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1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Sample kfifo int type 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 int type fifo.
16 */
17
18/* fifo size in elements (ints) */
19#define FIFO_SIZE 32
20
21/* name of the proc entry */
22#define PROC_FIFO "int-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 DECLARE_KFIFO_PTR(test, int);
41#else
42static DEFINE_KFIFO(test, int, FIFO_SIZE);
43#endif
44
45static const int 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 int buf[6];
55 int i, j;
56 unsigned int ret;
57
58 printk(KERN_INFO "int fifo test start\n");
59
60 /* put values into the fifo */
61 for (i = 0; i != 10; i++)
62 kfifo_put(&test, i);
63
64 /* show the number of used elements */
65 printk(KERN_INFO "fifo len: %u\n", kfifo_len(&test));
66
67 /* get max of 2 elements from the fifo */
68 ret = kfifo_out(&test, buf, 2);
69 printk(KERN_INFO "ret: %d\n", ret);
70 /* and put it back to the end of the fifo */
71 ret = kfifo_in(&test, buf, ret);
72 printk(KERN_INFO "ret: %d\n", ret);
73
74 /* skip first element of the fifo */
75 printk(KERN_INFO "skip 1st element\n");
76 kfifo_skip(&test);
77
78 /* put values into the fifo until is full */
79 for (i = 20; kfifo_put(&test, i); i++)
80 ;
81
82 printk(KERN_INFO "queue len: %u\n", kfifo_len(&test));
83
84 /* show the first value without removing from the fifo */
85 if (kfifo_peek(&test, &i))
86 printk(KERN_INFO "%d\n", i);
87
88 /* check the correctness of all values in the fifo */
89 j = 0;
90 while (kfifo_get(&test, &i)) {
91 printk(KERN_INFO "item = %d\n", i);
92 if (i != expected_result[j++]) {
93 printk(KERN_WARNING "value mismatch: test failed\n");
94 return -EIO;
95 }
96 }
97 if (j != ARRAY_SIZE(expected_result)) {
98 printk(KERN_WARNING "size mismatch: test failed\n");
99 return -EIO;
100 }
101 printk(KERN_INFO "test passed\n");
102
103 return 0;
104}
105
106static ssize_t fifo_write(struct file *file, const char __user *buf,
107 size_t count, loff_t *ppos)
108{
109 int ret;
110 unsigned int copied;
111
112 if (mutex_lock_interruptible(&write_access))
113 return -ERESTARTSYS;
114
115 ret = kfifo_from_user(&test, buf, count, &copied);
116
117 mutex_unlock(&write_access);
118 if (ret)
119 return ret;
120
121 return copied;
122}
123
124static ssize_t fifo_read(struct file *file, char __user *buf,
125 size_t count, loff_t *ppos)
126{
127 int ret;
128 unsigned int copied;
129
130 if (mutex_lock_interruptible(&read_access))
131 return -ERESTARTSYS;
132
133 ret = kfifo_to_user(&test, buf, count, &copied);
134
135 mutex_unlock(&read_access);
136 if (ret)
137 return ret;
138
139 return copied;
140}
141
142static const struct proc_ops fifo_proc_ops = {
143 .proc_read = fifo_read,
144 .proc_write = fifo_write,
145 .proc_lseek = noop_llseek,
146};
147
148static int __init example_init(void)
149{
150#ifdef DYNAMIC
151 int ret;
152
153 ret = kfifo_alloc(&test, FIFO_SIZE, GFP_KERNEL);
154 if (ret) {
155 printk(KERN_ERR "error kfifo_alloc\n");
156 return ret;
157 }
158#endif
159 if (testfunc() < 0) {
160#ifdef DYNAMIC
161 kfifo_free(&test);
162#endif
163 return -EIO;
164 }
165
166 if (proc_create(PROC_FIFO, 0, NULL, &fifo_proc_ops) == NULL) {
167#ifdef DYNAMIC
168 kfifo_free(&test);
169#endif
170 return -ENOMEM;
171 }
172 return 0;
173}
174
175static void __exit example_exit(void)
176{
177 remove_proc_entry(PROC_FIFO, NULL);
178#ifdef DYNAMIC
179 kfifo_free(&test);
180#endif
181}
182
183module_init(example_init);
184module_exit(example_exit);
185MODULE_DESCRIPTION("Sample kfifo int type implementation");
186MODULE_LICENSE("GPL");
187MODULE_AUTHOR("Stefani Seibold <[email protected]>");