Linux Kernel Modules and Device Drivers

Hands-on Linux kernel module and character device driver development, working through the boundary between user space and kernel space.

What's here

The modules build up from a bare "hello world" in kernel space to a working character device driver. Each one isolates a single idea so it's clear what changed.

Module	What it demonstrates
hello_kernel	A minimal loadable module with init/exit and printk
hello_mod	Module metadata, licensing, and the build basics
mod_parameter	Passing parameters at insmod time
dev_num	Registering and allocating device numbers (major/minor)
chardev	A full character device driver: dynamic major/minor allocation plus open, read, write, and release

Concepts covered

• Loadable kernel modules and the module lifecycle
• Dynamic device-number allocation
• The file_operations interface and the VFS entry points
• Moving data across the user/kernel boundary with copy_to_user and copy_from_user
• Kernel logging through printk and dmesg

Prerequisites

• Linux kernel headers (linux-headers-$(uname -r))
• gcc and make

Build and test

cd chardev            # or any module folder
make                  # builds the .ko against the running kernel
sudo insmod chardev.ko
dmesg | tail          # view the kernel log output
sudo rmmod chardev

A word of caution: build against a matching kernel-headers version, and load modules on a VM or test machine rather than anything you care about.

Skills demonstrated

Linux kernel, device drivers, character devices, kernel modules, the file_operations interface, user and kernel space, system calls, and C.