linux driver tutorial ( test on a Raspberry Pi 4B)

A tutorial to the linux driver

the code

The *hello world" example

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

MODULE_LICENSE("Dual BSD/GPL");

static int hello_init(void)
{
	printk(KERN_ALERT"Hello, world\n");
	return 0;
}

static int hello_exit(void)
{
	printk(KERN_ALERT"Goodbye, cruel world\n");
	return 0;
}

module_init(hello_init);
module_exit(hello_exit);

the makefile

ifneq (($KERNELRELEASE),)
	obj-m := hello.o
else
endif

HEADDIR := /lib/modules/4.19.97-v71+/build/
all:
	make -C $(HEADDIR) M=$(PWD) modules

clean:
	make -C $(HEADDIR) M=$(PWD) clean

put Makefile in the same folder with hello.c, then make

results

if compiled successfully, you will get the file hello.ko. In the next step,

insert the module

insmod hello.ko
dmesg | tail

here you will see “Hello, world”.

remove the module

rmmod hello
dmesg | tail

you will find “Goodbye, cruel world”.