[RFC PATCH 3/8] bind/rbind a shared/private/slave/unclone tree

[Ram <linuxram@us.ibm.com>]

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Adds the ability to bind/rbind a shared/private/slave subtree and set up
propogation wherever needed.

RP


[-- Attachment #2: rbind.patch --]
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Adds the ability to bind/rbind a shared/private/slave subtree and set up
propogation wherever needed.

RP

Signed by Ram Pai (linuxram@us.ibm.com)

 fs/namespace.c        |  510 ++++++++++++++++++++++++++++++++++++++++----------
 fs/pnode.c            |  244 +++++++++++++++++++++++
 include/linux/fs.h    |    4 
 include/linux/pnode.h |    5 
 4 files changed, 664 insertions(+), 99 deletions(-)

Index: 2.6.12/fs/namespace.c
===================================================================
--- 2.6.12.orig/fs/namespace.c
+++ 2.6.12/fs/namespace.c
@@ -42,7 +42,8 @@ static inline int sysfs_init(void)
 
 static struct list_head *mount_hashtable;
 static int hash_mask, hash_bits;
-static kmem_cache_t *mnt_cache; 
+static kmem_cache_t *mnt_cache;
+static struct rw_semaphore namespace_sem;
 
 static inline unsigned long hash(struct vfsmount *mnt, struct dentry *dentry)
 {
@@ -54,7 +55,7 @@ static inline unsigned long hash(struct 
 
 struct vfsmount *alloc_vfsmnt(const char *name)
 {
-	struct vfsmount *mnt = kmem_cache_alloc(mnt_cache, GFP_KERNEL); 
+	struct vfsmount *mnt = kmem_cache_alloc(mnt_cache, GFP_KERNEL);
 	if (mnt) {
 		memset(mnt, 0, sizeof(struct vfsmount));
 		atomic_set(&mnt->mnt_count,1);
@@ -109,6 +110,32 @@ struct vfsmount *lookup_mnt(struct vfsmo
 	return found;
 }
 
+static struct vfsmount *
+clone_mnt(struct vfsmount *old, struct dentry *root)
+{
+	struct super_block *sb = old->mnt_sb;
+	struct vfsmount *mnt = alloc_vfsmnt(old->mnt_devname);
+
+	if (mnt) {
+		mnt->mnt_flags = old->mnt_flags;
+		atomic_inc(&sb->s_active);
+		mnt->mnt_sb = sb;
+		mnt->mnt_root = dget(root);
+		mnt->mnt_mountpoint = mnt->mnt_root;
+		mnt->mnt_parent = mnt;
+		mnt->mnt_namespace = old->mnt_namespace;
+		mnt->mnt_pnode = get_pnode(old->mnt_pnode);
+
+		/* stick the duplicate mount on the same expiry list
+		 * as the original if that was on one */
+		spin_lock(&vfsmount_lock);
+		if (!list_empty(&old->mnt_fslink))
+			list_add(&mnt->mnt_fslink, &old->mnt_fslink);
+		spin_unlock(&vfsmount_lock);
+	}
+	return mnt;
+}
+
 static inline int check_mnt(struct vfsmount *mnt)
 {
 	return mnt->mnt_namespace == current->namespace;
@@ -122,7 +149,6 @@ static void detach_mnt(struct vfsmount *
 	mnt->mnt_mountpoint = mnt->mnt_root;
 	list_del_init(&mnt->mnt_child);
 	list_del_init(&mnt->mnt_hash);
-	list_del_init(&mnt->mnt_pnode_mntlist);
 	old_nd->dentry->d_mounted--;
 }
 
@@ -130,11 +156,68 @@ static void attach_mnt(struct vfsmount *
 {
 	mnt->mnt_parent = mntget(nd->mnt);
 	mnt->mnt_mountpoint = dget(nd->dentry);
+	mnt->mnt_namespace = nd->mnt->mnt_namespace;
 	list_add(&mnt->mnt_hash, mount_hashtable+hash(nd->mnt, nd->dentry));
 	list_add_tail(&mnt->mnt_child, &nd->mnt->mnt_mounts);
 	nd->dentry->d_mounted++;
 }
 
+static struct vfsmount *do_attach_mnt(struct vfsmount *mnt,
+		struct dentry *dentry,
+		struct vfsmount *child_mnt)
+{
+	struct nameidata nd;
+	LIST_HEAD(head);
+
+	nd.mnt = mnt;
+	nd.dentry = dentry;
+	attach_mnt(child_mnt, &nd);
+	list_add_tail(&head, &child_mnt->mnt_list);
+	list_splice(&head, child_mnt->mnt_namespace->list.prev);
+	return child_mnt;
+}
+
+static void attach_prepare_mnt(struct vfsmount *mnt, struct nameidata *nd)
+{
+	mnt->mnt_parent = mntget(nd->mnt);
+	mnt->mnt_mountpoint = dget(nd->dentry);
+	nd->dentry->d_mounted++;
+}
+
+void do_attach_real_mnt(struct vfsmount *mnt)
+{
+	struct vfsmount *parent = mnt->mnt_parent;
+	BUG_ON(parent==mnt);
+	if(list_empty(&mnt->mnt_hash))
+		list_add(&mnt->mnt_hash,
+			mount_hashtable+hash(parent, mnt->mnt_mountpoint));
+	if(list_empty(&mnt->mnt_child))
+		list_add_tail(&mnt->mnt_child, &parent->mnt_mounts);
+	mnt->mnt_namespace = parent->mnt_namespace;
+	list_add_tail(&mnt->mnt_list, &mnt->mnt_namespace->list);
+}
+
+struct vfsmount *do_attach_prepare_mnt(struct vfsmount *mnt,
+		struct dentry *dentry,
+		struct vfsmount *template_mnt,
+		int clone_flag)
+{
+	struct vfsmount *child_mnt;
+	struct nameidata nd;
+
+	if (clone_flag)
+		child_mnt = clone_mnt(template_mnt, template_mnt->mnt_root);
+	else
+		child_mnt = template_mnt;
+
+	nd.mnt = mnt;
+	nd.dentry = dentry;
+
+	attach_prepare_mnt(child_mnt, &nd);
+
+	return child_mnt;
+}
+
 static struct vfsmount *next_mnt(struct vfsmount *p, struct vfsmount *root)
 {
 	struct list_head *next = p->mnt_mounts.next;
@@ -151,37 +234,20 @@ static struct vfsmount *next_mnt(struct 
 	return list_entry(next, struct vfsmount, mnt_child);
 }
 
