Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752672AbaBMSWI (ORCPT ); Thu, 13 Feb 2014 13:22:08 -0500 Received: from mail-ve0-f172.google.com ([209.85.128.172]:53475 "EHLO mail-ve0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752534AbaBMSWD (ORCPT ); Thu, 13 Feb 2014 13:22:03 -0500 MIME-Version: 1.0 In-Reply-To: References: <1391791751-2533-1-git-send-email-miklos@szeredi.hu> <19258.1392306854@warthog.procyon.org.uk> <20140213162534.GB4026@tucsk.piliscsaba.szeredi.hu> <20106.1392309770@warthog.procyon.org.uk> From: Andy Lutomirski Date: Thu, 13 Feb 2014 10:21:42 -0800 Message-ID: Subject: Re: [PATCH 00/13] cross rename v4 To: Miklos Szeredi Cc: David Howells , Al Viro , Linus Torvalds , Linux-Fsdevel , Kernel Mailing List , Bruce Fields , Christoph Hellwig , Andrew Morton , Zach Brown , Jan Kara , "mszeredi@suse.cz" Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 13, 2014 at 9:28 AM, Miklos Szeredi wrote: > On Thu, Feb 13, 2014 at 5:42 PM, David Howells wrote: >> Miklos Szeredi wrote: >> >>> Regarding whiteouts, I raised a couple of questions that nobody answered >>> yet, so let me ask again. >>> >>> - If a filesystem containing whiteouts (fallthroughs, etc...) is mounted as >>> not part of a union, how are these special entities represented to >>> userspace? >> >> I would suggest that whiteouts appear as otherwise negative dentries and that >> they don't appear in getdents(). > > I'd argue that this is an administration nightmare. E.g. what if the > a backup needs to be made of the rw layer? > > Will rmdir work normally in a directory containing whiteouts? Will > the VFS take care of that, just like if it was part of a union? Or > will it fail with ENOTEMPTY despite *appearing* empty? > > And zillion other problems related to the fact that things happen to a > filesystem even when they do not appear to happen ("mv foo bar; mv bar > foo" has side effects). Are there any users of unions / overlays who will want to modify the bottom layer after creating the top layer? I'm starting to think that changing the bottom layer should require userspace to do a three-way merge or something and explicitly decide what it wants to do. --Andy -- 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/