Re: [Qemu-devel] [PATCH v2 36/36] qdev: HotplugHandler: add support for unplugging BUS-less devices

[Bharata B Rao <bharata@linux.vnet.ibm.com>]

On Fri, Sep 26, 2014 at 09:28:41AM +0000, Igor Mammedov wrote:
> Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> ---
> v2:
>   merged in Paolo's suggestion to reduce indentation in patch
> ---
>  hw/core/qdev.c | 61 ++++++++++++++++++++++++++++++++--------------------------
>  1 file changed, 34 insertions(+), 27 deletions(-)
> 
> diff --git a/hw/core/qdev.c b/hw/core/qdev.c
> index bc45a59..215effb 100644
> --- a/hw/core/qdev.c
> +++ b/hw/core/qdev.c
> @@ -223,9 +223,28 @@ void qdev_set_legacy_instance_id(DeviceState *dev, int alias_id,
>      dev->alias_required_for_version = required_for_version;
>  }
> 
> +static HotplugHandler *qdev_get_hotplug_handler(DeviceState *dev)
> +{
> +    HotplugHandler *hotplug_ctrl = NULL;
> +
> +    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);
> +        }
> +    }
> +    return hotplug_ctrl;
> +}
> +
>  void qdev_unplug(DeviceState *dev, Error **errp)
>  {
>      DeviceClass *dc = DEVICE_GET_CLASS(dev);
> +    HotplugHandler *hotplug_ctrl;
> +    HotplugHandlerClass *hdc;
> 
>      if (dev->parent_bus && !qbus_is_hotpluggable(dev->parent_bus)) {
>          error_set(errp, QERR_BUS_NO_HOTPLUG, dev->parent_bus->name);

Unlike x86 CPU that sits on ICC bus, PowerPC CPU doesn't sit on any bus.
I was under the impression that this patch helps in unplugging such
devices. However I do see some problems.

While trying to unplug a PowerPC CPU that has earlier been added using
device_add, qdev-monitor.c:qmp_device_del() fails to find/locate the
device since the device isn't on any bus and hence qdev_unplug() won't
be called for such a device. I thought I could make "main_system_bus" as
the parent bus of this CPU device but that wouldn't help during unplugging.
With that qmp_device_del() can find the device, but qdev_uplug() fails at the
above if condition since "main_system_bus" isn't hotpluggable.

So how should we deal with such devices which don't have any parent bus ?

Regards,
Bharata.