-static struct vfsmount *
-clone_mnt(struct vfsmount *old, struct dentry *root)
+static struct vfsmount *skip_mnt_tree(struct vfsmount *p)
 {
-	struct super_block *sb = old->mnt_sb;
-	struct vfsmount *mnt = alloc_vfsmnt(old->mnt_devname);
-
-	if (mnt) {
-		mnt->mnt_flags = old->mnt_flags;
-		atomic_inc(&sb->s_active);
-		mnt->mnt_sb = sb;
-		mnt->mnt_root = dget(root);
-		mnt->mnt_mountpoint = mnt->mnt_root;
-		mnt->mnt_parent = mnt;
-		mnt->mnt_namespace = old->mnt_namespace;
-		mnt->mnt_pnode = get_pnode(old->mnt_pnode);
-
-		/* stick the duplicate mount on the same expiry list
-		 * as the original if that was on one */
-		spin_lock(&vfsmount_lock);
-		if (!list_empty(&old->mnt_fslink))
-			list_add(&mnt->mnt_fslink, &old->mnt_fslink);
-		spin_unlock(&vfsmount_lock);
+	struct list_head *prev = p->mnt_mounts.prev;
+	while (prev != &p->mnt_mounts) {
+		p = list_entry(prev, struct vfsmount, mnt_child);
+		prev = p->mnt_mounts.prev;
 	}
-	return mnt;
+	return p;
 }
 
 void __mntput(struct vfsmount *mnt)
 {
 	struct super_block *sb = mnt->mnt_sb;
 	dput(mnt->mnt_root);
-	put_pnode(mnt->mnt_pnode);
 	free_vfsmnt(mnt);
 	deactivate_super(sb);
 }
@@ -195,7 +261,7 @@ static void *m_start(struct seq_file *m,
 	struct list_head *p;
 	loff_t l = *pos;
 
-	down_read(&n->sem);
+	down_read(&namespace_sem);
 	list_for_each(p, &n->list)
 		if (!l--)
 			return list_entry(p, struct vfsmount, mnt_list);
@@ -212,8 +278,7 @@ static void *m_next(struct seq_file *m, 
 
 static void m_stop(struct seq_file *m, void *v)
 {
-	struct namespace *n = m->private;
-	up_read(&n->sem);
+	up_read(&namespace_sem);
 }
 
 static inline void mangle(struct seq_file *m, const char *s)
@@ -437,7 +502,7 @@ static int do_umount(struct vfsmount *mn
 		return retval;
 	}
 
-	down_write(&current->namespace->sem);
+	down_write(&namespace_sem);
 	spin_lock(&vfsmount_lock);
 
 	if (atomic_read(&sb->s_active) == 1) {
@@ -459,7 +524,7 @@ static int do_umount(struct vfsmount *mn
 	spin_unlock(&vfsmount_lock);
 	if (retval)
 		security_sb_umount_busy(mnt);
-	up_write(&current->namespace->sem);
+	up_write(&namespace_sem);
 	return retval;
 }
 
@@ -499,9 +564,9 @@ out:
 #ifdef __ARCH_WANT_SYS_OLDUMOUNT
 
 /*
- *	The 2.0 compatible umount. No flags. 
+ *	The 2.0 compatible umount. No flags.
  */
- 
+
 asmlinkage long sys_oldumount(char __user * name)
 {
 	return sys_umount(name,0);
@@ -545,6 +610,9 @@ static struct vfsmount *copy_tree(struct
 	struct list_head *h;
 	struct nameidata nd;
 
+	if (IS_MNT_UNCLONABLE(mnt))
+		return NULL;
+
 	res = q = clone_mnt(mnt, dentry);
 	if (!q)
 		goto Enomem;
@@ -553,10 +621,15 @@ static struct vfsmount *copy_tree(struct
 	p = mnt;
 	for (h = mnt->mnt_mounts.next; h != &mnt->mnt_mounts; h = h->next) {
 		r = list_entry(h, struct vfsmount, mnt_child);
+
 		if (!lives_below_in_same_fs(r->mnt_mountpoint, dentry))
 			continue;
 
 		for (s = r; s; s = next_mnt(s, r)) {
+			if (IS_MNT_UNCLONABLE(s)) {
+				s = skip_mnt_tree(s);
+				continue;
+			}
 			while (p != s->mnt_parent) {
 				p = p->mnt_parent;
 				q = q->mnt_parent;
@@ -583,9 +656,163 @@ static struct vfsmount *copy_tree(struct
 	return NULL;
 }
 
