Chapter 11. Kernel module improvement

[CharlzKlug]

The kernel module, that was described in the chapter 11 does not work in the linux kernel version 5.4.0-139 ubuntu. The following program works fine:

#include <linux/proc_fs.h> // For file_operations, proc_file_read, proc_create
#include <linux/uaccess.h> // For copy_to_user

// The structure pointing to the proc file
struct proc_dir_entry *proc_file;

// The read callback function
ssize_t proc_file_read(struct file *file, char __user *ubuf,
               size_t count, loff_t *ppos) {
  int copied = 0;
  char message[] = "Hello World From Kernel Module!\n";
  int len= strlen(message);

  if (*ppos >0)
    return 0;

  copied= copy_to_user(ubuf, message, len);

  if (copied != 0)
    return -EFAULT;

  *ppos += len;
  return len;
}

static const struct file_operations proc_file_fops = {
                              .owner = THIS_MODULE,
                              .read = proc_file_read
};

// The module initialization callback
static int __init hwkm_init(void) {
  proc_file = proc_create("hwkm", 0, NULL, &proc_file_fops);
  if (!proc_file) {
    return -ENOMEM;
  }
  printk("Hello World module is loaded.\n");
  return 0;
}

// The module exit callback
static void __exit hkwm_exit(void) {
  proc_remove(proc_file);
  printk("Goodbye World!\n");
}

// Defining module callbacks
module_init(hwkm_init);
module_exit(hkwm_exit);

// Module license
MODULE_LICENSE("GPL");