<-- notes

Linux device drivers

Environment setup

You need linux headers to be able to compile new module.

To make sure you have linux headers, see if the following path exists:

$ ls /usr/src/linux-headers-`uname -r`
arch   crypto         drivers   fs       init  Kbuild   kernel  

If the above directory is not present, you can install the headers using:

sudo apt-get update && sudo apt-get install linux-headers-$(uname -r)

Once the headers are installed you are good to go.

Writing hello module

To start off, create the following file in any directory.

// hello.c
#include <linux/module.h>


Create the following Makefile to compile your module.

obj-m := hello.o
KDIR := /usr/src/linux-headers-3.2.0-23-generic

	make -C $(KDIR) M=$(PWD) modules
	make -C $(KDIR) M=$(PWD) clean

After running make, you should see following:

# Check that *.ko is created.
vagrant@precise64:~$ ls
hello.c  hello.ko  hello.mod.c  hello.mod.o  hello.o  Makefile  
# Install the module.
vagrant@precise64:~$ sudo insmod hello.ko
# Confirm the it's installed.
vagrant@precise64:~$ lsmod | grep hello
hello                   8217  0
# Remove the module.
vagrant@precise64:~$ sudo rmmod hello
# Confirm that it's removed.
vagrant@precise64:~$ lsmod | grep hello

Expanding further, each module needs to have an init and exit method.

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


static int hello_init(void) {
  printk("<1> Hola Mundo!\n");
  return 0;

static void hello_exit(void) {
  printk("<1>Hasta Luego\n");


Again, use inmod to install the command and you should see Hola Mundo! in dmesg. printk is important here; as kernel will print it to the syslog. Pretty useful in understanding other drivers.