Re: [Qemu-devel] [PATCH 23/35] acpi:piix4: make plug/unlug callbacks generic

[Michael S. Tsirkin]

On Mon, Apr 07, 2014 at 03:12:11PM +0200, Igor Mammedov wrote:
> On Mon, 7 Apr 2014 15:07:15 +0300
> "Michael S. Tsirkin" <address@hidden> wrote:
> 
> > On Mon, Apr 07, 2014 at 02:00:37PM +0200, Igor Mammedov wrote:
> > > On Mon, 7 Apr 2014 14:32:41 +0300
> > > "Michael S. Tsirkin" <address@hidden> wrote:
> > > 
> > > > On Fri, Apr 04, 2014 at 03:36:48PM +0200, Igor Mammedov wrote:
> > > > > ... and report error if plugged in device is not supported.
> > > > > Later generic callbacks will be used by memory hotplug.
> > > > > 
> > > > > Signed-off-by: Igor Mammedov <address@hidden>
> > > > 
> > > > 
> > > > OK in that case, how about teaching all hotplug callbacks about this?
> > > > 
> > > > There are two ATM:
> > > > shpc_device_hotplug_cb
> > > > pcie_cap_slot_hotplug_cb
> > > > 
> > > > Teach them both to fail gracefully if they get
> > > > an object that is not a pci device.
> > > > 
> > > > Afterwards, simply iterate over all objects of type
> > > > TYPE_HOTPLUG_HANDLER
> > > > and look for one that will accept your object.
> > > Then you would never know if any hotplug handler has actually
> > > handled event.
> > 
> > Why not? Check the error.
> > If no one accepts your object, return error to user.
> > 
> > > I think hotplug handler should return error if unsupported
> > > device passed in rather than ignore it. It makes catching
> > > wiring errors easier.
> > 
> > Absolutely.
> > 
> > > Dropping error so that we could not care which hotplug handler
> > > should be notified, looks like a wrong direction and makes
> > > system more fragile.
> > 
> > That's not what I was suggesting.
> > 
> > > It shouldn't be up to consumer to determine that event should
> > > be routed to it, but rather by external routing that knows
> > > what and when should be notified.
> > 
> > Yes. So
> > 
> >     for each hotplug handler (&err)
> >             handler->plug(device, &err)
> >             if (!err)
> >                     break;
> here it would break on the first handler that doesn't support device
> and tells so to caller.

This is pseudo-code, I really mean !err == no error reported.

> And there isn't any routing here, it just blindly broadcast to every
> handler, regardless whether it's right or not.

Yes - handlers verify what they can support.

> If broadcast should be ever done than it probably should be a part of
> DEVICE class and part of
>   [Qemu-devel] [PATCH 08/35] qdev: hotplug for buss-less devices
> patch and be generic to all devices.

Not sure what's suggested here.

> 
> Andreas,
>   since you care about QDEV
>   do you have an opinion on ^^^ discussion?
> 
> > 
> > 
> >     if (err)
> >             hotplug failed - destroy device
> > 
> > 
> > > > 
> > > > 
> > > > > ---
> > > > >  hw/acpi/piix4.c | 31 ++++++++++++++++++++++---------
> > > > >  1 file changed, 22 insertions(+), 9 deletions(-)
> > > > > 
> > > > > diff --git a/hw/acpi/piix4.c b/hw/acpi/piix4.c
> > > > > index 67dc075..4341f82 100644
> > > > > --- a/hw/acpi/piix4.c
> > > > > +++ b/hw/acpi/piix4.c
> > > > > @@ -310,19 +310,32 @@ static void piix4_pm_powerdown_req(Notifier *n, 
> > > > > void *opaque)
> > > > >      acpi_pm1_evt_power_down(&s->ar);
> > > > >  }
> > > > >  
> > > > > -static void piix4_pci_device_plug_cb(HotplugHandler *hotplug_dev,
> > > > > -                                     DeviceState *dev, Error **errp)
> > > > > +static void piix4_device_plug_cb(HotplugHandler *hotplug_dev,
> > > > > +                                 DeviceState *dev, Error **errp)
> > > > >  {
> > > > >      PIIX4PMState *s = PIIX4_PM(hotplug_dev);
> > > > > -    acpi_pcihp_device_plug_cb(&s->ar, s->irq, &s->acpi_pci_hotplug, 
> > > > > dev, errp);
> > > > > +
> > > > > +    if (object_dynamic_cast(OBJECT(dev), TYPE_PCI_DEVICE)) {
> > > > > +        acpi_pcihp_device_plug_cb(&s->ar, s->irq, 
> > > > > &s->acpi_pci_hotplug, dev,
> > > > > +                                  errp);
> > > > > +    } else {
> > > > > +        error_setg(errp, "acpi: device plug request for not 
> > > > > supported device"
> > > > > +                   " type: %s", object_get_typename(OBJECT(dev)));
> > > > > +    }
> > > > >  }
> > > > >  
> > > > > -static void piix4_pci_device_unplug_cb(HotplugHandler *hotplug_dev,
> > > > > -                                       DeviceState *dev, Error 
> > > > > **errp)
> > > > > +static void piix4_device_unplug_cb(HotplugHandler *hotplug_dev,
> > > > > +                                   DeviceState *dev, Error **errp)
> > > > >  {
> > > > >      PIIX4PMState *s = PIIX4_PM(hotplug_dev);
> > > > > -    acpi_pcihp_device_unplug_cb(&s->ar, s->irq, 
> > > > > &s->acpi_pci_hotplug, dev,
> > > > > -                                errp);
> > > > > +
> > > > > +    if (object_dynamic_cast(OBJECT(dev), TYPE_PCI_DEVICE)) {
> > > > > +        acpi_pcihp_device_unplug_cb(&s->ar, s->irq, 
> > > > > &s->acpi_pci_hotplug, dev,
> > > > > +                                    errp);
> > > > > +    } else {
> > > > > +        error_setg(errp, "acpi: device unplug request for not 
> > > > > supported device"
> > > > > +                   " type: %s", object_get_typename(OBJECT(dev)));
> > > > > +    }
> > > > >  }
> > > > >  
> > > > >  static void piix4_update_bus_hotplug(PCIBus *pci_bus, void *opaque)
> > > > > @@ -553,8 +566,8 @@ static void piix4_pm_class_init(ObjectClass 
> > > > > *klass, void *data)
> > > > >       */
> > > > >      dc->cannot_instantiate_with_device_add_yet = true;
> > > > >      dc->hotpluggable = false;
> > > > > -    hc->plug = piix4_pci_device_plug_cb;
> > > > > -    hc->unplug = piix4_pci_device_unplug_cb;
> > > > > +    hc->plug = piix4_device_plug_cb;
> > > > > +    hc->unplug = piix4_device_unplug_cb;
> > > > >  }
> > > > >  
> > > > >  static const TypeInfo piix4_pm_info = {
> > > > > -- 
> > > > > 1.9.0