Linux Device Driver Development Using Loadable Kernel Module

Linux device drivers are essential software components that enable the operating system to interact with hardware devices. They act as a bridge between the kernel and hardware, allowing the system to utilize various peripherals and components. In this guide, we’ll explore the basics of developing Linux device drivers using loadable kernel modules (LKMs).

What are Linux Device Drivers?

Device drivers are pieces of code that manage specific hardware devices. They provide a standardized interface for the operating system to communicate with hardware, hiding the complexities of different devices from the rest of the system. In Linux, device drivers can be built into the kernel or loaded as modules.

Why Use Loadable Kernel Modules?

Loadable kernel modules offer several advantages:

• Flexibility: Drivers can be loaded and unloaded dynamically without rebooting the system.
• Modularity: Keeps the base kernel small and efficient.
• Ease of development: Allows for faster testing and debugging.

Setting Up the Development Environment

To develop Linux device drivers, you’ll need:

1. A Linux system (e.g. Ubuntu, Fedora)
2. Essential development tools (gcc, make)
3. Linux kernel headers

Install the necessary packages:

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

Writing a Basic “Hello World” Driver

Let’s create a simple driver that prints “Hello, World!” when loaded. Create a file named hello_driver.c:

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

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Your Name");
MODULE_DESCRIPTION("A simple Hello World driver");
MODULE_VERSION("0.1");

static int __init hello_init(void)
{
    printk(KERN_INFO "Hello, World!\n");
    return 0;
}

static void __exit hello_exit(void)
{
    printk(KERN_INFO "Goodbye, World!\n");
}

module_init(hello_init);
module_exit(hello_exit);

Compiling the Driver

Create a Makefile in the same directory:

obj-m += hello_driver.o

all:
    make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules

clean:
    make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean

Compile the driver:

make

sudo insmod hello_driver.ko

sudo rmmod hello_driver

#include <linux/fs.h>

static int device_open(struct inode *inode, struct file *file)
{
    printk(KERN_INFO "Device opened\n");
    return 0;
}

static ssize_t device_read(struct file *filp, char *buffer, size_t length, loff_t *offset)
{
    printk(KERN_INFO "Read operation\n");
    return 0;
}

static ssize_t device_write(struct file *filp, const char *buffer, size_t length, loff_t *offset)
{
    printk(KERN_INFO "Write operation\n");
    return length;
}

static int device_release(struct inode *inode, struct file *file)
{
    printk(KERN_INFO "Device closed\n");
    return 0;
}

static struct file_operations fops = {
    .open = device_open,
    .read = device_read,
    .write = device_write,
    .release = device_release
};