Simple Module

/*
 * Copyright (C) 2011 - Raphael S.Carvalho (a.k.a Utroz)
 * Linux Device Drivers - A simple module
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the Free
 * Software Foundation; either version 2 of the License, or (at your option)
 * any later version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
 * more details.  You should have received a copy of the GNU General Public
 * License along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA.
 */

/* Makefile */
obj-m := module.o

/* How to set up the module */
make -C /lib/modules/`uname -r`/build/ M=$PWD modules
insmod module.ko howmany=10 whom="Test" // insert module
dmesg or cat /var/log/messages // show module
rmmod module // remove module.

/* Result in Display */
 [ 6186.736200] The process is "insmod" (pid 7523)
 [ 6186.736202] Kernel Version: 0020625

/* Module code */
#include <linux/init.h>
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/version.h>
#include <linux/kdev_t.h>
#include <linux/fs.h>

static char *whom = "world";
static int howmany = 1;
module_param(howmany, int, S_IRUGO);
module_param(whom, charp, S_IRUGO);

static dev_t major = 0;

static void inline dec_to_hex(char *s, unsigned dec)
{
    unsigned rest, i;

    memset (s, '0', 6);
    for (i = 6; dec >= 16; dec /= 16, i--)
    s[i] = ((rest = dec % 16) >= 10) ?
    rest - 10 + 'A' : rest + '0';

    s[i] = dec + '0';
}

static int __init start_module(void)
{
    char current_v[8] = { 0 };
    int result;
    dev_t dev, minor = 0;

    if(major) {
        dev = MKDEV(major, minor);
        result = register_chrdev_region(dev, 2, "scull");
    } else {
        result = alloc_chrdev_region(&dev, minor, 2, "scull");
        major = MAJOR(dev);
    }
    if (result < 0) {
        printk(KERN_WARNING "can't get major %d", major);
        return result;
    }

    printk(KERN_INFO "Minor: %d Major: %d", minor, major);

    dec_to_hex(current_v, LINUX_VERSION_CODE);

    printk(KERN_INFO "Whom: %s Howmany: %d", whom, howmany);

    printk(KERN_INFO "The process is \"%s\" (pid %i)\n",
           current->comm, current->pid);
    printk(KERN_INFO "Kernel Version: %s\n",
           current_v);
    return 0;
}

static void __exit clean_up(void)
{
    unregister_chrdev_region(major, 2);
    printk(KERN_ALERT "Closing the module.\n");
}
module_init(start_module);
module_exit(clean_up);

MODULE_LICENSE("Dual BSD/GPL");
MODULE_AUTHOR("Raphael S.Carvalho");
MODULE_DESCRIPTION("This module is only a test.");
MODULE_VERSION("0.0.1");