object: add object_get_canonical_path_component()

It is often useful to find an object's child property name.  Also use
this new function to simplify the implementation of
object_get_canonical_path().
Reviewed-by: NAndreas Färber <afaerber@suse.de>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

include/qom/object.h

@@ -973,6 +973,14 @@ const char *object_property_get_type(Object *obj, const char *name,
  */
 Object *object_get_root(void);
 
+/**
+ * object_get_canonical_path_component:
+ *
+ * Returns: The final component in the object's canonical path.  The canonical
+ * path is the path within the composition tree starting from the root.
+ */
+gchar *object_get_canonical_path_component(Object *obj);
+
 /**
  * object_get_canonical_path:
  *

qom/object.c

@@ -1102,14 +1102,11 @@ void object_property_add_link(Object *obj, const char *name,
     g_free(full_type);
 }
 
-gchar *object_get_canonical_path(Object *obj)
+gchar *object_get_canonical_path_component(Object *obj)
 {
-    Object *root = object_get_root();
-    char *newpath = NULL, *path = NULL;
-
-    while (obj != root) {
     ObjectProperty *prop = NULL;
 
+    g_assert(obj);
     g_assert(obj->parent != NULL);
 
     QTAILQ_FOREACH(prop, &obj->parent->properties, node) {
@@ -1118,23 +1115,36 @@ gchar *object_get_canonical_path(Object *obj)
         }
 
         if (prop->opaque == obj) {
+            return g_strdup(prop->name);
+        }
+    }
+
+    /* obj had a parent but was not a child, should never happen */
+    g_assert_not_reached();
+    return NULL;
+}
+
+gchar *object_get_canonical_path(Object *obj)
+{
+    Object *root = object_get_root();
+    char *newpath, *path = NULL;
+
+    while (obj != root) {
+        char *component = object_get_canonical_path_component(obj);
+
         if (path) {
-                    newpath = g_strdup_printf("%s/%s", prop->name, path);
+            newpath = g_strdup_printf("%s/%s", component, path);
+            g_free(component);
             g_free(path);
             path = newpath;
         } else {
-                    path = g_strdup(prop->name);
-                }
-                break;
+            path = component;
         }
-        }
-
-        g_assert(prop != NULL);
 
         obj = obj->parent;
     }
 
-    newpath = g_strdup_printf("/%s", path);
+    newpath = g_strdup_printf("/%s", path ? path : "");
     g_free(path);
 
     return newpath;