path: root/include/qemu/object.h

/*
 * QEMU Object Model
 *
 * Copyright IBM, Corp. 2011
 *
 * Authors:
 *  Anthony Liguori   <aliguori@us.ibm.com>
 *
 * This work is licensed under the terms of the GNU GPL, version 2 or later.
 * See the COPYING file in the top-level directory.
 *
 */

#ifndef QEMU_OBJECT_H
#define QEMU_OBJECT_H

#include <glib.h>
#include <stdint.h>
#include <stdbool.h>

struct TypeImpl;
typedef struct TypeImpl *Type;

typedef struct ObjectClass ObjectClass;
typedef struct Object Object;

typedef struct TypeInfo TypeInfo;

typedef struct InterfaceClass InterfaceClass;
typedef struct InterfaceInfo InterfaceInfo;

#define TYPE_OBJECT NULL

/**
 * SECTION:object.h
 * @title:Base Object Type System
 * @short_description: interfaces for creating new types and objects
 *
 * The QEMU Object Model provides a framework for registering user creatable
 * types and instantiating objects from those types.  QOM provides the following
 * features:
 *
 *  - System for dynamically registering types
 *  - Support for single-inheritance of types
 *  - Multiple inheritance of stateless interfaces
 *
 * <example>
 *   <title>Creating a minimal type</title>
 *   <programlisting>
 * #include "qdev.h"
 *
 * #define TYPE_MY_DEVICE "my-device"
 *
 * typedef struct MyDevice
 * {
 *     DeviceState parent;
 *
 *     int reg0, reg1, reg2;
 * } MyDevice;
 *
 * static TypeInfo my_device_info = {
 *     .name = TYPE_MY_DEVICE,
 *     .parent = TYPE_DEVICE,
 *     .instance_size = sizeof(MyDevice),
 * };
 *
 * static void my_device_module_init(void)
 * {
 *     type_register_static(&my_device_info);
 * }
 *
 * device_init(my_device_module_init);
 *   </programlisting>
 * </example>
 *
 * In the above example, we create a simple type that is described by #TypeInfo.
 * #TypeInfo describes information about the type including what it inherits
 * from, the instance and class size, and constructor/destructor hooks.
 *
 * Every type has an #ObjectClass associated with it.  #ObjectClass derivatives
 * are instantiated dynamically but there is only ever one instance for any
 * given type.  The #ObjectClass typically holds a table of function pointers
 * for the virtual methods implemented by this type.
 *
 * 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.
 *
 * # Class Initialization #
 *
 * Before an object is initialized, the class for the object must be
 * initialized.  There is only one class object for all instance objects
 * that is created lazily.
 *
 * Classes are initialized by first initializing any parent classes (if
 * necessary).  After the parent class object has initialized, it will be
 * copied into the current class object and any additional storage in the
 * class object is zero filled.
 *
 * The effect of this is that classes automatically inherit any virtual
 * function pointers that the parent class has already initialized.  All
 * other fields will be zero filled.
 *
 * 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.
 *
 * # Interfaces #
 *
 * Interfaces allow a limited form of multiple inheritance.  Instances are
 * similar to normal types except for the fact that are only defined by
 * their classes and never carry any state.  You can dynamically cast an object
 * to one of its #Interface types and vice versa.
 */

/**
 * ObjectClass:
 *
 * The base for all classes.  The only thing that #ObjectClass contains is an
 * integer type handle.
 */
struct ObjectClass
{
    /*< private >*/
    Type type;
};

/**
 * Object:
 *
 * The base for all objects.  The first member of this object is a pointer to
 * a #ObjectClass.  Since C guarantees that the first member of a structure
 * always begins at byte 0 of that structure, as long as any sub-object places
 * its parent as the first member, we can cast directly to a #Object.
 *
 * As a result, #Object contains a reference to the objects type as its
 * first member.  This allows identification of the real type of the object at
 * run time.
 *
 * #Object also contains a list of #Interfaces that this object
 * implements.
 */
struct Object
{
    /*< private >*/
    ObjectClass *class;

    GSList *interfaces;
};

