#define __KERNEL__
#define MODULE

#include <linux/modversions.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <asm/uaccess.h>

#if CONFIG_DEVFS_FS
# include <linux/devfs_fs_kernel.h>
#endif

#define DEVICE_NAME "hellodev"
#define DEVICE_MAJOR 123

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Fredrik Roubert");
MODULE_DESCRIPTION("Hello, world!");
MODULE_SUPPORTED_DEVICE(DEVICE_NAME);

#define PRINTK(...) printk(KERN_INFO DEVICE_NAME ": " __VA_ARGS__)


static const char msg[] = "Hello, world!\n";

#if CONFIG_DEVFS_FS
static devfs_handle_t devfs_handle;
#endif

static ssize_t hellodev_read(struct file *, char *, size_t, loff_t *);
static int hellodev_open(struct inode *, struct file *);
static int hellodev_release(struct inode *, struct file *);

static struct file_operations fops =
{
	.read = hellodev_read,
	.open = hellodev_open,
	.release = hellodev_release
};


static ssize_t
hellodev_read(struct file *filp, char *buf, size_t len, loff_t *off)
{
	loff_t i = *off;
	size_t j = 0;

	while (j < len && msg[i] != '\0')
		put_user(msg[i ++], &buf[j ++]);

	*off = i;
	return j;
}


static int
hellodev_open(struct inode *inop, struct file *filp)
{
	MOD_INC_USE_COUNT;
	return 0;
}


static int
hellodev_release(struct inode *inop, struct file *filp)
{
	MOD_DEC_USE_COUNT;
	return 0;
}


static int __init
hellodev_init(void)
{
	PRINTK("Initializing ...\n");

#if CONFIG_DEVFS_FS
	if ((devfs_handle = devfs_register(NULL, DEVICE_NAME, DEVFS_FL_DEFAULT,
		DEVICE_MAJOR, 0, S_IFCHR | S_IRUGO, &fops, NULL)) == NULL)
	{
		PRINTK("devfs_register() failed.\n");
		return -EIO;
	}
#else
	int s;
	if ((s = register_chrdev(DEVICE_MAJOR, DEVICE_NAME, &fops)) < 0)
	{
		PRINTK("register_chrdev() failed, error code %d.\n", s);
		return s;
	}
#endif

	PRINTK("Initialized.\n");
	return 0;
}


static void __exit
hellodev_exit(void)
{
#if CONFIG_DEVFS_FS
	devfs_unregister(devfs_handle);
#else
	int s;
	if ((s = unregister_chrdev(DEVICE_MAJOR, DEVICE_NAME)) < 0)
		PRINTK("unregister_chrdev() failed, error code %d.\n", s);
#endif

	PRINTK("Unloaded.\n");
}

module_init(hellodev_init);
module_exit(hellodev_exit);