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 X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 802FFC433E2 for ; Thu, 10 Sep 2020 08:18:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 42E5F20732 for ; Thu, 10 Sep 2020 08:18:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730136AbgIJIRS (ORCPT ); Thu, 10 Sep 2020 04:17:18 -0400 Received: from mx2.suse.de ([195.135.220.15]:55776 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730067AbgIJIOh (ORCPT ); Thu, 10 Sep 2020 04:14:37 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id AA6C5AF85; Thu, 10 Sep 2020 08:14:32 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id BD47C1E12EB; Thu, 10 Sep 2020 10:14:16 +0200 (CEST) Date: Thu, 10 Sep 2020 10:14:16 +0200 From: Jan Kara To: Amir Goldstein Cc: Jan Kara , Xiaoming Ni , Matthew Wilcox , linux-fsdevel , Linux Kernel Mailing List , wangle6@huawei.com Subject: Re: Question: Why is there no notification when a file is opened using filp_open()? Message-ID: <20200910081416.GF17540@quack2.suse.cz> References: <25817189-49a7-c64f-26ee-78d4a27496b6@huawei.com> <20200908171859.GA29953@casper.infradead.org> <96abf6e3-2442-8871-c9f3-be981c0a1965@huawei.com> <20200909111130.GD24207@quack2.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Wed 09-09-20 19:03:07, Amir Goldstein wrote: > On Wed, Sep 9, 2020 at 2:11 PM Jan Kara wrote: > > > > On Wed 09-09-20 10:36:57, Amir Goldstein wrote: > > > On Wed, Sep 9, 2020 at 10:00 AM Xiaoming Ni wrote: > > > > > > > > On 2020/9/9 11:44, Amir Goldstein wrote: > > > > > On Tue, Sep 8, 2020 at 8:19 PM Matthew Wilcox wrote: > > > > >> > > > > >> On Tue, Sep 08, 2020 at 04:18:29PM +0300, Amir Goldstein wrote: > > > > >>> On Tue, Sep 8, 2020 at 3:53 PM Xiaoming Ni wrote: > > > > >>>> For example, in fs/coredump.c, do_coredump() calls filp_open() to > > > > >>>> generate core files. > > > > >>>> In this scenario, the fsnotify_open() notification is missing. > > > > >>> > > > > >>> I am not convinced that we should generate an event. > > > > >>> You will have to explain in what is the real world use case that requires this > > > > >>> event to be generated. > > > > >> > > > > >> Take the typical usage for fsnotify of a graphical file manager. > > > > >> It would be nice if the file manager showed a corefile as soon as it > > > > >> appeared in a directory rather than waiting until some other operation > > > > >> in that directory caused those directory contents to be refreshed. > > > > > > > > > > fsnotify_open() is not the correct notification for file managers IMO. > > > > > fsnotify_create() is and it will be called in this case. > > > > > > > > > > If the reason you are interested in open events is because you want > > > > > to monitor the entire filesystem then welcome to the future - > > > > > FAN_CREATE is supported since kernel v5.1. > > > > > > > > > > Is there another real life case you have in mind where you think users > > > > > should be able to get an open fd for a file that the kernel has opened? > > > > > Because that is what FAN_OPEN will do. > > > > > > > > > > > > > There are also cases where file is opened in read-only mode using > > > > filp_open(). > > > > > > > > case1: nfsd4_init_recdir() call filp_open() > > > > filp_open() > > > > nfsd4_init_recdir() fs/nfsd/nfs4recover.c#L543 > > > > > > > > L70: static char user_recovery_dirname[PATH_MAX] = > > > > "/var/lib/nfs/v4recovery"; > > > > L543: nn->rec_file = filp_open(user_recovery_dirname, O_RDONLY | > > > > O_DIRECTORY, 0); > > > > > > > > > > > > case2: ima_read_policy() > > > > filp_open() > > > > kernel_read_file_from_path() fs/exec.c#L1004 > > > > ima_read_policy() security/integrity/ima/ima_fs.c#L286 > > > > ima_write_policy() security/integrity/ima/ima_fs.c#L335 > > > > ima_measure_policy_ops security/integrity/ima/ima_fs.c#L443 > > > > sys_write() > > > > > > > > case3: use do_file_open_root() to open file > > > > do_file_open_root() > > > > file_open_root() fs/open.c#L1159 > > > > kernel_read_file_from_path_initns() fs/exec.c#L1029 > > > > fw_get_filesystem_firmware() drivers/base/firmware_loader/main.c#L498 > > > > > > > > Do we need to add fsnotify_open() in these scenarios? > > > > > > We do not *need* to add fsnotify_open() if there is no concrete use case > > > from real life that needs it. > > > > > > Matthew gave an example of a real life use case and I explained why IMO > > > we don't need to add fsnotify_open() for the use case that he described. > > > > > > If you want to add fsnotify_open() to any call site, please come up with > > > a real life use case - not a made up one, one that really exists and where > > > the open event is really needed. > > > > > > grepping the code for callers of filp_open() is not enough. > > > > Yeah. So in kernel, things are both ways. There are filp_open() users that > > do take care to manually generate fsnotify_open() event (most notably > > io_uring, exec, or do_handle_open) and there are others as Xiaoming found > > which just don't bother. I'm not sure filp_open() should unconditionally > > generate fsnotify_open() event as IMO some of those notifications would be > > more confusing than useful. > > > > OTOH it is true that e.g. for core dumping we will generate other fsnotify > > events such as FSNOTIFY_CLOSE (which is generated in __fput()) so missing > > And to be fair, those kernel callers will probably also end up generating > FS_ACCESS/FS_MODIFY too. Yes. > > FSNOTIFY_OPEN is somewhat confusing. So having some consistency in this > > (either by generating FSNOTIFY_OPEN or by not generating FSNOTIFY_CLOSE) > > would be IMO desirable. > > Well, dropping events (FS_CLOSE in particular) didn't go down well the > last time we tried it: > https://lore.kernel.org/linux-fsdevel/CAOQ4uxg8E-im=B6L0PQNaTTKdtxVAO=MSJki7kxq875ME4hOLw@mail.gmail.com/ Right, I remember that one :) > I am just wondering who is using FS_OPEN these days and whether > they would care about this change and if not, why are we doing it? I'd be interested who is using FS_OPEN these days as well. And you're right that without users the discussion is kind of moot. > The argument that it is confusing to see FS_ACCESS/FS_MODIFY/FS_CLOSE > and not seeing FS_OPEN is only half true - it is common to see that > pattern when the file is already open when starting to watch, so application > should not break because of that pattern. Good point. Honza -- Jan Kara SUSE Labs, CR