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How to write Linux Kernel Modules

1) hello_driver.c program which conatins the init and exit functions

/* This is my first driver module program */
#include<linux/init.h>
#include<linux/module.h>
#include<linux/kernel.h>

static int __init hello_init(void)
{
        printk(KERN_ALERT "Hello my first module \n");
        return 0;
}

static void __exit hello_exit(void)
{
        printk(KERN_ALERT "Good Bye \n");
}
module_init(hello_init);
module_exit(hello_exit);
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Hello world Module");
MODULE_AUTHOR("SURENDRA PATIL");


2) Make file for the module

ifneq ($(KERNELRELEASE),)
        obj-m := hello_driver.o
else
        KDIR ?= /lib/modules/$(shell uname -r)/build
        PWD :=$(shell pwd)
default:
        $(MAKE) -C $(KDIR) M=$(PWD)
endif

Note:Both file should be in the same directory.

3) when this make file is run hello_driver.ko will be produced.
 

4) insmod ./hello_driver.ko -> will insert the module into kernel modules. To see the message print the kernel dmesg logs.
 
  you can see "Hello my first module" displayed in the dmesg log.

5) lsmod -> displays all the kernel modules




















see that "hello_driver" module is displayed in kernel modules.

6) rmmod hello_driver.ko -> will remove the module from kernel

Note that "Good Bye" message is printed in dmesg kernel logs


Hurray you wrote a Linux kernel module now :-) keep it up :-)


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