original development tree for Linux kernel GTP module; now long in mainline.
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/*
* Sample kfifo byte stream 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 byte stream fifo.
*/
/* fifo size in elements (bytes) */
#define FIFO_SIZE 32
/* name of the proc entry */
#define PROC_FIFO "bytestream-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 struct kfifo test;
#else
static DECLARE_KFIFO(test, unsigned char, FIFO_SIZE);
#endif
static const unsigned char 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)
{
unsigned char buf[6];
unsigned char i, j;
unsigned int ret;
printk(KERN_INFO "byte stream fifo test start\n");
/* put string into the fifo */
kfifo_in(&test, "hello", 5);
/* 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\n", kfifo_len(&test));
/* get max of 5 bytes from the fifo */
i = kfifo_out(&test, buf, 5);
printk(KERN_INFO "buf: %.*s\n", i, buf);
/* get max of 2 elements from the fifo */
ret = kfifo_out(&test, buf, 2);
printk(KERN_INFO "ret: %d\n", ret);
/* and put it back to the end of the fifo */
ret = kfifo_in(&test, buf, ret);
printk(KERN_INFO "ret: %d\n", ret);
/* skip first element of the fifo */
printk(KERN_INFO "skip 1st element\n");
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\n", kfifo_len(&test));
/* show the first value without removing from the fifo */
if (kfifo_peek(&test, &i))
printk(KERN_INFO "%d\n", i);
/* check the correctness of all values in the fifo */
j = 0;
while (kfifo_get(&test, &i)) {
printk(KERN_INFO "item = %d\n", i);
if (i != expected_result[j++]) {
printk(KERN_WARNING "value mismatch: test failed\n");
return -EIO;
}
}
if (j != ARRAY_SIZE(expected_result)) {
printk(KERN_WARNING "size mismatch: test failed\n");
return -EIO;
}
printk(KERN_INFO "test passed\n");
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\n");
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>");