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

[Igor Mammedov]

On Wed, 1 Oct 2014 16:22:23 +0530
Bharata B Rao <address@hidden> wrote:

> 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.
Thanks for confirming, I'll try to rewrite above path to a more
acceptable form and post it as follow up to this series, hopefully
tomorrow.

Andreas,
 is it acceptable or should I respin fixedup 36/36 instead?

> 
> 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 ?
device_del completion doesn't work yet.
there was patches on the list to this end /search for 'completion'
keyword in subject/

> 
> Regards,
> Bharata.
> 
>