vm: implement lazy-attach cow-duplication of vm-objects attached to a controller

include/kernel/vm-object.h

@@ -20,19 +20,25 @@ enum vm_object_flags {
 	 * be detached, allowing the server to close the last handle to the
 	 * object and dispose of it. */
 	VMO_AUTO_DETACH = 0x04u,
+	/* this vmo is a duplicate of a vmo that is attached to a vm-controller.
+	 * the duplicate vmo is scheduled to be attached to the same controller,
+	 * but this won't actually happen until the controller is needed to
+	 * fulfill a page request. once the duplicate vmo has been attached to
+	 * the controller, this flag will be cleared. */
+	VMO_LAZY_ATTACH = 0x08u,
 
 	/* these flags are for use with vm_object_get_page */
 	/**************************************************/
 
 	/* if the relevant page hasn't been allocated yet, it will be allocated
 	 * and returned. if this flag isn't specified, NULL will be returned. */
-	VMO_ALLOCATE_MISSING_PAGE = 0x08u,
+	VMO_ALLOCATE_MISSING_PAGE = 0x0100u,
 	/* if the vm-object is attached to a vm-controller, and the relevant
 	 * page is uncommitted, send a request to the vm-controller to provide
 	 * the missing page. will result in the vm-object being unlocked and
 	 * the current thread sleeping until the request is fulfilled. the
 	 * vm-object will be re-locked before the function returns. */
-	VMO_REQUEST_MISSING_PAGE = 0x10u,
+	VMO_REQUEST_MISSING_PAGE = 0x0200u,
 };
 
 struct vm_object {
@@ -45,7 +51,7 @@ struct vm_object {
 	struct queue vo_mappings;
 
 	struct vm_controller *vo_ctrl;
-	equeue_key_t vo_key;
+	equeue_key_t vo_key, vo_src_key;
 	struct btree_node vo_ctrl_node;
 
 	/* memory protection flags. mappings of this vm_object can only
@@ -86,6 +92,11 @@ extern struct vm_object *vm_object_create_in_place(
 
 /* create a copy-on-write duplicate of a vm-object */
 extern struct vm_object *vm_object_duplicate_cow(struct vm_object *vmo);
+/* attach a copy-on-write duplicate of a vm-object to the vm-controller that
+ * controlled the original vm-object */
+extern kern_status_t vm_object_attach_cow(
+	struct vm_object *vmo,
+	unsigned long *irq_flags);
 
 extern struct vm_page *vm_object_get_page(
 	struct vm_object *vo,