From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 01611C433F5 for ; Wed, 13 Apr 2022 01:36:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231474AbiDMBip (ORCPT ); Tue, 12 Apr 2022 21:38:45 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48104 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229546AbiDMBio (ORCPT ); Tue, 12 Apr 2022 21:38:44 -0400 Received: from outgoing.mit.edu (outgoing-auth-1.mit.edu [18.9.28.11]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7DCC444757 for ; Tue, 12 Apr 2022 18:36:24 -0700 (PDT) Received: from cwcc.thunk.org (pool-108-7-220-252.bstnma.fios.verizon.net [108.7.220.252]) (authenticated bits=0) (User authenticated as tytso@ATHENA.MIT.EDU) by outgoing.mit.edu (8.14.7/8.12.4) with ESMTP id 23D1Zumo012270 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Tue, 12 Apr 2022 21:35:56 -0400 Received: by cwcc.thunk.org (Postfix, from userid 15806) id 3627F15C003E; Tue, 12 Apr 2022 21:35:56 -0400 (EDT) Date: Tue, 12 Apr 2022 21:35:56 -0400 From: "Theodore Ts'o" To: Gabriel Krisman Bertazi Cc: Zhang Yi , linux-ext4@vger.kernel.org, adilger.kernel@dilger.ca, jack@suse.cz, yukuai3@huawei.com, yebin10@huawei.com, liuzhiqiang26@huawei.com, liangyun2@huawei.com Subject: Re: [RFC PATCH] ext4: add unmount filesystem message Message-ID: References: <20220412145320.2669897-1-yi.zhang@huawei.com> <87pmlmcmu6.fsf@collabora.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87pmlmcmu6.fsf@collabora.com> Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org On Tue, Apr 12, 2022 at 12:01:37PM -0400, Gabriel Krisman Bertazi wrote: > Zhang Yi writes: > > > Now that we have kernel message at mount time, system administrator "Now that we have...." is a bit misleading, since (at least to an English speaker) that this is something that was recently added, and that's not the case. > > could acquire the mount time, device and options easily. But we don't > > have corresponding unmounting message at umount time, so we cannot know > > if someone umount a filesystem easily. Some of the modern filesystems > > (e.g. xfs) have the umounting kernel message, so add one for ext4 > > filesystem for convenience. > > > > EXT4-fs (sdb): mounted filesystem with ordered data mode. Quota mode: none. > > EXT4-fs (sdb): unmounting filesystem. > > I don't think sysadmins should be relying on the kernel log for this, > since the information can easily be overwritten by new messages there. > Is there a reason why you can't just monitor /proc/self/mountinfo? You're right that it can be dangerous for sysadmins to be relying on the kernel log for mount and umount notifications --- but it depends on what they think it means, and the potential pitfalls are there for both the mount and unmount messages. The problem of course, is that bind mounts, and mount name spaces, so if the question is whether a file system is available at a particular mount point, then using the kernel log is definitely not going to be reliable. But if the goal is to determine whether a particular device is safe to run fsck or otherwise access directly, or for the purposes of debugging the kernel and looking at the logs to understand when the device is being accessed by the kernel and when the file system is done with the device, I can see how it might be useful. Cheers, - Ted