diff --git a/src/b-tree.c b/src/b-tree.c
index af89802..304632b 100644
--- a/src/b-tree.c
+++ b/src/b-tree.c
@@ -110,7 +110,7 @@ static int node_write(struct b_tree *tree, long id, const b_tree_node *in)
 
 static unsigned long node_get_nr_entries(struct b_tree *tree, b_tree_node *node)
 {
-	return tree->tree_ops->node_get_nr_entries(node);
+	return tree->tree_ops->node_get_nr_entries(tree, node);
 }
 
 static void node_set_nr_entries(
@@ -118,7 +118,7 @@ static void node_set_nr_entries(
 	b_tree_node *node,
 	unsigned long val)
 {
-	tree->tree_ops->node_set_nr_entries(node, val);
+	tree->tree_ops->node_set_nr_entries(tree, node, val);
 }
 
 static unsigned long node_get_child(
@@ -126,7 +126,7 @@ static unsigned long node_get_child(
 	b_tree_node *node,
 	unsigned long index)
 {
-	return tree->tree_ops->node_get_child(node, index);
+	return tree->tree_ops->node_get_child(tree, node, index);
 }
 
 static void node_set_child(
@@ -135,7 +135,7 @@ static void node_set_child(
 	unsigned long index,
 	unsigned long ptr)
 {
-	tree->tree_ops->node_set_child(node, index, ptr);
+	tree->tree_ops->node_set_child(tree, node, index, ptr);
 }
 
 static b_tree_node_entry *node_get_entry(
@@ -143,7 +143,7 @@ static b_tree_node_entry *node_get_entry(
 	b_tree_node *node,
 	unsigned long index)
 {
-	return tree->tree_ops->node_get_entry(node, index);
+	return tree->tree_ops->node_get_entry(tree, node, index);
 }
 
 static void node_set_entry(
@@ -152,7 +152,7 @@ static void node_set_entry(
 	unsigned long index,
 	const b_tree_node_entry *entry)
 {
-	tree->tree_ops->node_set_entry(node, index, entry);
+	tree->tree_ops->node_set_entry(tree, node, index, entry);
 }
 
 static void node_kill_entry(
@@ -160,7 +160,7 @@ static void node_kill_entry(
 	b_tree_node *node,
 	unsigned long index)
 {
-	tree->tree_ops->node_kill_entry(node, index);
+	tree->tree_ops->node_kill_entry(tree, node, index);
 }
 
 static void node_shift_entries(
@@ -307,7 +307,7 @@ static int entry_compare(
 	const b_tree_node_entry *a,
 	const b_tree_node_entry *b)
 {
-	return tree->tree_ops->entry_compare(a, b);
+	return tree->tree_ops->entry_compare(tree, a, b);
 }
 
 static int node_put(
diff --git a/src/b-tree.h b/src/b-tree.h
index 7f85c79..a75b3fc 100644
--- a/src/b-tree.h
+++ b/src/b-tree.h
@@ -23,18 +23,29 @@ struct b_tree_ops {
 		const b_tree_node *);
 	long (*tree_alloc_node)(struct b_tree *);
 
-	unsigned long (*node_get_nr_entries)(b_tree_node *);
-	void (*node_set_nr_entries)(b_tree_node *, unsigned long);
-	b_tree_node_entry *(*node_get_entry)(b_tree_node *, unsigned long);
+	unsigned long (*node_get_nr_entries)(struct b_tree *, b_tree_node *);
+	void (*node_set_nr_entries)(
+		struct b_tree *,
+		b_tree_node *,
+		unsigned long);
+	b_tree_node_entry *(
+		*node_get_entry)(struct b_tree *, b_tree_node *, unsigned long);
 	void (*node_set_entry)(
+		struct b_tree *,
 		b_tree_node *,
 		unsigned long,
 		const b_tree_node_entry *);
-	void (*node_kill_entry)(b_tree_node *, unsigned long);
-	unsigned long (*node_get_child)(b_tree_node *, unsigned long);
-	void (*node_set_child)(b_tree_node *, unsigned long, unsigned long);
+	void (*node_kill_entry)(struct b_tree *, b_tree_node *, unsigned long);
+	unsigned long (
+		*node_get_child)(struct b_tree *, b_tree_node *, unsigned long);
+	void (*node_set_child)(
+		struct b_tree *,
+		b_tree_node *,
+		unsigned long,
+		unsigned long);
 
 	int (*entry_compare)(
+		const struct b_tree *,
 		const b_tree_node_entry *,
 		const b_tree_node_entry *);
 };
diff --git a/src/cluster-table.c b/src/cluster-table.c
index 37fede5..794c2dd 100644
--- a/src/cluster-table.c
+++ b/src/cluster-table.c
@@ -97,25 +97,32 @@ static long tree_alloc_node(struct b_tree *p)
 	return (long)len;
 }
 
-static unsigned long node_get_nr_entries(b_tree_node *n)
+static unsigned long node_get_nr_entries(struct b_tree *tree, b_tree_node *n)
 {
 	struct ec3_cluster_group *node = (struct ec3_cluster_group *)n;
 	return b_i16_btoh(node->g_nr_clusters);
 }
 
-static void node_set_nr_entries(b_tree_node *n, unsigned long val)
+static void node_set_nr_entries(
+	struct b_tree *tree,
+	b_tree_node *n,
+	unsigned long val)
 {
 	struct ec3_cluster_group *node = (struct ec3_cluster_group *)n;
 	node->g_nr_clusters = b_i16_htob(val);
 }
 
-static b_tree_node_entry *node_get_entry(b_tree_node *n, unsigned long index)
+static b_tree_node_entry *node_get_entry(
+	struct b_tree *tree,
+	b_tree_node *n,
+	unsigned long index)
 {
 	struct ec3_cluster_group *node = (struct ec3_cluster_group *)n;
 	return (b_tree_node_entry *)&node->g_clusters[index];
 }
 
 static void node_set_entry(
+	struct b_tree *tree,
 	b_tree_node *n,
 	unsigned long index,
 	const b_tree_node_entry *entry)
@@ -124,13 +131,19 @@ static void node_set_entry(
 	memmove(&node->g_clusters[index], entry, sizeof(struct ec3_cluster));
 }
 
-static void node_kill_entry(b_tree_node *n, unsigned long index)
+static void node_kill_entry(
+	struct b_tree *tree,
+	b_tree_node *n,
+	unsigned long index)
 {
 	struct ec3_cluster_group *node = (struct ec3_cluster_group *)n;
 	memset(&node->g_clusters[index], 0x0, sizeof(struct ec3_cluster));
 }
 
-static unsigned long node_get_child(b_tree_node *n, unsigned long index)
+static unsigned long node_get_child(
+	struct b_tree *tree,
+	b_tree_node *n,
+	unsigned long index)
 {
 	struct ec3_cluster_group *node = (struct ec3_cluster_group *)n;
 	b_i32 enc_child = node->g_child_offsets[index];
@@ -139,6 +152,7 @@ static unsigned long node_get_child(b_tree_node *n, unsigned long index)
 }
 
 static void node_set_child(
+	struct b_tree *tree,
 	b_tree_node *n,
 	unsigned long index,
 	unsigned long ptr)
@@ -150,6 +164,7 @@ static void node_set_child(
 }
 
 static int entry_compare(
+	const struct b_tree *tree,
 	const b_tree_node_entry *e0,
 	const b_tree_node_entry *e1)
 {