pc: simplify MachineClass::get_hotplug_handler handling

By default MachineClass::get_hotplug_handler is NULL and concrete board
should set it to it's own handler.
Considering there isn't any default handler, drop saving empty
MachineClass::get_hotplug_handler in child class and make PC code
consistent with spapr/s390x boards.

We can bring this back when actual usecase surfaces and do it
consistently across boards that use get_hotplug_handler().

Suggested-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Message-id: 1525691524-32265-2-git-send-email-imammedo@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

hw/i386/pc.c

@@ -2051,15 +2051,12 @@ static void pc_machine_device_unplug_cb(HotplugHandler *hotplug_dev,
 static HotplugHandler *pc_get_hotpug_handler(MachineState *machine,
                                              DeviceState *dev)
 {
-    PCMachineClass *pcmc = PC_MACHINE_GET_CLASS(machine);
-
     if (object_dynamic_cast(OBJECT(dev), TYPE_PC_DIMM) ||
         object_dynamic_cast(OBJECT(dev), TYPE_CPU)) {
         return HOTPLUG_HANDLER(machine);
     }
 
-    return pcmc->get_hotplug_handler ?
-        pcmc->get_hotplug_handler(machine, dev) : NULL;
+    return NULL;
 }
 
 static void
@@ -2339,7 +2336,6 @@ static void pc_machine_class_init(ObjectClass *oc, void *data)
     HotplugHandlerClass *hc = HOTPLUG_HANDLER_CLASS(oc);
     NMIClass *nc = NMI_CLASS(oc);
 
-    pcmc->get_hotplug_handler = mc->get_hotplug_handler;
     pcmc->pci_enabled = true;
     pcmc->has_acpi_build = true;
     pcmc->rsdp_in_ram = true;

include/hw/i386/pc.h

@@ -83,10 +83,6 @@ struct PCMachineState {
 /**
  * PCMachineClass:
  *
- * Methods:
- *
- * @get_hotplug_handler: pointer to parent class callback @get_hotplug_handler
- *
  * Compat fields:
  *
  * @enforce_aligned_dimm: check that DIMM's address/size is aligned by
@@ -106,10 +102,6 @@ struct PCMachineClass {
 
     /*< public >*/
 
-    /* Methods: */
-    HotplugHandler *(*get_hotplug_handler)(MachineState *machine,
-                                           DeviceState *dev);
-
     /* Device configuration: */
     bool pci_enabled;
     bool kvmclock_enabled;