#include <linux/module.h>
#include <linux/fs.h>
#include <linux/cdev.h>

MODULE_LICENSE("GPL v2");

static ssize_t demo_read(struct file *filp, char __user *buff, size_t size, loff_t *pos)
{
	printk("%s %d\n", __func__, __LINE__);
	return size;
}

static ssize_t demo_write(struct file *filp, const char __user *buff, size_t size, loff_t *pos)
{
	printk("%s %d\n", __func__, __LINE__);
	return size;
}

static int demo_open(struct inode *inode, struct file *filp)
{
	printk("%s %d\n", __func__, __LINE__);
	return 0;
}

static int demo_release(struct inode *inode, struct file *filp)
{
	printk("%s %d\n", __func__, __LINE__);
	return 0;
}

struct file_operations demo_fops = {
	.owner      = THIS_MODULE,
	.read       = demo_read,
	.write      = demo_write,
	.open       = demo_open,
	.release    = demo_release,
};

static dev_t dev;
static struct cdev *cdev;

int demo_init(void)
{
	int rc;

	rc = alloc_chrdev_region(&dev, 0, 1, "demo");
	if (rc) {
		printk("failed to alloc chrdev number\n");
		return rc;
	}

	cdev = cdev_alloc();
	if (!cdev) {
		printk("failed to alloc cdev\n");
		rc = -ENOMEM;
		goto out_unregister_chrdev;
	}

	cdev->owner = THIS_MODULE;
	cdev_init(cdev, &demo_fops);

	rc = cdev_add(cdev, dev, 1);
	if (rc) {
		printk("failed to add char device\n");
		goto out_free_cdev;
	}

	return 0;

out_free_cdev:
	kobject_put(&cdev->kobj);	

out_unregister_chrdev:
	unregister_chrdev_region(dev, 1);

	return rc;
}

void demo_exit(void)
{
	cdev_del(cdev);
	unregister_chrdev_region(dev, 1);
}

module_init(demo_init);
module_exit(demo_exit);