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=-2.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 6C2BAC433C1 for ; Tue, 30 Mar 2021 13:55:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3BC47619C5 for ; Tue, 30 Mar 2021 13:55:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232053AbhC3Nyb (ORCPT ); Tue, 30 Mar 2021 09:54:31 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37872 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230369AbhC3NyO (ORCPT ); Tue, 30 Mar 2021 09:54:14 -0400 Received: from mail-io1-xd36.google.com (mail-io1-xd36.google.com [IPv6:2607:f8b0:4864:20::d36]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1B812C061574; Tue, 30 Mar 2021 06:54:14 -0700 (PDT) Received: by mail-io1-xd36.google.com with SMTP id v26so16493942iox.11; Tue, 30 Mar 2021 06:54:14 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=eRKAgRXuGQrtNoTXHmvfGZA8o3MRnH58cBnWJ68/uhw=; b=ZoSVsUxJLy2nzh7TGegCTN2v3pTIsMDFpzS2MKbbyHWn2Y9+XdGppU9t6vRb1rtkmU RwV0BBA+skkAmhtG7l3KV0Xr11fjXDs0DzAvd56wPTt9wfUR42rAsigy7dHl3zGZL+JL n/sc1BshGUyOHGmD9i/ydhr7kSxYGbbYDwLHT1aoFwhEShSrU7HQXDZ3U9dF4jpX7ud8 i4VmbSPlsIX3Z9wwxgjbHh+I7wYB4fzbwDesA8G77AIrkbwuU94CBDy8Wiq+IkKo2E2M /zxEuNqCLrg4fYBIe0eC//V5VHfQm6yIAB/aaNd0v4s+LDo4HFX4nKe7TzeurX2xT+U6 Lp+Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=eRKAgRXuGQrtNoTXHmvfGZA8o3MRnH58cBnWJ68/uhw=; b=iRRUeMVVlPyutkBoSzjyZA3cDzP9z/Fpi7lfGkNKTn33qYvDcCNiJ+sqsW6BGNdaoY OKVxzQzgyGA2ehpIHxuldQywRlnkKHbgjRGtBkvkVAUAOO51GBDdDRm5vNGHtizpcSpT LyH6G7q/3+PnWiPI2Ner3XJQIi7oI+xRi34fP2HiziNqXPLWSLgZd2utdMjiH3Lgqusz QwCDQWPb9ot+DXU+PfC4sZCH2L0YYqXQqpnjQj2cdBWfV3jigM85BTe+mhcPIlsNP8UD yDw+AjWPSqoM8vISBQVC2e66fDaStGF7LAaP586P6Wqf+ePOhufxlUFV6jysBurzmaM1 0sJA== X-Gm-Message-State: AOAM530fPniGBqDP5rUIqSxZ7Z2aRDKpz+xbblrlR9y/+ojsVsu/MEdx lN28EQd/VLHoYhzhMP0CiNRg57FAhd1UkW9vUTFVlJfHSzs= X-Google-Smtp-Source: ABdhPJxjWdKm8QHnq0tIyX+PCkYPsQXnm4mnTjLZGT+yTbtePbhWIsz2t7OxdKGUg3G9mDO7y/7iBs7qCs40dB60kjQ= X-Received: by 2002:a05:6638:1388:: with SMTP id w8mr23178139jad.30.1617112453495; Tue, 30 Mar 2021 06:54:13 -0700 (PDT) MIME-Version: 1.0 References: <20210328155624.930558-1-amir73il@gmail.com> <20210330121204.b7uto3tesqf6m7hb@wittgenstein> <20210330125336.vj2hkgwhyrh5okee@wittgenstein> In-Reply-To: <20210330125336.vj2hkgwhyrh5okee@wittgenstein> From: Amir Goldstein Date: Tue, 30 Mar 2021 16:54:02 +0300 Message-ID: Subject: Re: [RFC][PATCH] fanotify: allow setting FAN_CREATE in mount mark mask To: Christian Brauner Cc: Jan Kara , linux-fsdevel , Linux API , Miklos Szeredi Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Tue, Mar 30, 2021 at 3:53 PM Christian Brauner wrote: > > On Tue, Mar 30, 2021 at 03:33:23PM +0300, Amir Goldstein wrote: > > On Tue, Mar 30, 2021 at 3:12 PM Christian Brauner > > wrote: > > > > > > On Sun, Mar 28, 2021 at 06:56:24PM +0300, Amir Goldstein wrote: > > > > Add a high level hook fsnotify_path_create() which is called from > > > > syscall context where mount context is available, so that FAN_CREATE > > > > event can be added to a mount mark mask. > > > > > > > > This high level hook is called in addition to fsnotify_create(), > > > > fsnotify_mkdir() and fsnotify_link() hooks in vfs helpers where the mount > > > > context is not available. > > > > > > > > In the context where fsnotify_path_create() will be called, a dentry flag > > > > flag is set on the new dentry the suppress the FS_CREATE event in the vfs > > > > level hooks. > > > > > > Ok, just to make sure this scheme would also work for overlay-style > > > filesystems like ecryptfs where you possible generate two notify events: > > > - in the ecryptfs layer > > > - in the lower fs layer > > > at least when