1/*
2 * Sample kfifo byte stream implementation
3 *
4 * Copyright (C) 2010 Stefani Seibold <stefani@seibold.net>
5 *
6 * Released under the GPL version 2 only.
7 *
8 */
9
10#include <linux/init.h>
11#include <linux/module.h>
12#include <linux/proc_fs.h>
13#include <linux/mutex.h>
14#include <linux/kfifo.h>
15
16/*
17 * This module shows how to create a byte stream fifo.
18 */
19
20/* fifo size in elements (bytes) */
21#define FIFO_SIZE	32
22
23/* name of the proc entry */
24#define	PROC_FIFO	"bytestream-fifo"
25
26/* lock for procfs read access */
27static DEFINE_MUTEX(read_lock);
28
29/* lock for procfs write access */
30static DEFINE_MUTEX(write_lock);
31
32/*
33 * define DYNAMIC in this example for a dynamically allocated fifo.
34 *
35 * Otherwise the fifo storage will be a part of the fifo structure.
36 */
37#if 0
38#define DYNAMIC
39#endif
40
41#ifdef DYNAMIC
42static struct kfifo test;
43#else
44static DECLARE_KFIFO(test, unsigned char, FIFO_SIZE);
45#endif
46
47static const unsigned char expected_result[FIFO_SIZE] = {
48	 3,  4,  5,  6,  7,  8,  9,  0,
49	 1, 20, 21, 22, 23, 24, 25, 26,
50	27, 28, 29, 30, 31, 32, 33, 34,
51	35, 36, 37, 38, 39, 40, 41, 42,
52};
53
54static int __init testfunc(void)
55{
56	unsigned char	buf[6];
57	unsigned char	i, j;
58	unsigned int	ret;
59
60	printk(KERN_INFO "byte stream fifo test start\n");
61
62	/* put string into the fifo */
63	kfifo_in(&test, "hello", 5);
64
65	/* put values into the fifo */
66	for (i = 0; i != 10; i++)
67		kfifo_put(&test, i);
68
69	/* show the number of used elements */
70	printk(KERN_INFO "fifo len: %u\n", kfifo_len(&test));
71
72	/* get max of 5 bytes from the fifo */
73	i = kfifo_out(&test, buf, 5);
74	printk(KERN_INFO "buf: %.*s\n", i, buf);
75
76	/* get max of 2 elements from the fifo */
77	ret = kfifo_out(&test, buf, 2);
78	printk(KERN_INFO "ret: %d\n", ret);
79	/* and put it back to the end of the fifo */
80	ret = kfifo_in(&test, buf, ret);
81	printk(KERN_INFO "ret: %d\n", ret);
82
83	/* skip first element of the fifo */
84	printk(KERN_INFO "skip 1st element\n");
85	kfifo_skip(&test);
86
87	/* put values into the fifo until is full */
88	for (i = 20; kfifo_put(&test, i); i++)
89		;
90
91	printk(KERN_INFO "queue len: %u\n", kfifo_len(&test));
92
93	/* show the first value without removing from the fifo */
94	if (kfifo_peek(&test, &i))
95		printk(KERN_INFO "%d\n", i);
96
97	/* check the correctness of all values in the fifo */
98	j = 0;
99	while (kfifo_get(&test, &i)) {
100		printk(KERN_INFO "item = %d\n", i);
101		if (i != expected_result[j++]) {
102			printk(KERN_WARNING "value mismatch: test failed\n");
103			return -EIO;
104		}
105	}
106	if (j != ARRAY_SIZE(expected_result)) {
107		printk(KERN_WARNING "size mismatch: test failed\n");
108		return -EIO;
109	}
110	printk(KERN_INFO "test passed\n");
111
112	return 0;
113}
114
115static ssize_t fifo_write(struct file *file, const char __user *buf,
116						size_t count, loff_t *ppos)
117{
118	int ret;
119	unsigned int copied;
120
121	if (mutex_lock_interruptible(&write_lock))
122		return -ERESTARTSYS;
123
124	ret = kfifo_from_user(&test, buf, count, &copied);
125
126	mutex_unlock(&write_lock);
127
128	return ret ? ret : copied;
129}
130
131static ssize_t fifo_read(struct file *file, char __user *buf,
132						size_t count, loff_t *ppos)
133{
134	int ret;
135	unsigned int copied;
136
137	if (mutex_lock_interruptible(&read_lock))
138		return -ERESTARTSYS;
139
140	ret = kfifo_to_user(&test, buf, count, &copied);
141
142	mutex_unlock(&read_lock);
143
144	return ret ? ret : copied;
145}
146
147static const struct file_operations fifo_fops = {
148	.owner		= THIS_MODULE,
149	.read		= fifo_read,
150	.write		= fifo_write,
151	.llseek		= noop_llseek,
152};
153
154static int __init example_init(void)
155{
156#ifdef DYNAMIC
157	int ret;
158
159	ret = kfifo_alloc(&test, FIFO_SIZE, GFP_KERNEL);
160	if (ret) {
161		printk(KERN_ERR "error kfifo_alloc\n");
162		return ret;
163	}
164#else
165	INIT_KFIFO(test);
166#endif
167	if (testfunc() < 0) {
168#ifdef DYNAMIC
169		kfifo_free(&test);
170#endif
171		return -EIO;
172	}
173
174	if (proc_create(PROC_FIFO, 0, NULL, &fifo_fops) == NULL) {
175#ifdef DYNAMIC
176		kfifo_free(&test);
177#endif
178		return -ENOMEM;
179	}
180	return 0;
181}
182
183static void __exit example_exit(void)
184{
185	remove_proc_entry(PROC_FIFO, NULL);
186#ifdef DYNAMIC
187	kfifo_free(&test);
188#endif
189}
190
191module_init(example_init);
192module_exit(example_exit);
193MODULE_LICENSE("GPL");
194MODULE_AUTHOR("Stefani Seibold <stefani@seibold.net>");
195