Learn What a Device Driver Is and How the Kernel Uses It

A device driver is a specialized program that allows the Linux kernel to communicate with hardware devices. Its core purpose is to translate generic kernel commands into device-specific operations, so the operating system can control and interact with a wide variety of hardware without needing to know the intricate details of each device. Device drivers act as a bridge between the kernel and the physical components of a computer, such as disks, network cards, or USB peripherals. By providing a standard interface, drivers enable the kernel to manage devices efficiently and securely.

minimal_driver.c


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

// Initialization function
static int __init minimal_driver_init(void) {
    printk(KERN_INFO "Minimal driver loaded\n");
    return 0;
}

// Exit function
static void __exit minimal_driver_exit(void) {
    printk(KERN_INFO "Minimal driver unloaded\n");
}

module_init(minimal_driver_init);
module_exit(minimal_driver_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Your Name");
MODULE_DESCRIPTION("A minimal example device driver");

The kernel interacts with device drivers through specific entry points, most notably the initialization and exit functions. When a driver is loaded, the kernel calls the function registered with module_init, which is responsible for setting up the driver, registering devices, and preparing resources. When the driver is unloaded, the function registered with module_exit is called to clean up and free any resources. In the minimal driver example above, minimal_driver_init and minimal_driver_exit serve these roles, providing a controlled way for the kernel to manage the driver's lifecycle.

log_message_driver.c


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

static int __init log_message_driver_init(void) {
    printk(KERN_INFO "Hello from the kernel driver!\n");
    return 0;
}

static void __exit log_message_driver_exit(void) {
    printk(KERN_INFO "Goodbye from the kernel driver!\n");
}

module_init(log_message_driver_init);
module_exit(log_message_driver_exit);

MODULE_LICENSE("GPL");

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Section 1. Chapter 1

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minimal_driver.c


              123456789101112131415161718192021
            
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>

// Initialization function
static int __init minimal_driver_init(void) {
    printk(KERN_INFO "Minimal driver loaded\n");
    return 0;
}

// Exit function
static void __exit minimal_driver_exit(void) {
    printk(KERN_INFO "Minimal driver unloaded\n");
}

module_init(minimal_driver_init);
module_exit(minimal_driver_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Your Name");
MODULE_DESCRIPTION("A minimal example device driver");

log_message_driver.c


              1234567891011121314151617
            
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>

static int __init log_message_driver_init(void) {
    printk(KERN_INFO "Hello from the kernel driver!\n");
    return 0;
}

static void __exit log_message_driver_exit(void) {
    printk(KERN_INFO "Goodbye from the kernel driver!\n");
}

module_init(log_message_driver_init);
module_exit(log_message_driver_exit);

MODULE_LICENSE("GPL");

Everything was clear?

Thanks for your feedback!

Section 1. Chapter 1