usb_register(&usbfs_driver)、usb_devio_init()、usbfs_init()都是usbfs相关的初始化。usbfs为咱们提供了在用户空间直接访问usb硬件设备的接口，但它需要内核的大力支持，usbfs_driver就是用来完成这个光荣任务的。

1. usbfs简介：

2. usbfs驱动

retval = usb_register(&usbfs_driver); //usbfs驱动注册
struct usb_driver usbfs_driver = {
  .name =    "usbfs", //usbfs驱动名称
  .probe =  driver_probe, //探测函数
  .disconnect =  driver_disconnect, 
  .suspend =  driver_suspend, //设备挂起
  .resume =  driver_resume, //设备恢复
};

关于usbfs文件系统的使用我是没有搞清楚，后续在了解...!!!!!


3. usb设备io初始化

retval = usb_devio_init();
int __init usb_devio_init(void)
{
  int retval;

  retval = register_chrdev_region(USB_DEVICE_DEV, USB_DEVICE_MAX, //注册字符设备“usb_device”
          "usb_device");
  if (retval) {
    printk(KERN_ERR "Unable to register minors for usb_device\n");
    goto out;
  }
  cdev_init(&usb_device_cdev, &usbdev_file_operations);
  retval = cdev_add(&usb_device_cdev, USB_DEVICE_DEV, USB_DEVICE_MAX);
  if (retval) {
    printk(KERN_ERR "Unable to get usb_device major %d\n",
           USB_DEVICE_MAJOR);
    goto error_cdev;
  }
  usb_register_notify(&usbdev_nb); //注册通知链
out:
  return retval;

error_cdev:
  unregister_chrdev_region(USB_DEVICE_DEV, USB_DEVICE_MAX);
  goto out;
}
const struct file_operations usbdev_file_operations = {
  .owner =    THIS_MODULE,
  .llseek =    usbdev_lseek,
  .read =      usbdev_read,
  .poll =      usbdev_poll,
  .unlocked_ioctl = usbdev_ioctl,
#ifdef CONFIG_COMPAT
  .compat_ioctl =   usbdev_compat_ioctl,
#endif
  .open =      usbdev_open,
  .release =    usbdev_release,
};
static struct notifier_block usbdev_nb = {
  .notifier_call =  usbdev_notify,
};

这里先贴出源码，源码内容很容易理解，我这里有个疑问，这里创建的usbfs、usbdevio_init是如何在文件系统体现的？