Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262718AbUCOTW6 (ORCPT ); Mon, 15 Mar 2004 14:22:58 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262726AbUCOTW6 (ORCPT ); Mon, 15 Mar 2004 14:22:58 -0500 Received: from inti.inf.utfsm.cl ([200.1.21.155]:35011 "EHLO inti.inf.utfsm.cl") by vger.kernel.org with ESMTP id S262718AbUCOTW4 (ORCPT ); Mon, 15 Mar 2004 14:22:56 -0500 Message-Id: <200403151922.i2FJMfIh004411@eeyore.valparaiso.cl> To: =?iso-8859-1?Q?J=F6rn?= Engel cc: Linux Kernel Mailing List Subject: Re: unionfs In-Reply-To: Message from =?iso-8859-1?Q?J=F6rn?= Engel of "Mon, 15 Mar 2004 17:13:23 +0100." <20040315161323.GD16615@wohnheim.fh-wedel.de> X-Mailer: MH-E 7.4.2; nmh 1.0.4; XEmacs 21.4 (patch 14) Date: Mon, 15 Mar 2004 15:22:41 -0400 From: Horst von Brand Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1739 Lines: 37 =?iso-8859-1?Q?J=F6rn?= Engel said: > On Mon, 15 March 2004 22:35:20 +0800, Ian Kent wrote: > > I don't understand the requirement properly. Sorry. > Depends on who you ask, but imo it boils down to this: > - Use one filesystem as backing store, usually ro. > - Have another filesystem on top for extra functionality, usually rw > access. > > Famous example is a rw-CDROM, where writes go to hard drive and > unchanged data is read from CDROM. But it makes sense for other > things as well. And what if the underlying filesystem is RW too? What should happen if you unite several (>= 3) filesystems? What if some are RO, others RW? What do you do if a file shows up several times, each different? Assuming one RW on top of a RO only now: What should happen when a file/directory is missing from the top? If the bottom one "shows through", you can't delete anything; if it doesn't, you win nothing (because you will have to keep a complete copy RW on top). IIRC, this has been discussed a couple of times before, and the consensus each time was that it isn't /that hard/ to do, it is /hard or impossible/ to find a sensible, simple semantics for this. The idea was then dropped... -- Dr. Horst H. von Brand User #22616 counter.li.org Departamento de Informatica Fono: +56 32 654431 Universidad Tecnica Federico Santa Maria +56 32 654239 Casilla 110-V, Valparaiso, Chile Fax: +56 32 797513 - 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/