Summary - Driver basics

Combine module structure and fops to write a character driver skeleton.

Summary - Driver basics

This group covered the basics of writing a kernel module: loading with insmod/rmmod, the module_init/module_exit skeleton, logging with printk, the device number dev_t, and the user-facing file_operations.

On load, the init function runs, takes resources and registers a device number. When the user opens the /dev file, .open fires; reads and writes go through .read and .write. Now you'll write a mini task that combines the five concepts.

Exercise Print driver info

Define void print_driver_info(const char *topic, const char *detail) with body printf("%s -> %s\n", topic, detail);. In main call it for five topics: ("insmod", "load"), ("module_init", "start"), ("printk", "log"), ("dev_t", "major:minor"), ("fops", "open/read/write").

Show example solution

#include <stdio.h>

void print_driver_info(const char *topic, const char *detail) {
    printf("%s -> %s\n", topic, detail);
}

int main(void) {
    print_driver_info("insmod", "load");
    print_driver_info("module_init", "start");
    print_driver_info("printk", "log");
    print_driver_info("dev_t", "major:minor");
    print_driver_info("fops", "open/read/write");
    return 0;
}

Driver basics done

Congratulations! You've finished the driver basics. You saw the whole skeleton of writing a kernel module: loading, init/exit, logging, device numbers and file operations. You can now lay out a simple character driver.

The next group moves to compiler construction: lexer, parser, AST, code generation and symbol table. You'll build a tool that analyses code; the C skills you learned for drivers apply there too. Continue when ready.

Test yourself

When is a module's init function called?
- On removal
- Only at build time
- On every read call
- On load
Show answer

On load — The module_init function runs on load.
Match five driver concepts

insmod

Loads a module
module_init

Initialization
printk

Writes a log
dev_t

Device number
fops

User interface

Next lesson: Lexer

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