Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161279AbXAHXSK (ORCPT ); Mon, 8 Jan 2007 18:18:10 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1161269AbXAHXSK (ORCPT ); Mon, 8 Jan 2007 18:18:10 -0500 Received: from filer.fsl.cs.sunysb.edu ([130.245.126.2]:51869 "EHLO filer.fsl.cs.sunysb.edu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1161266AbXAHXSI (ORCPT ); Mon, 8 Jan 2007 18:18:08 -0500 Date: Mon, 8 Jan 2007 18:15:24 -0500 From: Josef Sipek To: Andrew Morton Cc: "Josef 'Jeff' Sipek" , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, hch@infradead.org, viro@ftp.linux.org.uk, torvalds@osdl.org, mhalcrow@us.ibm.com, David Quigley , Erez Zadok Subject: Re: [PATCH 01/24] Unionfs: Documentation Message-ID: <20070108231524.GA1269@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> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070108111852.ee156a90.akpm@osdl.org> User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2002 Lines: 50 On Mon, Jan 08, 2007 at 11:18:52AM -0800, Andrew Morton wrote: > On Sun, 7 Jan 2007 23:12:53 -0500 > "Josef 'Jeff' Sipek" wrote: > > > +Modifying a Unionfs branch directly, while the union is mounted, is > > +currently unsupported. > > Does this mean that if I have /a/b/ and /c/d/ unionised under /mnt/union, I > am not allowed to alter anything under /a/b/ and /c/d/? That I may only > alter stuff under /mnt/union? That's correct. > If so, that sounds like a significant limitation. It is significant, and I am trying to figure out a nice clean way to allow _all_ stackable filesystems (yes, ecryptfs which is in vanilla has the same problem too) to have data modified under them without any cache incoherence. > > Any such change can cause Unionfs to oops, or stay > > silent and even RESULT IN DATA LOSS. > > With a rather rough user interface ;) That statement is meant to scare people away from modifying the lower fs :) I tortured unionfs quite a bit, and it can oops but it takes some effort. > Also, is it possible to add new branches to an existing union mount? And > to take old ones away? Not in the code in the 20-odd patches, it is a minimal version of the code, maade to be as clean as possible. I hope to port the more complex features into this code when things like lower branch manipulation are fixed in a real way - there have been suggestions of (ab)using inotify to keep track of the lower files, but I would prefer to find a real solution. Josef "Jeff" Sipek. -- Research, n.: Consider Columbus: He didn't know where he was going. When he got there he didn't know where he was. When he got back he didn't know where he had been. And he did it all on someone else's money. - 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/