Creating the Module

First, find the source that your current Linux kernel was compiled from. You can save the mymodule.c in any one of the folder under staging or drivers directory


mymodule.c

#include <linux/module.h>
#include <linux/config.h>
#include <linux/init.h>

static int __init mymodule_init(void)
{
 printk ("My module worked!\n");
        return 0;
}

static void __exit mymodule_exit(void)
{
 printk ("Unloading my module.\n");
        return;
}

module_init(mymodule_init);
module_exit(mymodule_exit);

MODULE_LICENSE("GPL");

Edit the Makefile in the same directory. Add this line

obj-m += mymodule.o

Compile your module:

 # make -C [top directory of your kernel source] SUBDIRS=$PWD modules

Load the module:

 # insmod ./mymodule.o

And check to see if your message printed out:

# dmesg

At the end of the output:

My module worked!

Now remove the kernel module:

 # rmmod mymodule

Check the output of dmesg again, you could see the output:
 Unloading my module.