From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933094AbXHHKKi (ORCPT ); Wed, 8 Aug 2007 06:10:38 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1760750AbXHHKKU (ORCPT ); Wed, 8 Aug 2007 06:10:20 -0400 Received: from e4.ny.us.ibm.com ([32.97.182.144]:51868 "EHLO e4.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757212AbXHHKKQ (ORCPT ); Wed, 8 Aug 2007 06:10:16 -0400 Date: Wed, 8 Aug 2007 15:40:11 +0530 From: Bharata B Rao To: Jan Blunck Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC 18/26] union-mount: Changes to the namespace handling Message-ID: <20070808101011.GA6294@in.ibm.com> Reply-To: bharata@linux.vnet.ibm.com References: <20070730161323.100048969@weierstrass.suse.de> <20070730161324.806938495@weierstrass.suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070730161324.806938495@weierstrass.suse.de> User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 30, 2007 at 06:13:41PM +0200, Jan Blunck wrote: > Creates the proper struct union_mount when mounting something into a > union. If the topmost filesystem isn't capable of handling the white-out > filetype it could only be mount read-only. > Jan, I think it is important to allow pivot_root of union mount points. Here is an attempt to achieve that. From: Bharata B Rao Allow pivot_root to work with union mount points. If the current root filesystem is a union, then allow pivot_root only if it's last component is a root, which allows it to be detached as a complete union. Similarly if the new root filesystem is a union, it's last component should be a root, so that it can be completely detached from it's current mount point as a union and mounted back as root filesystem. Signed-off-by: Bharata B Rao --- fs/namespace.c | 17 +++++++++++++++-- fs/union.c | 12 ++++++++++++ include/linux/union.h | 2 ++ 3 files changed, 29 insertions(+), 2 deletions(-) --- a/fs/namespace.c +++ b/fs/namespace.c @@ -171,6 +171,13 @@ static void detach_mnt(struct vfsmount * old_nd->dentry->d_mounted--; } +static void detach_last_mnt(struct nameidata *nd, struct nameidata *old_nd) +{ + if (IS_MNT_UNION(nd->mnt)) + while (follow_union_down(&nd->mnt, &nd->dentry)); + detach_mnt(nd->mnt, old_nd); +} + void mnt_set_mountpoint(struct vfsmount *mnt, struct dentry *dentry, struct vfsmount *child_mnt) { @@ -1878,6 +1885,9 @@ asmlinkage long sys_pivot_root(const cha if (!check_mnt(new_nd.mnt)) goto out1; + if (IS_MNT_UNION(new_nd.mnt) && !last_union_is_root(&new_nd)) + goto out1; + error = __user_walk(put_old, LOOKUP_FOLLOW | LOOKUP_DIRECTORY, &old_nd); if (error) goto out1; @@ -1901,6 +1911,9 @@ asmlinkage long sys_pivot_root(const cha goto out2; if (!check_mnt(user_nd.mnt)) goto out2; + if (IS_MNT_UNION(user_nd.mnt) && !last_union_is_root(&user_nd)) + goto out2; + error = -ENOENT; if (IS_DEADDIR(new_nd.dentry->d_inode)) goto out2; @@ -1934,8 +1947,8 @@ asmlinkage long sys_pivot_root(const cha goto out3; } else if (!is_subdir(old_nd.dentry, new_nd.dentry)) goto out3; - detach_mnt(new_nd.mnt, &parent_nd); - detach_mnt(user_nd.mnt, &root_parent); + detach_last_mnt(&new_nd, &parent_nd); + detach_last_mnt(&user_nd, &root_parent); attach_mnt(user_nd.mnt, &old_nd); /* mount old root on put_old */ attach_mnt(new_nd.mnt, &root_parent); /* mount new_root on / */ touch_mnt_namespace(current->nsproxy->mnt_ns); --- a/fs/union.c +++ b/fs/union.c @@ -507,6 +507,18 @@ void detach_mnt_union(struct vfsmount *m return; } +/* + * last_union_is_root - Check if the last component of the union stack + * is a root. + */ +int last_union_is_root(struct nameidata *nd) +{ + struct vfsmount *mnt = nd->mnt; + struct dentry *dentry = nd->dentry; + + while (follow_union_down(&mnt, &dentry)); + return IS_ROOT(dentry) ? 1: 0; +} /* * Union mounts support for readdir. --- a/include/linux/union.h +++ b/include/linux/union.h @@ -53,6 +53,7 @@ extern void __shrink_d_unions(struct den extern int attach_mnt_union(struct vfsmount *, struct vfsmount *, struct dentry *); extern void detach_mnt_union(struct vfsmount *); +extern int last_union_is_root(struct nameidata *nd); extern int readdir_union(struct file *, void *, filldir_t); extern int is_dir_unioned(struct path *); extern int union_relookup_topmost(struct nameidata *, int); @@ -74,6 +75,7 @@ extern int union_copyup(struct nameidata #define __shrink_d_unions(x) do { } while (0) #define attach_mnt_union(x, y, z) do { } while (0) #define detach_mnt_union(x) do { } while (0) +#define last_union_is_root(x) ({ (0); }) #define union_relookup_topmost(x, y) ({ BUG(); (0); }) #define union_create_topmost(x, y, z) ({ BUG(); (NULL); }) #define __union_copyup(x, y, z) ({ BUG(); (0); }) This applies on top of your patchset plus my subsequent fixes [1] and [2]. [1] http://lkml.org/lkml/2007/8/6/10. [2] http://lkml.org/lkml/2007/8/6/114. Regards, Bharata.