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1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Sample dynamic sized record fifo 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 variable sized record fifo.
16 */
17
18/* fifo size in elements (bytes) */
19#define FIFO_SIZE 128
20
21/* name of the proc entry */
22#define PROC_FIFO "record-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/*
40 * struct kfifo_rec_ptr_1 and STRUCT_KFIFO_REC_1 can handle records of a
41 * length between 0 and 255 bytes.
42 *
43 * struct kfifo_rec_ptr_2 and STRUCT_KFIFO_REC_2 can handle records of a
44 * length between 0 and 65535 bytes.
45 */
46
47#ifdef DYNAMIC
48struct kfifo_rec_ptr_1 test;
49
50#else
51typedef STRUCT_KFIFO_REC_1(FIFO_SIZE) mytest;
52
53static mytest test;
54#endif
55
56static const char *expected_result[] = {
57 "a",
58 "bb",
59 "ccc",
60 "dddd",
61 "eeeee",
62 "ffffff",
63 "ggggggg",
64 "hhhhhhhh",
65 "iiiiiiiii",
66 "jjjjjjjjjj",
67};
68
69static int __init testfunc(void)
70{
71 char buf[100];
72 unsigned int i;
73 unsigned int ret;
74 struct { unsigned char buf[6]; } hello = { "hello" };
75
76 printk(KERN_INFO "record fifo test start\n");
77
78 kfifo_in(&test, &hello, sizeof(hello));
79
80 /* show the size of the next record in the fifo */
81 printk(KERN_INFO "fifo peek len: %u\n", kfifo_peek_len(&test));
82
83 /* put in variable length data */
84 for (i = 0; i < 10; i++) {
85 memset(buf, 'a' + i, i + 1);
86 kfifo_in(&test, buf, i + 1);
87 }
88
89 /* skip first element of the fifo */
90 printk(KERN_INFO "skip 1st element\n");
91 kfifo_skip(&test);
92
93 printk(KERN_INFO "fifo len: %u\n", kfifo_len(&test));
94
95 /* show the first record without removing from the fifo */
96 ret = kfifo_out_peek(&test, buf, sizeof(buf));
97 if (ret)
98 printk(KERN_INFO "%.*s\n", ret, buf);
99
100 /* check the correctness of all values in the fifo */
101 i = 0;
102 while (!kfifo_is_empty(&test)) {
103 ret = kfifo_out(&test, buf, sizeof(buf));
104 buf[ret] = '\0';
105 printk(KERN_INFO "item = %.*s\n", ret, buf);
106 if (strcmp(buf, expected_result[i++])) {
107 printk(KERN_WARNING "value mismatch: test failed\n");
108 return -EIO;
109 }
110 }
111 if (i != ARRAY_SIZE(expected_result)) {
112 printk(KERN_WARNING "size mismatch: test failed\n");
113 return -EIO;
114 }
115 printk(KERN_INFO "test passed\n");
116
117 return 0;
118}
119
120static ssize_t fifo_write(struct file *file, const char __user *buf,
121 size_t count, loff_t *ppos)
122{
123 int ret;
124 unsigned int copied;
125
126 if (mutex_lock_interruptible(&write_access))
127 return -ERESTARTSYS;
128
129 ret = kfifo_from_user(&test, buf, count, &copied);
130
131 mutex_unlock(&write_access);
132 if (ret)
133 return ret;
134
135 return copied;
136}
137
138static ssize_t fifo_read(struct file *file, char __user *buf,
139 size_t count, loff_t *ppos)
140{
141 int ret;
142 unsigned int copied;
143
144 if (mutex_lock_interruptible(&read_access))
145 return -ERESTARTSYS;
146
147 ret = kfifo_to_user(&test, buf, count, &copied);
148
149 mutex_unlock(&read_access);
150 if (ret)
151 return ret;
152
153 return copied;
154}
155
156static const struct proc_ops fifo_proc_ops = {
157 .proc_read = fifo_read,
158 .proc_write = fifo_write,
159 .proc_lseek = noop_llseek,
160};
161
162static int __init example_init(void)
163{
164#ifdef DYNAMIC
165 int ret;
166
167 ret = kfifo_alloc(&test, FIFO_SIZE, GFP_KERNEL);
168 if (ret) {
169 printk(KERN_ERR "error kfifo_alloc\n");
170 return ret;
171 }
172#else
173 INIT_KFIFO(test);
174#endif
175 if (testfunc() < 0) {
176#ifdef DYNAMIC
177 kfifo_free(&test);
178#endif
179 return -EIO;
180 }
181
182 if (proc_create(PROC_FIFO, 0, NULL, &fifo_proc_ops) == NULL) {
183#ifdef DYNAMIC
184 kfifo_free(&test);
185#endif
186 return -ENOMEM;
187 }
188 return 0;
189}
190
191static void __exit example_exit(void)
192{
193 remove_proc_entry(PROC_FIFO, NULL);
194#ifdef DYNAMIC
195 kfifo_free(&test);
196#endif
197}
198
199module_init(example_init);
200module_exit(example_exit);
201MODULE_DESCRIPTION("Sample dynamic sized record fifo implementation");
202MODULE_LICENSE("GPL");
203MODULE_AUTHOR("Stefani Seibold <[email protected]>");