QEMU源码全解析 —— virtio（10）

已于 2024-08-19 22:38:55 修改
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分类专栏： QEMU/KVM KVM 文章标签： QEMU KVM virtio
于 2023-12-16 16:58:05 首次发布
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本文详细解析了QEMU中virtio_balloon_pci_realize函数，介绍了如何通过VIRTIO_BALLOON_PCI宏将设备转换为VirtIOBalloonPCI类型，并详细阐述了DEVICE宏的展开过程，最后提到了qdev_realize函数的主要作用，包括设备挂载到virtio总线及设备具现化。
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接前一篇文章：

realize函数 parent_dc_realize函数
DeviceClass virtio_pci_dc_realize
PCIDeviceClass virtio_pci_realize
VirtioPCIClass virtio_balloon_pci_realize pci_qdev_realize

上一回开始，沿着device_set_realized() -> pci_qdev_realize() -> virtio_pci_realize()这一调用线，对于virtio_pci_realize函数进行了详细解析。最后，讲到virtio_pci_realize函数的最后一步调用了virtio_balloon_pci_realize函数。本回就来对于virtio_balloon_pci_realize函数进行解析。

virtio_balloon_pci_realize函数在hw/ virtio /virtio-balloon-pci.c中，如下： 

  1. static void virtio_balloon_pci_realize(VirtIOPCIProxy *vpci_dev, Error **errp)
  2. {
  3.     VirtIOBalloonPCI *dev = VIRTIO_BALLOON_PCI(vpci_dev);
  4.     DeviceState *vdev = DEVICE(&dev->vdev);
  5.  
  6.     vpci_dev->class_code = PCI_CLASS_OTHERS;
  7.     qdev_realize(vdev, BUS(&vpci_dev->bus), errp);
  8. }

virtio_balloon_pci_realize函数首先通过VIRTIO_BALLOON_PCI宏将VirtIOPCIProxy类型的设备转换为VirtIOBalloonPCI设备，相当于从一个父类转换为一个子类。代码片段如下： 

    VirtIOBalloonPCI *dev = VIRTIO_BALLOON_PCI(vpci_dev);

VIRTIO_BALLOON_PCI的具体定义如果在 QEMU 源码根目录下搜索是搜不到的，需要进行转换才可以。相关代码在hw/virtio/virtio-balloon-pci.c中，如下： 

  1. /*
  2.  * virtio-balloon-pci: This extends VirtioPCIProxy.
  3.  */
  4. #define TYPE_VIRTIO_BALLOON_PCI "virtio-balloon-pci-base"
  5. DECLARE_INSTANCE_CHECKER(VirtIOBalloonPCI, VIRTIO_BALLOON_PCI,
  6.                          TYPE_VIRTIO_BALLOON_PCI)

这段代码最终展开为： 

  1. static inline G_GNUC_UNUSED VirtIOBalloonPCI* VIRTIO_BALLOON_PCI(const void *obj)
  2. {
  3.     return OBJECT_CHECK(VirtIOBalloonPCI, obj, "virtio-balloon-pci-base");
  4. }
  1. static inline G_GNUC_UNUSED VirtIOBalloonPCI* VIRTIO_BALLOON_PCI(const void *obj)
  2. {
  3.     return ((VirtIOBalloonPCI*)object_dynamic_cast_assert ((ObjectClass *)(obj), ("virtio-balloon-pci-base"), __FILE__, __LINE__, __func__));
  4. }

接下来，得到设备VirtIOBalloonPCI的VirtIOBalloon部分，这就是实际的virtio balloon设备了。代码片段如下： 

    DeviceState *vdev = DEVICE(&dev->vdev);

和VIRTIO_BALLOON_PCI一样，DEVICE的具体定义如果在QEMU源码根目录下搜索是搜不到的，需要进行转换才可以。相关代码在include/hw/qdev-core.h中，如下： 

  1. #define TYPE_DEVICE "device"
  2. OBJECT_DECLARE_TYPE(DeviceState, DeviceClass, DEVICE)

OBJECT_DECLARE_TYPE宏的定义在include/qom/object.h中，如下： 

  1. /**
  2.  * OBJECT_DECLARE_TYPE:
  3.  * @InstanceType: instance struct name
  4.  * @ClassType: class struct name
  5.  * @MODULE_OBJ_NAME: the object name in uppercase with underscore separators
  6.  *
  7.  * This macro is typically used in a header file, and will:
  8.  *
  9.  *   - create the typedefs for the object and class structs
  10.  *   - register the type for use with g_autoptr
  11.  *   - provide three standard type cast functions
  12.  *
  13.  * The object struct and class struct need to be declared manually.
  14.  */
  15. #define OBJECT_DECLARE_TYPE(InstanceType, ClassType, MODULE_OBJ_NAME) \
  16.     typedef struct InstanceType InstanceType; \
  17.     typedef struct ClassType ClassType; \
  18.     \
  19.     G_DEFINE_AUTOPTR_CLEANUP_FUNC(InstanceType, object_unref) \
  20.     \
  21.     DECLARE_OBJ_CHECKERS(InstanceType, ClassType, \
  22.                          MODULE_OBJ_NAME, TYPE_##MODULE_OBJ_NAME)

