From mboxrd@z Thu Jan 1 00:00:00 1970 From: Al Boldi Subject: Re: [RFC] VFS: FS CoW using redirection Date: Sun, 9 Jul 2006 15:50:36 +0300 Message-ID: <200607091550.36407.a1426z@gawab.com> References: <200607082041.54489.a1426z@gawab.com> Mime-Version: 1.0 Content-Type: text/plain; charset="windows-1256" Content-Transfer-Encoding: 7bit Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Return-path: 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 To: "Eric Van Hensbergen" In-Reply-To: Content-Disposition: inline Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-fsdevel.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