Make use persistent device path /dev/v4l/by-id/.*

[whvneo]

The ordering of video devices is not persistent.

In akvconfig.ini it is only possible to use a number.

This is because of the following lines attributes.c:

static ssize_t akvcam_attributes_connected_devices_show(struct device *dev,
                                                        struct device_attribute *attribute,
                                                        char *buffer)
{
    struct video_device *vdev = to_video_device(dev);
    akvcam_device_t device = video_get_drvdata(vdev);
    akvcam_devices_list_t devices;
    akvcam_list_element_t it = NULL;
    size_t n = 0;
    size_t i;

    UNUSED(attribute);
    devices = akvcam_device_connected_devices_nr(device);
    memset(buffer, 0, PAGE_SIZE);

    for (i = 0; i < 64 && PAGE_SIZE > n; i++) {
        device = akvcam_list_next(devices, &it);

        if (!it)
            break;

        n = snprintf(buffer + n,
                     PAGE_SIZE - n,
                     "/dev/video%d\n",
                     akvcam_device_num(device));
    }   

    return n;
}

It would make more sense to use a path instead a number.
When listing all capable devices:

ls -l /dev/v4l/*/*
lrwxrwxrwx 1 root root 12 Aug 23 09:27 /dev/v4l/by-id/usb-046d_HD_Pro_Webcam_C920-video-index0 -> ../../video1
lrwxrwxrwx 1 root root 12 Aug 23 09:27 /dev/v4l/by-id/usb-046d_HD_Pro_Webcam_C920-video-index1 -> ../../video3
lrwxrwxrwx 1 root root 12 Aug 23 09:27 /dev/v4l/by-id/usb-Sonix_Technology_Co.__Ltd._BisonCam_NB_Pro-video-index0 -> ../../video4
lrwxrwxrwx 1 root root 12 Aug 23 09:27 /dev/v4l/by-id/usb-Sonix_Technology_Co.__Ltd._BisonCam_NB_Pro-video-index1 -> ../../video5
lrwxrwxrwx 1 root root 12 Aug 23 09:27 /dev/v4l/by-path/pci-0000:00:14.0-usb-0:2:1.0-video-index0 -> ../../video1
lrwxrwxrwx 1 root root 12 Aug 23 09:27 /dev/v4l/by-path/pci-0000:00:14.0-usb-0:2:1.0-video-index1 -> ../../video3
lrwxrwxrwx 1 root root 12 Aug 23 09:27 /dev/v4l/by-path/pci-0000:00:14.0-usb-0:8:1.0-video-index0 -> ../../video4
lrwxrwxrwx 1 root root 12 Aug 23 09:27 /dev/v4l/by-path/pci-0000:00:14.0-usb-0:8:1.0-video-index1 -> ../../video5

So when specifying a new config parameter saying "path" we could easily enter the meaningfull path by id and akvcam will use this instead.

Thanks for checking