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=-15.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 DBAF8C48BE8 for ; Fri, 18 Jun 2021 14:11:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AAF5A613C2 for ; Fri, 18 Jun 2021 14:11:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234280AbhFRONH (ORCPT ); Fri, 18 Jun 2021 10:13:07 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:37383 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231877AbhFRONE (ORCPT ); Fri, 18 Jun 2021 10:13:04 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1624025454; 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=Ajv9GHZqwhwdqHmInEP3t514hzTn+CylcSgzTQPjYrk=; b=LOErCS6Zv1mCHF5RO+Vp8M3ZMzIn2gV00N6DNhzpd+U9KchaneW+g3AwjkEA/LyQL2/lfp Fo43BfYhlDnpngsJ0+evTtYQ2XhwBbitlZwSt9+ZLDCvq0hfha5Bcty3iI39XKeU0W8qsL XXMbu4tZuODfqM892SQACeDaLlj9tQo= 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-589-ziznzbOoNd6RDq0QxqqqLA-1; Fri, 18 Jun 2021 10:10:45 -0400 X-MC-Unique: ziznzbOoNd6RDq0QxqqqLA-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 C5E8E801B33; Fri, 18 Jun 2021 14:10:43 +0000 (UTC) Received: from horse.redhat.com (ovpn-114-2.rdu2.redhat.com [10.10.114.2]) by smtp.corp.redhat.com (Postfix) with ESMTP id 93B3060BE5; Fri, 18 Jun 2021 14:10:31 +0000 (UTC) Received: by horse.redhat.com (Postfix, from userid 10451) id 2E22722054F; Fri, 18 Jun 2021 10:10:31 -0400 (EDT) Date: Fri, 18 Jun 2021 10:10:31 -0400 From: Vivek Goyal To: Christoph Hellwig Cc: viro@zeniv.linux.org.uk, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, virtio-fs@redhat.com, Dominique Martinet Subject: Re: [PATCH 2/2] init: allow mounting arbitrary non-blockdevice filesystems as root Message-ID: <20210618141031.GC1234055@redhat.com> References: <20210617153649.1886693-1-hch@lst.de> <20210617153649.1886693-3-hch@lst.de> <20210617162610.GC1142820@redhat.com> <20210618132038.GA13406@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210618132038.GA13406@lst.de> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Fri, Jun 18, 2021 at 03:20:38PM +0200, Christoph Hellwig wrote: > On Thu, Jun 17, 2021 at 12:26:10PM -0400, Vivek Goyal wrote: > > Not sure what FS_BINARY_MOUNTDATA is why fs should not have that set. nfs > > seems to set it too. So that means they can't use try_mount_nodev(). > > We can't really pass actual binary mountdata using the string separation > scheme used by the rootfstype= option. But given that NFS only uses > binary mountdata for legacy reasons and people get what they ask for > using the option I think we can drop the check. > > > In case of success err == 0, but we still panic(). We will need to > > check for success as well. > > Indeed. > > > root_fs_names can be NULL and it crashes with NULL pointer dereference. > > True. > > What do you think of this version? [ Cc Dominique Martinet ] Hi Christoph, This one works well for me. Just one minor nit. root_device_name, can be NULL as well if user passes following. "rootfstype=virtiofs rw". And currently mount_nodev_root() is assuming root_device_name is not NULL and we crash with null pointer dereference. May be something like this. if (ROOT_DEV == 0 && root_device_name && root_fs_names) { if (mount_nodev_root() == 0) return; } Strangely people are using "rootfstype=virtiofs rw" to mount virtiofs as rootfs. They give their filesystem a tag named "/dev/root". And currently it works and they can mount virtiofs as rootfs. With above change, current hackish way will also continue to work and not break existing setups. Thanks Vivek > > --- > From 141caa79a619b5f5d100eeb8e94ecf8b3b1c9af7 Mon Sep 17 00:00:00 2001 > From: Christoph Hellwig > Date: Fri, 18 Jun 2021 15:10:39 +0200 > Subject: init: allow mounting arbitrary non-blockdevice filesystems as root > > Currently the only non-blockdevice filesystems that can be used as the > initial root filesystem are NFS and CIFS, which use the magic > "root=/dev/nfs" and "root=/dev/cifs" syntax that requires the root > device file system details to come from filesystem specific kernel > command line options. > > Add a little bit of new code that allows to just pass arbitrary > string mount options to any non-blockdevice filesystems so that it can > be mounted as the root file system. > > For example a virtiofs root file system can be mounted using the > following syntax: > > "root=myfs rootfstype=virtiofs rw" > > Based on an earlier patch from Vivek Goyal . > > Signed-off-by: Christoph Hellwig > --- > init/do_mounts.c | 43 +++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 43 insertions(+) > > diff --git a/init/do_mounts.c b/init/do_mounts.c > index ec32de3ad52b..66c47193e9ee 100644 > --- a/init/do_mounts.c > +++ b/init/do_mounts.c > @@ -534,6 +534,45 @@ static int __init mount_cifs_root(void) > } > #endif > > +static bool __init fs_is_nodev(char *fstype) > +{ > + struct file_system_type *fs = get_fs_type(fstype); > + bool ret = false; > + > + if (fs) { > + ret = !(fs->fs_flags & FS_REQUIRES_DEV); > + put_filesystem(fs); > + } > + > + return ret; > +} > + > +static int __init mount_nodev_root(void) > +{ > + char *fs_names, *fstype; > + int err = -EINVAL; > + > + fs_names = (void *)__get_free_page(GFP_KERNEL); > + if (!fs_names) > + return -EINVAL; > + split_fs_names(fs_names, root_fs_names); > + > + for (fstype = fs_names; *fstype; fstype += strlen(fstype) + 1) { > + if (!fs_is_nodev(fstype)) > + continue; > + err = do_mount_root(root_device_name, fstype, root_mountflags, > + root_mount_data); > + if (!err) > + break; > + if (err != -EACCES && err != -EINVAL) > + panic("VFS: Unable to mount root \"%s\" (%s), err=%d\n", > + root_device_name, fstype, err); > + } > + > + free_page((unsigned long)fs_names); > + return err; > +} > + > void __init mount_root(void) > { > #ifdef CONFIG_ROOT_NFS > @@ -550,6 +589,10 @@ void __init mount_root(void) > return; > } > #endif > + if (ROOT_DEV == 0 && root_fs_names) { > + if (mount_nodev_root() == 0) > + return; > + } > #ifdef CONFIG_BLOCK > { > int err = create_dev("/dev/root", ROOT_DEV); > -- > 2.30.2 >