[Qemu-devel] [PATCH] qdev: Check for the availability of a hotplug controller before adding a device

[Thomas Huth <thuth@redhat.com>]

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 4c93950659487c7ad
or 84ebd3e8c7d4fe955 for example). So devices clearly need a hotplug
controller when they are suitable for 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. 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.

Signed-off-by: Thomas Huth <thuth@redhat.com>
---
 This is the follow-up patch from my earlier try "hw/core/qdev: Do not
 allow hot-plugging without hotplug controller" ... AFAICS the function
 qdev_device_add() is now the right spot to do the check.

 hw/core/qdev.c         | 28 ++++++++++++++++++++--------
 include/hw/qdev-core.h |  1 +
 qdev-monitor.c         |  9 +++++++++
 3 files changed, 30 insertions(+), 8 deletions(-)

diff --git a/hw/core/qdev.c b/hw/core/qdev.c
index 606ab53..a953ec9 100644
--- a/hw/core/qdev.c
+++ b/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;
 }
diff --git a/include/hw/qdev-core.h b/include/hw/qdev-core.h
index 0891461..5aa536d 100644
--- a/include/hw/qdev-core.h
+++ b/include/hw/qdev-core.h
@@ -285,6 +285,7 @@ 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,
diff --git a/qdev-monitor.c b/qdev-monitor.c
index 8fd6df9..2891dde 100644
--- a/qdev-monitor.c
+++ b/qdev-monitor.c
@@ -626,6 +626,15 @@ DeviceState *qdev_device_add(QemuOpts *opts, Error **errp)
         return NULL;
     }
 
+    /* In case we don't have a bus, there must be a machine hotplug handler */
+    if (qdev_hotplug && !bus && !qdev_get_machine_hotplug_handler(dev)) {
+        error_setg(errp, "Device '%s' can not be hotplugged on this machine",
+                   driver);
+        object_unparent(OBJECT(dev));
+        object_unref(OBJECT(dev));
+        return NULL;
+    }
+
     dev->opts = opts;
     object_property_set_bool(OBJECT(dev), true, "realized", &err);
     if (err != NULL) {
-- 
1.8.3.1