HID源码DeviceExtension之间关系

HidClassAddDevice中创建设备时传递的设备扩展结构体大小：

    DeviceExtensionSize = sizeof(HIDCLASS_FDO_EXTENSION) + DriverExtension->DeviceExtensionSize;
       /* now create the device */
    Status = IoCreateDevice(DriverObject, DeviceExtensionSize, &DeviceName, FILE_DEVICE_UNKNOWN, 0, FALSE, &NewDeviceObject);
    if (!NT_SUCCESS(Status))
    {
        /* failed to create device object */
        ASSERT(FALSE);
        return Status;
    }

而USBHid中设置DriverExtension->DeviceExtensionSize的值为：

    Registration.DeviceExtensionSize = sizeof(HID_USB_DEVICE_EXTENSION);

所以最终的扩展结象为 HIDCLASS_FDO_EXTENSION + HID_USB_DEVICE_EXTENSION

• HID_USB_DEVICE_EXTENSION 结构体为MiniPort小端口驱动的私有扩展单元。
• HIDCLASS_FDO_EXTENSION 是HIDClass类驱动维护的数据单元。但类驱动同时承担着两个功能
  1.创建PDO,所以每次进行IRP调用时需判断是FDO和PDO
  2.提供一个不透时的指针HidUsb.
  所以HIDCLASS_FDO_EXTENSION的定义如下：

typedef struct
{
    //
    // parts shared by fdo and pdo
    //
    HIDCLASS_COMMON_DEVICE_EXTENSION Common;

    //
    // device capabilities
    //
    DEVICE_CAPABILITIES Capabilities;

    //
    // hid descriptor
    //
    HID_DESCRIPTOR HidDescriptor;

    //
    // report descriptor
    //
    PUCHAR ReportDescriptor;

    //
    // device relations
    //
    PDEVICE_RELATIONS DeviceRelations;

} HIDCLASS_FDO_EXTENSION, *PHIDCLASS_FDO_EXTENSION;

可以看到其有一个与PDO其同的数据结构HIDCLASS_COMMON_DEVICE_EXTENSION,其定义如下：

typedef struct
{
    //
    // hid device extension
    //
    HID_DEVICE_EXTENSION HidDeviceExtension;

    //
    // if it is a pdo
    //
    BOOLEAN IsFDO;

    //
    // driver extension
    //
    PHIDCLASS_DRIVER_EXTENSION DriverExtension;

    //
    // device description
    //
    HIDP_DEVICE_DESC DeviceDescription;

    //
    // hid attributes
    //
    HID_DEVICE_ATTRIBUTES Attributes;

} HIDCLASS_COMMON_DEVICE_EXTENSION, *PHIDCLASS_COMMON_DEVICE_EXTENSION;

而无论是PDO还是FDO，都有2个DeveiObject，只是其含义不同而已，并且为了给HIDBUS提供其各个设备结构，所以又定义了一个结构体HID_DEVICE_EXTENSION

typedef struct _HID_DEVICE_EXTENSION {
    PDEVICE_OBJECT PhysicalDeviceObject;
    PDEVICE_OBJECT NextDeviceObject;
    PVOID          MiniDeviceExtension;
} HID_DEVICE_EXTENSION, * PHID_DEVICE_EXTENSION;

所以关系图如下：

• HIDCLASS_FDO_EXTENSION
  • HIDCLASS_COMMON_DEVICE_EXTENSION
    • HID_DEVICE_EXTENSION
• HID_USB_DEVICE_EXTENSION