/*  The 99 Bottles of Beer Linux Kernel Module v1.1
 *  (supports multiple driver instances)
 *
 *  by Stefan Scheler <sts[at]synflood[dot]de>
 *  August 2nd, 2005 - Ernstthal, Germany
 *
 *  Usage:
 *  1) compile the module
 *  2) create the device: mknod /dev/bottles c 240 0
 *  3) load the module: insmod bottles.ko
 *  4) print the song with: cat /dev/bottles
 */

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

#define DRIVER_MAJOR 240
#define BUFFERSIZE 160
#define PLURALS(b) (b>1)?"s":""

MODULE_AUTHOR("Stefan Scheler <sts[at]synflood[dot]de>");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("The 99 Bottles of Beer Linux Kernel Module");
MODULE_SUPPORTED_DEVICE("Bottle of Beer");

struct _instance_data {
    int bytes_avail, bytes_sent, bottles;
    char buf[BUFFERSIZE];
};

static void fill_buffer(char *buf, int b) {
    char line[BUFFERSIZE/2];
    if (b>0) {
        sprintf(buf, "%d bottle%s of beer on the wall, %d bottle%s of beer.\n" \
                     "Take one down and pass it around, ", b, PLURALS(b), b, PLURALS(b));
        if (b==1)
            strcat(buf, "no more bottles of beer on the wall.\n");
        else {
            sprintf(line, "%d bottle%s of beer on the wall.\n", b-1, PLURALS(b-1));
            strcat(buf, line);
        }
    } else {
        sprintf(buf, "No more bottles of beer on the wall, no more bottles of beer.\n" \
                     "Go to the store and buy some more, 99 bottles of beer on the wall.\n");
    }
}

static ssize_t driver_read(struct file *instance, char *userbuffer, size_t count, loff_t *offset) {
    struct _instance_data *iptr = (struct _instance_data *)instance->private_data;

    int to_copy;
    int not_copied;

refillbuffer:
    fill_buffer(iptr->buf, iptr->bottles);
    iptr->bytes_avail = strlen(iptr->buf)+1;
    to_copy = iptr->bytes_avail-iptr->bytes_sent;

    if (to_copy>0) {
        if (to_copy> count) to_copy=count;
        not_copied=copy_to_user(userbuffer, iptr->buf+iptr->bytes_sent, to_copy);
        iptr->bytes_sent += to_copy-not_copied;
        return (to_copy-not_copied);
    }

    if ((to_copy==0) && (iptr->bottles>0)) {
        iptr->bytes_sent=0; 
        iptr->bottles--;
        goto refillbuffer;
    }

    return 0;
}

int driver_open(struct inode *devicefile, struct file *instance)  {
    struct _instance_data *iptr;
    iptr = (struct _instance_data *)kmalloc(sizeof(struct _instance_data), GFP_KERNEL);
    
    if (!iptr) 
        return -1;

    iptr->bytes_sent = 0;
    iptr->bottles = 99;
    instance->private_data = iptr;

    return 0;
}

int driver_close(struct inode *devicefile, struct file *instance)  {
    if (instance->private_data)
        kfree(instance->private_data);
    return 0;
}

static struct file_operations fops = {
    .owner   = THIS_MODULE,
    .open    = driver_open,
    .release = driver_close,
    .read    = driver_read,
};

static int __init __init_module(void) {
    if(register_chrdev(DRIVER_MAJOR, "99 Bottles of Beer", &fops) == 0) 
        return 0;
    return -EIO;
}

static void __exit __cleanup_module(void) {
    unregister_chrdev(DRIVER_MAJOR, "99 Bottles of Beer");
}

module_init(__init_module);
module_exit(__cleanup_module);