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

, miklos@szeredi.hu, Janak Desai <janak@us.ibm.com>, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH 3/7] shared subtree
Content-Type: text/x-patch; name=rbind.patch
Content-Disposition: inline; filename=rbind.patch

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            |  660 ++++++++++++++++++++++++++++++++++++++++------
 fs/pnode.c                |  235 ++++++++++++++++
 include/linux/dcache.h    |    2 
 include/linux/fs.h        |    5 
 include/linux/namespace.h |    1 
 5 files changed, 826 insertions(+), 77 deletions(-)

Index: 2.6.12.work2/fs/namespace.c
===================================================================
--- 2.6.12.work2.orig/fs/namespace.c
+++ 2.6.12.work2/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);
@@ -86,7 +87,8 @@ void free_vfsmnt(struct vfsmount *mnt)
  * Now, lookup_mnt increments the ref count before returning
  * the vfsmount struct.
  */
-struct vfsmount *lookup_mnt(struct vfsmount *mnt, struct dentry *dentry)
+struct vfsmount *__lookup_mnt(struct vfsmount *mnt, struct dentry *dentry,
+		struct dentry *root)
 {
 	struct list_head * head = mount_hashtable + hash(mnt, dentry);
 	struct list_head * tmp = head;
@@ -99,7 +101,8 @@ struct vfsmount *lookup_mnt(struct vfsmo
 		if (tmp == head)
 			break;
 		p = list_entry(tmp, struct vfsmount, mnt_hash);
-		if (p->mnt_parent == mnt && p->mnt_mountpoint == dentry) {
+		if (p->mnt_parent == mnt && p->mnt_mountpoint == dentry &&
+				(root == NULL || p->mnt_root == root)) {
 			found = mntget(p);
 			break;
 		}
@@ -108,6 +111,37 @@ struct vfsmount *lookup_mnt(struct vfsmo
 	return found;
 }
 
+struct vfsmount *lookup_mnt(struct vfsmount *mnt, struct dentry *dentry)
+{
+	return __lookup_mnt(mnt, dentry, NULL);
+}
+
+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;
@@ -128,11 +162,71 @@ static void attach_mnt(struct vfsmount *
 {
 	mnt->mnt_parent = mntget(nd->mnt);
 	mnt->mnt_mountpoint = dget(nd->dentry);
-	list_add(&mnt->mnt_hash, mount_hashtable+hash(nd->mnt, nd->dentry));
+	mnt->mnt_namespace = nd->mnt->mnt_namespace;
+	list_add_tail(&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 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_commit_mnt(struct vfsmount *mnt)
+{
+	struct vfsmount *parent = mnt->mnt_parent;
+	BUG_ON(parent==mnt);
+	if(list_empty(&mnt->mnt_hash))
+		list_add_tail(&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) {
+		if(!(child_mnt = clone_mnt(template_mnt,
+				template_mnt->mnt_root)))
+			return NULL;
+	} else
+		child_mnt = template_mnt;
+
+	nd.mnt = mnt;
+	nd.dentry = dentry;
+
+	attach_prepare_mnt(child_mnt, &nd);
+
+	return child_mnt;
+}
+
+void do_detach_prepare_mnt(struct vfsmount *mnt, int free_flag)
+{
+	mnt->mnt_mountpoint->d_mounted--;
+	mntput(mnt->mnt_parent);
+	dput(mnt->mnt_mountpoint);
+	if (free_flag) {
+		BUG_ON(atomic_read(&mnt->mnt_count) != 1);
+		spin_lock(&vfsmount_lock);
+		list_del_init(&mnt->mnt_fslink);
+		spin_unlock(&vfsmount_lock);
+		mntput(mnt);
+	}
+}
+
 static struct vfsmount *next_mnt(struct vfsmount *p, struct vfsmount *root)
 {
 	struct list_head *next = p->mnt_mounts.next;
@@ -149,29 +243,14 @@ 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;
-
-		/* 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)
@@ -191,7 +270,7 @@ 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);
@@ -208,8 +287,7 @@ 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)
@@ -433,7 +511,7 @@ 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) {
@@ -455,7 +533,7 @@ 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;
 }
 
@@ -495,9 +573,9 @@ 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);
@@ -541,6 +619,9 @@ static struct vfsmount *copy_tree(struct
 	struct list_head *h;
 	struct nameidata nd;
 
