QEMU源码全解析38 —— Machine（8）-Toy模板网

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接前一篇文章：QEMU源码全解析37 —— Machine（7）

本文内容参考：

《趣谈Linux操作系统》 —— 刘超，极客时间

《QEMU/KVM》源码解析与应用 —— 李强，机械工业出版社

特此致谢！

上一回经过了重重周折，终于找到了MACHINE的定义所在：

OBJECT_DECLARE_TYPE(MachineState, MachineClass, MACHINE)

本回就详细解析一下这段代码。别看代码只有一行，内容还是蛮多的。

OBJECT_DECLARE_TYPE是一个宏，在include/qom/object.h中定义，代码如下：

/**
 * OBJECT_DECLARE_TYPE:
 * @InstanceType: instance struct name
 * @ClassType: class struct name
 * @MODULE_OBJ_NAME: the object name in uppercase with underscore separators
 *
 * This macro is typically used in a header file, and will:
 *
 *   - create the typedefs for the object and class structs
 *   - register the type for use with g_autoptr
 *   - provide three standard type cast functions
 *
 * The object struct and class struct need to be declared manually.
 */
#define OBJECT_DECLARE_TYPE(InstanceType, ClassType, MODULE_OBJ_NAME) \
    typedef struct InstanceType InstanceType; \
    typedef struct ClassType ClassType; \
    \
    G_DEFINE_AUTOPTR_CLEANUP_FUNC(InstanceType, object_unref) \
    \
    DECLARE_OBJ_CHECKERS(InstanceType, ClassType, \
                         MODULE_OBJ_NAME, TYPE_##MODULE_OBJ_NAME)

这里边又涉及到两个宏：G_DEFINE_AUTOPTR_CLEANUP_FUNC和DECLARE_OBJ_CHECKERS。重点关注后一个。

DECLARE_OBJ_CHECKERS宏实际上就在OBJECT_DECLARE_TYPE宏的上边，代码如下：

/**
 * DECLARE_OBJ_CHECKERS:
 * @InstanceType: instance struct name
 * @ClassType: class struct name
 * @OBJ_NAME: the object name in uppercase with underscore separators
 * @TYPENAME: type name
 *
 * Direct usage of this macro should be avoided, and the complete
 * OBJECT_DECLARE_TYPE macro is recommended instead.
 *
 * This macro will provide the three standard type cast functions for a
 * QOM type.
 */
#define DECLARE_OBJ_CHECKERS(InstanceType, ClassType, OBJ_NAME, TYPENAME) \
    DECLARE_INSTANCE_CHECKER(InstanceType, OBJ_NAME, TYPENAME) \
    \
    DECLARE_CLASS_CHECKERS(ClassType, OBJ_NAME, TYPENAME)

这里边又包含了DECLARE_INSTANCE_CHECKER和DECLARE_CLASS_CHECKERS两个宏定义。打破砂锅问到底，看看这两个宏的代码，实际上就在DECLARE_OBJ_CHECKERS宏的上边。

/**
 * DECLARE_INSTANCE_CHECKER:
 * @InstanceType: instance struct name
 * @OBJ_NAME: the object name in uppercase with underscore separators
 * @TYPENAME: type name
 *
 * Direct usage of this macro should be avoided, and the complete
 * OBJECT_DECLARE_TYPE macro is recommended instead.
 *
 * This macro will provide the instance type cast functions for a
 * QOM type.
 */
#define DECLARE_INSTANCE_CHECKER(InstanceType, OBJ_NAME, TYPENAME) \
    static inline G_GNUC_UNUSED InstanceType * \
    OBJ_NAME(const void *obj) \
    { return OBJECT_CHECK(InstanceType, obj, TYPENAME); }

