1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Sample kfifo byte stream implementation
4 *
5 * Copyright (C) 2010 Stefani Seibold <stefani@seibold.net>
6 */
7
8#include <linux/init.h>
9#include <linux/module.h>
10#include <linux/proc_fs.h>
11#include <linux/mutex.h>
12#include <linux/kfifo.h>
13
14/*
15 * This module shows how to create a byte stream fifo.
16 */
17
18/* fifo size in elements (bytes) */
19#define FIFO_SIZE	32
20
21/* name of the proc entry */
22#define	PROC_FIFO	"bytestream-fifo"
23
24/* lock for procfs read access */
25static DEFINE_MUTEX(read_access);
26
27/* lock for procfs write access */
28static DEFINE_MUTEX(write_access);
29
30/*
31 * define DYNAMIC in this example for a dynamically allocated fifo.
32 *
33 * Otherwise the fifo storage will be a part of the fifo structure.
34 */
35#if 0
36#define DYNAMIC
37#endif
38
39#ifdef DYNAMIC
40static struct kfifo test;
41#else
42static DECLARE_KFIFO(test, unsigned char, FIFO_SIZE);
43#endif
44
45static const unsigned char expected_result[FIFO_SIZE] = {
46	 3,  4,  5,  6,  7,  8,  9,  0,
47	 1, 20, 21, 22, 23, 24, 25, 26,
48	27, 28, 29, 30, 31, 32, 33, 34,
49	35, 36, 37, 38, 39, 40, 41, 42,
50};
51
52static int __init testfunc(void)
53{
54	unsigned char	buf[6];
55	unsigned char	i, j;
56	unsigned int	ret;
57
58	printk(KERN_INFO "byte stream fifo test start\n");
59
60	/* put string into the fifo */
61	kfifo_in(&test, "hello", 5);
62
63	/* put values into the fifo */
64	for (i = 0; i != 10; i++)
65		kfifo_put(&test, i);
66
67	/* show the number of used elements */
68	printk(KERN_INFO "fifo len: %u\n", kfifo_len(&test));
69
70	/* get max of 5 bytes from the fifo */
71	i = kfifo_out(&test, buf, 5);
72	printk(KERN_INFO "buf: %.*s\n", i, buf);
73
74	/* get max of 2 elements from the fifo */
75	ret = kfifo_out(&test, buf, 2);
76	printk(KERN_INFO "ret: %d\n", ret);
77	/* and put it back to the end of the fifo */
78	ret = kfifo_in(&test, buf, ret);
79	printk(KERN_INFO "ret: %d\n", ret);
80
81	/* skip first element of the fifo */
82	printk(KERN_INFO "skip 1st element\n");
83	kfifo_skip(&test);
84
85	/* put values into the fifo until is full */
86	for (i = 20; kfifo_put(&test, i); i++)
87		;
88
89	printk(KERN_INFO "queue len: %u\n", kfifo_len(&test));
90
91	/* show the first value without removing from the fifo */
92	if (kfifo_peek(&test, &i))
93		printk(KERN_INFO "%d\n", i);
94
95	/* check the correctness of all values in the fifo */
96	j = 0;
97	while (kfifo_get(&test, &i)) {
98		printk(KERN_INFO "item = %d\n", i);
99		if (i != expected_result[j++]) {
100			printk(KERN_WARNING "value mismatch: test failed\n");
101			return -EIO;
102		}
103	}
104	if (j != ARRAY_SIZE(expected_result)) {
105		printk(KERN_WARNING "size mismatch: test failed\n");
106		return -EIO;
107	}
108	printk(KERN_INFO "test passed\n");
109
110	return 0;
111}
112
113static ssize_t fifo_write(struct file *file, const char __user *buf,
114						size_t count, loff_t *ppos)
115{
116	int ret;
117	unsigned int copied;
118
119	if (mutex_lock_interruptible(&write_access))
120		return -ERESTARTSYS;
121
122	ret = kfifo_from_user(&test, buf, count, &copied);
123
124	mutex_unlock(&write_access);
125	if (ret)
126		return ret;
127
128	return 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_access))
138		return -ERESTARTSYS;
139
140	ret = kfifo_to_user(&test, buf, count, &copied);
141
142	mutex_unlock(&read_access);
143	if (ret)
144		return ret;
145
146	return copied;
147}
148
149static const struct proc_ops fifo_proc_ops = {
150	.proc_read	= fifo_read,
151	.proc_write	= fifo_write,
152	.proc_lseek	= noop_llseek,
153};
154
155static int __init example_init(void)
156{
157#ifdef DYNAMIC
158	int ret;
159
160	ret = kfifo_alloc(&test, FIFO_SIZE, GFP_KERNEL);
161	if (ret) {
162		printk(KERN_ERR "error kfifo_alloc\n");
163		return ret;
164	}
165#else
166	INIT_KFIFO(test);
167#endif
168	if (testfunc() < 0) {
169#ifdef DYNAMIC
170		kfifo_free(&test);
171#endif
172		return -EIO;
173	}
174
175	if (proc_create(PROC_FIFO, 0, NULL, &fifo_proc_ops) == NULL) {
176#ifdef DYNAMIC
177		kfifo_free(&test);
178#endif
179		return -ENOMEM;
180	}
181	return 0;
182}
183
184static void __exit example_exit(void)
185{
186	remove_proc_entry(PROC_FIFO, NULL);
187#ifdef DYNAMIC
188	kfifo_free(&test);
189#endif
190}
191
192module_init(example_init);
193module_exit(example_exit);
194MODULE_LICENSE("GPL");
195MODULE_AUTHOR("Stefani Seibold <stefani@seibold.net>");
196