v4l2-dev dev_set_name

`v4l2-dev dev_set_name`是一个函数调用，它用于设置一个v4l2设备的名称。v4l2是一个视频设备驱动程序接口，它允许用户空间程序与视频设备（如摄像头）进行通信。`dev_set_name`函数可以在驱动程序中使用，以便为v4l2设备设置一个有意义的名称，便于用户空间程序识别该设备。

相关问题

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。

生成一个基于v4l2的获取USB摄像头图像的C++程序

好的，可以参考以下代码：

#include <opencv2/opencv.hpp>
#include <iostream>

#include <linux/videodev2.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <sys/mman.h>

using namespace std;
using namespace cv;

int main(int argc, char* argv[])
{
    const char* dev_name = "/dev/video0";
    int fd = open(dev_name, O_RDWR | O_NONBLOCK, 0);

    if (fd < 0)
    {
        perror("open");
        exit(1);
    }

    struct v4l2_capability cap;
    if (ioctl(fd, VIDIOC_QUERYCAP, &cap) < 0)
    {
        perror("VIDIOC_QUERYCAP");
        exit(1);
    }

    cout << "Driver Name: " << cap.driver << endl;
    cout << "Card Name: " << cap.card << endl;
    cout << "Bus info: " << cap.bus_info << endl;
    cout << "Version: " << (cap.version >> 16) << "." << ((cap.version >> 8) & 0xff) << "." << (cap.version & 0xff) << endl;

    struct v4l2_format fmt;
    memset(&fmt, 0, sizeof(fmt));
    fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    fmt.fmt.pix.width = 640;
    fmt.fmt.pix.height = 480;
    fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_MJPEG;
    fmt.fmt.pix.field = V4L2_FIELD_INTERLACED;

    if (ioctl(fd, VIDIOC_S_FMT, &fmt) < 0)
    {
        perror("VIDIOC_S_FMT");
        exit(1);
    }

    struct v4l2_requestbuffers req;
    memset(&req, 0, sizeof(req));
    req.count = 1;
    req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    req.memory = V4L2_MEMORY_MMAP;

    if (ioctl(fd, VIDIOC_REQBUFS, &req) < 0)
    {
        perror("VIDIOC_REQBUFS");
        exit(1);
    }

    struct v4l2_buffer buf;
    memset(&buf, 0, sizeof(buf));
    buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    buf.memory = V4L2_MEMORY_MMAP;
    buf.index = 0;

    if (ioctl(fd, VIDIOC_QUERYBUF, &buf) < 0)
    {
        perror("VIDIOC_QUERYBUF");
        exit(1);
    }

    void* buffer = mmap(NULL, buf.length, PROT_READ | PROT_WRITE, MAP_SHARED, fd, buf.m.offset);

    if (buffer == MAP_FAILED)
    {
        perror("mmap");
        exit(1);
    }

    memset(buffer, 0, buf.length);

    if (ioctl(fd, VIDIOC_QBUF, &buf) < 0)
    {
        perror("VIDIOC_QBUF");
        exit(1);
    }

    if (ioctl(fd, VIDIOC_STREAMON, &buf.type) < 0)
    {
        perror("VIDIOC_STREAMON");
        exit(1);
    }

    Mat frame;
    for (int i = 0; i < 100; i++)
    {
        fd_set fds;
        FD_ZERO(&fds);
        FD_SET(fd, &fds);

        struct timeval tv = {0};
        tv.tv_sec = 2;
        tv.tv_usec = 0;

        int r = select(fd+1, &fds, NULL, NULL, &tv);

        if (r == -1)
        {
            perror("select");
            exit(1);
        }

        if (r == 0)
        {
            fprintf(stderr, "select timeout\n");
            exit(1);
        }

        if (ioctl(fd, VIDIOC_DQBUF, &buf) < 0)
        {
            perror("VIDIOC_DQBUF");
            exit(1);
        }

        frame = Mat(Size(fmt.fmt.pix.width, fmt.fmt.pix.height), CV_8UC3, (char*)buffer);

        if (ioctl(fd, VIDIOC_QBUF, &buf) < 0)
        {
            perror("VIDIOC_QBUF");
            exit(1);
        }

        imshow("Frame", frame);
        waitKey(1);
    }

    if (ioctl(fd, VIDIOC_STREAMOFF, &buf.type) < 0)
    {
        perror("VIDIOC_STREAMOFF");
        exit(1);
    }

    close(fd);

    return 0;
}

这段代码是一个简单的基于v4l2的获取USB摄像头图像的C程序，其中使用了OpenCV库来显示图像。需要注意的是，这段代码只是一个基础示例，读者可以根据自己的需求进行修改和扩展。