qdev: Check for the availability of a hotplug controller before adding a device

The qdev_unplug() function contains a g_assert(hotplug_ctrl) statement,
so QEMU crashes when the user tries to device_add + device_del a device
that does not have a corresponding hotplug controller. This could be
provoked for a couple of devices in the past (see commit 4c939506
or 84ebd3e8 for example), and can currently for example also be
triggered like this:

$ s390x-softmmu/qemu-system-s390x -M none -nographic
QEMU 2.10.50 monitor - type 'help' for more information
(qemu) device_add qemu-s390x-cpu,id=x
(qemu) device_del x
**
ERROR:qemu/qdev-monitor.c:872:qdev_unplug: assertion failed: (hotplug_ctrl)
Aborted (core dumped)

So devices clearly need a hotplug controller when they should be usable
with device_add.
The code in qdev_device_add() already checks whether the bus has a proper
hotplug controller, but for devices that do not have a corresponding bus,
there is no appropriate check available yet. In that case we should check
whether the machine itself provides a suitable hotplug controller and
refuse to plug the device if none is available.
Reviewed-by: NIgor Mammedov <imammedo@redhat.com>
Signed-off-by: NThomas Huth <thuth@redhat.com>
Message-Id: <1509617407-21191-3-git-send-email-thuth@redhat.com>
Reviewed-by: NCornelia Huck <cohuck@redhat.com>
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>

hw/core/qdev.c

@@ -253,19 +253,31 @@ void qdev_set_legacy_instance_id(DeviceState *dev, int alias_id,
     dev->alias_required_for_version = required_for_version;
 }
 
+HotplugHandler *qdev_get_machine_hotplug_handler(DeviceState *dev)
+{
+    MachineState *machine;
+    MachineClass *mc;
+    Object *m_obj = qdev_get_machine();
+
+    if (object_dynamic_cast(m_obj, TYPE_MACHINE)) {
+        machine = MACHINE(m_obj);
+        mc = MACHINE_GET_CLASS(machine);
+        if (mc->get_hotplug_handler) {
+            return mc->get_hotplug_handler(machine, dev);
+        }
+    }
+
+    return NULL;
+}
+
 HotplugHandler *qdev_get_hotplug_handler(DeviceState *dev)
 {
-    HotplugHandler *hotplug_ctrl = NULL;
+    HotplugHandler *hotplug_ctrl;
 
     if (dev->parent_bus && dev->parent_bus->hotplug_handler) {
         hotplug_ctrl = dev->parent_bus->hotplug_handler;
-    } else if (object_dynamic_cast(qdev_get_machine(), TYPE_MACHINE)) {
-        MachineState *machine = MACHINE(qdev_get_machine());
-        MachineClass *mc = MACHINE_GET_CLASS(machine);
-
-        if (mc->get_hotplug_handler) {
-            hotplug_ctrl = mc->get_hotplug_handler(machine, dev);
-        }
+    } else {
+        hotplug_ctrl = qdev_get_machine_hotplug_handler(dev);
     }
     return hotplug_ctrl;
 }

include/hw/qdev-core.h

@@ -286,6 +286,7 @@ DeviceState *qdev_try_create(BusState *bus, const char *name);
 void qdev_init_nofail(DeviceState *dev);
 void qdev_set_legacy_instance_id(DeviceState *dev, int alias_id,
                                  int required_for_version);
+HotplugHandler *qdev_get_machine_hotplug_handler(DeviceState *dev);
 HotplugHandler *qdev_get_hotplug_handler(DeviceState *dev);
 void qdev_unplug(DeviceState *dev, Error **errp);
 void qdev_simple_device_unplug_cb(HotplugHandler *hotplug_dev,

qdev-monitor.c

@@ -613,6 +613,11 @@ DeviceState *qdev_device_add(QemuOpts *opts, Error **errp)
 
     if (bus) {
         qdev_set_parent_bus(dev, bus);
+    } else if (qdev_hotplug && !qdev_get_machine_hotplug_handler(dev)) {
+        /* No bus, no machine hotplug handler --> device is not hotpluggable */
+        error_setg(&err, "Device '%s' can not be hotplugged on this machine",
+                   driver);
+        goto err_del_dev;
     }
 
     qdev_set_id(dev, qemu_opts_id(opts));