qom: allow creating an alias of a child<> property

Child properties must be unique.  Fix this problem by
turning their aliases into links.

The resolve function that forwards to the target property
does not have any knowledge of the target property's type,
so it works fine.
Reviewed-by: NPeter Crosthwaite <peter.crosthwaite@xilinx.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

qom/object.c

@@ -1607,22 +1607,32 @@ void object_property_add_alias(Object *obj, const char *name,
     AliasProperty *prop;
     ObjectProperty *op;
     ObjectProperty *target_prop;
+    gchar *prop_type;
 
     target_prop = object_property_find(target_obj, target_name, errp);
     if (!target_prop) {
         return;
     }
 
+    if (object_property_is_child(target_prop)) {
+        prop_type = g_strdup_printf("link%s",
+                                    target_prop->type + strlen("child"));
+    } else {
+        prop_type = g_strdup(target_prop->type);
+    }
+
     prop = g_malloc(sizeof(*prop));
     prop->target_obj = target_obj;
     prop->target_name = target_name;
 
-    op = object_property_add(obj, name, target_prop->type,
+    op = object_property_add(obj, name, prop_type,
                              property_get_alias,
                              property_set_alias,
                              property_release_alias,
                              prop, errp);
     op->resolve = property_resolve_alias;
+
+    g_free(prop_type);
 }
 
 static void object_instance_init(Object *obj)