+	if (IS_MNT_UNCLONE(mnt))
+		return NULL;
+
 	res = q = clone_mnt(mnt, dentry);
 	if (!q)
 		goto Enomem;
@@ -549,10 +630,15 @@ 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_UNCLONE(s)) {
+				s = skip_mnt_tree(s);
+				continue;
+			}
 			while (p != s->mnt_parent) {
 				p = p->mnt_parent;
 				q = q->mnt_parent;
@@ -579,9 +665,276 @@ static struct vfsmount *copy_tree(struct
 	return NULL;
 }
 
+/*
+ * return 1 if the mount tree contains a shared or slave mount
+ */
+static inline int tree_contains_sharedorslave(struct vfsmount *mnt)
+{
+	struct vfsmount *p;
+	for (p = mnt; p; p = next_mnt(p, mnt)) {
+		if (IS_MNT_SHARED(p) || IS_MNT_SLAVE(p))
+			return 1;
+	}
+	return 0;
+}
+
+/*
+ * commit the operations done in attach_recursive_mnt(). run through pnode list
+ * headed at 'pnodehead', and commit the operation done in
+ * attach_recursive_mnt();
+ */
+
+static void commit_attach_recursive_mnt(struct list_head *pnodehead)
+{
+	struct vfspnode *t_p, *tmp_pnode;
+
+	/*
+	 * Merge or delete or slave each of 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);
+		int slave_flag = IS_PNODE_SLAVE(tmp_pnode);
+		struct vfspnode *master_pnode = tmp_pnode->pnode_master;
+
+		list_del_init(&tmp_pnode->pnode_peer_slave);
+		pnode_commit_mount(tmp_pnode, del_flag);
+
+		if (!del_flag && master_pnode) {
+			tmp_pnode->pnode_master = NULL;
+
+			if (slave_flag)
+				pnode_add_slave_pnode(master_pnode, tmp_pnode);
+			else
+				pnode_merge_pnode(tmp_pnode, master_pnode);
+
+			/*
+			 * we don't need the extra reference to
+			 * the master_pnode, which 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);
+}
+
+/*
+ * abort the operations done in attach_recursive_mnt(). run through the mount
+ * tree, till vfsmount 'last' and undo the changes.  Ensure that all the mounts
+ * in the tree are all back in the mnt_list headed at 'source_mnt'.
+ * NOTE: This function is closely tied to the logic in
+ * 'attach_recursive_mnt()'
+ */
+static void abort_attach_recursive_mnt(struct vfsmount *source_mnt, struct
+		vfsmount *last, struct list_head *head) { struct vfsmount *p =
+	source_mnt, *m; struct vfspnode *src_pnode;
+
+	if (!last)
+		return;
+
+	do {
+		int is_unclone, is_pnode_slave;
+
+		m = p;
+		is_unclone = IS_MNT_UNCLONE(m);
+
+		BUG_ON(!m->mnt_pnode);
+
+		is_pnode_slave = IS_PNODE_SLAVE(m->mnt_pnode);
+		src_pnode = m->mnt_pnode->pnode_master;
+		m->mnt_pnode->pnode_master = NULL;
+		pnode_abort_mount(m->mnt_pnode, m);
+
+		m->mnt_pnode = src_pnode;
+		if (src_pnode) {
+			if(is_pnode_slave)
+				set_mnt_slave(m);
+			else
+				set_mnt_shared(m);
+		} else {
+			if (is_unclone)
+				set_mnt_unclone(m);
+			else
+				set_mnt_private(m);
+		}
+
+
+		list_add_tail(&m->mnt_list, head);
+		p = next_mnt(m, source_mnt);
+
+	} while ( p && m != last );
+	source_mnt->mnt_parent = source_mnt;
+	list_del_init(head);
+}
+
+ /*
+ *  @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|    nomount	|       nomount	 |  nomount | nomount 	|
