Re: [Qemu-devel] [PATCH v5] qom, qmp, hmp, qapi: create qom-type-prop-list for class properties

[Eduardo Habkost]

On Sun, Jan 31, 2016 at 04:40:54PM +0300, Valentin Rakush wrote:
> Hi Eduardo,
> 
> I will try to answer some of your questions at this email and will answer
> other questions later.
> 
> > Can you clarify what you mean by "TYPE_DEVICE has its own
> > properties"? TYPE_DEVICE properties are registered as normal QOM
> > properties.
> 
> It is possible that I do not understand object model correctly....
> 
> This commit 16bf7f522a2f adds GHashTable *properties; to the ObjectClass
> struct in the include/qom/object.h
> The typedef struct DeviceClass from include/hw/qdev-core.h is inherited
> from ObjectClass. Also DeviceClass has it own properties
> Property *props.
> 
> In the device_list_properties we call
> 
> static DevicePropertyInfo *make_device_property_info
> 
> Which tries to downcast class to DEVICE_CLASS
> 
> for (prop = DEVICE_CLASS(klass)->props; prop && prop->name; prop++) {
> 
> So we are using Property *props, defined in the DeviceClass, but we do not
> use GHashTable * properties, defined in the ObjectClass. Here I mean that
> DeviceClass has its own properties.

Oh, I misunderstood you. I was talking about object properties,
the ones at Object::properties. Yes, in this case we have
duplication between DeviceClass::props and
ObjectClass::properties.

> 
> > I don't understand what you mean, here. GlobalProperties are not
> > machine properties, they are just property=value pairs to be
> > registered as global properties. They are unrelated to the
> > properties TYPE_MACHINE actually has.
> 
> Same here. The struct MachineClass is defined in the include/hw/boards.h It
> has a member GlobalProperty *compat_props;
> But after commit 16bf7f522a2f it would be better to use ObjectClass
> properties. IMHO. I did not check how compat_props are used in the code yet.

In this case it's different: ObjectClass::compat_props are not
machine properties. They are just property=value pairs to be
registered as global properties when running the machine. They
will never appear in qom-type-prop-list because they are a
completely different thing.

> 
> > Could you clarify what you mean by "process different classes
> > differently"?
> 
> In the list_device_properties function we should have several conditional
> statements like
> 
> if (machine = object_class_dynamic_cast(class, TYPE_MACHINE)) {
> /* process machine properties using MachineClass GlobalProperty
> *compat_props; */
> }
> else if (machine = object_class_dynamic_cast(class, TYPE_DEVICE)) {
> /* process device class properties, using DeviceClass Property *props; */
> }
> else if (machine = object_class_dynamic_cast(class, TYPE_CPU)) {
> /* process CPU, using ObjectClass GHashTable *properties; */
> }

You don't have to, if you just do object_new() like
qmp_device_list_properties() does. Both ObjectClass::properties
and DeviceClas::props are translated to object instance
properties (Object::properties).

> 
> > 5) -cpu options:
> >
> > Ditto. the list will be incomplete unless all CPU subclasses are
> > converted to use only class-properties, or the new command uses
> > object_new().
> 
> This is a use case that I initially tried to implement.

This use case can be implemented easily using object_new(), like
qmp_device_list_properties() already does.

-- 
Eduardo