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 B991AC433ED for ; Thu, 1 Apr 2021 10:30:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7177F606A5 for ; Thu, 1 Apr 2021 10:30:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233629AbhDAKaM (ORCPT ); Thu, 1 Apr 2021 06:30:12 -0400 Received: from mx2.suse.de ([195.135.220.15]:49068 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233917AbhDAK3t (ORCPT ); Thu, 1 Apr 2021 06:29:49 -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 B7C7CB0B3; Thu, 1 Apr 2021 10:29:47 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 713D31E4415; Thu, 1 Apr 2021 12:29:47 +0200 (CEST) Date: Thu, 1 Apr 2021 12:29:47 +0200 From: Jan Kara To: Amir Goldstein Cc: Jan Kara , Christian Brauner , linux-fsdevel , Linux API , Miklos Szeredi , "J. Bruce Fields" Subject: Re: fsnotify path hooks Message-ID: <20210401102947.GA29690@quack2.suse.cz> References: <20210330125336.vj2hkgwhyrh5okee@wittgenstein> <20210330141703.lkttbuflr5z5ia7f@wittgenstein> <20210331094604.xxbjl3krhqtwcaup@wittgenstein> <20210331125412.GI30749@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) Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Wed 31-03-21 23:59:27, Amir Goldstein wrote: > On Wed, Mar 31, 2021 at 5:06 PM Amir Goldstein wrote: > > > > > > As long as "exp_export: export of idmapped mounts not yet supported.\n" > > > > I don't think it matters much. > > > > It feels like adding idmapped mounts to nfsd is on your roadmap. > > > > When you get to that we can discuss adding fsnotify path hooks to nfsd > > > > if Jan agrees to the fsnotify path hooks concept. > > > > > > I was looking at the patch and thinking about it for a few days already. I > > > think that generating fsnotify event later (higher up the stack where we > > > have mount information) is fine and a neat idea. I just dislike the hackery > > > with dentry flags. > > > > Me as well. I used this hack for fast POC. > > > > If we stick with the dual hooks approach, we will have to either pass a new > > argument to vfs helpers or use another trick: > > > > Convert all the many calls sites that were converted by Christian to: > > vfs_XXX(&init_user_ns, ... > > because they do not have mount context, to: > > vfs_XXX(NULL, ... > > > > Inside the vfs helpers, use init_user_ns when mnt_userns is NULL, > > but pass the original mnt_userns argument to fsnotify_ns_XXX hooks. > > A non-NULL mnt_userns arg means "path_notify" context. > > I have already POC code for passing mnt_userns to fsnotify hooks [1]. > > > > I did not check if this assumption always works, but there seems to > > be a large overlap between idmapped aware callers and use cases > > that will require sending events to a mount mark. > > > > The above "trick" is pretty silly as I believe Christian intends > to fix all those call sites that pass init_user_ns. If he does that we also should have the mountpoint there to use for fsnotify, shouldn't we? :) > > > Also I'm somewhat uneasy that it is random (from > > > userspace POV) when path event is generated and when not (at least that's > > > my impression from the patch - maybe I'm wrong). How difficult would it be > > > to get rid of it? I mean what if we just moved say fsnotify_create() call > > > wholly up the stack? It would mean more explicit calls to fsnotify_create() > > > from filesystems - as far as I'm looking nfsd, overlayfs, cachefiles, > > > ecryptfs. But that would seem to be manageable. Also, to maintain sanity, > > > > 1. I don't think we can do that for all the fsnotify_create() hooks, such as > > debugfs for example > > 2. It is useless to pass the mount from overlayfs to fsnotify, its a private > > mount that users cannot set a mark on anyway and Christian has > > promised to propose the same change for cachefiles and ecryptfs, > > so I think it's not worth the churn in those call sites > > 3. I am uneasy with removing the fsnotify hooks from vfs helpers and > > trusting that new callers of vfs_create() will remember to add the high > > level hooks, so I prefer the existing behavior remains for such callers > > > > So I read your proposal the wrong way. > You meant move fsnotify_create() up *without* passing mount context > from overlayfs and friends. Well, I was thinking that we could find appropriate mount context for overlayfs or ecryptfs (which just shows how little I know about these filesystems ;) I didn't think of e.g. debugfs. Anyway, if we can make mountpoint marks work for directory events at least for most filesystems, I think that is OK as well. However it would be then needed to detect whether a given filesystem actually supports mount marks for dir events and if not, report error from fanotify_mark() instead of silently not generating events. > So yeh, I do think it is manageable. I think the best solution would be > something along the lines of wrappers like the following: > > static inline int vfs_mkdir(...) > { > int error = __vfs_mkdir_nonotify(...); > if (!error) > fsnotify_mkdir(dir, dentry); > return error; > } > > And then the few call sites that call the fsnotify_path_ hooks > (i.e. in syscalls and perhaps later in nfsd) will call the > __vfs_xxx_nonotify() variant. Yes, that is OK with me. Or we could have something like: static inline void fsnotify_dirent(struct vfsmount *mnt, struct inode *dir, struct dentry *dentry, __u32 mask) { if (!mnt) { fsnotify(mask, d_inode(dentry), FSNOTIFY_EVENT_INODE, dir, &dentry->d_name, NULL, 0); } else { struct path path = { .mnt = mnt, .dentry = d_find_any_alias(dir) }; fsnotify(mask, d_inode(dentry), FSNOTIFY_EVENT_PATH, &path, &dentry->d_name, NULL, 0); } } static inline void fsnotify_mkdir(struct vfsmount *mnt, struct inode *inode, struct dentry *dentry) { audit_inode_child(inode, dentry, AUDIT_TYPE_CHILD_CREATE); fsnotify_dirent(mnt, inode, dentry, FS_CREATE | FS_ISDIR); } static inline int vfs_mkdir(mnt, ...) { int error = __vfs_mkdir_nonotify(...); if (!error) fsnotify_mkdir(mnt, dir, dentry); } And pass mnt to vfs_mkdir() for filesystems where we have it... Honza -- Jan Kara SUSE Labs, CR