+ *  |		|		|       	 |   	    |    	|
+ *  |		|		|       	 |   	    |    	|
+ *   ********************************************************************
+ *
+ * (++)  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 int attach_recursive_mnt(struct vfsmount *source_mnt,
+		struct nameidata *nd)
+{
+	struct vfsmount *mntpt_mnt, *last, *m, *p;
+	struct vfspnode *src_pnode, *dest_pnode, *tmp_pnode;
+	struct dentry *mntpt_dentry;
+	int ret;
+	LIST_HEAD(pnodehead);
+	LIST_HEAD(mnt_list_head);
+
+	/*
+	 * if the source tree has no shared or slave mounts and
+	 * the destination mount is not shared, fastpath.
+	 */
+	mntpt_mnt = nd->mnt;
+	dest_pnode = IS_MNT_SHARED(mntpt_mnt) ? mntpt_mnt->mnt_pnode : NULL;
+	if (!dest_pnode && !tree_contains_sharedorslave(source_mnt)) {
+		spin_lock(&vfsmount_lock);
+		attach_mnt(source_mnt, nd);
+		list_add_tail(&mnt_list_head, &source_mnt->mnt_list);
+		list_splice(&mnt_list_head, mntpt_mnt->mnt_namespace->list.prev);
+		spin_unlock(&vfsmount_lock);
+		goto out;
+	}
+
+	/*
+	 * Create temporary pnodes 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;
+	last = NULL;
+	list_add_tail(&mnt_list_head, &source_mnt->mnt_list);
+
+	for (m = source_mnt; m; m = next_mnt(m, source_mnt)) {
+
+		BUG_ON(IS_MNT_UNCLONE(m));
+
+		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;
+
+		/*
+		 * get a temporary pnode into which add the new vfs, and keep
+		 * track of these pnodes and their real pnode.
+		 */
+		if (!(tmp_pnode = pnode_alloc())) {
+			ret =  -ENOMEM;
+			goto error;
+		}
+
+		m->mnt_pnode = NULL;
+		list_del_init(&m->mnt_list);
+		list_add_tail(&tmp_pnode->pnode_peer_slave, &pnodehead);
+
+		if (dest_pnode) {
+			if ((ret = pnode_prepare_mount(dest_pnode, tmp_pnode,
+					mntpt_dentry, m, mntpt_mnt))) {
+				tmp_pnode->pnode_master = src_pnode;
+				m->mnt_pnode = tmp_pnode;
+				last = m;
+				goto error;
+			}
+		} else {
+			if (m == m->mnt_parent)
+				do_attach_prepare_mnt(mntpt_mnt,
+					mntpt_dentry, m, 0);
+			pnode_add_member_mnt(tmp_pnode, m);
+			if (!src_pnode) {
+				set_mnt_private(m);
+				/*
+				 * NOTE: set_mnt_private()
+				 * resets m->mnt_pnode.
+				 * Reinitialize it. This is needed to
+				 * decrement the refcount on the
+				 * pnode when the mount 'm' is
+				 * unlinked in pnode_commit_mount().
+				 */
+				m->mnt_pnode = tmp_pnode;
+				SET_PNODE_DELETE(tmp_pnode);
+			}
+		}
+
+		/*
+		 * temporarily track the pnode with which the tmp_pnode
+		 * has to merge with; in the pnode_master field.
+		 */
+		tmp_pnode->pnode_master = src_pnode;
+		last = m;
+	}
+	commit_attach_recursive_mnt(&pnodehead);
+out:
+	mntget(source_mnt);
+	return 0;
+error:
+	/*
+	 * ok we have errored out either because of memory exhaustion
+	 * or something else not in our control. Gracefully return
+	 * leaving no mess behind. Else it will haunt you. :(
+	 */
+	abort_attach_recursive_mnt(source_mnt, last, &mnt_list_head);
+	return 1;
+}
+
 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;
 
