Chinaunix

标题: 关于usb自带的例子usb-skeleton.c [打印本页]

作者: mxgsgtc 时间: 2017-03-17 16:01
标题: 关于usb自带的例子usb-skeleton.c
本帖最后由 mxgsgtc 于 2017-03-17 16:23 编辑

static struct usb_class_driver skel_class = {             .name =             "skel%d",
      .fops =             &skel_fops,
      .minor_base =       USB_SKEL_MINOR_BASE,
};

在skel_probe 函数中
{
----
----
      retval = usb_register_dev(interface, &skel_class);
      if (retval) {
            /* something prevented us from registering this driver */
            err("Not able to get a minor for this device.");
            usb_set_intfdata(interface, NULL);
            goto error;
      }

------
-----

}
我想问下关于:usb_register_dev这个函数的问题,这个函数会创建一个usb子设备A，并在/dev/生成节点
问题1: 这个子设备A是字符设备还是块设备,如何判断的呢？
根据我的分析
usb_register_dev-->device_add-->devtmpfs_create_node
devtmpfs_create_node函数中
{
----
      nodename = device_get_devnode(dev, &mode, &tmp);
      if (!nodename)
            return -ENOMEM;

      if (mode == 0)
            mode = 0600;
      if (is_blockdev(dev))
            mode |= S_IFBLK;
      else
            mode |= S_IFCHR;//这里有个字符设备的赋值

-----
}
所以我大致判断, usb_register_dev生成出来的是字符设备,不知道对不对
问题2:假设通过usb_register_dev生成出来的是字符设备, 但是在此函数中我并没有找到cdev结构的分配(字符设备都需要分配这个结构吧),那cdev是从哪里分配的呢？

问题3：skel_class中的.fops在VFS的角度上讲是如何被调用的呢?
static const struct file_operations skel_fops = {
      .owner =       THIS_MODULE,
      .read =             skel_read,
      .write =       skel_write,
      .open =             skel_open,
      .release =       skel_release,
      .flush =       skel_flush,
      .llseek =       noop_llseek,
};

/*
* usb class driver info in order to get a minor number from the usb core,
* and to have the device registered with the driver core
*/
static struct usb_class_driver skel_class = {
      .name =             "skel%d",
      .fops =             &skel_fops,
      .minor_base =       USB_SKEL_MINOR_BASE,
};

usb_register_dev(interface, &skel_class);调用后, 新生成子设备A，但是cdev结构并没有被分配，既然没有分配,就没有在内核全局变量cdev_map中注册
那么open("/dev/A"); 是如何调用的skel_open呢？

作者: nswcfd 时间: 2017-03-20 18:00
更早版本的代码
http://lxr.free-electrons.com/so ... skeleton.c?v=2.4.37

602       dev->devfs = devfs_register (usb_devfs_handle, name,
603                                     DEVFS_FL_DEFAULT, USB_MAJOR,
604                                     USB_SKEL_MINOR_BASE + dev->minor,
605                                     S_IFCHR | S_IRUSR | S_IWUSR |
606                                     S_IRGRP | S_IWGRP | S_IROTH,
607                                     &skel_fops, NULL);

作者: nswcfd 时间: 2017-03-20 18:08
154 int usb_register_dev(struct usb_interface *intf,
155                   struct usb_class_driver *class_driver)

183       for (minor = minor_base; minor < MAX_USB_MINORS; ++minor) {
184                if (usb_minors[minor])
185                      continue;
186
187             usb_minors[minor] = class_driver->fops;
188                intf->minor = minor;
189                break;
190       }

33 static int usb_open(struct inode *inode, struct file *file)
34 {
35       int err = -ENODEV;
36       const struct file_operations *new_fops;
37
38       down_read(&minor_rwsem);
39       new_fops = fops_get(usb_minors[iminor(inode)]);

作者: nswcfd 时间: 2017-03-20 18:28
usb_major_init -> register_chrdev -> cdev_add

usb_fops/usb_open is also registered here

作者: mxgsgtc 时间: 2017-03-24 08:34
回复 4# nswcfd

非常感谢！

欢迎光临 Chinaunix (http://bbs.chinaunix.net/)