qdev: Clean up qdev_connect_gpio_out_named()

Both qdev_connect_gpio_out_named() and device_set_realized() put
objects without a parent into the "/machine/unattached/" orphanage.

qdev_connect_gpio_out_named() needs a lengthy comment to explain how
it works.  It exploits that object_property_add_child() can fail only
when we got a parent already, and ignoring that error does what we
want.  True.  If it failed due to "duplicate property", we'd be in
trouble, but that would be a programming error.

device_set_realized() is cleaner: it checks whether we need a parent,
then calls object_property_add_child(), aborting on failure.  No need
for a comment, and programming errors get caught.

Change qdev_connect_gpio_out_named() to match.

Cc: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20200505152926.18877-14-armbru@redhat.com>

hw/core/qdev.c

@@ -542,15 +542,12 @@ void qdev_connect_gpio_out_named(DeviceState *dev, const char *name, int n,
 {
     char *propname = g_strdup_printf("%s[%d]",
                                      name ? name : "unnamed-gpio-out", n);
-    if (pin) {
-        /* We need a name for object_property_set_link to work.  If the
-         * object has a parent, object_property_add_child will come back
-         * with an error without doing anything.  If it has none, it will
-         * never fail.  So we can just call it with a NULL Error pointer.
-         */
+    if (pin && !OBJECT(pin)->parent) {
+        /* We need a name for object_property_set_link to work */
         object_property_add_child(container_get(qdev_get_machine(),
                                                 "/unattached"),
-                                  "non-qdev-gpio[*]", OBJECT(pin), NULL);
+                                  "non-qdev-gpio[*]", OBJECT(pin),
+                                  &error_abort);
     }
     object_property_set_link(OBJECT(dev), OBJECT(pin), propname, &error_abort);
     g_free(propname);