@@ -599,17 +952,12 @@ 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);
-		err = 0;
-	}
+	spin_lock(&vfsmount_lock);
+	ret = (IS_ROOT(nd->dentry) || !d_unhashed(nd->dentry));
 	spin_unlock(&vfsmount_lock);
+	if (ret)
+		err = attach_recursive_mnt(mnt, nd);
 out_unlock:
 	up(&nd->dentry->d_inode->i_sem);
 	if (!err)
@@ -681,6 +1029,147 @@ static int do_make_unclone(struct vfsmou
 	return 0;
 }
 
+ /*
+ * This operation is equivalent of mount --bind dir dir
+ * create a new mount at the dentry, and unmount all child mounts
+ * mounted on top of dentries below 'dentry', and mount them
+ * under the new mount.
+  */
+struct vfsmount *do_make_mounted(struct vfsmount *mnt, struct dentry *dentry)
+{
+	struct vfsmount *child_mnt, *next;
+	struct nameidata nd;
+	struct vfsmount *newmnt = clone_mnt(mnt, dentry);
+	LIST_HEAD(head);
+
+	/*
+	 * 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) {
+		/*
+		 * walk through the mount list of mnt and move
+		 * them under the new mount
+		 */
+		spin_lock(&vfsmount_lock);
+		list_del_init(&newmnt->mnt_fslink);
+
+		list_for_each_entry_safe(child_mnt, next,
+				&mnt->mnt_mounts, mnt_child) {
+
+			if(child_mnt->mnt_mountpoint == dentry)
+				continue;
+
+			if(!is_subdir(child_mnt->mnt_mountpoint, dentry))
+				continue;
+
+			detach_mnt(child_mnt, &nd);
+			nd.mnt = newmnt;
+			attach_mnt(child_mnt, &nd);
+		}
+
+		nd.mnt = mnt;
+		nd.dentry = dentry;
+		attach_mnt(newmnt, &nd);
+		list_add_tail(&newmnt->mnt_list, &newmnt->mnt_namespace->list);
+ 		spin_unlock(&vfsmount_lock);
+ 	}
+	return newmnt;
+}
+
+ /*
+ * Inverse operation of do_make_mounted()
+  */
+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;
+}
+
+/*
+ * @nd: contains the vfsmount and the dentry where the new mount
+ * 	is the be created
+ * @mnt: returns the newly created mount.
+ * Create a new mount at the location specified by 'nd' and
+ * propogate the mount to all other mounts if the mountpoint
+ * is under a shared mount.
+ */
+int make_mounted(struct nameidata *nd, struct vfsmount **mnt)
+{
+	struct vfsmount *parent_mnt;
+	struct dentry *parent_dentry;
+	int err = mount_is_safe(nd);
+	if (err)
+		return err;
+	parent_dentry = nd->dentry;
+	parent_mnt = nd->mnt;
+ 	/*
+	 * check if dentry already has a vfsmount
+	 * 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 = IS_MNT_SHARED(parent_mnt) ?
+			 pnode_make_mounted(parent_mnt->mnt_pnode,
+					 parent_mnt, parent_dentry) :
+			 do_make_mounted(parent_mnt, parent_dentry);
+		if (!*mnt)
+			err = -ENOMEM;
+ 	} else
+		*mnt = parent_mnt;
+	return err;
+}
+
+ /*
+ * Inverse operation of make_mounted()
+  */
+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.
  */
@@ -724,7 +1213,7 @@ 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;
@@ -734,14 +1223,31 @@ static int do_loopback(struct nameidata 
 	if (err)
 		return err;
 
-	down_write(&current->namespace->sem);
+	if (IS_MNT_UNCLONE(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) {
@@ -752,15 +1258,25 @@ 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;
 }
 
@@ -808,7 +1324,7 @@ 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;
@@ -852,7 +1368,7 @@ 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);
@@ -891,7 +1407,7 @@ 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))
 		;
@@ -920,7 +1436,7 @@ int do_add_mount(struct vfsmount *newmnt
 	}
 
 unlock:
-	up_write(&current->namespace->sem);
+	up_write(&namespace_sem);
 	mntput(newmnt);
 	return err;
 }
@@ -976,7 +1492,7 @@ 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
@@ -1020,7 +1536,7 @@ void mark_mounts_for_expiry(struct list_
 			spin_unlock(&vfsmount_lock);
 		}
 
-		up_write(&namespace->sem);
+		up_write(&namespace_sem);
 
 		mntput(mnt);
 		put_namespace(namespace);
@@ -1066,7 +1582,7 @@ int copy_mount_options(const void __user
 	int i;
 	unsigned long page;
 	unsigned long size;
-	
+
 	*where = 0;
 	if (!data)
 		return 0;
@@ -1085,7 +1601,7 @@ 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)
@@ -1191,14 +1707,13 @@ 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;
 	}
@@ -1232,7 +1747,7 @@ 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;
 
@@ -1414,7 +1929,7 @@ 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))
@@ -1460,7 +1975,7 @@ 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:
@@ -1487,7 +2002,6 @@ 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;
@@ -1510,6 +2024,8 @@ 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);
 
@@ -1557,7 +2073,7 @@ 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) {
@@ -1566,6 +2082,6 @@ 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.work2/fs/pnode.c
===================================================================
--- 2.6.12.work2.orig/fs/pnode.c
+++ 2.6.12.work2/fs/pnode.c
@@ -26,7 +26,6 @@
 #include <asm/unistd.h>
 #include <stdarg.h>
 
-
 static kmem_cache_t * pnode_cachep;
 