/**
 * TypeInfo:
 * @name: The name of the type.
 * @parent: The name of the parent type.
 * @instance_size: The size of the object (derivative of #Object).  If
 *   @instance_size is 0, then the size of the object will be the size of the
 *   parent object.
 * @instance_init: This function is called to initialize an object.  The parent
 *   class will have already been initialized so the type is only responsible
 *   for initializing its own members.
 * @instance_finalize: This function is called during object destruction.  This
 *   is called before the parent @instance_finalize function has been called.
 *   An object should only free the members that are unique to its type in this
 *   function.
 * @abstract: If this field is true, then the class is considered abstract and
 *   cannot be directly instantiated.
 * @class_size: The size of the class object (derivative of #ObjectClass)
 *   for this object.  If @class_size is 0, then the size of the class will be
 *   assumed to be the size of the parent class.  This allows a type to avoid
 *   implementing an explicit class type if they are not adding additional
 *   virtual functions.
 * @class_init: This function is called after all parent class initialization
 *   has occured to allow a class to set its default virtual method pointers.  
 *   This is also the function to use to override virtual methods from a parent
 *   class.
 * @class_finalize: This function is called during class destruction and is
 *   meant to release and dynamic parameters allocated by @class_init.
 * @class_data: Data to pass to the @class_init and @class_finalize functions.
 *   This can be useful when building dynamic classes.
 * @interfaces: The list of interfaces associated with this type.  This
 *   should point to a static array that's terminated with a zero filled
 *   element.
 */
struct TypeInfo
{
    const char *name;
    const char *parent;

    size_t instance_size;
    void (*instance_init)(Object *obj);
    void (*instance_finalize)(Object *obj);

    bool abstract;
    size_t class_size;

    void (*class_init)(ObjectClass *klass, void *data);
    void (*class_finalize)(ObjectClass *klass, void *data);
    void *class_data;

    InterfaceInfo *interfaces;
};

/**
 * OBJECT:
 * @obj: A derivative of #Object
 *
 * Converts an object to a #Object.  Since all objects are #Objects,
 * this function will always succeed.
 */
#define OBJECT(obj) \
    ((Object *)(obj))

/**
 * OBJECT_CHECK:
 * @type: The C type to use for the return value.
 * @obj: A derivative of @type to cast.
 * @name: The QOM typename of @type
 *
 * A type safe version of @object_dynamic_cast_assert.  Typically each class
 * will define a macro based on this type to perform type safe dynamic_casts to
 * this object type.
 *
 * If an invalid object is passed to this function, a run time assert will be
 * generated.
 */
#define OBJECT_CHECK(type, obj, name) \
    ((type *)object_dynamic_cast_assert((Object *)(obj), (name)))

/**
 * OBJECT_CLASS_CHECK:
 * @class: The C type to use for the return value.
 * @obj: A derivative of @type to cast.
 * @name: the QOM typename of @class.
 *
 * A type safe version of @object_check_class.  This macro is typically wrapped
 * by each type to perform type safe casts of a class to a specific class type.
 */
#define OBJECT_CLASS_CHECK(class, obj, name) \
    ((class *)object_class_dynamic_cast_assert((ObjectClass *)(obj), (name)))

/**
 * OBJECT_GET_CLASS:
 * @class: The C type to use for the return value.
 * @obj: The object to obtain the class for.
 * @name: The QOM typename of @obj.
 *
 * This function will return a specific class for a given object.  Its generally
 * used by each type to provide a type safe macro to get a specific class type
 * from an object.
 */
#define OBJECT_GET_CLASS(class, obj, name) \
    OBJECT_CLASS_CHECK(class, object_get_class(OBJECT(obj)), name)

#define OBJECT_CLASS(class) \
    ((ObjectClass *)(class))

/**
 * InterfaceClass:
 * @parent_class: the base class
 *
 * The class for all interfaces.  Subclasses of this class should only add
 * virtual methods.
 */
struct InterfaceClass
{
    ObjectClass parent_class;
};

/**
 * InterfaceInfo:
 * @type: The name of the interface.
 * @interface_initfn: This method is called during class initialization and is
 *   used to initialize an interface associated with a class.  This function
 *   should initialize any default virtual functions for a class and/or override
 *   virtual functions in a parent class.
 *
 * The information associated with an interface.
 */
struct InterfaceInfo
{
    const char *type;

    void (*interface_initfn)(ObjectClass *class, void *data);
};

