/*
   * Sample kfifo int type implementation
   *
   * Copyright (C) 2010 Stefani Seibold <stefani@seibold.net>
   *
   * Released under the GPL version 2 only.
   *
   */
  
  #include <linux/init.h>
  #include <linux/module.h>
  #include <linux/proc_fs.h>
  #include <linux/mutex.h>
  #include <linux/kfifo.h>
  
  /*
   * This module shows how to create a int type fifo.
   */
  
  /* fifo size in elements (ints) */
  #define FIFO_SIZE	32
  
  /* name of the proc entry */
  #define	PROC_FIFO	"int-fifo"
  
  /* lock for procfs read access */
  static DEFINE_MUTEX(read_lock);
  
  /* lock for procfs write access */
  static DEFINE_MUTEX(write_lock);
  
  /*
   * define DYNAMIC in this example for a dynamically allocated fifo.
   *
   * Otherwise the fifo storage will be a part of the fifo structure.
   */
  #if 0
  #define DYNAMIC
  #endif
  
  #ifdef DYNAMIC
  static DECLARE_KFIFO_PTR(test, int);
  #else
  static DEFINE_KFIFO(test, int, FIFO_SIZE);
  #endif

  static const int expected_result[FIFO_SIZE] = {
  	 3,  4,  5,  6,  7,  8,  9,  0,
  	 1, 20, 21, 22, 23, 24, 25, 26,
  	27, 28, 29, 30, 31, 32, 33, 34,
  	35, 36, 37, 38, 39, 40, 41, 42,
  };

  static int __init testfunc(void)
  {
  	int		buf[6];

  	int		i, j;

  	unsigned int	ret;
  
  	printk(KERN_INFO "int fifo test start
  ");
  
  	/* put values into the fifo */
  	for (i = 0; i != 10; i++)
  		kfifo_put(&test, &i);
  
  	/* show the number of used elements */
  	printk(KERN_INFO "fifo len: %u
  ", kfifo_len(&test));
  
  	/* get max of 2 elements from the fifo */
  	ret = kfifo_out(&test, buf, 2);
  	printk(KERN_INFO "ret: %d
  ", ret);
  	/* and put it back to the end of the fifo */
  	ret = kfifo_in(&test, buf, ret);
  	printk(KERN_INFO "ret: %d
  ", ret);

  	/* skip first element of the fifo */
  	printk(KERN_INFO "skip 1st element
  ");
  	kfifo_skip(&test);
  
  	/* put values into the fifo until is full */
  	for (i = 20; kfifo_put(&test, &i); i++)
  		;

  
  	printk(KERN_INFO "queue len: %u
  ", kfifo_len(&test));
  
  	/* show the first value without removing from the fifo */
  	if (kfifo_peek(&test, &i))
  		printk(KERN_INFO "%d
  ", i);

  	/* check the correctness of all values in the fifo */
  	j = 0;
  	while (kfifo_get(&test, &i)) {
  		printk(KERN_INFO "item = %d
  ", i);
  		if (i != expected_result[j++]) {
  			printk(KERN_WARNING "value mismatch: test failed
  ");
  			return -EIO;
  		}
  	}
  	if (j != ARRAY_SIZE(expected_result)) {
  		printk(KERN_WARNING "size mismatch: test failed
  ");
  		return -EIO;
  	}
  	printk(KERN_INFO "test passed
  ");

  
  	return 0;
  }
  
  static ssize_t fifo_write(struct file *file, const char __user *buf,
  						size_t count, loff_t *ppos)
  {
  	int ret;
  	unsigned int copied;
  
  	if (mutex_lock_interruptible(&write_lock))
  		return -ERESTARTSYS;
  
  	ret = kfifo_from_user(&test, buf, count, &copied);
  
  	mutex_unlock(&write_lock);
  
  	return ret ? ret : copied;
  }
  
  static ssize_t fifo_read(struct file *file, char __user *buf,
  						size_t count, loff_t *ppos)
  {
  	int ret;
  	unsigned int copied;
  
  	if (mutex_lock_interruptible(&read_lock))
  		return -ERESTARTSYS;
  
  	ret = kfifo_to_user(&test, buf, count, &copied);
  
  	mutex_unlock(&read_lock);
  
  	return ret ? ret : copied;
  }
  
  static const struct file_operations fifo_fops = {
  	.owner		= THIS_MODULE,
  	.read		= fifo_read,
  	.write		= fifo_write,

  	.llseek		= noop_llseek,

  };
  
  static int __init example_init(void)
  {
  #ifdef DYNAMIC
  	int ret;
  
  	ret = kfifo_alloc(&test, FIFO_SIZE, GFP_KERNEL);
  	if (ret) {
  		printk(KERN_ERR "error kfifo_alloc
  ");
  		return ret;
  	}
  #endif

  	if (testfunc() < 0) {
  #ifdef DYNAMIC
  		kfifo_free(&test);
  #endif
  		return -EIO;
  	}

  
  	if (proc_create(PROC_FIFO, 0, NULL, &fifo_fops) == NULL) {
  #ifdef DYNAMIC
  		kfifo_free(&test);
  #endif
  		return -ENOMEM;
  	}
  	return 0;
  }
  
  static void __exit example_exit(void)
  {
  	remove_proc_entry(PROC_FIFO, NULL);
  #ifdef DYNAMIC
  	kfifo_free(&test);
  #endif
  }
  
  module_init(example_init);
  module_exit(example_exit);
  MODULE_LICENSE("GPL");
  MODULE_AUTHOR("Stefani Seibold <stefani@seibold.net>");