v4l2_ioctl测试与训练（v4l2版本）

    ioctl(dev->fd, VIDIOC_DQBUF, &buf))
    ioctl(dev->fd, VIDIOC_QBUF, &buf)

    v4L2_fops.unlocked_ioctl
    -->.v4L2_ioctl
    	-->vdev = video_devdata(filp);
    	   vdev->fops->unlocked_ioctl(filp, cmd, arg);//调用设备提供的unlocked_ioctl 如果是uvc则指向.unlocked_ioctl= video_ioctl2
    	   video_ioctl2//函数位置为kernel\drivers\media\v4l2-core\v4l2-ioctl.c
    	   		-->video_usercopy(file, cmd, arg, __video_do_ioctl)//__video_do_ioctl为一个回调函数，在video_userco