Re: [Qemu-devel] [PATCH v2 17/19] s390x: CPU hot unplug via device_del cannot work

[Matthew Rosato <mjrosato@linux.vnet.ibm.com>]

On 09/04/2017 11:43 AM, David Hildenbrand wrote:
> device_del on a CPU will currently do nothing. Let's emmit an error
> telling that this is will never work (there is no architecture support
> on s390x). Error message copied from ppc.
> 
> (qemu) device_del cpu1
> device_del cpu1
> CPU hot unplug not supported on this machine
> 
> Signed-off-by: David Hildenbrand <david@redhat.com>

Architecture discussions aside, this code will work as-is to prevent CPU
unplug.  Add "currently" as Christian suggests and:

Reviewed-by: Matthew Rosato <mjrosato@linux.vnet.ibm.com>

> ---
>  hw/s390x/s390-virtio-ccw.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
> index 22a8a1b45d..dd149567bb 100644
> --- a/hw/s390x/s390-virtio-ccw.c
> +++ b/hw/s390x/s390-virtio-ccw.c
> @@ -338,6 +338,15 @@ static void s390_machine_device_plug(HotplugHandler *hotplug_dev,
>      }
>  }
> 
> +static void s390_machine_device_unplug_request(HotplugHandler *hotplug_dev,
> +                                               DeviceState *dev, Error **errp)
> +{
> +    if (object_dynamic_cast(OBJECT(dev), TYPE_CPU)) {
> +        error_setg(errp, "CPU hot unplug not supported on this machine");
> +        return;
> +    }
> +}
> +
>  static HotplugHandler *s390_get_hotplug_handler(MachineState *machine,
>                                                  DeviceState *dev)
>  {
> @@ -387,6 +396,7 @@ static void ccw_machine_class_init(ObjectClass *oc, void *data)
>      mc->max_cpus = 248;
>      mc->get_hotplug_handler = s390_get_hotplug_handler;
>      hc->plug = s390_machine_device_plug;
> +    hc->unplug_request = s390_machine_device_unplug_request;
>      nc->nmi_monitor_handler = s390_nmi;
>  }
>