libudev为C中的特定tty获取devnum

Question

我想获得devnum特定的tty，例如/dev/ttyUSB1。为此，我修改了答案https://stackoverflow.com/a/20341112/2429333，如下所示：

int get_devnum(const char *filename)
{
    if( filename == NULL) return -1;

    int retval;
    const char *path;
    const char *sysattr;
    struct udev *udev;
    struct udev_enumerate *enumerate;
    struct udev_list_entry *devices, *dev_list_entry;
    struct udev_device *dev;

    retval = -1;

    udev = udev_new();

    enumerate = udev_enumerate_new(udev);
    udev_enumerate_add_match_subsystem(enumerate, "tty");
    udev_enumerate_scan_devices(enumerate);
    devices = udev_enumerate_get_list_entry(enumerate);

    udev_list_entry_foreach(dev_list_entry, devices) {

        path = udev_list_entry_get_name(dev_list_entry);
        dev = udev_device_new_from_syspath(udev, path);

        if(strcmp(udev_device_get_devnode(dev), filename) == 0)
        {
            dev = udev_device_get_parent_with_subsystem_devtype(
                    dev,
                    "usb",
                    "usb_device");
            sysattr = udev_device_get_sysattr_value(dev, "devnum");
            if(sysattr != NULL)
            {
                retval = strtol(sysattr, NULL, 10);
            }
            udev_device_unref(dev);
            break;
        }
        udev_device_unref(dev);
    }

    udev_enumerate_unref(enumerate);
    udev_unref(udev);

    return retval;
}

我不喜欢这个解决方案是我必须迭代特定子系统中的所有列表条目。有没有办法可以使用devnode信息（文件名）来获取带有libudev的portnum？