you set a regular inode watch. > > > > > > If you set a mount watch you ideally would generate two events in both > > > layers too, right? But afaict that wouldn't work. > > > > > > Say, someone creates a new link in ecryptfs the DENTRY_PATH_CREATE > > > flag will be set on the new ecryptfs dentry and so no notify event will > > > be generated for the ecryptfs layer again. Then ecryptfs calls > > > vfs_link() to create a new dentry in the lower layer. The new dentry in > > > the lower layer won't have DCACHE_PATH_CREATE set. Ok, that makes sense. > > > > > > But since vfs_link() doesn't have access to the mnt context itself you > > > can't generate a notify event for the mount associated with the lower > > > fs. This would cause people who a FAN_MARK_MOUNT watch on that lower fs > > > mount to not get notified about creation events going through the > > > ecryptfs layer. Is that right? Seems like this could be a problem. > > > > > > > Not sure I follow what the problem might be. > > > > FAN_MARK_MOUNT subscribes to get only events that were > > generated via that vfsmount - that has been that way forever. > > > > A listener may subscribe to (say) FAN_CREATE on a certain > > mount AND also also on a specific parent directory. > > > > If the listener is watching the entire ecryptfs mount and the > > specific lower directory where said vfs_link() happens, both > > events will be reported. One from fsnotify_create_path() and > > the lower from fsnotify_create(). > > > > If one listener is watching the ecryptfs mount and another > > listener is watching the specific ecryptfs directory, both > > listeners will get a single event each. They will both get > > the event that is emitted from fsnotify_path_create(). > > > > Besides I am not sure about ecryptfs, but overlayfs uses > > private mount clone for accessing lower layer, so by definition > > I know. That's why I was using ecryptfs as an example which doesn't do > that (And I think it should be switched tbh.). It simply uses > kern_path() and then stashes that path. > > My example probably would be something like: > > mount -t ext4 /dev/sdb /A > > 1. FAN_MARK_MOUNT(/A) > > mount --bind /A /B > > 2. FAN_MARK_MOUNT(/B) > > mount -t ecryptfs /B /C > > 3. FAN_MARK_MOUNT(/C) > > let's say I now do > > touch /C/bla > > I may be way off here but intuitively it seems both 1. and 2. should get > a creation event but not 3., right? > Why not 3? You explicitly set a mark on /C requesting to be notified when objects are created via /C. > But with your proposal would both 1. and 2. still get a creation event? > They would not get an event, because fsnotify() looks for CREATE event subscribers on inode->i_fsnotify_marks and inode->i_sb_s_fsnotify_marks and does not find any. The vfs_create() -> fsnotify_create() hook passes data_type inode to fsnotify() so there is no fsnotify_data_path() to extract mnt event subscribers from. The same fate would be to files created by overlayfs, nfsd and cachefiles. Only the create event on /C/bla from the syscall context would call fsnoity_path_create() and result with path data in fsnotify(), so the mnt event subscriber would be found. > > users cannot watch the underlying overlayfs operations using > > a mount mark. Also, overlayfs suppresses fsnotify events on > > underlying files intentionally with FMODE_NONOTIFY. > > Probably ecryptfs should too? > :) FMODE_NONOTIFY is there not because there was a requirement not to send events, but because the path of the internal file is "fake", so it has a weird looking path. After all there are many other events that would be sent (not on open files). At least I think that's the reason... Thanks, Amir.