请给出一个在linux内核4.9下能用的V4L2驱动程序注册控制曝光等接口的示例

这里提供一个简单的示例代码，用于在Linux内核4.9下注册V4L2驱动程序，并实现曝光控制：

#include <linux/videodev2.h>
#include <linux/module.h>
#include <media/v4l2-device.h>

#define DRIVER_NAME "example"

struct example_dev {
    struct v4l2_device v4l2_dev;
    struct video_device *vdev;
    struct v4l2_ctrl_handler ctrl_handler;
    struct v4l2_ctrl *exposure;
};

static int example_open(struct file *filep)
{
    struct video_device *vdev = video_devdata(filep);
    struct example_dev *dev = video_get_drvdata(vdev);

    return v4l2_fh_open(filep);
}

static int example_release(struct file *filep)
{
    return v4l2_fh_release(filep);
}

static const struct v4l2_file_operations example_fops = {
    .owner          = THIS_MODULE,
    .open           = example_open,
    .release        = example_release,
    .unlocked_ioctl = video_ioctl2,
};

static int example_init_controls(struct example_dev *dev)
{
    int ret;

    v4l2_ctrl_handler_init(&dev->ctrl_handler, 1);
    dev->exposure = v4l2_ctrl_new_std(&dev->ctrl_handler,
                                      &v4l2_ctrl_ops_int64,
                                      V4L2_CID_EXPOSURE,
                                      0, 1000000, 1, 0);
    if (dev->ctrl_handler.error) {
        ret = dev->ctrl_handler.error;
        pr_err("%s: Failed to init controls (%d)\n", DRIVER_NAME, ret);
        goto err_handler_free;
    }

    ret = v4l2_ctrl_handler_setup(&dev->ctrl_handler);
    if (ret) {
        pr_err("%s: Failed to setup controls (%d)\n", DRIVER_NAME, ret);
        goto err_handler_free;
    }

    return 0;

err_handler_free:
    v4l2_ctrl_handler_free(&dev->ctrl_handler);
    return ret;
}

static int example_probe(struct platform_device *pdev)
{
    struct example_dev *dev;
    struct video_device *vdev;
    int ret;

    dev = devm_kzalloc(&pdev->dev, sizeof(*dev), GFP_KERNEL);
    if (!dev)
        return -ENOMEM;

    v4l2_device_init(&dev->v4l2_dev, &v4l2_dummy_fops);
    ret = v4l2_device_register(&pdev->dev, &dev->v4l2_dev);
    if (ret) {
        pr_err("%s: Failed to register V4L2 device (%d)\n", DRIVER_NAME, ret);
        return ret;
    }

    ret = example_init_controls(dev);
    if (ret) {
        pr_err("%s: Failed to init controls (%d)\n", DRIVER_NAME, ret);
        goto err_device_unregister;
    }

    vdev = video_device_alloc();
    if (!vdev) {
        ret = -ENOMEM;
        goto err_ctrl_handler_free;
    }

    vdev->v4l2_dev = &dev->v4l2_dev;
    vdev->fops     = &example_fops;
    vdev->ioctl_ops = &video_ioctl2_ops;
    vdev->release  = video_device_release;
    snprintf(vdev->name, sizeof(vdev->name), "%s", DRIVER_NAME);

    ret = video_register_device(vdev, VFL_TYPE_GRABBER, -1);
    if (ret) {
        pr_err("%s: Failed to register video device (%d)\n", DRIVER_NAME, ret);
        goto err_device_free;
    }

    dev->vdev = vdev;
    platform_set_drvdata(pdev, dev);

    return 0;

err_device_free:
    video_device_release(vdev);
err_ctrl_handler_free:
    v4l2_ctrl_handler_free(&dev->ctrl_handler);
err_device_unregister:
    v4l2_device_unregister(&dev->v4l2_dev);

    return ret;
}

static int example_remove(struct platform_device *pdev)
{
    struct example_dev *dev = platform_get_drvdata(pdev);

    video_unregister_device(dev->vdev);
    v4l2_ctrl_handler_free(&dev->ctrl_handler);
    v4l2_device_unregister(&dev->v4l2_dev);

    return 0;
}

static const struct of_device_id example_of_match[] = {
    { .compatible = "example", },
    {},
};
MODULE_DEVICE_TABLE(of, example_of_match);

static struct platform_driver example_driver = {
    .probe = example_probe,
    .remove = example_remove,
    .driver = {
        .name = DRIVER_NAME,
        .of_match_table = example_of_match,
    },
};
module_platform_driver(example_driver);

MODULE_AUTHOR("Your Name");
MODULE_DESCRIPTION("Example V4L2 driver");
MODULE_LICENSE("GPL");

上述示例代码中，struct example_dev 结构体定义了 V4L2 设备的数据结构，包括了曝光控制等所需的控制器。在 example_probe 函数中，注册了 V4L2 设备、控制器和视频设备，并最终将其加入到系统中。同时，在 example_init_controls 函数中，实现了曝光控制器的初始化。

需要注意的是，这个示例代码只是一个简单的实现，实际应用时可能需要根据具体需求进行修改。同时，为了让示例代码更加易读易懂，我省略了一些必要的错误处理和注释，实际使用时需要进行补充。