1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Sample dynamic sized record fifo 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 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_LICENSE("GPL");
202MODULE_AUTHOR("Stefani Seibold <stefani@seibold.net>");
203