+ /*
+ *  @source_mnt : mount tree to be attached
+ *  @nd		: place the mount tree @source_mnt is attached
+ *
+ *  NOTE: in the table below explains the semantics when a source vfsmount
+ *  of a given type is attached to a destination vfsmount of a give type.
+ *  -----------------------------------------------------------------------------
+ *  |				BIND MOUNT OPERATION				|
+ *  |***************************************************************************|
+ *  |  dest --> | shared	 |	private	     |   slave	    |unclonable	|
+ *  | source	|		 |       	     |   	    |    	|
+ *  |   |   	|		 |       	     |   	    |    	|
+ *  |   v 	|		 |       	     |   	    |    	|
+ *  |***************************************************************************|
+ *  |	     	|		 |       	     |   	    |    	|
+ *  |  shared	| shared (++) 	 |      shared (+)   | shared (+)   | shared (+)|
+ *  |		|		 |       	     |   	    |    	|
+ *  |		|		 |       	     |   	    |    	|
+ *  | private	| shared (+)	 |      private	     | private 	    | private  	|
+ *  |		|		 |       	     |   	    |    	|
+ *  |		|		 |       	     |   	    |    	|
+ *  | slave	| shared (+)	 |      private      | private 	    | private  	|
+ *  |		|		 |       	     |   	    |    	|
+ *  |		|		 |       	     |   	    |    	|
+ *  | unclonable|    -		 |       -	     |   -	    |   - 	|
+ *  |		|		 |       	     |   	    |    	|
+ *  |		|		 |       	     |   	    |    	|
+ *   ***************************************************************************
+ *
+ * (++)  the mount will be propogated to all the vfsmounts in the pnode tree
+ *    	  of the destination vfsmount, and all the non-slave new mounts in
+ *    	  destination vfsmount will be added the source vfsmount's pnode.
+ * (+)  the mount will be propogated to the destination vfsmount
+ *    	  and the new mount will be added to the source vfsmount's pnode.
+ *
+ * if the source mount is a tree, the operations explained above is applied to each
+ * vfsmount in the tree.
+ *
+ * Should be called without spinlocks held, because this function can sleep
+ * in allocations.
+ *
+  */
+static void
+attach_recursive_mnt(struct vfsmount *source_mnt, struct nameidata *nd)
+{
+	struct vfsmount *mntpt_mnt, *m, *p;
+	struct vfspnode *src_pnode, *t_p, *dest_pnode, *tmp_pnode;
+	struct dentry *mntpt_dentry;
+	LIST_HEAD(pnodehead);
+
+	mntpt_mnt = nd->mnt;
+	dest_pnode = IS_MNT_SHARED(mntpt_mnt) ? mntpt_mnt->mnt_pnode : NULL;
+	src_pnode = IS_MNT_SHARED(source_mnt) ? source_mnt->mnt_pnode : NULL;
+
+	if (!dest_pnode && !src_pnode) {
+		LIST_HEAD(head);
+		spin_lock(&vfsmount_lock);
+		do_attach_mnt(nd->mnt, nd->dentry, source_mnt);
+		spin_unlock(&vfsmount_lock);
+		goto out;
+	}
+
+	/*
+	 * Ok, the source or the destination pnode exists.
+	 * Get ready for pnode operations.
+	 * Create a temporary pnode which shall hold all the
+	 * new mounts. Merge or delete or slave that pnode
+	 * later in a separate operation, depending on
+	 * the type of source and destination mounts.
+	 */
+	p = NULL;
+	for (m = source_mnt; m; m = next_mnt(m, source_mnt)) {
+		int unclone = IS_MNT_UNCLONABLE(m);
+
+		list_del_init(&m->mnt_list);
+
+		while (p && p != m->mnt_parent) {
+			p = p->mnt_parent;
+		}
+
+		if (!p) {
+			mntpt_dentry = nd->dentry;
+			mntpt_mnt = nd->mnt;
+		} else {
+			mntpt_dentry = m->mnt_mountpoint;
+			mntpt_mnt    = p;
+		}
+
+		p=m;
+		dest_pnode = IS_MNT_SHARED(mntpt_mnt) ?
+			mntpt_mnt->mnt_pnode : NULL;
+		src_pnode = (IS_MNT_SHARED(m))?
+				m->mnt_pnode : NULL;
+
+		m->mnt_pnode = NULL;
+		/*
+		 * get a temporary pnode into which add the new vfs, and keep
+		 * track of these pnodes and their real pnode.
+		 */
+		while (!(tmp_pnode = pnode_alloc()))
+			schedule();
+
+
+		if (dest_pnode && !unclone)
+			pnode_prepare_mount(dest_pnode, tmp_pnode,
+					mntpt_dentry, m, mntpt_mnt);
+		else {
+			if (m == m->mnt_parent)
+				do_attach_prepare_mnt(mntpt_mnt,
+					mntpt_dentry, m, 0);
+			pnode_add_member_mnt(tmp_pnode, m);
+			if (unclone)
+				SET_MNT_UNCLONABLE(m);
+		}
+
+		if ((!src_pnode && !dest_pnode) || unclone)
+			SET_PNODE_DELETE(tmp_pnode);
+		tmp_pnode->pnode_master = src_pnode;
+		/*
+		 * temporarily track the pnode with which the tmp_pnode
+		 * has to merge with; in the pnode_master field.
+		 */
+		list_add_tail(&tmp_pnode->pnode_peer_slave, &pnodehead);
+	}
+
+	/*
+	 * new mounts. Merge or delete or slave the temporary pnode
+	 */
+	spin_lock(&vfsmount_lock);
+	list_for_each_entry_safe(tmp_pnode, t_p, &pnodehead, pnode_peer_slave) {
+		int del_flag = IS_PNODE_DELETE(tmp_pnode);
+		struct vfspnode *master_pnode = tmp_pnode->pnode_master;
+		list_del_init(&tmp_pnode->pnode_peer_slave);
+		pnode_real_mount(tmp_pnode, del_flag);
+		if (!del_flag && master_pnode) {
+			tmp_pnode->pnode_master = NULL;
+			pnode_merge_pnode(tmp_pnode, master_pnode);
+			/*
+			 * we don't need the extra reference to
+			 * the master_pnode, that was created either
+			 * (a) pnode_add_slave_pnode: when the mnt was made as
+			 * 		a slave mnt.
+			 * (b) pnode_merge_pnode: during clone_mnt().
+			 */
+			put_pnode(master_pnode);
+		}
+	}
+	spin_unlock(&vfsmount_lock);
+out:
+	mntget(source_mnt);
+	return;
+}
+
 static int graft_tree(struct vfsmount *mnt, struct nameidata *nd)
 {
-	int err;
+	int err, ret;
+
 	if (mnt->mnt_sb->s_flags & MS_NOUSER)
 		return -EINVAL;
 
