspace + cowd as well as evms and > lvm snapshots). The idea here, is to do things completely transparent while being as unintrusive as possible, by relying on the current FS infrastructure, w/o introducing another VFS. Consider something simple like this: VFS - anyFS1 (r/w) used normally, unless ENotFound, then redirect read to \ anyFS2, or CoW from anyFS2 to anyFS1. anyFS2 (r/o) used normally. i.e: Does the VFS provide hooks for perMount Handlers? Thanks! -- Al