#define TYPE_INTERFACE "interface"

/**
 * object_new:
 * @typename: The name of the type of the object to instantiate.
 *
 * This function will initialize a new object using heap allocated memory.  This
 * function should be paired with object_delete() to free the resources
 * associated with the object.
 *
 * Returns: The newly allocated and instantiated object.
 */
Object *object_new(const char *typename);

/**
 * object_new_with_type:
 * @type: The type of the object to instantiate.
 *
 * This function will initialize a new object using heap allocated memory.  This
 * function should be paired with object_delete() to free the resources
 * associated with the object.
 *
 * Returns: The newly allocated and instantiated object.
 */
Object *object_new_with_type(Type type);

/**
 * object_delete:
 * @obj: The object to free.
 *
 * Finalize an object and then free the memory associated with it.  This should
 * be paired with object_new() to free the resources associated with an object.
 */
void object_delete(Object *obj);

/**
 * object_initialize_with_type:
 * @obj: A pointer to the memory to be used for the object.
 * @type: The type of the object to instantiate.
 *
 * This function will initialize an object.  The memory for the object should
 * have already been allocated.
 */
void object_initialize_with_type(void *data, Type type);

/**
 * object_initialize:
 * @obj: A pointer to the memory to be used for the object.
 * @typename: The name of the type of the object to instantiate.
 *
 * This function will initialize an object.  The memory for the object should
 * have already been allocated.
 */
void object_initialize(void *obj, const char *typename);

/**
 * object_finalize:
 * @obj: The object to finalize.
 *
 * This function destroys and object without freeing the memory associated with
 * it.
 */
void object_finalize(void *obj);

/**
 * object_dynamic_cast:
 * @obj: The object to cast.
 * @typename: The @typename to cast to.
 *
 * This function will determine if @obj is-a @typename.  @obj can refer to an
 * object or an interface associated with an object.
 *
 * Returns: This function returns @obj on success or #NULL on failure.
 */
Object *object_dynamic_cast(Object *obj, const char *typename);

/**
 * @object_dynamic_cast_assert:
 *
 * See object_dynamic_cast() for a description of the parameters of this
 * function.  The only difference in behavior is that this function asserts
 * instead of returning #NULL on failure.
 */
Object *object_dynamic_cast_assert(Object *obj, const char *typename);

/**
 * object_get_class:
 * @obj: A derivative of #Object
 *
 * Returns: The #ObjectClass of the type associated with @obj.
 */
ObjectClass *object_get_class(Object *obj);

/**
 * object_get_typename:
 * @obj: A derivative of #Object.
 *
 * Returns: The QOM typename of @obj.
 */
const char *object_get_typename(Object *obj);

/**
 * type_register_static:
 * @info: The #TypeInfo of the new type.
 *
 * @info and all of the strings it points to should exist for the life time
 * that the type is registered.
 *
 * Returns: 0 on failure, the new #Type on success.
 */
Type type_register_static(const TypeInfo *info);

/**
 * type_register:
 * @info: The #TypeInfo of the new type
 *
 * Unlike type_register_static(), this call does not require @info or it's
 * string members to continue to exist after the call returns.
 *
 * Returns: 0 on failure, the new #Type on success.
 */
Type type_register(const TypeInfo *info);

/**
 * object_class_dynamic_cast_assert:
 * @klass: The #ObjectClass to attempt to cast.
 * @typename: The QOM typename of the class to cast to.
 *
 * Returns: This function always returns @klass and asserts on failure.
 */
ObjectClass *object_class_dynamic_cast_assert(ObjectClass *klass,
                                              const char *typename);

ObjectClass *object_class_dynamic_cast(ObjectClass *klass,
                                       const char *typename);

/**
 * object_class_get_name:
 * @klass: The class to obtain the QOM typename for.
 *
 * Returns: The QOM typename for @klass.
 */
const char *object_class_get_name(ObjectClass *klass);

ObjectClass *object_class_by_name(const char *typename);

void object_class_foreach(void (*fn)(ObjectClass *klass, void *opaque),
                          void *opaque);

#endif