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1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Sample kfifo byte stream implementation
4 *
5 * Copyright (C) 2010 Stefani Seibold <[email protected]>
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_DESCRIPTION("Sample kfifo byte stream implementation");
195MODULE_LICENSE("GPL");
196MODULE_AUTHOR("Stefani Seibold <[email protected]>");