[PATCH 3/5] qdev: Make device_set_realized() always safe in tests

[Peter Xu <peterx@redhat.com>]

Currently, a device can be realized even before machine is created, but
only in one of QEMU's qtest, test-global-qdev-props.c.

Right now, the test_static_prop_subprocess() test (which creates one simple
object without machine created) will internally make "/machine" to be a
container, which may not be expected when developing the test.

Now explicitly support that case when there's no real "/machine" object
around, then unattached devices will be put under root ("/") rather than
"/machine".  Mostly only for this single test case, or for any future test
cases when some device needs to be realized before the machine is present.

This shouldn't affect anything else when QEMU runs as an emulator, as that
always relies on a real machine being created before realizing any devices.
It's because if "/machine" is wrongly created as a container, it'll fail
QEMU very soon later on qemu_create_machine() trying to create the real
machine, conflicting with the "/machine" container.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
 hw/core/qdev.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/hw/core/qdev.c b/hw/core/qdev.c
index 5f13111b77..eff297e584 100644
--- a/hw/core/qdev.c
+++ b/hw/core/qdev.c
@@ -475,9 +475,17 @@ static void device_set_realized(Object *obj, bool value, Error **errp)
 
         if (!obj->parent) {
             gchar *name = g_strdup_printf("device[%d]", unattached_count++);
+            Object *root = qdev_get_machine();
 
-            object_property_add_child(container_get(qdev_get_machine(),
-                                                    "/unattached"),
+            /*
+             * We could have qdev test cases trying to realize() a device
+             * without machine created.  In that case we use the root.
+             */
+            if (!root) {
+                root = object_get_root();
+            }
+
+            object_property_add_child(container_get(root, "/unattached"),
                                       name, obj);
             unattached_parent = true;
             g_free(name);
-- 
2.45.0