Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751609AbcKFTQS (ORCPT ); Sun, 6 Nov 2016 14:16:18 -0500 Received: from mail-lf0-f65.google.com ([209.85.215.65]:34211 "EHLO mail-lf0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751187AbcKFTOu (ORCPT ); Sun, 6 Nov 2016 14:14:50 -0500 MIME-Version: 1.0 In-Reply-To: References: <1477380887-21333-1-git-send-email-mszeredi@redhat.com> <1477380887-21333-4-git-send-email-mszeredi@redhat.com> <20161025115748.ydhkkp5cfcdnjzwn@home.ouaza.com> From: Konstantin Khlebnikov Date: Sun, 6 Nov 2016 22:14:47 +0300 Message-ID: Subject: Re: [PATCH 3/3] ovl: redirect on rename-dir To: Miklos Szeredi Cc: Raphael Hertzog , Miklos Szeredi , "linux-unionfs@vger.kernel.org" , Guillem Jover , linux-fsdevel , Linux Kernel Mailing List Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2037 Lines: 44 On Wed, Oct 26, 2016 at 2:12 PM, Miklos Szeredi wrote: > On Tue, Oct 25, 2016 at 1:57 PM, Raphael Hertzog wrote: > >> Do you plan to make it the default in the future when it has been >> available for a while? >> >> Barring any regression introduced by your patch, it seems that the feature >> is best available by default since it allows legitimate operations to >> succeed that are otherwise refused. I understand that it makes it >> impossible to mount the overlay filesystem with an older kernel but is >> that problem more widespread than the one we're fixing here? On my side, >> overlayfs is only used in scenarios where the kernel is always the same >> (or newer compared to what created the initial filesystem). > > I think it would be safe to make it the default if upperdir is empty. > Nonempty implies that it was created with old kernel (or it was > crafted by hand). But there should be a way to explicitly turn it > off; either because of the need for backward compatibility or because > the old format is simply easier to work with for humans. > > How about: > > - If upper is nonempty, then leave redirect feature alone except when > mount option "-oredirect=on" is used to force enabling it. > - If upper is empty, then enable redirect feature except when mount > option "-oredirect=off" is used to force disabling it. I don't like this empty-nonempty upper logic. I think this feature should be off by default and be enabled explicitly in mount option. Available features could be listed in sysfs /sys/fs/overlay/..., like ext4 does. Overlayfs mounting anyway is complicated operation. User must know a lot about it and provide persistent state for each mount: list layers in correct order, work and uppder directory on the same disk, etc. Enabled features is a part of this state. Probably this could be solved in userspace tool "mount.overlay" - it could load features and layers from config file or xattr and set required mount options automatically. -- Konstantin