null.c

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/cdev.h>
#include <linux/errno.h>
#include <asm/uaccess.h>

#define FIRST_MINOR 0
#define MINOR_CNT 1

/* Add your variables here */

static char t;
static dev_t dev;
static struct cdev c_dev;

static int my_open(struct inode *i, struct file *f)
{
    printk(KERN_INFO "Driver: In open\n");
    /* Add code here */
    return 0;
}
static int my_close(struct inode *i, struct file *f)
{
    printk(KERN_INFO "Driver: In close\n");
    /* Add code here */
    return 0;
}
static ssize_t my_read(struct file *f, char __user *buf, size_t len, loff_t *off)
{
    printk(KERN_INFO "Driver: In read - Buf: %p; Len: %d; Off: %Ld\nData:\n", buf, len, *off);
    /* Add code here */
        if (copy_to_user(buf, &t, 1)!=0)
        {
            return -EFAULT;
        }
        /*printk("(%c) ", buf);*/
    return 1 /* read cnt */;
}
static ssize_t my_write(struct file *f, const char __user *buf, size_t len, loff_t *off)
{
    int i;

    printk(KERN_INFO "Driver: In write - Buf: %p; Len: %d; Off: %Ld\nData:\n", buf, len, *off);
    printk(KERN_INFO);
    for (i = 0; i < len; i++)
    {
        if (copy_from_user(&t, buf + i, 1))
        {
            return -EFAULT;
        }
        printk("%02X(%c) ", t, t);
    }
    printk("\n");
    /* Add code here */

    return len /* wrote cnt */;
}

static struct file_operations driver_fops =
{
    .owner = THIS_MODULE,
    .open = my_open,
    .release = my_close,
    .read = my_read,
    .write = my_write
};

int __init init_module()
{
    int ret;

    printk(KERN_INFO "Hello Universe\n");
    if ((ret = alloc_chrdev_region(&dev, FIRST_MINOR, MINOR_CNT, "null")) < 0)
    {
        return ret;
    }

    printk(KERN_INFO "(Major, Minor): (%d, %d)\n", MAJOR(dev), MINOR(dev));

    cdev_init(&c_dev, &driver_fops);

    if ((ret = cdev_add(&c_dev, dev, MINOR_CNT)) < 0)
    {
        unregister_chrdev_region(dev, MINOR_CNT);
        return ret;
    }
  
    return 0;
}

void __exit cleanup_module()
{
    cdev_del(&c_dev);
    unregister_chrdev_region(dev, MINOR_CNT);
    printk(KERN_INFO "Bye Universe\n");
}

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Anil Kumar Pugalia <anil@sysplay.in>");
MODULE_DESCRIPTION("First Character Driver");