Why device exist in /proc/devices evethough module is unloaded

Question

I am writing a simple charcter driver scull based on ldd. For my sample character driver, evethough module is unloaded device with major number exist in /proc/devices. How to remove that?

My module exit function has

void scull_exit(void)
{
    unregister_chrdev(Major, "scull1");
    cdev_del(my_cdev);  
    printk(KERN_ALERT "Good Bye\n");

}

I could see the old device with its major number when I load new module after unloading the same.

Do you get any warnings on `insmod` or on compilation? – Levente Kurusa Oct 19 '13 at 08:59 — Levente Kurusa, Oct 19 '13 at 08:59

score 3 · Accepted Answer · answered Oct 19 '13 at 12:03

cdev_del takes a pointer, ensure that your my_cdev is a pointer.

void cdev_del(struct cdev *);
It is cdev_del, first and unregister_chrdev later, it seems you have done it the other way, use cdev_del first and then unregister_chrdev_region
You have mixed up old notation of unregister_chrdev and new notation of cdev_del.
- either unregister_chrdev should be used when you use register_chrdev for registering
  
  OR
- "cdev_init/cdev_add after register_chrdev_region" should be used in conjunction with "cdev_del before unregister_chrdev_region"

score 0 · Answer 2 · answered Apr 14 '15 at 06:16

0

struct cdev has an owner field that should be set to THIS_MODULE. Make sure it is set

answered Apr 14 '15 at 06:16

davidh

1
3

Could you please elaborate more your answer adding a little more description about the solution you provide? – abarisone Apr 14 '15 at 06:41
In order to successfully unregister a device its owner should be the relevant module, owner is determined using owner field. for example: cdev.owner = THIS_MODULE – davidh Dec 15 '15 at 15:33

Why device exist in /proc/devices evethough module is unloaded

2 Answers2