Hello World Kernel Module

hello.c

#include <linux/module.h>

MODULE_LICENSE("GPL v2");
MODULE_DESCRIPTION("Hello world kernel module");

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

static void mymodule_exit(void) {
        printk(KERN_ALERT "Good Bye world!\n");
}

module_init(mymodule_init);
module_exit(mymodule_exit);

Makefile

obj-m := hello.o

KDIR    := /lib/modules/$(shell uname -r)/build
PWD     := $(shell pwd)
VERBOSE = 0

default:
	$(MAKE) -C $(KDIR) M=$(PWD) KBUILD_VERBOSE=$(VERBOSE) modules

clean:
	rm -f *.o *.ko *.mod.c