Nucleus

diff --git a/object/list.c b/object/list.c
index 4b3f3c7..e1b2d08 100644
--- a/object/list.c
+++ b/object/list.c
@@ -8,6 +8,7 @@
 
 #include <nucleus/object.h>
 #include <nucleus/memory.h>
+#include <nucleus/panic.h>
 
 /* Structure for a List Entry */
 struct ListEntry {
@@ -21,6 +22,12 @@ struct ObjectList {
 	ObjectType *type;
 	Spinlock lock;
 };
+/* Iterator */
+struct Iterator {
+	ObjectList *list;
+	struct ListEntry *prev, *entry, *next;
+	off_t pos;
+};
 
 void init_lock(Spinlock *lock);
 void acquire(Spinlock *lock);
@@ -49,6 +56,7 @@ void
 add(ObjectList *list, void *addr)
 {
 	Object *obj = addr;
+	ASSERT(obj->magic == OBJECT_MAGIC);
 	if (list->type && obj->type != list->type)
 		return;
 
@@ -70,6 +78,7 @@ void
 remove(ObjectList *list, void *addr)
 {
 	Object *obj = addr;
+	ASSERT(obj->magic == OBJECT_MAGIC);
 	if (!list->start)
 		return;
 	if (list->type && obj->type != list->type)
@@ -159,21 +168,6 @@ get_nth_item(ObjectList *list, off_t n)
 	return entry->obj;
 }
 
-/* Iterate a List with a callback */
-void
-iterate(ObjectList *list, iterate_callback_t callback, void *data)
-{
-	acquire(&list->lock);
-	struct ListEntry *entry;
-	for (entry = list->start; entry; entry = entry->next) {
-		get(entry->obj);
-		if (callback(entry->obj, data))
-			break;
-		put(entry->obj);
-	}
-	release(&list->lock);
-}
-
 /* Copy list */
 ObjectList *
 copy_list(ObjectList *list)
@@ -197,3 +191,74 @@ concat_list(ObjectList *src, ObjectList *dest)
 		add(dest, entry->obj);
 	release(&src->lock);
 }
+
+/* Iterate a List */
+Iterator *
+iterate(ObjectList *list)
+{
+	Iterator *i = kmalloc(sizeof(Iterator));
+	i->list = list;
+	return i;
+}
+
+/* Get first iteratable element */
+void *
+first(Iterator *iter)
+{
+	iter->entry = iter->list->start;
+	if (iter->entry) {
+		iter->next = iter->entry->next;
+		iter->pos = 0;
+		return iter->entry->obj;
+	}
+	return NULL;
+}
+
+/* Get last iteratable element */
+void *
+last(Iterator *iter)
+{
+	iter->entry = iter->list->end;
+	if (iter->entry) {
+		iter->prev = iter->entry->prev;
+		iter->pos = iter->list->entries - 1;
+		return iter->entry->obj;
+	}
+	return NULL;
+}
+
+/* Get next iteratable element */
+void *
+next(Iterator *iter)
+{
+	iter->entry = iter->next;
+	if (iter->entry) {
+		iter->prev = iter->entry->prev;
+		iter->next = iter->entry->next;
+		iter->pos++;
+		return iter->entry->obj;
+	}
+	return NULL;
+}
+
+/* Get previous iteratable element */
+void *
+prev(Iterator *iter)
+{
+	iter->entry = iter->prev;
+	if (iter->entry) {
+		iter->prev = iter->entry->prev;
+		iter->next = iter->entry->next;
+		iter->pos--;
+		return iter->entry->obj;
+	}
+	return NULL;
+}
+
+/* End iteration */
+int
+done_iterating(Iterator *iter)
+{
+	kfree(iter);
+	return 0;
+}