Re: [Xen-devel] [PATCH v3 1/2] Add device listener interface

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Igor Mammedov [mailto:imammedo@xxxxxxxxxx]
> Sent: 15 October 2014 10:54
> To: Paul Durrant
> Cc: qemu-devel@xxxxxxxxxx; xen-devel@xxxxxxxxxxxxxxxxxxxx; Michael S.
> Tsirkin; Andreas Faerber"; Paolo Bonzini; Peter Crosthwaite; Igor
> Mammedov; Markus Armbruster; Thomas Huth; Christian Borntraeger
> Subject: Re: [PATCH v3 1/2] Add device listener interface
> 
> On Wed, 15 Oct 2014 10:16:38 +0100
> Paul Durrant <paul.durrant@xxxxxxxxxx> wrote:
> 
> > The Xen ioreq-server API, introduced in Xen 4.5, requires that PCI
> > device models explicitly register with Xen for config space accesses.
> > This patch adds a listener interface into qdev-core which can be used
> > by the Xen interface code to monitor for arrival and departure of PCI
> > devices.
> 
> If you need only one listener handler for your case, why you couldn't
> use hotplug interface instead of listerners?
> to me it looks like it should work for this case.
> To make it work xen code would need to override default plug/unplug
> handlers on PCI bus and do register/unregister from there.
> 

That sounds a bit ugly. A pci or now qdev listener interface seems more elegant 
and generally useful.

> One thing is that unplug handler is not defined for PCI bus yet,
> to get it work one would need to refactor pcihp/bridge/pcie unplug
> path to call unplug handler before object_unparent().
> 

Yes - that makes it a much more intrusive modification.

  Paul

> 
> >
> > Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
> > Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>
> > Cc: Andreas Faerber" <afaerber@xxxxxxx>
> > Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> > Cc: Peter Crosthwaite <peter.crosthwaite@xxxxxxxxxx>
> > Cc: Igor Mammedov <imammedo@xxxxxxxxxx>
> > Cc: Markus Armbruster <armbru@xxxxxxxxxx>
> > Cc: Thomas Huth <thuth@xxxxxxxxxxxxxxxxxx>
> > Cc: Christian Borntraeger <borntraeger@xxxxxxxxxx>
> > ---
> >  hw/core/qdev.c          |   54
> > +++++++++++++++++++++++++++++++++++++++++++++++
> > include/hw/qdev-core.h  |   10 +++++++++ include/qemu/typedefs.h |
> > 1 + 3 files changed, 65 insertions(+)
> >
> > diff --git a/hw/core/qdev.c b/hw/core/qdev.c
> > index fcb1638..4a9c1f6 100644
> > --- a/hw/core/qdev.c
> > +++ b/hw/core/qdev.c
> > @@ -175,6 +175,56 @@ int qdev_init(DeviceState *dev)
> >      return 0;
> >  }
> >
> > +static QTAILQ_HEAD(qdev_listeners, DeviceListener) qdev_listeners
> > +    = QTAILQ_HEAD_INITIALIZER(qdev_listeners);
> > +
> > +enum ListenerDirection { Forward, Reverse };
> > +
> > +#define QDEV_LISTENER_CALL(_callback, _direction, _args...)     \
> > +    do {                                                        \
> > +        DeviceListener *_listener;                              \
> > +                                                                \
> > +        switch (_direction) {                                   \
> > +        case Forward:                                           \
> > +            QTAILQ_FOREACH(_listener, &qdev_listeners, link) {  \
> > +                if (_listener->_callback) {                     \
> > +                    _listener->_callback(_listener, ##_args);   \
> > +                }                                               \
> > +            }                                                   \
> > +            break;                                              \
> > +        case Reverse:                                           \
> > +            QTAILQ_FOREACH_REVERSE(_listener, &qdev_listeners,  \
> > +                                   qdev_listeners, link) {      \
> > +                if (_listener->_callback) {                     \
> > +                    _listener->_callback(_listener, ##_args);   \
> > +                }                                               \
> > +            }                                                   \
> > +            break;                                              \
> > +        default:                                                \
> > +            abort();                                            \
> > +        }                                                       \
> > +    } while (0)
> > +
> > +static int qdev_listener_add(DeviceState *dev, void *opaque)
> > +{
> > +    QDEV_LISTENER_CALL(realize, Forward, dev);
> > +
> > +    return 0;
> > +}
> > +
> > +void qdev_listener_register(DeviceListener *listener)
> > +{
> > +    QTAILQ_INSERT_TAIL(&qdev_listeners, listener, link);
> > +
> > +    qbus_walk_children(sysbus_get_default(), NULL, NULL,
> > qdev_listener_add,
> > +                       NULL, NULL);
> > +}
> > +
> > +void qdev_listener_unregister(DeviceListener *listener)
> > +{
> > +    QTAILQ_REMOVE(&qdev_listeners, listener, link);
> > +}
> > +
> >  static void device_realize(DeviceState *dev, Error **errp)
> >  {
> >      DeviceClass *dc = DEVICE_GET_CLASS(dev);
> > @@ -186,12 +236,16 @@ static void device_realize(DeviceState *dev,
> > Error **errp) return;
> >          }
> >      }
> > +
> > +    QDEV_LISTENER_CALL(realize, Forward, dev);
> >  }
> >
> >  static void device_unrealize(DeviceState *dev, Error **errp)
> >  {
> >      DeviceClass *dc = DEVICE_GET_CLASS(dev);
> >
> > +    QDEV_LISTENER_CALL(unrealize, Reverse, dev);
> > +
> >      if (dc->exit) {
> >          int rc = dc->exit(dev);
> >          if (rc < 0) {
> > diff --git a/include/hw/qdev-core.h b/include/hw/qdev-core.h
> > index 178fee2..f2dc267 100644
> > --- a/include/hw/qdev-core.h
> > +++ b/include/hw/qdev-core.h
> > @@ -167,6 +167,12 @@ struct DeviceState {
> >      int alias_required_for_version;
> >  };
> >
> > +struct DeviceListener {
> > +    void (*realize)(DeviceListener *listener, DeviceState *dev);
> > +    void (*unrealize)(DeviceListener *listener, DeviceState *dev);
> > +    QTAILQ_ENTRY(DeviceListener) link;
> > +};
> > +
> >  #define TYPE_BUS "bus"
> >  #define BUS(obj) OBJECT_CHECK(BusState, (obj), TYPE_BUS)
> >  #define BUS_CLASS(klass) OBJECT_CLASS_CHECK(BusClass, (klass),
> > TYPE_BUS) @@ -368,4 +374,8 @@ static inline void
> > qbus_set_hotplug_handler(BusState *bus, DeviceState *handler,
> > QDEV_HOTPLUG_HANDLER_PROPERTY, errp); bus->allow_hotplug = 1;
> >  }
> > +
> > +void qdev_listener_register(DeviceListener *listener);
> > +void qdev_listener_unregister(DeviceListener *listener);
> > +
> >  #endif
> > diff --git a/include/qemu/typedefs.h b/include/qemu/typedefs.h
> > index 04df51b..e32bca2 100644
> > --- a/include/qemu/typedefs.h
> > +++ b/include/qemu/typedefs.h
> > @@ -20,6 +20,7 @@ typedef struct Property Property;
> >  typedef struct PropertyInfo PropertyInfo;
> >  typedef struct CompatProperty CompatProperty;
> >  typedef struct DeviceState DeviceState;
> > +typedef struct DeviceListener DeviceListener;
> >  typedef struct BusState BusState;
> >  typedef struct BusClass BusClass;
> >


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