[2/3] add object_property_add_alias

Index: qemu/include/qom/object.h
===================================================================
--- qemu.orig/include/qom/object.h
+++ qemu/include/qom/object.h
@@ -1073,6 +1073,19 @@  typedef enum {
 } ObjectPropertyLinkFlags;
 
 /**
+ * object_property_add_alias:
+ * @obj: the object to add a property to
+ * @name: the name of the property
+ * @alias: the alias object
+ * @errp: if an error occurs, a pointer to an area to store the area
+ *
+ * Add a link under obj, named name, pointing to alias.
+ *
+ */
+void object_property_add_alias(Object *obj, const char *name,
+                               Object *alias, Error **errp);
+
+/**
  * object_property_allow_set_link:
  *
  * The default implementation of the object_property_add_link() check()
Index: qemu/qom/object.c
===================================================================
--- qemu.orig/qom/object.c
+++ qemu/qom/object.c
@@ -1023,27 +1023,71 @@  out:
     g_free(type);
 }
 
+typedef struct {
+    Object *child;
+    Object **childp;
+    void (*check)(Object *, const char *, Object *, Error **);
+    ObjectPropertyLinkFlags flags;
+} LinkProperty;
+
+static void object_get_alias_property(Object *obj, Visitor *v, void *opaque,
+                                      const char *name, Error **errp)
+{
+    LinkProperty *prop = opaque;
+    Object *child = prop->child;
+    gchar *path;
+
+    path = object_get_canonical_path(child);
+    visit_type_str(v, &path, name, errp);
+    g_free(path);
+}
+
+static void object_release_alias_property(Object *obj, const char *name,
+                                         void *opaque)
+{
+    LinkProperty *prop = opaque;
+
+    g_free(prop);
+}
+
+void object_property_add_alias(Object *obj, const char *name,
+                               Object *alias, Error **errp)
+{
+    Error *local_err = NULL;
+    gchar *type;
+    LinkProperty *prop = g_malloc(sizeof(*prop));
+
+    type = g_strdup_printf("link<%s>", object_get_typename(OBJECT(alias)));
+
+    prop->child = alias;
+    prop->check = NULL;
+    prop->flags = 0;
+
+    object_property_add(obj, name, type, object_get_alias_property, NULL,
+                        object_release_alias_property, prop, &local_err);
+    if (local_err) {
+        g_free(prop);
+        error_propagate(errp, local_err);
+    }
+
+    g_free(type);
+}
+
 void object_property_allow_set_link(Object *obj, const char *name,
                                     Object *val, Error **errp)
 {
     /* Allow the link to be set, always */
 }
 
-typedef struct {
-    Object **child;
-    void (*check)(Object *, const char *, Object *, Error **);
-    ObjectPropertyLinkFlags flags;
-} LinkProperty;
-
 static void object_get_link_property(Object *obj, Visitor *v, void *opaque,
                                      const char *name, Error **errp)
 {
     LinkProperty *lprop = opaque;
-    Object **child = lprop->child;
+    Object *child = lprop->child;
     gchar *path;
 
-    if (*child) {
-        path = object_get_canonical_path(*child);
+    if (child) {
+        path = object_get_canonical_path(child);
         visit_type_str(v, &path, name, errp);
         g_free(path);
     } else {
@@ -1096,7 +1140,7 @@  static void object_set_link_property(Obj
 {
     Error *local_err = NULL;
     LinkProperty *prop = opaque;
-    Object **child = prop->child;
+    Object **child = prop->childp;
     Object *old_target = *child;
     Object *new_target = NULL;
     char *path = NULL;
@@ -1133,8 +1177,8 @@  static void object_release_link_property
 {
     LinkProperty *prop = opaque;
 
-    if ((prop->flags & OBJ_PROP_LINK_UNREF_ON_RELEASE) && *prop->child) {
-        object_unref(*prop->child);
+    if ((prop->flags & OBJ_PROP_LINK_UNREF_ON_RELEASE) && prop->child) {
+        object_unref(prop->child);
     }
     g_free(prop);
 }
@@ -1150,7 +1194,8 @@  void object_property_add_link(Object *ob
     LinkProperty *prop = g_malloc(sizeof(*prop));
     gchar *full_type;
 
-    prop->child = child;
+    prop->childp = child;
+    prop->child = *child;
     prop->check = check;
     prop->flags = flags;
 
@@ -1227,7 +1272,7 @@  Object *object_resolve_path_component(Ob
 
     if (object_property_is_link(prop)) {
         LinkProperty *lprop = prop->opaque;
-        return *lprop->child;
+        return lprop->child;
     } else if (object_property_is_child(prop)) {
         return prop->opaque;
     } else {