qom: Create system containers explicitly

Always explicitly create QEMU system containers upfront.

Root containers will be created when trying to fetch the root object the
1st time.  They are:

  /objects
  /chardevs
  /backend

Machine sub-containers will be created only until machine is being
initialized.  They are:

  /machine/unattached
  /machine/peripheral
  /machine/peripheral-anon

Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20241121192202.4155849-8-peterx@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>

hw/core/machine.c

@@ -1229,9 +1229,6 @@ static void machine_initfn(Object *obj)
     MachineState *ms = MACHINE(obj);
     MachineClass *mc = MACHINE_GET_CLASS(obj);
 
-    container_get(obj, "/peripheral");
-    container_get(obj, "/peripheral-anon");
-
     ms->dump_guest_core = true;
     ms->mem_merge = (QEMU_MADV_MERGEABLE != QEMU_MADV_INVALID);
     ms->enable_graphics = true;

qom/object.c

@@ -1729,12 +1729,34 @@ const char *object_property_get_type(Object *obj, const char *name, Error **errp
     return prop->type;
 }
 
+static const char *const root_containers[] = {
+    "chardevs",
+    "objects",
+    "backend"
+};
+
+static Object *object_root_initialize(void)
+{
+    Object *root = object_new(TYPE_CONTAINER);
+    int i;
+
+    /*
+     * Create all QEMU system containers.  "machine" and its sub-containers
+     * are only created when machine initializes (qemu_create_machine()).
+     */
+    for (i = 0; i < ARRAY_SIZE(root_containers); i++) {
+        object_property_add_new_container(root, root_containers[i]);
+    }
+
+    return root;
+}
+
 Object *object_get_root(void)
 {
     static Object *root;
 
     if (!root) {
-        root = object_new(TYPE_CONTAINER);
+        root = object_root_initialize();
     }
 
     return root;

system/vl.c

@@ -2113,6 +2113,21 @@ static void parse_memory_options(void)
     loc_pop(&loc);
 }
 
+static const char *const machine_containers[] = {
+    "unattached",
+    "peripheral",
+    "peripheral-anon"
+};
+
+static void qemu_create_machine_containers(Object *machine)
+{
+    int i;
+
+    for (i = 0; i < ARRAY_SIZE(machine_containers); i++) {
+        object_property_add_new_container(machine, machine_containers[i]);
+    }
+}
+
 static void qemu_create_machine(QDict *qdict)
 {
     MachineClass *machine_class = select_machine(qdict, &error_fatal);
@@ -2121,6 +2136,7 @@ static void qemu_create_machine(QDict *qdict)
     current_machine = MACHINE(object_new_with_class(OBJECT_CLASS(machine_class)));
     object_property_add_child(object_get_root(), "machine",
                               OBJECT(current_machine));
+    qemu_create_machine_containers(OBJECT(current_machine));
     object_property_add_child(container_get(OBJECT(current_machine),
                                             "/unattached"),
                               "sysbus", OBJECT(sysbus_get_default()));