 /* spinlock for pnode related operations */
@@ -90,10 +89,12 @@ static void inline pnode_add_mnt(struct 
 	mnt->mnt_pnode = pnode;
 	if (slave) {
 		set_mnt_slave(mnt);
-		list_add(&mnt->mnt_pnode_mntlist, &pnode->pnode_slavevfs);
+		list_add(&mnt->mnt_pnode_mntlist,
+				&pnode->pnode_slavevfs);
 	} else {
 		set_mnt_shared(mnt);
-		list_add(&mnt->mnt_pnode_mntlist, &pnode->pnode_vfs);
+		list_add(&mnt->mnt_pnode_mntlist,
+				&pnode->pnode_vfs);
 	}
 	get_pnode(pnode);
 	spin_unlock(&vfspnode_lock);
@@ -111,7 +112,6 @@ void pnode_add_slave_mnt(struct vfspnode
 	pnode_add_mnt(pnode, mnt, 1);
 }
 
-
 void pnode_add_slave_pnode(struct vfspnode *pnode,
 		struct vfspnode *slave_pnode)
 {
@@ -439,3 +439,230 @@ error:
 	pnode_end(&context);
 	goto out;
 }
+
+int pnode_mount_func(struct vfspnode *pnode, void *indata,
+		void **outdata, va_list args)
+{
+	struct vfspnode *pnode_slave, *pnode_master;
+	int ret=0;
+
+	pnode_master = indata;
+
+	if (*outdata)
+		pnode_slave = *outdata;
+	else if (!(pnode_slave = pnode_alloc()))
+		return -ENOMEM;
+
+	*outdata = pnode_slave;
+
+	if (pnode_slave && pnode_master)
+		pnode_add_slave_pnode(pnode_master, pnode_slave);
+	return ret;
+}
+
+int vfs_make_mounted_func(struct vfsmount *mnt, enum pnode_vfs_type flag,
+		void *indata, va_list args)
+{
+	struct dentry *target_dentry;
+	int ret=0;
+	struct vfsmount *child_mount;
+	struct vfspnode *pnode;
+
+	target_dentry = va_arg(args, struct dentry *);
+	if (!(child_mount = do_make_mounted(mnt, target_dentry))) {
+		ret = -ENOMEM;
+		goto out;
+	}
+	pnode = (struct vfspnode *)indata;
+	switch (flag) {
+	case PNODE_SLAVE_VFS :
+		pnode_add_slave_mnt(pnode, child_mount);
+		break;
+	case PNODE_MEMBER_VFS :
+		pnode_add_member_mnt(pnode, child_mount);
+		break;
+	}
+
+out:
+	return ret;
+}
+
+/*
+ * @pnode: pnode that contains the vfsmounts, on which the
+ *  		new mount is created at dentry 'dentry'
+ * @dentry: the dentry on which the new mount is created
+ * @mnt:   return the mount created on this vfsmount
+ * walk through all the vfsmounts belonging to this pnode
+ * as well as its slave pnodes and for each vfsmount create
+ * a new vfsmount at 'dentry'.  Return the vfsmount created
+ * at 'dentry' of vfsmount 'mnt'.
+ */
+struct vfsmount *pnode_make_mounted(struct vfspnode *pnode,
+		struct vfsmount *mnt, struct dentry *dentry)
+{
+	struct vfsmount *child_mnt;
+	struct vfspnode *child_pnode;
+
+	if (!(child_pnode = pnode_alloc()))
+		return NULL;
+
+	if (pnode_traverse(pnode, child_pnode, (void *)NULL,
+			pnode_mount_func, NULL, vfs_make_mounted_func,
+			(void *)dentry))
+  		goto error;
+	child_mnt = __lookup_mnt(mnt, dentry, dentry);
+	mntput(child_mnt);
+	return child_mnt;
+
+error:
+	pnode_make_unmounted(child_pnode);
+	return NULL;
+}
+
+int vfs_make_unmounted_func(struct vfsmount *mnt, enum pnode_vfs_type flag,
+		void *indata, va_list args)
+{
+	struct vfspnode *pnode;
+	int ret=0;
+
+	if (do_make_unmounted(mnt)) {
+		ret = 1;
+		goto out;
+	}
+
+	pnode = mnt->mnt_pnode;
+	spin_lock(&vfspnode_lock);
+	list_del_init(&mnt->mnt_pnode_mntlist);
+	put_pnode_locked(pnode);
+	spin_unlock(&vfspnode_lock);
+out:
+	return ret;
+}
+
+int pnode_make_unmounted(struct vfspnode *pnode)
+{
+	return pnode_traverse(pnode, NULL, (void *)NULL,
+			NULL, NULL, vfs_make_unmounted_func);
+}
+
+int vfs_prepare_mount_func(struct vfsmount *mnt, enum pnode_vfs_type flag,
+		void *indata, va_list args)
+{
+	struct vfsmount *source_mnt, *child_mnt, *p_mnt;
+	struct dentry *mountpoint_dentry;
+	struct vfspnode *pnode = (struct vfspnode *)indata;