@@ -603,17 +830,14 @@ static int graft_tree(struct vfsmount *m
 		goto out_unlock;
 
 	err = -ENOENT;
-	spin_lock(&vfsmount_lock);
-	if (IS_ROOT(nd->dentry) || !d_unhashed(nd->dentry)) {
-		struct list_head head;
 
-		attach_mnt(mnt, nd);
-		list_add_tail(&head, &mnt->mnt_list);
-		list_splice(&head, current->namespace->list.prev);
-		mntget(mnt);
+	spin_lock(&vfsmount_lock);
+	ret = (IS_ROOT(nd->dentry) || !d_unhashed(nd->dentry));
+	spin_unlock(&vfsmount_lock);
+	if (ret) {
+		attach_recursive_mnt(mnt, nd);
 		err = 0;
 	}
-	spin_unlock(&vfsmount_lock);
 out_unlock:
 	up(&nd->dentry->d_inode->i_sem);
 	if (!err)
@@ -621,6 +845,11 @@ out_unlock:
 	return err;
 }
 
+ /*
+ * create a new mount at the dentry, and move all child mounts
+ * underneath it, if those mounts were below the dentry on the
+ * parent mount.
+  */
 struct vfsmount *do_make_mounted(struct vfsmount *mnt, struct dentry *dentry)
 {
 	struct vfsmount *child_mnt, *next;
@@ -628,6 +857,14 @@ struct vfsmount *do_make_mounted(struct 
 	struct vfsmount *newmnt = clone_mnt(mnt, dentry);
 	LIST_HEAD(move);
 
+	/*
+	 * note clone_mnt() gets a reference to the pnode.
+	 * we won't use that pnode anyway. So just let it
+	 * go
+	 */
+	put_pnode(newmnt->mnt_pnode);
+	newmnt->mnt_pnode = NULL;
+
 	if (newmnt) {
 		/* put in code for mount expiry */
 		/* TOBEDONE */
@@ -653,14 +890,41 @@ struct vfsmount *do_make_mounted(struct 
 
 		nd.mnt = mnt;
 		nd.dentry = dentry;
-		attach_mnt(newmnt, &nd);
+		do_attach_mnt(nd.mnt, nd.dentry, newmnt);
  		spin_unlock(&vfsmount_lock);
  	}
 	return newmnt;
 }
 
-int
-_do_make_mounted(struct nameidata *nd, struct vfsmount **mnt)
+int do_make_unmounted(struct vfsmount *mnt)
+{
+	struct vfsmount *parent_mnt, *child_mnt, *next;
+	struct nameidata nd;
+
+	/* validate if mount has a different parent */
+	parent_mnt = mnt->mnt_parent;
+	if (mnt == parent_mnt)
+		return 0;
+	/*
+	 * cannot unmount a mount that is not created
+	 * as a overlay mount.
+	 */
+	if (mnt->mnt_mountpoint != mnt->mnt_root)
+		return -EINVAL;
+
+	/* for each submounts in the parent, put the mounts back */
+	spin_lock(&vfsmount_lock);
+	list_for_each_entry_safe(child_mnt, next, &mnt->mnt_mounts, mnt_child) {
+		detach_mnt(child_mnt, &nd);
+		nd.mnt = parent_mnt;
+		attach_mnt(child_mnt, &nd);
+ 	}
+	detach_mnt(mnt, &nd);
+ 	spin_unlock(&vfsmount_lock);
+	return 0;
+}
+
+int make_mounted(struct nameidata *nd, struct vfsmount **mnt)
 {
 	struct vfsmount *parent_mnt;
 	struct dentry *parent_dentry;
@@ -671,9 +935,10 @@ _do_make_mounted(struct nameidata *nd, s
 	parent_mnt = nd->mnt;
  	/*
 	 * check if dentry already has a vfsmount
-	 * if it does not, create a vfsmount there.
-	 * which means you need to propogate it
-	 * across all vfsmounts.
+	 * if it does not, create and attach
+	 * a new vfsmount at that dentry.
+	 * Also propogate the mount if parent_mnt
+	 * is shared.
  	 */
 	if(parent_dentry == parent_mnt->mnt_root) {
 		*mnt = parent_mnt;
@@ -688,6 +953,25 @@ _do_make_mounted(struct nameidata *nd, s
 	return err;
 }
 
