Re: [Qemu-devel] [PATCH v2 02/27] qom: more documentation on subclassing

[Anthony Liguori <anthony@codemonkey.ws>]

On 02/04/2012 02:02 AM, Paolo Bonzini wrote:
> Signed-off-by: Paolo Bonzini<pbonzini@redhat.com>

Reviewed-by: Anthony Liguori <aliguori@us.ibm.com>

And thank you very much for adding to the docs!

Regards,

Anthony Liguori

> ---
>   include/qemu/object.h |   76 +++++++++++++++++++++++++++++++++++++++++++++++--
>   1 files changed, 73 insertions(+), 3 deletions(-)
>
> diff --git a/include/qemu/object.h b/include/qemu/object.h
> index ab1c48c..ad7d32d 100644
> --- a/include/qemu/object.h
> +++ b/include/qemu/object.h
> @@ -55,6 +55,9 @@ typedef struct InterfaceInfo InterfaceInfo;
>    *
>    * #define TYPE_MY_DEVICE "my-device"
>    *
> + * // No new virtual functions: we can reuse the typedef for the
> + * // superclass.
> + * typedef DeviceClass MyDeviceClass;
>    * typedef struct MyDevice
>    * {
>    *     DeviceState parent;
> @@ -88,8 +91,21 @@ typedef struct InterfaceInfo InterfaceInfo;
>    *
>    * Using object_new(), a new #Object derivative will be instantiated.  You can
>    * cast an #Object to a subclass (or base-class) type using
> - * object_dynamic_cast().  You typically want to define a macro wrapper around
> - * object_dynamic_cast_assert() to make it easier to convert to a specific type.
> + * object_dynamic_cast().  You typically want to define macro wrappers around
> + * OBJECT_CHECK() and OBJECT_CLASS_CHECK() to make it easier to convert to a
> + * specific type:
> + *
> + *<example>
> + *<title>Typecasting macros</title>
> + *<programlisting>
> + *    #define MY_DEVICE_GET_CLASS(obj) \
> + *       OBJECT_GET_CLASS(MyDeviceClass, obj, TYPE_MY_DEVICE)
> + *    #define MY_DEVICE_CLASS(klass) \
> + *       OBJECT_CLASS_CHECK(MyDeviceClass, klass, TYPE_MY_DEVICE)
> + *    #define MY_DEVICE(obj) \
> + *       OBJECT_CHECK(MyDevice, obj, TYPE_MY_DEVICE)
> + *</programlisting>
> + *</example>
>    *
>    * # Class Initialization #
>    *
> @@ -108,7 +124,61 @@ typedef struct InterfaceInfo InterfaceInfo;
>    *
>    * Once all of the parent classes have been initialized, #TypeInfo::class_init
>    * is called to let the class being instantiated provide default initialize for
> - * it's virtual functions.
> + * it's virtual functions.  Here is how the above example might be modified
> + * to introduce an overridden virtual function:
> + *
> + *<example>
> + *<title>Overriding a virtual function</title>
> + *<programlisting>
> + * #include "qdev.h"
> + *
> + * void my_device_class_init(ObjectClass *klass, void *class_data)
> + * {
> + *     DeviceClass *dc = DEVICE_CLASS(klass);
> + *     dc->reset = my_device_reset;
> + * }
> + *
> + * static TypeInfo my_device_info = {
> + *     .name = TYPE_MY_DEVICE,
> + *     .parent = TYPE_DEVICE,
> + *     .instance_size = sizeof(MyDevice),
> + *     .class_init = my_device_class_init,
> + * };
> + *</programlisting>
> + *</example>
> + *
> + * Introducing new virtual functions requires a class to define its own
> + * struct and to add a .class_size member to the TypeInfo.  Each function
> + * will also have a wrapper to call it easily:
> + *
> + *<example>
> + *<title>Defining an abstract class</title>
> + *<programlisting>
> + * #include "qdev.h"
> + *
> + * typedef struct MyDeviceClass
> + * {
> + *     DeviceClass parent;
> + *
> + *     void (*frobnicate) (MyDevice *obj);
> + * } MyDeviceClass;
> + *
> + * static TypeInfo my_device_info = {
> + *     .name = TYPE_MY_DEVICE,
> + *     .parent = TYPE_DEVICE,
> + *     .instance_size = sizeof(MyDevice),
> + *     .abstract = true, // or set a default in my_device_class_init
> + *     .class_size = sizeof(MyDeviceClass),
> + * };
> + *
> + * void my_device_frobnicate(MyDevice *obj)
> + * {
> + *     MyDeviceClass *klass = MY_DEVICE_GET_CLASS(obj);
> + *
> + *     klass->frobnicate(obj);
> + * }
> + *</programlisting>
> + *</example>
>    *
>    * # Interfaces #
>    *