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

[Bharata B Rao]

On Wed, Oct 01, 2014 at 11:57:37AM +0200, Igor Mammedov wrote:
> On Wed, 1 Oct 2014 14:27:19 +0530
> Bharata B Rao <address@hidden> wrote:
> 
> > On Fri, Sep 26, 2014 at 09:28:41AM +0000, Igor Mammedov wrote:
> > > Signed-off-by: Igor Mammedov <address@hidden>
> > > ---
> > > 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.
> Indeed, this patch goes only half way for supporting unplug of bussless
> devices (i.e. it only fetches unplug handler without addressing device
> lookup issue)
> 
> > 
> > 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 ?
> There is no need to invent non existing BUS. We should fix lookup issue
> instead of it. Doing something along this lines:
> https://lists.nongnu.org/archive/html/qemu-devel/2014-08/msg04574.html
> 
> Above of cause assumes that device is placed in 'peripherals' tree.
> Does above patch fixes issue?

Yes it does fix the issue. Thanks.

However device_del command completion isn't showing my CPU device. I guess
the patch you mentioned should take care of looking up in the peripherals
tree in monitor.c:device_del_bus_completion() too ?

Regards,
Bharata.