+
+	source_mnt = va_arg(args, struct vfsmount * );
+	mountpoint_dentry =  va_arg(args, struct dentry *);
+	p_mnt =  va_arg(args, struct vfsmount *);
+
+	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)
+			return -ENOMEM;
+
+		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)
+{
+	return  pnode_traverse(pnode,
+			master_child_pnode,
+			(void *)NULL,
+			pnode_mount_func,
+			NULL,
+			vfs_prepare_mount_func,
+			source_mnt,
+			mountpoint_dentry,
+			mnt);
+}
+
+int pnode_commit_mount_post_func(struct vfspnode *pnode, void *indata,
+		va_list args)
+{
+	if (va_arg(args, int)) {
+		spin_lock(&vfspnode_lock);
+		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_locked(pnode);
+		spin_unlock(&vfspnode_lock);
+	}
+	return 0;
+}
+
+int vfs_commit_mount_func(struct vfsmount *mnt, enum pnode_vfs_type flag,
+		void *indata, va_list args)
+{
+	BUG_ON(mnt == mnt->mnt_parent);
+	do_attach_commit_mnt(mnt);
+	if (va_arg(args, int)) {
+		spin_lock(&vfspnode_lock);
+		list_del_init(&mnt->mnt_pnode_mntlist);
+		put_pnode_locked(mnt->mnt_pnode);
+		spin_unlock(&vfspnode_lock);
+		mnt->mnt_pnode = NULL;
+	}
+	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_commit_mount(struct vfspnode *pnode, int flag)
+{
+	return  pnode_traverse(pnode,
+			NULL, (void *)NULL, NULL, pnode_commit_mount_post_func,
+			vfs_commit_mount_func, flag);
+}
+
+int vfs_abort_mount_func(struct vfsmount *mnt,
+		enum pnode_vfs_type flag, void *indata, va_list args)
+
+{
+	struct vfsmount *exception_mnt = va_arg(args, struct vfsmount *);
+	BUG_ON(!mnt->mnt_pnode);
+	pnode_disassociate_mnt(mnt);
+	do_detach_prepare_mnt(mnt, (exception_mnt != mnt));
+	return 0;
+}
+
+/*
+ * clean the propogation tree under pnode, releasing all
+ * the mounts, except exception_mnt
+ * @pnode: the pnode tree to be cleanup unlinking and
+ * 	releasing all pnodes in the tree as well as
+ * 	unlinking any mounts, except 'exception_mnt'
+ * @exception_mnt: the mnt to be unlinked from pnode
+ * 		bug not released.
+ */
+int pnode_abort_mount(struct vfspnode *pnode,
+		struct vfsmount *exception_mnt)
+{
+	return  pnode_traverse(pnode,
+			NULL, (void *)NULL, NULL, NULL,
+			vfs_abort_mount_func, exception_mnt);
+}
Index: 2.6.12.work2/include/linux/fs.h
===================================================================
--- 2.6.12.work2.orig/include/linux/fs.h
+++ 2.6.12.work2/include/linux/fs.h
@@ -1216,7 +1216,12 @@ 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_commit_mnt(struct vfsmount *);
 extern struct vfsmount *do_make_mounted(struct vfsmount *, struct dentry *);
+extern int do_make_unmounted(struct vfsmount *);
+extern void do_detach_prepare_mnt(struct vfsmount *, int);
 
 extern int vfs_statfs(struct super_block *, struct kstatfs *);
 
Index: 2.6.12.work2/include/linux/namespace.h
===================================================================
--- 2.6.12.work2.orig/include/linux/namespace.h
+++ 2.6.12.work2/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 *);
Index: 2.6.12.work2/include/linux/dcache.h
===================================================================
--- 2.6.12.work2.orig/include/linux/dcache.h
+++ 2.6.12.work2/include/linux/dcache.h
@@ -329,6 +329,8 @@ static inline int d_mountpoint(struct de
 }
 
 extern struct vfsmount *lookup_mnt(struct vfsmount *, struct dentry *);
+extern struct vfsmount *__lookup_mnt(struct vfsmount *,
+		struct dentry *, struct dentry *);
 extern struct dentry *lookup_create(struct nameidata *nd, int is_dir);
 
 extern int sysctl_vfs_cache_pressure;