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

#define MAX_BUF_SIZE 1024
#define DEVICE_NAME "MY_AUDIO_DEVICE"
#define TRUE 1
#define FALSE !TRUE

static ssize_t device_read(struct file*, char*, size_t, loff_t*);
static ssize_t device_write(struct file*, const char*, size_t, loff_t*);
static int device_open(struct inode*, struct file*);
static int device_release(struct inode*, struct file*);

static char audio_buffer[MAX_BUF_SIZE] = {"THIS BUFFER DOES NOT REALLY INCLUDE AUDIO DATA"};

static struct file_operations fops =
{
    .read = device_read,
    .write = device_write,
    .open = device_open,
    .release = device_release
};

static int major_number = 0;
static char is_opened = FALSE;

static int driver_init(void)
{
    if ((major_number = register_chrdev(0, DEVICE_NAME, &fops)) < 0)
    {
        printk("register_chrdev failed with status = %d\n", major_number);
        return major_number;
    }

    printk("Device driver was successfully loaded. The major number is: %d\n", major_number);
    printk("'mknod /dev/%s c %d 0'.\n", DEVICE_NAME, major_number);
    return 0;
}


static void driver_cleanup(void)
{
    unregister_chrdev(major_number, DEVICE_NAME);
}

static int device_open(struct inode* node, struct file* f)
{
    if (is_opened)
        return -EBUSY;

    is_opened = TRUE;

    return 0;
}

static int device_release(struct inode* node, struct file* f)
{
    is_opened = FALSE;
    return 0;
}

static ssize_t device_write(struct file* file, const char* buffer, size_t length, loff_t* offset)
{
    printk("Write operation is not supported on this device.\n");
    return -EINVAL;
}

static ssize_t device_read(struct file* file, char* buffer, size_t length, loff_t* offset)
{
    if (length >= MAX_BUF_SIZE)
        length = MAX_BUF_SIZE - 1;
    if (copy_to_user(buffer, audio_buffer, length))
        return -EINVAL;
    return length;
}

module_init(driver_init);
module_exit(driver_cleanup);