/*
   * Sample dynamic sized record fifo 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 variable sized record fifo.
   */
  
  /* fifo size in elements (bytes) */
  #define FIFO_SIZE	128
  
  /* name of the proc entry */
  #define	PROC_FIFO	"record-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
  
  /*
   * struct kfifo_rec_ptr_1 and  STRUCT_KFIFO_REC_1 can handle records of a
   * length between 0 and 255 bytes.
   *
   * struct kfifo_rec_ptr_2 and  STRUCT_KFIFO_REC_2 can handle records of a
   * length between 0 and 65535 bytes.
   */
  
  #ifdef DYNAMIC
  struct kfifo_rec_ptr_1 test;
  
  #else
  typedef STRUCT_KFIFO_REC_1(FIFO_SIZE) mytest;
  
  static mytest test;
  #endif

  static const char *expected_result[] = {
  	"a",
  	"bb",
  	"ccc",
  	"dddd",
  	"eeeee",
  	"ffffff",
  	"ggggggg",
  	"hhhhhhhh",
  	"iiiiiiiii",
  	"jjjjjjjjjj",
  };

  static int __init testfunc(void)
  {
  	char		buf[100];
  	unsigned int	i;
  	unsigned int	ret;
  	struct { unsigned char buf[6]; } hello = { "hello" };
  
  	printk(KERN_INFO "record fifo test start
  ");
  
  	kfifo_in(&test, &hello, sizeof(hello));
  
  	/* show the size of the next record in the fifo */
  	printk(KERN_INFO "fifo peek len: %u
  ", kfifo_peek_len(&test));
  
  	/* put in variable length data */
  	for (i = 0; i < 10; i++) {
  		memset(buf, 'a' + i, i + 1);
  		kfifo_in(&test, buf, i + 1);
  	}

  	/* skip first element of the fifo */
  	printk(KERN_INFO "skip 1st element
  ");
  	kfifo_skip(&test);

  	printk(KERN_INFO "fifo len: %u
  ", kfifo_len(&test));
  
  	/* show the first record without removing from the fifo */
  	ret = kfifo_out_peek(&test, buf, sizeof(buf));
  	if (ret)
  		printk(KERN_INFO "%.*s
  ", ret, buf);

  	/* check the correctness of all values in the fifo */
  	i = 0;

  	while (!kfifo_is_empty(&test)) {
  		ret = kfifo_out(&test, buf, sizeof(buf));

  		buf[ret] = '\0';
  		printk(KERN_INFO "item = %.*s
  ", ret, buf);
  		if (strcmp(buf, expected_result[i++])) {
  			printk(KERN_WARNING "value mismatch: test failed
  ");
  			return -EIO;
  		}
  	}
  	if (i != 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;
  	}
  #else
  	INIT_KFIFO(test);
  #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>");