1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * Sample kfifo int type 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 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 */
25 static DEFINE_MUTEX(read_lock);
26
27 /* lock for procfs write access */
28 static DEFINE_MUTEX(write_lock);
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
40 static DECLARE_KFIFO_PTR(test, int);
41 #else
42 static DEFINE_KFIFO(test, int, FIFO_SIZE);
43 #endif
44
45 static 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
testfunc(void)52 static 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
fifo_write(struct file * file,const char __user * buf,size_t count,loff_t * ppos)106 static 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_lock))
113 return -ERESTARTSYS;
114
115 ret = kfifo_from_user(&test, buf, count, &copied);
116
117 mutex_unlock(&write_lock);
118
119 return ret ? ret : copied;
120 }
121
fifo_read(struct file * file,char __user * buf,size_t count,loff_t * ppos)122 static ssize_t fifo_read(struct file *file, char __user *buf,
123 size_t count, loff_t *ppos)
124 {
125 int ret;
126 unsigned int copied;
127
128 if (mutex_lock_interruptible(&read_lock))
129 return -ERESTARTSYS;
130
131 ret = kfifo_to_user(&test, buf, count, &copied);
132
133 mutex_unlock(&read_lock);
134
135 return ret ? ret : copied;
136 }
137
138 static const struct file_operations fifo_fops = {
139 .owner = THIS_MODULE,
140 .read = fifo_read,
141 .write = fifo_write,
142 .llseek = noop_llseek,
143 };
144
example_init(void)145 static int __init example_init(void)
146 {
147 #ifdef DYNAMIC
148 int ret;
149
150 ret = kfifo_alloc(&test, FIFO_SIZE, GFP_KERNEL);
151 if (ret) {
152 printk(KERN_ERR "error kfifo_alloc\n");
153 return ret;
154 }
155 #endif
156 if (testfunc() < 0) {
157 #ifdef DYNAMIC
158 kfifo_free(&test);
159 #endif
160 return -EIO;
161 }
162
163 if (proc_create(PROC_FIFO, 0, NULL, &fifo_fops) == NULL) {
164 #ifdef DYNAMIC
165 kfifo_free(&test);
166 #endif
167 return -ENOMEM;
168 }
169 return 0;
170 }
171
example_exit(void)172 static void __exit example_exit(void)
173 {
174 remove_proc_entry(PROC_FIFO, NULL);
175 #ifdef DYNAMIC
176 kfifo_free(&test);
177 #endif
178 }
179
180 module_init(example_init);
181 module_exit(example_exit);
182 MODULE_LICENSE("GPL");
183 MODULE_AUTHOR("Stefani Seibold <stefani@seibold.net>");
184
