Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754978AbZJUTU2 (ORCPT ); Wed, 21 Oct 2009 15:20:28 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754948AbZJUTU1 (ORCPT ); Wed, 21 Oct 2009 15:20:27 -0400 Received: from mx1.redhat.com ([209.132.183.28]:14268 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754935AbZJUTUU (ORCPT ); Wed, 21 Oct 2009 15:20:20 -0400 From: Valerie Aurora To: Jan Blunck , Alexander Viro , Christoph Hellwig , Andy Whitcroft , Scott James Remnant , Sandu Popa Marius , Jan Rekorajski , "J. R. Okajima" , Arnd Bergmann , Vladimir Dronnikov , Felix Fietkau Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH 07/41] VFS: Add read-only users count to superblock Date: Wed, 21 Oct 2009 12:19:05 -0700 Message-Id: <1256152779-10054-8-git-send-email-vaurora@redhat.com> In-Reply-To: <1256152779-10054-7-git-send-email-vaurora@redhat.com> References: <1256152779-10054-1-git-send-email-vaurora@redhat.com> <1256152779-10054-2-git-send-email-vaurora@redhat.com> <1256152779-10054-3-git-send-email-vaurora@redhat.com> <1256152779-10054-4-git-send-email-vaurora@redhat.com> <1256152779-10054-5-git-send-email-vaurora@redhat.com> <1256152779-10054-6-git-send-email-vaurora@redhat.com> <1256152779-10054-7-git-send-email-vaurora@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2402 Lines: 71 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 conceivable 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 --- fs/super.c | 14 ++++++++++++++ include/linux/fs.h | 5 +++++ 2 files changed, 19 insertions(+), 0 deletions(-) diff --git a/fs/super.c b/fs/super.c index 2761d3e..c8140ac 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 +898,11 @@ vfs_kern_mount(struct file_system_type *type, int flags, const char *name, void if (error) goto out_sb; + error = -EROFS; + if (!(flags & MS_RDONLY) && + (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 73e9b64..5fb7343 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -1379,6 +1379,11 @@ 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); -- 1.6.3.3 -- 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/