/**
 * DECLARE_CLASS_CHECKERS:
 * @ClassType: class struct name
 * @OBJ_NAME: the object name in uppercase with underscore separators
 * @TYPENAME: type name
 *
 * Direct usage of this macro should be avoided, and the complete
 * OBJECT_DECLARE_TYPE macro is recommended instead.
 *
 * This macro will provide the class type cast functions for a
 * QOM type.
 */
#define DECLARE_CLASS_CHECKERS(ClassType, OBJ_NAME, TYPENAME) \
    static inline G_GNUC_UNUSED ClassType * \
    OBJ_NAME##_GET_CLASS(const void *obj) \
    { return OBJECT_GET_CLASS(ClassType, obj, TYPENAME); } \
    \
    static inline G_GNUC_UNUSED ClassType * \
    OBJ_NAME##_CLASS(const void *klass) \
    { return OBJECT_CLASS_CHECK(ClassType, klass, TYPENAME); }

好了，现在各个宏定义基本都已经给出了（G_DEFINE_AUTOPTR_CLEANUP_FUNC暂时不展开），开始逐层展开，到底看看完全展开之后是个内容。

第1层：

#define OBJECT_DECLARE_TYPE(InstanceType, ClassType, MODULE_OBJ_NAME) \
    typedef struct InstanceType InstanceType; \
    typedef struct ClassType ClassType; \
    \
    G_DEFINE_AUTOPTR_CLEANUP_FUNC(InstanceType, object_unref) \
    \
    DECLARE_OBJ_CHECKERS(InstanceType, ClassType, \
                         MODULE_OBJ_NAME, TYPE_##MODULE_OBJ_NAME)

代入

OBJECT_DECLARE_TYPE(MachineState, MachineClass, MACHINE)

中的实际值：InstanceType <-> MachineState，ClassType <-> MachineClass，MODULE_OBJ_NAME <-> MACHINE，得到：

    typedef struct MachineState MachineState;
    typedef struct MachineClass MachineClass;

    G_DEFINE_AUTOPTR_CLEANUP_FUNC(MachineState, object_unref)

    DECLARE_OBJ_CHECKERS(MachineState, MachineClass, \
                         MACHINE, TYPE_MACHINE)

第2层：

#define DECLARE_OBJ_CHECKERS(InstanceType, ClassType, OBJ_NAME, TYPENAME) \
    DECLARE_INSTANCE_CHECKER(InstanceType, OBJ_NAME, TYPENAME) \
    \
    DECLARE_CLASS_CHECKERS(ClassType, OBJ_NAME, TYPENAME)

代入

DECLARE_OBJ_CHECKERS(MachineState, MachineClass, \
                         MACHINE, TYPE_MACHINE)

中的实际值：InstanceType <-> MachineState，ClassType <-> MachineClass，OBJ_NAME <-> MACHINE，TYPENAME <-> TYPE_MACHINE，得到：

    DECLARE_INSTANCE_CHECKER(MachineState, MACHINE, TYPE_MACHINE) 

    DECLARE_CLASS_CHECKERS(MachineClass, MACHINE, TYPE_MACHINE)

第3层：

#define DECLARE_INSTANCE_CHECKER(InstanceType, OBJ_NAME, TYPENAME) \
    static inline G_GNUC_UNUSED InstanceType * \
    OBJ_NAME(const void *obj) \
    { return OBJECT_CHECK(InstanceType, obj, TYPENAME); }

和

#define DECLARE_CLASS_CHECKERS(ClassType, OBJ_NAME, TYPENAME) \
    static inline G_GNUC_UNUSED ClassType * \
    OBJ_NAME##_GET_CLASS(const void *obj) \
    { return OBJECT_GET_CLASS(ClassType, obj, TYPENAME); } \
    \
    static inline G_GNUC_UNUSED ClassType * \
    OBJ_NAME##_CLASS(const void *klass) \
    { return OBJECT_CLASS_CHECK(ClassType, klass, TYPENAME); }

分别代入

    DECLARE_INSTANCE_CHECKER(MachineState, MACHINE, TYPE_MACHINE) 

    DECLARE_CLASS_CHECKERS(MachineClass, MACHINE, TYPE_MACHINE)

