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.

Answer 1

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

   void cdev_del(struct cdev *);

2. 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

3. 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"

Answer 2

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