代入上边的值，初步展开为： 

  1. typedef struct DeviceState DeviceState;
  2. typedef struct DeviceClass DeviceClass;
  3.  
  4. G_DEFINE_AUTOPTR_CLEANUP_FUNC(DeviceState, object_unref)
  5.  
  6. DECLARE_OBJ_CHECKERS(DeviceState, DeviceClass, DEVICE, TYPE_DEVICE)

DECLARE_OBJ_CHECKERS宏的定义也在include/qom/object.h中，如下： 

  1. /**
  2.  * DECLARE_OBJ_CHECKERS:
  3.  * @InstanceType: instance struct name
  4.  * @ClassType: class struct name
  5.  * @OBJ_NAME: the object name in uppercase with underscore separators
  6.  * @TYPENAME: type name
  7.  *
  8.  * Direct usage of this macro should be avoided, and the complete
  9.  * OBJECT_DECLARE_TYPE macro is recommended instead.
  10.  *
  11.  * This macro will provide the three standard type cast functions for a
  12.  * QOM type.
  13.  */
  14. #define DECLARE_OBJ_CHECKERS(InstanceType, ClassType, OBJ_NAME, TYPENAME) \
  15.     DECLARE_INSTANCE_CHECKER(InstanceType, OBJ_NAME, TYPENAME) \
  16.     \
  17.     DECLARE_CLASS_CHECKERS(ClassType, OBJ_NAME, TYPENAME)

因此，上式进一步展开为： 

  1. typedef struct DeviceState DeviceState;
  2. typedef struct DeviceClass DeviceClass;
  3.  
  4. G_DEFINE_AUTOPTR_CLEANUP_FUNC(DeviceState, object_unref)
  5.  
  6. DECLARE_INSTANCE_CHECKER(DeviceState, DEVICE, TYPE_DEVICE)
  7.  
  8. DECLARE_CLASS_CHECKERS(DeviceClass, DEVICE, TYPE_DEVICE)

DECLARE_INSTANCE_CHECKER和DECLARE_CLASS_CHECKERS宏也都是在include/qom/object.h中，定义分别如下： 

  1. /**
  2.  * DECLARE_INSTANCE_CHECKER:
  3.  * @InstanceType: instance struct name
  4.  * @OBJ_NAME: the object name in uppercase with underscore separators
  5.  * @TYPENAME: type name
  6.  *
  7.  * Direct usage of this macro should be avoided, and the complete
  8.  * OBJECT_DECLARE_TYPE macro is recommended instead.
  9.  *
  10.  * This macro will provide the instance type cast functions for a
  11.  * QOM type.
  12.  */
  13. #define DECLARE_INSTANCE_CHECKER(InstanceType, OBJ_NAME, TYPENAME) \
  14.     static inline G_GNUC_UNUSED InstanceType * \
  15.     OBJ_NAME(const void *obj) \
  16.     { return OBJECT_CHECK(InstanceType, obj, TYPENAME); }
  1. /**
  2.  * DECLARE_CLASS_CHECKERS:
  3.  * @ClassType: class struct name
  4.  * @OBJ_NAME: the object name in uppercase with underscore separators
  5.  * @TYPENAME: type name
  6.  *
  7.  * Direct usage of this macro should be avoided, and the complete
  8.  * OBJECT_DECLARE_TYPE macro is recommended instead.
  9.  *
  10.  * This macro will provide the class type cast functions for a
  11.  * QOM type.
  12.  */
  13. #define DECLARE_CLASS_CHECKERS(ClassType, OBJ_NAME, TYPENAME) \
  14.     static inline G_GNUC_UNUSED ClassType * \
  15.     OBJ_NAME##_GET_CLASS(const void *obj) \
  16.     { return OBJECT_GET_CLASS(ClassType, obj, TYPENAME); } \
  17.     \
  18.     static inline G_GNUC_UNUSED ClassType * \
  19.     OBJ_NAME##_CLASS(const void *klass) \
  20.     { return OBJECT_CLASS_CHECK(ClassType, klass, TYPENAME); }

