Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932185AbWIENDi (ORCPT ); Tue, 5 Sep 2006 09:03:38 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932181AbWIENDi (ORCPT ); Tue, 5 Sep 2006 09:03:38 -0400 Received: from cs.columbia.edu ([128.59.16.20]:7334 "EHLO cs.columbia.edu") by vger.kernel.org with ESMTP id S932179AbWIENDg (ORCPT ); Tue, 5 Sep 2006 09:03:36 -0400 Subject: Re: [PATCH 00/22][RFC] Unionfs: Stackable Namespace Unification Filesystem From: Shaya Potter To: Jan Engelhardt Cc: Pavel Machek , Josef Sipek , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, hch@infradead.org, akpm@osdl.org, viro@ftp.linux.org.uk In-Reply-To: References: <20060901013512.GA5788@fsl.cs.sunysb.edu> <20060903110507.GD4884@ucw.cz> <1157376506.4398.15.camel@localhost.localdomain> <20060904203346.GA6646@elf.ucw.cz> <1157406184.4398.24.camel@localhost.localdomain> Content-Type: text/plain Date: Tue, 05 Sep 2006 09:02:39 -0400 Message-Id: <1157461359.23523.11.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Evolution 2.8.0 Content-Transfer-Encoding: 7bit X-PerlMx-Spam: Gauge=IIIIIII, Probability=7%, X-Seen-By filter2.cs.columbia.edu Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1783 Lines: 46 On Tue, 2006-09-05 at 08:02 +0200, Jan Engelhardt wrote: > > > >I agree that unionfs shouldn't oops, it should handle that situation in > >a more graceful manner, but once the "backing store" is modified > >underneath it, all bets are off for either unionfs or ext2/3 behaving > >"correctly" (where "correctly" doesn't just mean handle the error > >gracefully). > > > >But are you also 100% sure that messing with the underlying backing > >store wouldn't be considered an admin bug as opposed to an administrator > >bug? I mean there's nothing that we can do to prevent an administrator > >from FUBAR'ing their system by > > > >dd if=/dev/random of=/dev/kmem. > > > >where does one draw the line? I agree that stackable file systems make > >this a more pressing issue, as the "backing store" can be visible within > >the file system namespace as a regular file system that people are > >generally accustomed to interacting with. > > So here's an idea. When a branch is added, mount an empty space onto the > branch. (From within the kernel, so it appears as a side-effect of mount(2)) > > mount -t unionfs -o dirs=/a=rw:/b=ro none /union > > should imply something like > > mount --bind /var/lib/empty /a > mount --bind /var/lib/empty /b > > Or better, yet, make them read-only: > > mount --rbind -o ro /a /a > mount --rbind -o ro /b /b > (hope this works as intended?) > > So that no one can tinker with /a and /b while the union is mounted. I thought about that, but that doesn't help you w/ the NFS as branch case. - 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/