Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755234AbZGMT1t (ORCPT ); Mon, 13 Jul 2009 15:27:49 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755068AbZGMT1s (ORCPT ); Mon, 13 Jul 2009 15:27:48 -0400 Received: from mx1.redhat.com ([66.187.233.31]:33451 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751572AbZGMT1r (ORCPT ); Mon, 13 Jul 2009 15:27:47 -0400 Date: Mon, 13 Jul 2009 15:27:44 -0400 From: Valerie Aurora To: Alexander Viro , Jan Blunck , linux-fsdevel@vger.kernel.org Cc: linux-kernel@vger.kernel.org Subject: [PATCH] VFS: Add read-only users count to superblock Message-ID: <20090713192743.GA27582@shell> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.4.2.2i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2948 Lines: 78 During the last FS summit, Al Viro suggested creating a superblock level read-only marker so that union mounts could guarantee that the underlying fs would not become writable. This patch implements the VFS support, but doesn't add any users. The patch making union mounts use the support is in our union mounts tree. I think we also need some way to pass this through NFS mounts, since a read-only NFS mount for the bottom layer of a union mount is a common use case. -VAL commit b0bfe1b9023467184e138c8520a084ca1e7bf8ab Author: Valerie Aurora (Henson) Date: Mon Jul 13 09:30:49 2009 -0700 VFS: Add read-only users count to superblock While we can check if a file system is currently read-only, we can't guarantee that it will stay read-only. The file system can be remounted read-write at any time; it's also concievable that a file system can be mounted a second time and converted to read-write if the underlying fs allows it. This is a problem for union mounts, which require the underlying file system be read-only. Add a read-only users count and don't allow remounts to change the file system to read-write or read-write mounts if there are any read-only users. Signed-off-by: Valerie Aurora (Henson) diff --git a/fs/super.c b/fs/super.c index 2761d3e..65972df 100644 --- a/fs/super.c +++ b/fs/super.c @@ -553,6 +553,15 @@ int do_remount_sb(struct super_block *sb, int flags, void *data, int force) } remount_rw = !(flags & MS_RDONLY) && (sb->s_flags & MS_RDONLY); + /* If we are remounting read/write, make sure that none of the + users require read-only for correct operation (such as + union mounts). */ + if (remount_rw && sb->s_readonly_users) { + printk(KERN_INFO "%s: In use by %d read-only user(s)\n", + sb->s_id, sb->s_readonly_users); + return -EROFS; + } + if (sb->s_op->remount_fs) { retval = sb->s_op->remount_fs(sb, &flags, data); if (retval) @@ -889,6 +898,10 @@ vfs_kern_mount(struct file_system_type *type, int flags, const char *name, void if (error) goto out_sb; + error = -EROFS; + if (mnt->mnt_sb->s_readonly_users) + goto out_sb; + mnt->mnt_mountpoint = mnt->mnt_root; mnt->mnt_parent = mnt; up_write(&mnt->mnt_sb->s_umount); diff --git a/include/linux/fs.h b/include/linux/fs.h index 0872372..aff3dca 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -1379,6 +1379,10 @@ struct super_block { * generic_show_options() */ char *s_options; + /* + * Users who require read-only access - e.g., union mounts + */ + int s_readonly_users; }; extern struct timespec current_fs_time(struct super_block *sb); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/