+int make_unmounted(struct vfsmount *mnt)
+{
+	if (mnt == mnt->mnt_parent)
+		return 0;
+	/*
+	 * cannot unmount a mount that is not created
+	 * as a overlay mount.
+	 */
+	if (mnt->mnt_mountpoint != mnt->mnt_root)
+		return -EINVAL;
+
+	if (IS_MNT_SHARED(mnt))
+		pnode_make_unmounted(mnt->mnt_pnode);
+ 	else
+		do_make_unmounted(mnt);
+
+	return 0;
+}
+
 /*
  * recursively change the type of the mountpoint.
  */
@@ -702,7 +986,7 @@ static int do_change_type(struct nameida
 			&& !(flag & MS_SLAVE))
 		return -EINVAL;
 
-	if ((err = _do_make_mounted(nd, &mnt)))
+	if ((err = make_mounted(nd, &mnt)))
 		return err;
 
 	spin_lock(&vfsmount_lock);
@@ -735,9 +1019,8 @@ static int do_change_type(struct nameida
 			break;
 
 		case MS_SLAVE:
-			if (IS_MNT_SLAVE(m)) {
+			if (IS_MNT_SLAVE(m))
 				break;
-			}
 			/*
 			 * only shared mounts can
 			 * be made slave
@@ -775,7 +1058,7 @@ static int do_change_type(struct nameida
 static int do_loopback(struct nameidata *nd, char *old_name, int recurse)
 {
 	struct nameidata old_nd;
-	struct vfsmount *mnt = NULL;
+	struct vfsmount *mnt = NULL, *overlay_mnt=NULL;
 	int err = mount_is_safe(nd);
 	if (err)
 		return err;
@@ -785,14 +1068,31 @@ static int do_loopback(struct nameidata 
 	if (err)
 		return err;
 
-	down_write(&current->namespace->sem);
+	if (IS_MNT_UNCLONABLE(old_nd.mnt)) {
+		err = -EINVAL;
+		goto path_release;
+	}
+
+	down_write(&namespace_sem);
 	err = -EINVAL;
 	if (check_mnt(nd->mnt) && (!recurse || check_mnt(old_nd.mnt))) {
+
+		/*
+		 * If the dentry is not the root dentry, and if a bind
+		 * from a shared subtree is attempted, create a mount
+		 * at the dentry, and use the new mount as the starting
+		 * point for the bind/rbind operation.
+		 */
+		overlay_mnt = old_nd.mnt;
+		if(IS_MNT_SHARED(old_nd.mnt) &&
+			(err = make_mounted(&old_nd, &overlay_mnt)))
+			goto out;
+
 		err = -ENOMEM;
 		if (recurse)
-			mnt = copy_tree(old_nd.mnt, old_nd.dentry);
+			mnt = copy_tree(overlay_mnt, old_nd.dentry);
 		else
-			mnt = clone_mnt(old_nd.mnt, old_nd.dentry);
+			mnt = clone_mnt(overlay_mnt, old_nd.dentry);
 	}
 
 	if (mnt) {
@@ -803,15 +1103,25 @@ static int do_loopback(struct nameidata 
 
 		err = graft_tree(mnt, nd);
 		if (err) {
-			spin_lock(&vfsmount_lock);
-			umount_tree(mnt);
-			spin_unlock(&vfsmount_lock);
-		} else
-			mntput(mnt);
-	}
+ 			spin_lock(&vfsmount_lock);
+ 			umount_tree(mnt);
+ 			spin_unlock(&vfsmount_lock);
+			/*
+			 * ok we failed! so undo any overlay
+			 * mount that we did earlier.
+			 */
+			if (old_nd.mnt !=  overlay_mnt)
+				make_unmounted(overlay_mnt);
+ 		} else
+ 			mntput(mnt);
+ 	}
+
+ out:
+	up_write(&namespace_sem);
+
+ path_release:
+ 	path_release(&old_nd);
 
-	up_write(&current->namespace->sem);
-	path_release(&old_nd);
 	return err;
 }
 
@@ -859,7 +1169,7 @@ static int do_move_mount(struct nameidat
 	if (err)
 		return err;
 
-	down_write(&current->namespace->sem);
+	down_write(&namespace_sem);
 	while(d_mountpoint(nd->dentry) && follow_down(&nd->mnt, &nd->dentry))
 		;
 	err = -EINVAL;
@@ -903,7 +1213,7 @@ out2:
 out1:
 	up(&nd->dentry->d_inode->i_sem);
 out:
-	up_write(&current->namespace->sem);
+	up_write(&namespace_sem);
 	if (!err)
 		path_release(&parent_nd);
 	path_release(&old_nd);
@@ -942,7 +1252,7 @@ int do_add_mount(struct vfsmount *newmnt
 {
 	int err;
 
-	down_write(&current->namespace->sem);
+	down_write(&namespace_sem);
 	/* Something was mounted here while we slept */
 	while(d_mountpoint(nd->dentry) && follow_down(&nd->mnt, &nd->dentry))
 		;
@@ -971,7 +1281,7 @@ int do_add_mount(struct vfsmount *newmnt
 	}
 
 unlock:
-	up_write(&current->namespace->sem);
+	up_write(&namespace_sem);
 	mntput(newmnt);
 	return err;
 }
@@ -1027,7 +1337,7 @@ void mark_mounts_for_expiry(struct list_
 		get_namespace(namespace);
 
 		spin_unlock(&vfsmount_lock);
-		down_write(&namespace->sem);
+		down_write(&namespace_sem);
 		spin_lock(&vfsmount_lock);
 
