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=-15.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 27322C433B4 for ; Thu, 20 May 2021 11:34:03 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 9A6FE6105A for ; Thu, 20 May 2021 11:34:02 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9A6FE6105A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:48582 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ljgwD-00040C-EV for qemu-devel@archiver.kernel.org; Thu, 20 May 2021 07:34:01 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:48032) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1ljgrQ-0007bL-Ra for qemu-devel@nongnu.org; Thu, 20 May 2021 07:29:04 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:32637) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1ljgrN-0006mO-9d for qemu-devel@nongnu.org; Thu, 20 May 2021 07:29:03 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1621510134; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=lE97Ce1HvrjbPWxnkONGXWggB4bk+WBOSto/+27nh+E=; b=a9ivzRp32INDIQZ/FYJPZ9dDsB901BTXiKmwuXv1lLTiuNjQkyce67hYGdyFihgj9nAIWm 9r1eL+1dpGEdktbr2CcMZmYhX5TisrhAzsNTRy4woOUIf04CyVrksYAQKfIoqgzN52vLDs uW8wqTQk9FhzVC0QDZRU54FTgCifcoo= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-168-9GsDH9e4NZuI8tWGLQQkgA-1; Thu, 20 May 2021 07:28:51 -0400 X-MC-Unique: 9GsDH9e4NZuI8tWGLQQkgA-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 5604080476A for ; Thu, 20 May 2021 11:28:47 +0000 (UTC) Received: from work-vm (ovpn-115-44.ams2.redhat.com [10.36.115.44]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 06C0860C04; Thu, 20 May 2021 11:28:45 +0000 (UTC) Date: Thu, 20 May 2021 12:28:43 +0100 From: "Dr. David Alan Gilbert" To: Max Reitz Subject: Re: [PATCH 1/3] virtiofsd: Find original inode ID of mount points Message-ID: References: <20210512125544.9536-1-mreitz@redhat.com> <20210512125544.9536-2-mreitz@redhat.com> <20210517145739.GE546943@horse.lan> <13641be2-e875-ca43-1cc4-8d06a4e6f81c@redhat.com> MIME-Version: 1.0 In-Reply-To: <13641be2-e875-ca43-1cc4-8d06a4e6f81c@redhat.com> User-Agent: Mutt/2.0.7 (2021-05-04) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dgilbert@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.39, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: virtio-fs-list , Stefan Hajnoczi , qemu-devel@nongnu.org, Vivek Goyal Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Max Reitz (mreitz@redhat.com) wrote: > On 17.05.21 16:57, Vivek Goyal wrote: > > On Wed, May 12, 2021 at 02:55:42PM +0200, Max Reitz wrote: > > > Mount point directories represent two inodes: On one hand, they are a > > > normal directory on their parent filesystem. On the other, they are the > > > root node of the filesystem mounted there. Thus, they have two inode > > > IDs. > > > > > > Right now, we only report the latter inode ID (i.e. the inode ID of the > > > mounted filesystem's root node). This is fine once the guest has > > > auto-mounted a submount there (so this inode ID goes with a device ID > > > that is distinct from the parent filesystem), but before the auto-mount, > > > they have the device ID of the parent and the inode ID for the submount. > > > This is problematic because this is likely exactly the same > > > st_dev/st_ino combination as the parent filesystem's root node. This > > > leads to problems for example with `find`, which will thus complain > > > about a filesystem loop if it has visited the parent filesystem's root > > > node before, and then refuse to descend into the submount. > > > > > > There is a way to find the mount directory's original inode ID, and that > > > is to readdir(3) the parent directory, look for the mount directory, and > > > read the dirent.d_ino field. Using this, we can let lookup and > > > readdirplus return that original inode ID, which the guest will thus > > > show until the submount is auto-mounted. (Then, it will invoke getattr > > > and that stat(2) call will return the inode ID for the submount.) > > > > > > Signed-off-by: Max Reitz > > > --- > > > tools/virtiofsd/passthrough_ll.c | 104 +++++++++++++++++++++++++++++-- > > > 1 file changed, 99 insertions(+), 5 deletions(-) > > > > > > diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c > > > index 1553d2ef45..110b6e7e5b 100644 > > > --- a/tools/virtiofsd/passthrough_ll.c > > > +++ b/tools/virtiofsd/passthrough_ll.c > > > @@ -968,14 +968,87 @@ static int do_statx(struct lo_data *lo, int dirfd, const char *pathname, > > > return 0; > > > } > > > +/* > > > + * Use readdir() to find mp_name's inode ID on the parent's filesystem. > > > + * (For mount points, stat() will only return the inode ID on the > > > + * filesystem mounted there, i.e. the root directory's inode ID. The > > > + * mount point originally was a directory on the parent filesystem, > > > + * though, and so has a different inode ID there. When passing > > > + * submount information to the guest, we need to pass this other ID, > > > + * so the guest can use it as the inode ID until the submount is > > > + * auto-mounted. (At which point the guest will invoke getattr and > > > + * find the inode ID on the submount.)) > > > + * > > > + * Return 0 on success, and -errno otherwise. *pino is set only in > > > + * case of