From mboxrd@z Thu Jan 1 00:00:00 1970 From: Josef Sipek Subject: Re: [PATCH 01/24] Unionfs: Documentation Date: Tue, 9 Jan 2007 05:36:59 -0500 Message-ID: <20070109103659.GB25438@filer.fsl.cs.sunysb.edu> References: <1168229596580-git-send-email-jsipek@cs.sunysb.edu> <1168229596875-git-send-email-jsipek@cs.sunysb.edu> <20070108111852.ee156a90.akpm@osdl.org> <20070108131957.cbaf6736.akpm@osdl.org> <20070108232516.GB1269@filer.fsl.cs.sunysb.edu> <20070109094935.GA12406@infradead.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from filer.fsl.cs.sunysb.edu ([130.245.126.2]:42142 "EHLO filer.fsl.cs.sunysb.edu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751316AbXAIKm7 (ORCPT ); Tue, 9 Jan 2007 05:42:59 -0500 To: Christoph Hellwig , Andrew Morton , Shaya Potter , "Josef 'Jeff' Sipek" , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, viro@ftp.linux.org.uk, torvalds@osdl.org, mhalcrow@us.ibm.com, David Quigley , Erez Zadok Content-Disposition: inline In-Reply-To: <20070109094935.GA12406@infradead.org> Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Tue, Jan 09, 2007 at 09:49:35AM +0000, Christoph Hellwig wrote: > On Mon, Jan 08, 2007 at 06:25:16PM -0500, Josef Sipek wrote: > > > There's no such problem with bind mounts. It's surprising to see such a > > > restriction with union mounts. > > > > Bind mounts are a purely VFS level construct. Unionfs is, as the name > > implies, a filesystem. Last year at OLS, it seemed that a lot of people > > agreed that unioning is neither purely a fs construct, nor purely a vfs > > construct. > > > > I'm using Unionfs (and ecryptfs) as guinea pigs to make linux fs stacking > > friendly - a topic to be discussed at LSF in about a month. > > And unionfs is the wrong thing do use for this. Unioning is a complex > namespace operation and needs to be implemented in the VFS or at least > needs a lot of help from the VFS. Getting namespace cache coherency > and especially locking right is imposisble with out that. What I meant was that I use them as an example for a linear and fanout stacking examples. While unioning itself is a complex operation, the general idea of one set of vfs objects (dentry, inode, etc.) pointing to several lower ones is very generic and applies to all fan-out stackable fs. Josef "Jeff" Sipek. -- Linux, n.: Generous programmers from around the world all join forces to help you shoot yourself in the foot for free.