 		/* check that it is still dead: the count should now be 2 - as
@@ -1071,7 +1381,7 @@ void mark_mounts_for_expiry(struct list_
 			spin_unlock(&vfsmount_lock);
 		}
 
-		up_write(&namespace->sem);
+		up_write(&namespace_sem);
 
 		mntput(mnt);
 		put_namespace(namespace);
@@ -1117,7 +1427,7 @@ int copy_mount_options(const void __user
 	int i;
 	unsigned long page;
 	unsigned long size;
-	
+
 	*where = 0;
 	if (!data)
 		return 0;
@@ -1136,7 +1446,7 @@ int copy_mount_options(const void __user
 
 	i = size - exact_copy_from_user((void *)page, data, size);
 	if (!i) {
-		free_page(page); 
+		free_page(page);
 		return -EFAULT;
 	}
 	if (i != PAGE_SIZE)
@@ -1242,14 +1552,13 @@ int copy_namespace(int flags, struct tas
 		goto out;
 
 	atomic_set(&new_ns->count, 1);
-	init_rwsem(&new_ns->sem);
 	INIT_LIST_HEAD(&new_ns->list);
 
-	down_write(&tsk->namespace->sem);
+	down_write(&namespace_sem);
 	/* First pass: copy the tree topology */
 	new_ns->root = copy_tree(namespace->root, namespace->root->mnt_root);
 	if (!new_ns->root) {
-		up_write(&tsk->namespace->sem);
+		up_write(&namespace_sem);
 		kfree(new_ns);
 		goto out;
 	}
@@ -1283,7 +1592,7 @@ int copy_namespace(int flags, struct tas
 		p = next_mnt(p, namespace->root);
 		q = next_mnt(q, new_ns->root);
 	}
-	up_write(&tsk->namespace->sem);
+	up_write(&namespace_sem);
 
 	tsk->namespace = new_ns;
 
@@ -1465,7 +1774,7 @@ asmlinkage long sys_pivot_root(const cha
 	user_nd.mnt = mntget(current->fs->rootmnt);
 	user_nd.dentry = dget(current->fs->root);
 	read_unlock(&current->fs->lock);
-	down_write(&current->namespace->sem);
+	down_write(&namespace_sem);
 	down(&old_nd.dentry->d_inode->i_sem);
 	error = -EINVAL;
 	if (!check_mnt(user_nd.mnt))
@@ -1511,7 +1820,7 @@ asmlinkage long sys_pivot_root(const cha
 	path_release(&parent_nd);
 out2:
 	up(&old_nd.dentry->d_inode->i_sem);
-	up_write(&current->namespace->sem);
+	up_write(&namespace_sem);
 	path_release(&user_nd);
 	path_release(&old_nd);
 out1:
@@ -1538,7 +1847,6 @@ static void __init init_mount_tree(void)
 		panic("Can't allocate initial namespace");
 	atomic_set(&namespace->count, 1);
 	INIT_LIST_HEAD(&namespace->list);
-	init_rwsem(&namespace->sem);
 	list_add(&mnt->mnt_list, &namespace->list);
 	namespace->root = mnt;
 	mnt->mnt_namespace = namespace;
@@ -1561,6 +1869,8 @@ void __init mnt_init(unsigned long mempa
 	unsigned int nr_hash;
 	int i;
 
+	init_rwsem(&namespace_sem);
+
 	mnt_cache = kmem_cache_create("mnt_cache", sizeof(struct vfsmount),
 			0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL, NULL);
 
@@ -1608,7 +1918,7 @@ void __put_namespace(struct namespace *n
 {
 	struct vfsmount *mnt;
 
-	down_write(&namespace->sem);
+	down_write(&namespace_sem);
 	spin_lock(&vfsmount_lock);
 
 	list_for_each_entry(mnt, &namespace->list, mnt_list) {
@@ -1617,6 +1927,6 @@ void __put_namespace(struct namespace *n
 
 	umount_tree(namespace->root);
 	spin_unlock(&vfsmount_lock);
-	up_write(&namespace->sem);
+	up_write(&namespace_sem);
 	kfree(namespace);
 }
Index: 2.6.12/fs/pnode.c
===================================================================
--- 2.6.12.orig/fs/pnode.c
+++ 2.6.12/fs/pnode.c
@@ -287,6 +287,52 @@ pnode_disassociate_mnt(struct vfsmount *
 	mnt->mnt_flags &= ~MNT_SHARED;
 }
 
