From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753590AbbAGPFJ (ORCPT ); Wed, 7 Jan 2015 10:05:09 -0500 Received: from mail-pa0-f54.google.com ([209.85.220.54]:38072 "EHLO mail-pa0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752484AbbAGPFF (ORCPT ); Wed, 7 Jan 2015 10:05:05 -0500 Message-ID: <54AD4B1B.1030801@gmail.com> Date: Thu, 08 Jan 2015 00:04:59 +0900 From: Seunghun Lee User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.3.0 MIME-Version: 1.0 To: hujianyang CC: miklos@szeredi.hu, sedat.dilek@gmail.com, richard.weinberger@gmail.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-unionfs@vger.kernel.org Subject: Re: [PATCH] ovl: Prevent rw remount when it should be ro mount References: <1420219609-2568-1-git-send-email-waydi1@gmail.com> <54A8AC74.2060106@huawei.com> <54ABEB06.2010008@gmail.com> <54ACA052.8010800@huawei.com> In-Reply-To: <54ACA052.8010800@huawei.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Hu, On 01/07/2015 11:56 AM, hujianyang wrote: > Hi, > > There maybe some misunderstandings here. I think your patch really > fix an important problem, but not in correct way. > > On 2015/1/6 22:02, Seunghun Lee wrote: >> After patch: >> root@qemux86:~# mount -t overlay overlay -olowerdir=lower:lower2 merged >> mount: warning: merged seems to be mounted read-only. >> root@qemux86:~# mount | grep overlay >> overlay on /home/root/merged type overlay (ro,relatime,lowerdir=lower:lower2) >> root@qemux86:~# mount -o remount,rw merged >> mount: warning: /home/root/merged seems to be mounted read-only. >> root@qemux86:~# mount | grep overlay >> overlay on /home/root/merged type overlay (ro,relatime,lowerdir=lower:lower2) >> root@qemux86:~# echo hi > merged/hi >> -sh: merged/hi: Read-only file system >> root@qemux86:~# >> > If users want a rw mount, can we give them a ro mount? I think it's > wrong, .remount_fs should refuse this request. > > So I think your .remount_fs should check both what users in userpace > want and what kernel can offer, then realize legal requests and > refuse illegal requests. Not changing the requests from users. Many file systems just change flags when user requests read-write remount. (romfs, squashfs, sysv...) I thought this case is similar above filesystems. > Further more, can we replace upper/lower/work directories or mount > point by this .remount_fs? > > If you want to export a new function, I think you should considering > more about these. > > Thanks, > Hu > Yes, you are right. However, this patch is a minimal support to prevent kernel panic when file system is remounted to read-write mode. And many file systems have remount_fs function of this kind. I think what you mentioned is can be added later if it is necessary. Thanks.