3. V4L2_device结构体：

这个结构体中包含了一个非常重要的结构体v4l2_device：

struct v4l2_device {
    /* dev->driver_data points to this struct.
       Note: dev might be NULL if there is no parent device
       as is the case with e.g. ISA devices. */
    struct device *dev;
#if defined(CONFIG_MEDIA_CONTROLLER)
    struct media_device *mdev;
#endif
    /* used to keep track of the registered subdevs */
    struct list_head subdevs;
    /* lock this struct; can be used by the driver as well if this
       struct is embedded into a larger struct. */
    spinlock_t lock;
    /* unique device name, by default the driver name + bus ID */
    char name[V4L2_DEVICE_NAME_SIZE];
    /* notify callback called by some sub-devices. */
    void (*notify)(struct v4l2_subdev *sd,
            unsigned int notification, void *arg);
    /* The control handler. May be NULL. */
    struct v4l2_ctrl_handler *ctrl_handler;
    /* Device's priority state */
    struct v4l2_prio_state prio;
    /* BKL replacement mutex. Temporary solution only. */
    struct mutex ioctl_lock;
    /* Keep track of the references to this struct. */
    struct kref ref;
    /* Release function that is called when the ref count goes to 0. */
    void (*release)(struct v4l2_device *v4l2_dev);
};

3.1 v4l2_device的注册和注销：

int v4l2_device_register(struct device*dev, struct v4l2_device *v4l2_dev)

static void v4l2_device_release(struct kref *ref)

4. v4l2_subdev结构体

V4l2_subdev代表子设备，包含了子设备的相关属性和操作。先来看下结构体原型：

struct v4l2_subdev {
 
         struct v4l2_device *v4l2_dev;  //指向父设备
 
         //提供一些控制v4l2设备的接口
 
         const struct v4l2_subdev_ops *ops;
 
         //向V4L2框架提供的接口函数
 
         const struct v4l2_subdev_internal_ops *internal_ops;
 
         //subdev控制接口
 
         struct v4l2_ctrl_handler *ctrl_handler;
 
         /* name must be unique */
 
         charname[V4L2_SUBDEV_NAME_SIZE];
 
         /*subdev device node */
 
         struct video_device *devnode;  
 
};

其中 list 域作为链表节点链接至 v4l2_dev 指向的 v4l2_device 结构中，这个结构中最重要的成员就是 struct v4l2_subdev_ops *ops，该域包含了 v4l2 设备支持的所有操作，定义如下：

struct v4l2_subdev_ops {
    const struct v4l2_subdev_core_ops  *core;   /* 通用操作合集 */
    const struct v4l2_subdev_tuner_ops *tuner;  /* 调谐器操作合集 */
    const struct v4l2_subdev_audio_ops *audio;  /* 音频操作合集 */
    const struct v4l2_subdev_video_ops *video;  /* 视频操作合集 */
};

v4l2_subdev_core_ops 包含的操作合集是各种类型设备通用的：