+// merge pnode into peer_pnode and get rid of pnode
+int
+pnode_merge_pnode(struct vfspnode *pnode, struct vfspnode *peer_pnode)
+{
+	struct vfspnode *slave_pnode, *pnext;
+	struct vfsmount *mnt, *slave_mnt, *next;
+	int i,count;
+
+	spin_lock(&vfspnode_lock);
+	list_for_each_entry_safe(slave_pnode,  pnext,
+			&pnode->pnode_slavepnode, pnode_peer_slave) {
+		slave_pnode->pnode_master = peer_pnode;
+		list_move(&slave_pnode->pnode_peer_slave,
+				&peer_pnode->pnode_slavepnode);
+	}
+
+	list_for_each_entry_safe(slave_mnt,  next,
+			&pnode->pnode_slavevfs, mnt_pnode_mntlist) {
+		slave_mnt->mnt_pnode = peer_pnode;
+		list_move(&slave_mnt->mnt_pnode_mntlist,
+				&peer_pnode->pnode_slavevfs);
+	}
+
+	list_for_each_entry_safe(mnt, next,
+			&pnode->pnode_vfs, mnt_pnode_mntlist) {
+		mnt->mnt_pnode = peer_pnode;
+		list_move(&mnt->mnt_pnode_mntlist,
+				&peer_pnode->pnode_vfs);
+	}
+
+	count = atomic_read(&pnode->pnode_count);
+	atomic_add(count, &peer_pnode->pnode_count);
+	spin_unlock(&vfspnode_lock);
+
+	/*
+	 * delete all references to 'pnode'.
+	 * A better implementation can simply
+	 * call free_pnode(pnode). But this is
+	 * a cleaner way of doing it. Offcourse
+	 * with some cost.
+	 */
+	for (i=0 ; i <count; i++)
+		put_pnode(pnode);
+	return 0;
+}
+
 struct vfsmount *
 pnode_make_mounted(struct vfspnode *pnode, struct vfsmount *mnt, struct dentry *dentry)
 {
@@ -360,3 +406,223 @@ out:
 	mntput(child_mnt);
 	return child_mnt;
 }
+
+int
+vfs_make_unmounted(struct vfsmount *mnt)
+{
+	struct vfspnode *pnode;
+	int ret=0;
+
+	if (do_make_unmounted(mnt)) {
+		ret = 1;
+		goto out;
+	}
+	pnode = mnt->mnt_pnode;
+	list_del_init(&mnt->mnt_pnode_mntlist);
+	put_pnode(pnode);
+out:
+	return ret;
+}
+
+int
+pnode_make_unmounted(struct vfspnode *pnode)
+{
+	int ret=0,traversal;
+     	struct vfsmount *slave_mnt, *member_mnt, *t_m;
+	struct pcontext context;
+
+	context.start = pnode;
+	context.pnode = NULL;
+	while(pnode_next(&context)) {
+		traversal = context.traversal;
+		pnode = context.pnode;
+		if(traversal == PNODE_UP) {
+			// traverse member vfsmounts
+			spin_lock(&vfspnode_lock);
+			list_for_each_entry_safe(member_mnt,
+				t_m, &pnode->pnode_vfs, mnt_pnode_mntlist) {
+				spin_unlock(&vfspnode_lock);
+				if ((ret = vfs_make_unmounted(member_mnt)))
+					goto out;
+				spin_lock(&vfspnode_lock);
+			}
+			list_for_each_entry_safe(slave_mnt,
+				t_m, &pnode->pnode_slavevfs, mnt_pnode_mntlist) {
+				spin_unlock(&vfspnode_lock);
+				if ((ret = vfs_make_unmounted(slave_mnt)))
+					goto out;
+				spin_lock(&vfspnode_lock);
+			}
+			spin_unlock(&vfspnode_lock);
+		}
+	}
+
+out:
+	return ret;
+}
+
+
+int
+vfs_prepare_mount_func(struct vfsmount *mnt, int flag, struct vfspnode *pnode,
+		struct vfsmount *source_mnt,
+		struct dentry *mountpoint_dentry,
+		struct vfsmount *p_mnt)
+
+{
+	struct vfsmount *child_mnt;
+
+	if ((p_mnt != mnt) || (source_mnt == source_mnt->mnt_parent)) {
+		child_mnt = do_attach_prepare_mnt(mnt, mountpoint_dentry,
+				source_mnt, (p_mnt != mnt));
+		if (child_mnt != source_mnt)
+			put_pnode(source_mnt->mnt_pnode);
+	} else
+		child_mnt = source_mnt;
+
+	switch (flag) {
+	case PNODE_SLAVE_VFS :
+		pnode_add_slave_mnt(pnode, child_mnt);
+		break;
+	case PNODE_MEMBER_VFS :
+		pnode_add_member_mnt(pnode, child_mnt);
+		break;
+	}
+
+	return 0;
+}
+
+
+int
+pnode_prepare_mount(struct vfspnode *pnode,
+		struct vfspnode *master_child_pnode,
+		struct dentry *mountpoint_dentry,
+		struct vfsmount *source_mnt,
+		struct vfsmount *mnt)
+{
+	int ret=0,traversal,level;
+     	struct vfspnode *slave_pnode, *master_pnode, *slave_child_pnode, *child_pnode;
+     	struct vfsmount *slave_mnt, *member_mnt, *t_m;
+	struct pcontext context;
+	static struct inoutdata p_array[PNODE_MAX_SLAVE_LEVEL];
+
+	context.start = pnode;
+	context.pnode = NULL;
+	while(pnode_next(&context)) {
+		traversal = context.traversal;
+		level = context.level;
+		pnode = context.pnode;
+		slave_pnode = context.slave_pnode;
+		master_pnode = context.master_pnode;
+
+		if (traversal == PNODE_DOWN ) {
+
+			child_pnode = NULL;
+			if (!master_pnode)
+				child_pnode = master_child_pnode;
+
+			while (!(child_pnode = pnode_alloc()))
+				schedule();
+
+			p_array[level].my_data = child_pnode;
+
+		} else if(traversal == PNODE_MID) {
+
+			child_pnode = (struct vfspnode *)p_array[level].my_data;
+			slave_child_pnode = p_array[level+1].out_data;
+			pnode_add_slave_pnode(child_pnode, slave_child_pnode);
+
+		} else if(traversal == PNODE_UP) {
+
+			child_pnode = p_array[level].my_data;
+			spin_lock(&vfspnode_lock);
+			list_for_each_entry_safe(member_mnt,
+				t_m, &pnode->pnode_vfs, mnt_pnode_mntlist) {
+				spin_unlock(&vfspnode_lock);
+				if((ret=vfs_prepare_mount_func(member_mnt,
+					PNODE_MEMBER_VFS, child_pnode, source_mnt,
+					mountpoint_dentry, mnt)))
+					goto out;
+				spin_lock(&vfspnode_lock);
+			}
+			list_for_each_entry_safe(slave_mnt,
+				t_m, &pnode->pnode_slavevfs, mnt_pnode_mntlist) {
+				spin_unlock(&vfspnode_lock);
+				if((ret = vfs_prepare_mount_func(slave_mnt,
+					PNODE_SLAVE_VFS, child_pnode, source_mnt,
+					mountpoint_dentry, mnt)))
+					goto out;
+				spin_lock(&vfspnode_lock);
+			}
+			spin_unlock(&vfspnode_lock);
+			p_array[level].out_data = child_pnode;
+
+		}
+	}
+
+out:
+	return ret;
+}
+
+
+int
+vfs_real_mount_func(struct vfsmount *mnt, int delflag)
+{
+	BUG_ON(mnt == mnt->mnt_parent);
+	do_attach_real_mnt(mnt);
+	if (delflag) {
+		list_del_init(&mnt->mnt_pnode_mntlist);
+		mnt->mnt_pnode = NULL;
+		SET_MNT_PRIVATE(mnt);
+	}
+	return 0;
+}
+
+/*
+ * @pnode: walk the propogation tree and complete the
+ * 	attachments of the child mounts to the parents
+ * 	correspondingly.
+ * @flag: if set destroy the propogation tree
+ */
+int
+pnode_real_mount(struct vfspnode *pnode, int flag)
+{
+	int ret=0,traversal;
+     	struct vfsmount *slave_mnt, *member_mnt, *t_m;
+	struct pcontext context;
+
+	context.start = pnode;
+	context.pnode = NULL;
+	while(pnode_next(&context)) {
+		traversal = context.traversal;
+		pnode = context.pnode;
+		if(traversal == PNODE_MID) {
+			if (flag) {
+				BUG_ON(!list_empty(&pnode->pnode_vfs));
+				BUG_ON(!list_empty(&pnode->pnode_slavevfs));
+				BUG_ON(!list_empty(&pnode->pnode_slavepnode));
+				list_del_init(&pnode->pnode_peer_slave);
+				put_pnode(pnode);
+			}
+		} else if(traversal == PNODE_UP) {
+			// traverse member vfsmounts
+			spin_lock(&vfspnode_lock);
+			list_for_each_entry_safe(member_mnt,
+				t_m, &pnode->pnode_vfs, mnt_pnode_mntlist) {
+				spin_unlock(&vfspnode_lock);
+				if ((ret = vfs_real_mount_func(member_mnt, flag)))
+					goto out;
+			}
+			list_for_each_entry_safe(slave_mnt,
+				t_m, &pnode->pnode_slavevfs, mnt_pnode_mntlist) {
+				spin_unlock(&vfspnode_lock);
+				if ((ret = vfs_real_mount_func(slave_mnt, flag)))
+					goto out;
+				spin_lock(&vfspnode_lock);
+			}
+			spin_unlock(&vfspnode_lock);
+		}
+	}
+
+out:
+	return ret;
+}
Index: 2.6.12/include/linux/fs.h
===================================================================
--- 2.6.12.orig/include/linux/fs.h
+++ 2.6.12/include/linux/fs.h
@@ -1216,7 +1216,11 @@ extern struct vfsmount *kern_mount(struc
 extern int may_umount_tree(struct vfsmount *);
 extern int may_umount(struct vfsmount *);
 extern long do_mount(char *, char *, char *, unsigned long, void *);
+extern struct vfsmount *do_attach_prepare_mnt(struct vfsmount *,
+		struct dentry *, struct vfsmount *, int );
+extern void do_attach_real_mnt(struct vfsmount *);
 extern struct vfsmount *do_make_mounted(struct vfsmount *, struct dentry *);
+extern int do_make_unmounted(struct vfsmount *);
 