success. > > > + */ > > > +static int get_mp_ino_on_parent(const struct lo_inode *dir, const char *mp_name, > > > + ino_t *pino) > > > +{ > > > + int dirfd = -1; > > > + int ret; > > > + DIR *dp = NULL; > > > + > > > + dirfd = openat(dir->fd, ".", O_RDONLY); > > > + if (dirfd < 0) { > > > + ret = -errno; > > > + goto out; > > > + } > > > + > > > + dp = fdopendir(dirfd); > > > + if (!dp) { > > > + ret = -errno; > > > + goto out; > > > + } > > > + /* Owned by dp now */ > > > + dirfd = -1; > > > + > > > + while (true) { > > > + struct dirent *de; > > > + > > > + errno = 0; > > > + de = readdir(dp); > > > + if (!de) { > > > + ret = errno ? -errno : -ENOENT; > > > + goto out; > > > + } > > > + > > > + if (!strcmp(de->d_name, mp_name)) { > > > + *pino = de->d_ino; > > > + ret = 0; > > > + goto out; > > > + } > > > + } > > > + > > > +out: > > > + if (dp) { > > > + closedir(dp); > > > + } > > > + if (dirfd >= 0) { > > > + close(dirfd); > > > + } > > > + return ret; > > > +} > > > + > > > /* > > > * Increments nlookup on the inode on success. unref_inode_lolocked() must be > > > * called eventually to decrement nlookup again. If inodep is non-NULL, the > > > * inode pointer is stored and the caller must call lo_inode_put(). > > > + * > > > + * If parent_fs_st_ino is true, the entry is a mount point, and submounts are > > > + * announced to the guest, set e->attr.st_ino to the entry's inode ID on its > > > + * parent filesystem instead of its inode ID on the filesystem mounted on it. > > > + * (For mount points, the entry encompasses two inodes: One on the parent FS, > > > + * and one on the mounted FS (where it is the root node), so it has two inode > > > + * IDs. When looking up entries, we should show the guest the parent FS's inode > > > + * ID, because as long as the guest has not auto-mounted the submount, it should > > > + * see that original ID. Once it does perform the auto-mount, it will invoke > > > + * getattr and see the root node's inode ID.) > > > */ > > > static int lo_do_lookup(fuse_req_t req, fuse_ino_t parent, const char *name, > > > struct fuse_entry_param *e, > > > - struct lo_inode **inodep) > > > + struct lo_inode **inodep, > > > + bool parent_fs_st_ino) > > > { > > > int newfd; > > > int res; > > > @@ -984,6 +1057,7 @@ static int lo_do_lookup(fuse_req_t req, fuse_ino_t parent, const char *name, > > > struct lo_data *lo = lo_data(req); > > > struct lo_inode *inode = NULL; > > > struct lo_inode *dir = lo_inode(req, parent); > > > + ino_t ino_id_for_guest; > > > if (inodep) { > > > *inodep = NULL; /* in case there is an error */ > > > @@ -1018,9 +1092,22 @@ static int lo_do_lookup(fuse_req_t req, fuse_ino_t parent, const char *name, > > > goto out_err; > > > } > > > + ino_id_for_guest = e->attr.st_ino; > > > + > > > if (S_ISDIR(e->attr.st_mode) && lo->announce_submounts && > > > (e->attr.st_dev != dir->key.dev || mnt_id != dir->key.mnt_id)) { > > > e->attr_flags |= FUSE_ATTR_SUBMOUNT; > > > + > > > + if (parent_fs_st_ino) { > > > + /* > > > + * Best effort, so ignore errors. > > > + * Also note that using readdir() means there may be races: > > > + * The directory entry we find (if any) may be different > > > + * from newfd. Again, this is a best effort. Reporting > > > + * the wrong inode ID to the guest is not catastrophic. > > > + */ > > > + get_mp_ino_on_parent(dir, name, &ino_id_for_guest); > > > > Hi Max, > > > > [CC virtio-fs list ] > > > > In general patch looks good to me. A minor nit. get_mp_ino_on_parent() > > is retruning error. It might be better to capture error and print a > > message and continue. > > Sure, why not. > > > I have couple of general questions about submounts. > > > > - What happens in case of single file mounted on top of another file. > > > > mount --bind foo.txt bar.txt > > > > Do submounts work when mount point is not a directory. > > No, as you can see in the condition quoted above, we only set the > FUSE_ATTR_SUBMOUNT flag for directories. That seemed the most common case > for me, and I didn’t want to have to worry about weirdness that might ensue > for file mounts. It might be worth checking file mounts don't break too badly; I'm pretty sure I've seen the container systems use them a lot in /etc Dave > > - Say a directory is not a mount point yet and lookup instantiates an > > inode. Later user mounts something on that directory. When does > > client/server notice this change. I am assuming this is probably > > part of revalidation path. > > I guess at least before this patch this is no different from any other > filesystem change. Because st_dev+st_ino changed, it should basically look > like the old directory was removed and a different one was put in its place. > > Now, with this patch, we will return the old st_ino to the guest, but > internally virtiofsd will still use the submount’s st_dev/st_ino, so a new > lo_inode should be created, and so fuse_dentry_revalidate()’s lookup should > return a different node ID, resulting it to consider the entry expired. > > Besides, fuse_dentry_revalidate() has a condition on IS_AUTOMOUNT(inode) != > flags & FUSE_ATTR_SUBMOUNT. Considering the previous paragraph, this > doesn’t seem necessary to me, but it can’t hurt. > > Max -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK