qom: add object_property_add_const_link

Suggested-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

include/qom/object.h

@@ -1289,6 +1289,24 @@ void object_property_add_alias(Object *obj, const char *name,
                                Object *target_obj, const char *target_name,
                                Error **errp);
 
+/**
+ * object_property_add_const_link:
+ * @obj: the object to add a property to
+ * @name: the name of the property
+ * @target: the object to be referred by the link
+ * @errp: if an error occurs, a pointer to an area to store the error
+ *
+ * Add an unmodifiable link for a property on an object.  This function will
+ * add a property of type link<TYPE> where TYPE is the type of @target.
+ *
+ * The caller must ensure that @target stays alive as long as
+ * this property exists.  In the case @target is a child of @obj,
+ * this will be the case.  Otherwise, the caller is responsible for
+ * taking a reference.
+ */
+void object_property_add_const_link(Object *obj, const char *name,
+                                    Object *target, Error **errp);
+
 /**
  * object_property_set_description:
  * @obj: the object owning the property

qom/object.c

@@ -1266,6 +1266,22 @@ out:
     g_free(full_type);
 }
 
+void object_property_add_const_link(Object *obj, const char *name,
+                                    Object *target, Error **errp)
+{
+    char *link_type;
+    ObjectProperty *op;
+
+    link_type = g_strdup_printf("link<%s>", object_get_typename(target));
+    op = object_property_add(obj, name, link_type,
+                             object_get_child_property, NULL,
+                             NULL, target, errp);
+    if (op != NULL) {
+        op->resolve = object_resolve_child_property;
+    }
+    g_free(link_type);
+}
+
 gchar *object_get_canonical_path_component(Object *obj)
 {
     ObjectProperty *prop = NULL;