Simple kernel module example. Lists process list and count.

lkm_hello1.c

#include <linux/module.h>       // Needed by all modules
#include <linux/kernel.h>       // KERN_INFO
#include <linux/sched.h>        // for_each_process, pr_info


void procs_info_print(void)
{
        struct task_struct* task_list;
        size_t process_counter = 0;
        for_each_process(task_list) {
                pr_info("== %s [%d]\n", task_list->comm, task_list->pid);
                ++process_counter;
        }
        printk(KERN_INFO "== Number of process: %zu\n", process_counter);
}

int init_module(void)
{
        printk(KERN_INFO "[ INIT ==\n");

        procs_info_print();

        return 0;
}

void cleanup_module(void)
{
        printk(KERN_INFO "== CLEANUP ]\n");
}

MODULE_LICENSE("MIT");

Makefile

obj-m += lkm_hello1.o
KDIR ?= /lib/modules/$(shell uname -r)/build

all:
	make -C $(KDIR) M=$(PWD) modules

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