From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Suchanek Subject: Re: [PATCH 0/7] overlay filesystem: request for inclusion Date: Thu, 9 Jun 2011 15:57:48 +0200 Message-ID: References: <1306932380-10280-1-git-send-email-miklos@szeredi.hu> <20110608153208.dc705cda.akpm@linux-foundation.org> <20110609115934.3c53f78f@notabene.brown> <20110608205233.ebfedc4d.akpm@linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: NeilBrown , Miklos Szeredi , viro@zeniv.linux.org.uk, torvalds@linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, apw@canonical.com, nbd@openwrt.org, jordipujolp@gmail.com, ezk@fsl.cs.sunysb.edu, mszeredi@suse.cz To: Andrew Morton Return-path: In-Reply-To: <20110608205233.ebfedc4d.akpm@linux-foundation.org> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On 9 June 2011 05:52, Andrew Morton wrote: > On Thu, 9 Jun 2011 11:59:34 +1000 NeilBrown wrote: > >> On Wed, 8 Jun 2011 15:32:08 -0700 Andrew Morton >> wrote: >> >> > On Wed, =C2=A01 Jun 2011 14:46:13 +0200 >> > Miklos Szeredi wrote: >> > >> > > I'd like to ask for overlayfs to be merged into 3.1. >> > >> > Dumb questions: >> > >> > I've never really understood the need for fs overlaying. =C2=A0Who= wants it? >> > What are the use-cases? >> >> https://lwn.net/Articles/324291/ >> >> I think the strongest use case is that LIVE-DVD's want it to have a = write-able >> root filesystem which is stored on the DVD. > > Well, these things have been around for over 20 years. =C2=A0What mot= ivated > the developers of other OS's to develop these things and how are thei= r > users using them? =46WIW there is an union solution in NetBSD. I am not sure it is used i= n the LiveCD but you can definitely use it to build a piece of software without actually touching the source directory. > >> > >> > This sort of thing could be implemented in userspace and wired up = via >> > fuse, I assume. =C2=A0Has that been attempted and why is it inadeq= uate? >> >> I think that would be a valid question if the proposal was large and >> complex. =C2=A0But overlayfs is really quite small and self-containe= d. > > Not merging it would be even smaller and simpler. =C2=A0If there is a > userspace alternative then that option should be evaluated and compar= ed > in a rational manner. The problem with the userspace alternative is that it does not work. I tried to run my live CD on top of unionfs-fuse and the filesystem would fail intermittently leading to random errors during boot. > > > > Another issue: there have been numerous attempts at Linux overlay > filesystems from numerous parties. =C2=A0Does (or will) this implemen= tation > satisfy all their requirements? No implementation will satisfy all needs. There is always some compromise between availability (userspace/in-tree/easy to patch in) feature completeness (eg. AuFS is not so easy to forward-port to new kernels but has numerous features) performance, reliability. > > Because if not, we're in a situation where the in-kernel code is > unfixably inadequate so we end up merging another similar-looking > thing, or the presence of this driver makes it harder for them to get > other drivers merged and the other parties' requirements remain > unsatisfied. One of the major use cases is building live CDs. That and other things can be done with overlayfs. Thanks Michal