 extern int vfs_statfs(struct super_block *, struct kstatfs *);
 
Index: 2.6.12/include/linux/pnode.h
===================================================================
--- 2.6.12.orig/include/linux/pnode.h
+++ 2.6.12/include/linux/pnode.h
@@ -73,6 +73,11 @@ void pnode_del_slave_mnt(struct vfsmount
 void pnode_del_member_mnt(struct vfsmount *);
 void pnode_disassociate_mnt(struct vfsmount *);
 void pnode_add_slave_pnode(struct vfspnode *, struct vfspnode *);
+int pnode_merge_pnode(struct vfspnode *, struct vfspnode *);
 struct vfsmount * pnode_make_mounted(struct vfspnode *, struct vfsmount *, struct dentry *);
+int  pnode_make_unmounted(struct vfspnode *);
+int pnode_prepare_mount(struct vfspnode *, struct vfspnode *, struct dentry *,
+		struct vfsmount *, struct vfsmount *);
+int pnode_real_mount(struct vfspnode *, int);
 #endif /* KERNEL */
 #endif /* _LINUX_PNODE_H */
Index: 2.6.12/include/linux/namespace.h
===================================================================
--- 2.6.12.orig/include/linux/namespace.h
+++ 2.6.12/include/linux/namespace.h
@@ -9,7 +9,6 @@ struct namespace {
 	atomic_t		count;
 	struct vfsmount *	root;
 	struct list_head	list;
-	struct rw_semaphore	sem;
 };
 
 extern void umount_tree(struct vfsmount *);