中的实际值：InstanceType <-> MachineState，OBJ_NAME <-> MACHINE，TYPENAME <-> TYPE_MACHINE；ClassType <-> MachineClass，OBJ_NAME <-> MACHINE，TYPENAME <-> TYPE_MACHINE分别得到：

    static inline G_GNUC_UNUSED MachineState * 
    MACHINE(const void *obj)
    { return OBJECT_CHECK(MachineState, obj, TYPE_MACHINE); }

    static inline G_GNUC_UNUSED MachineClass * 
    MACHINE_GET_CLASS(const void *obj) 
    { return OBJECT_GET_CLASS(MachineClass, obj, TYPE_MACHINE); } 

    static inline G_GNUC_UNUSED MachineClass * 
    MACHINE_CLASS(const void *klass) 
    { return OBJECT_CLASS_CHECK(MachineClass, klass, TYPE_MACHINE); }

与上面综合，得到：

    typedef struct MachineState MachineState;
    typedef struct MachineClass MachineClass;

    G_DEFINE_AUTOPTR_CLEANUP_FUNC(MachineState, object_unref)

    static inline G_GNUC_UNUSED MachineState * 
    MACHINE(const void *obj)
    { return OBJECT_CHECK(MachineState, obj, TYPE_MACHINE); }

    static inline G_GNUC_UNUSED MachineClass * 
    MACHINE_GET_CLASS(const void *obj) 
    { return OBJECT_GET_CLASS(MachineClass, obj, TYPE_MACHINE); } 

    static inline G_GNUC_UNUSED MachineClass * 
    MACHINE_CLASS(const void *klass) 
    { return OBJECT_CLASS_CHECK(MachineClass, klass, TYPE_MACHINE); }

整理成更好理解的格式：

    typedef struct MachineState MachineState;
    typedef struct MachineClass MachineClass;

    G_DEFINE_AUTOPTR_CLEANUP_FUNC(MachineState, object_unref)

    static inline G_GNUC_UNUSED MachineState *MACHINE(const void *obj)
    {
        return OBJECT_CHECK(MachineState, obj, TYPE_MACHINE);
    }

    static inline G_GNUC_UNUSED MachineClass *MACHINE_GET_CLASS(const void *obj)
    {
        return OBJECT_GET_CLASS(MachineClass, obj, TYPE_MACHINE);
    }

    static inline G_GNUC_UNUSED MachineClass *MACHINE_CLASS(const void *klass)
    {
        return OBJECT_CLASS_CHECK(MachineClass, klass, TYPE_MACHINE);
    }

这就得到了初步形式。再将TYPE_MACHINE宏的定义（在include/hw/boards.h中）代入：

#define TYPE_MACHINE "machine"

得到：

    typedef struct MachineState MachineState;
    typedef struct MachineClass MachineClass;

    G_DEFINE_AUTOPTR_CLEANUP_FUNC(MachineState, object_unref)

    static inline G_GNUC_UNUSED MachineState *MACHINE(const void *obj)
    {
        return OBJECT_CHECK(MachineState, obj, "machine");
    }

    static inline G_GNUC_UNUSED MachineClass *MACHINE_GET_CLASS(const void *obj)
    {
        return OBJECT_GET_CLASS(MachineClass, obj, "machine");
    }

    static inline G_GNUC_UNUSED MachineClass *MACHINE_CLASS(const void *klass)
    {
        return OBJECT_CLASS_CHECK(MachineClass, klass, "machine");
    }

对比一下在VSCode中展开的截图：

QEMU源码全解析38 —— Machine（8）,QEMU,KVM,QEMU,KVM

终于看到了MACHINE函数的庐山真面目！原来是这样：

static inline G_GNUC_UNUSED MachineState *MACHINE(const void *obj)
{
    return OBJECT_CHECK(MachineState, obj, TYPE_MACHINE);
}

下一回将对MACHINE函数及其相关函数进行进一步解析。文章来源地址https://www.toymoban.com/news/detail-650805.html

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