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=-13.6 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 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 40B64C47083 for ; Wed, 2 Jun 2021 18:21:26 +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 AC58961027 for ; Wed, 2 Jun 2021 18:21:25 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AC58961027 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]:54546 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1loVUa-000463-PB for qemu-devel@archiver.kernel.org; Wed, 02 Jun 2021 14:21:24 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:54962) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1loVTR-0002sG-CG for qemu-devel@nongnu.org; Wed, 02 Jun 2021 14:20:13 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:37837) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1loVTO-0002Kp-Kc for qemu-devel@nongnu.org; Wed, 02 Jun 2021 14:20:12 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1622658009; 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: in-reply-to:in-reply-to:references:references; bh=jPkQ8G1YhdYRrj17FFd1ou4OfoVELyNpQB2xevXT4go=; b=eG+TZC07JofPi4/AkA2LVx9mrtMN5kr4kHE2PT9zw5FJBTrlmxQDVbqzYV/iXms0cCC1pX NDTtNmPq+8NV1AkaUp444X2AufjFPmjVBIuJUsE/0K204Eyo5nReRgJHI6Hvz0mG5su02e hSSThENRDiW5YH/qOZuNzzKri8MzfAo= 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-126-kTqkGhhEPnyKQbXfxJA1GA-1; Wed, 02 Jun 2021 14:20:07 -0400 X-MC-Unique: kTqkGhhEPnyKQbXfxJA1GA-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 91BD1818401; Wed, 2 Jun 2021 18:20:06 +0000 (UTC) Received: from horse.redhat.com (ovpn-114-190.rdu2.redhat.com [10.10.114.190]) by smtp.corp.redhat.com (Postfix) with ESMTP id 71CC160D43; Wed, 2 Jun 2021 18:19:59 +0000 (UTC) Received: by horse.redhat.com (Postfix, from userid 10451) id D7F5322054F; Wed, 2 Jun 2021 14:19:58 -0400 (EDT) Date: Wed, 2 Jun 2021 14:19:58 -0400 From: Vivek Goyal To: Max Reitz Subject: Re: [PATCH 1/3] virtiofsd: Find original inode ID of mount points Message-ID: <20210602181958.GC115492@redhat.com> References: <20210512125544.9536-1-mreitz@redhat.com> <20210512125544.9536-2-mreitz@redhat.com> MIME-Version: 1.0 In-Reply-To: <20210512125544.9536-2-mreitz@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=vgoyal@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=170.10.133.124; envelope-from=vgoyal@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=-0.371, 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 , Miklos Szeredi , qemu-devel@nongnu.org, Stefan Hajnoczi , "Dr . David Alan Gilbert" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 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.) [ CC miklos ] Hi Max, Though we discussed this in chat room, I am still responding to this email with the concern I have, so that there is a record of it. So with this patch for FUSE_LOOKUP we always return submount's parentinode id and with GETATTR request we return actual inode id of submount. That kind of bothers me a bit as we are assuming that there is always going to be a GETATTR request after FUSE_LOOKUP. FUSE_LOOKUP itself has attrs returned with it and it might happen that after FUSE_LOOKUP, FUSE_GETATTR might not be called at all because FUSE_LOOKUP itself got the latest updated attrs with certain timeout. For example, if I call stat on a normal file (not submount), I see that after FUSE_LOOKUP, no FUSE_GETATTR request is going and fuse_update_get_attr() is using attrs from locally cached inode attrs. But same thing does not seem to be happening in case of submount. Once submount is created in guest, I see that we never seem to be calling ->revalidate() on newly created dentry of submount root. I am not sure why. And that means we don't do FUSE_LOOKUP and that means FUSE_GETATTR always gets called. I am not sure if this is a bug or expected behavior. I am not confident that we can rely on this behavior of submount dentries. Ccing Miklos. He might have thoughts on this. As we discussed, may be it is a better idea to create two inodes in virtiofsd (like we do in guest). One for submount parent and one for actual submount. Thanks Vivek > > 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); > + } > } > > inode = lo_find(lo, &e->attr, mnt_id); > @@ -1043,6 +1130,10 @@ static int lo_do_lookup(fuse_req_t req, fuse_ino_t parent, const char *name, > > inode->nlookup = 1; > inode->fd = newfd; > + /* > + * For the inode key, use the dev/ino/mnt ID as reported by stat() > + * (i.e. not ino_id_for_guest) > + */ > inode->key.ino = e->attr.st_ino; > inode->key.dev = e->attr.st_dev; > inode->key.mnt_id = mnt_id; > @@ -1058,6 +1149,9 @@ static int lo_do_lookup(fuse_req_t req, fuse_ino_t parent, const char *name, > } > e->ino = inode->fuse_ino; > > + /* Report ino_id_for_guest to the guest */ > + e->attr.st_ino = ino_id_for_guest; > + > /* Transfer ownership of inode pointer to caller or drop it */ > if (inodep) { > *inodep = inode; > @@ -1104,7 +1198,7 @@ static void lo_lookup(fuse_req_t req, fuse_ino_t parent, const char *name) > return; > } > > - err = lo_do_lookup(req, parent, name, &e, NULL); > + err = lo_do_lookup(req, parent, name, &e, NULL, true); > if (err) { > fuse_reply_err(req, err); > } else { > @@ -1217,7 +1311,7 @@ static void lo_mknod_symlink(fuse_req_t req, fuse_ino_t parent, > goto out; > } > > - saverr = lo_do_lookup(req, parent, name, &e, NULL); > + saverr = lo_do_lookup(req, parent, name, &e, NULL, false); > if (saverr) { > goto out; > } > @@ -1714,7 +1808,7 @@ static void lo_do_readdir(fuse_req_t req, fuse_ino_t ino, size_t size, > > if (plus) { > if (!is_dot_or_dotdot(name)) { > - err = lo_do_lookup(req, ino, name, &e, NULL); > + err = lo_do_lookup(req, ino, name, &e, NULL, true); > if (err) { > goto error; > } > @@ -1936,7 +2030,7 @@ static void lo_create(fuse_req_t req, fuse_ino_t parent, const char *name, > goto out; > } > > - err = lo_do_lookup(req, parent, name, &e, &inode); > + err = lo_do_lookup(req, parent, name, &e, &inode, false); > if (err) { > goto out; > } > -- > 2.31.1 > >