hmp: fix regression of HMP device_del auto-completion

The commits:
 - 6a1fa9f5 (monitor: add del completion for peripheral device)
 - 66e56b13 (qdev: add qdev_build_hotpluggable_device_list helper)

cause a QEMU crash when trying to use HMP device_del auto-completion.
It can be easily reproduced by:
    <qemu-bin> -enable-kvm  ~/images/fedora.qcow2 -monitor stdio -device virtio-net-pci,id=vnet

    (qemu) device_del
    /home/mapfelba/git/upstream/qemu/hw/core/qdev.c:941:qdev_build_hotpluggable_device_list: Object 0x7f6ce04e4fe0 is not an instance of type device
    Aborted (core dumped)

The root cause is qdev_build_hotpluggable_device_list going recursively over
all peripherals and their children assuming all are devices. It doesn't work
since PCI devices have at least on child which is a memory region (bus master).

Solved by observing that all devices appear as direct children of
/machine/peripheral container. No need of going recursively
over all the children.

Signed-off-by: Marcel Apfelbaum <marcel.a@redhat.com>
Reported-by: Gal Hammer <ghammer@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Message-id: 1417002601-20799-1-git-send-email-marcel.a@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

hw/core/qdev.c

@@ -935,7 +935,7 @@ void qdev_alias_all_properties(DeviceState *target, Object *source)
     } while (class != object_class_by_name(TYPE_DEVICE));
 }
 
-int qdev_build_hotpluggable_device_list(Object *obj, void *opaque)
+static int qdev_add_hotpluggable_device(Object *obj, void *opaque)
 {
     GSList **list = opaque;
     DeviceState *dev = DEVICE(obj);
@@ -944,10 +944,18 @@ int qdev_build_hotpluggable_device_list(Object *obj, void *opaque)
         *list = g_slist_append(*list, dev);
     }
 
-    object_child_foreach(obj, qdev_build_hotpluggable_device_list, opaque);
     return 0;
 }
 
+GSList *qdev_build_hotpluggable_device_list(Object *peripheral)
+{
+    GSList *list = NULL;
+
+    object_child_foreach(peripheral, qdev_add_hotpluggable_device, &list);
+
+    return list;
+}
+
 static bool device_get_realized(Object *obj, Error **errp)
 {
     DeviceState *dev = DEVICE(obj);

include/hw/qdev-core.h

@@ -365,7 +365,7 @@ extern int qdev_hotplug;
 
 char *qdev_get_dev_path(DeviceState *dev);
 
-int qdev_build_hotpluggable_device_list(Object *obj, void *opaque);
+GSList *qdev_build_hotpluggable_device_list(Object *peripheral);
 
 void qbus_set_hotplug_handler(BusState *bus, DeviceState *handler,
                               Error **errp);

monitor.c

@@ -4321,17 +4321,14 @@ void object_add_completion(ReadLineState *rs, int nb_args, const char *str)
 static void peripheral_device_del_completion(ReadLineState *rs,
                                              const char *str, size_t len)
 {
-    Object *peripheral;
-    GSList *list = NULL, *item;
+    Object *peripheral = container_get(qdev_get_machine(), "/peripheral");
+    GSList *list, *item;
 
-    peripheral = object_resolve_path("/machine/peripheral/", NULL);
-    if (peripheral == NULL) {
+    list = qdev_build_hotpluggable_device_list(peripheral);
+    if (!list) {
         return;
     }
 
-    object_child_foreach(peripheral, qdev_build_hotpluggable_device_list,
-                         &list);
-
     for (item = list; item; item = g_slist_next(item)) {
         DeviceState *dev = item->data;