From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753583AbbKGOea (ORCPT ); Sat, 7 Nov 2015 09:34:30 -0500 Received: from forward11j.cmail.yandex.net ([5.255.227.175]:49964 "EHLO forward11j.cmail.yandex.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753056AbbKGOe1 (ORCPT ); Sat, 7 Nov 2015 09:34:27 -0500 X-Greylist: delayed 330 seconds by postgrey-1.27 at vger.kernel.org; Sat, 07 Nov 2015 09:34:27 EST From: Arseny Sher To: linux-kernel@vger.kernel.org Subject: Changes to underlying filesystems in overlayfs MIME-Version: 1.0 Message-Id: <435311446906534@web17j.yandex.ru> X-Mailer: Yamail [ http://yandex.ru ] 5.0 Date: Sat, 07 Nov 2015 17:28:54 +0300 Content-Transfer-Encoding: 7bit Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi all, I have some questions regarding making changes to underlying filesystems in overlayfs. From the documentation: "Changes to the underlying filesystems while part of a mounted overlay filesystem are not allowed. If the underlying filesystem is changed, the behavior of the overlay is undefined, though it will not result in a crash or deadlock." Could you tell me, is it safe to - freeze the merged mountpoint, remounting it as ro to prevent any external changes - directly make changes to lowerdir or upperdir - immediate reboot I hope the rebooting will clean the cache and thus manipulating underlying filesystems in this way can be considered safe. Am I right? There is a project overlayroot developed for mounting / as an overlay filesystem: http://blog.dustinkirkland.com/2012/08/introducing-overlayroot-overlayfs.html It provides utility overlayroot-chroot which lets to modify lowerdir partition while overlayfs on / is mounted. It does this by adding proc, run, sys mounts inside lowerdir, than remounting it as rw and finally chrootting into it. It is mainly used for modyfing overlayroot config, so the next action after exiting chroot is usually reboot. The utility even doesn't freezes / while doing this, as far as I know. Is this allowed? P.S. I know that this mail list is for unionfs'es development, not for users. Unfortunately, I couldn't find more appropriate place for such questions. I'd be happy if someone would tell me the right place. -- Arseny Sher