How to query all devices in ffmpeg?

Question

How to properly query all video devices in system using libavdevice? opening input with int err = avformat_open_input(&context, NULL, fmt, NULL); fails because device name is not provided (second parameter is device name, if one provides "/dev/video0" for example it finds that device only):

    avcodec_register_all();
    avdevice_register_all();
    AVFormatContext* context = avformat_alloc_context();
    AVInputFormat *fmt = av_find_input_format("video4linux");
    printf("trying to open input");
    int err = avformat_open_input(&context, "/dev/video0", fmt, NULL);
    if(err != 0){
        fprintf(stderr, "ffmpeg failed to open input");
    }
    static struct AVDeviceInfoList* devices_list;
    avdevice_list_devices(context, &devices_list);
    int devices_count = devices_list->nb_devices;
    for(int i = 0; i < devices_count; i++){
        printf("Checking device nr. %d \n", i);
        AVDeviceInfo* current_device_info = devices_list->devices[i];

       printf("Find Device: %s", current_device_info->device_description);
    }

    avformat_free_context(context);

How Can AVFormatContext can be initialized to find all v4l2 devices? I imagine that if context partially initialized (let's say takes all v4l2devices) it should query everything properly. When context run with avformat_open_input one must provide exact device name beforehand.

Charbonneau