因此，上式进一步展开为： 

  1. typedef struct DeviceState DeviceState;
  2. typedef struct DeviceClass DeviceClass;
  3.  
  4. G_DEFINE_AUTOPTR_CLEANUP_FUNC(DeviceState, object_unref)
  5.  
  6. static inline G_GNUC_UNUSED DeviceState *DEVICE(const void *obj)
  7. {
  8.     return OBJECT_CHECK(DeviceState, obj, TYPE_DEVICE);
  9. }
  10.  
  11. static inline G_GNUC_UNUSED DeviceClass* DEVICE_GET_CLASS(const void *obj)
  12. {
  13.     return OBJECT_GET_CLASS(DeviceClass, obj, TYPE_DEVICE);
  14. }
  15.  
  16. static inline G_GNUC_UNUSED DeviceClass* DEVICE_CLASS(const void *klass)
  17. {
  18.     return OBJECT_CLASS_CHECK(DeviceClass, klass, TYPE_DEVICE);
  19. }

再把TYPE_DEVICE的实际值代入，最终得到： 

  1. typedef struct DeviceState DeviceState;
  2. typedef struct DeviceClass DeviceClass;
  3.  
  4. G_DEFINE_AUTOPTR_CLEANUP_FUNC(DeviceState, object_unref)
  5.  
  6. static inline G_GNUC_UNUSED DeviceState *DEVICE(const void *obj)
  7. {
  8.     return OBJECT_CHECK(DeviceState, obj, "device");
  9. }
  10.  
  11. static inline G_GNUC_UNUSED DeviceClass* DEVICE_GET_CLASS(const void *obj)
  12. {
  13.     return OBJECT_GET_CLASS(DeviceClass, obj, "device");
  14. }
  15.  
  16. static inline G_GNUC_UNUSED DeviceClass* DEVICE_CLASS(const void *klass)
  17. {
  18.     return OBJECT_CLASS_CHECK(DeviceClass, klass, "device");
  19. }

这里就不再深入展开了。

总之，通过DEVICE宏得到设备VirtIOBalloonPCI的VirtIOBalloon部分，这就是实际的virtio balloon设备了。 

    DeviceState *vdev = DEVICE(&dev->vdev);

539e3e833e090bc7edd784e48609c32a.png

接下来，调用hw/core/qdev.c中的qdev_realize函数。代码片段如下： 

    qdev_realize(vdev, BUS(&vpci_dev->bus), errp);

qdev_realize函数代码如下： 

  1. bool qdev_realize(DeviceState *dev, BusState *bus, Error **errp)
  2. {
  3.     assert(!dev->realized && !dev->parent_bus);
  4.  
  5.     if (bus) {
  6.         if (!qdev_set_parent_bus(dev, bus, errp)) {
  7.             return false;
  8.         }
  9.     } else {
  10.         assert(!DEVICE_GET_CLASS(dev)->bus_type);
  11.     }
  12.  
  13.     return object_property_set_bool(OBJECT(dev), "realized", true, errp);
  14. }

qdev_realize函数主要做了两件事情：

1）设置virtio balloon设备的总线为VirtIOPCIProxy设备中的bus成员，也就是把这个virtio balloon设备挂到virtio总线上。

2）调用object_property_bool函数，将virtio balloon设备具现化，这会导致virtio_device_realize函数的执行。

注：实际上在老版本中，并没有qdev_realize函数，它里边的两项工作是直接在virtio_balloon_pci_realize函数中完成的。

7cf531c21d7f91e255f3e058124ff81f.png

virtio_device_realize函数在hw/virtio/virtio.c中，代码如下： 

  1. static void virtio_device_realize(DeviceState *dev, Error **errp)
  2. {
  3.     VirtIODevice *vdev = VIRTIO_DEVICE(dev);
  4.     VirtioDeviceClass *vdc = VIRTIO_DEVICE_GET_CLASS(dev);
  5.     Error *err = NULL;
  6.  
  7.     /* Devices should either use vmsd or the load/save methods */
  8.     assert(!vdc->vmsd || !vdc->load);
  9.  
  10.     if (vdc->realize != NULL) {
  11.         vdc->realize(dev, &err);
  12.         if (err != NULL) {
  13.             error_propagate(errp, err);
  14.             return;
  15.         }
  16.     }
  17.  
  18.     virtio_bus_device_plugged(vdev, &err);
  19.     if (err != NULL) {
  20.         error_propagate(errp, err);
  21.         vdc->unrealize(dev);
  22.         return;
  23.     }
  24.  
  25.     vdev->listener.commit = virtio_memory_listener_commit;
  26.     vdev->listener.name = "virtio";
  27.     memory_listener_register(&vdev->listener, vdev->dma_as);
  28.     QTAILQ_INSERT_TAIL(&virtio_list, vdev, next);
  29. }

对于virtio_device_realize函数的深入解析，请看下回。

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