1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * Sample kfifo byte stream 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 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 */
25 static DEFINE_MUTEX(read_access);
26 
27 /* lock for procfs write access */
28 static 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
40 static struct kfifo test;
41 #else
42 static DECLARE_KFIFO(test, unsigned char, FIFO_SIZE);
43 #endif
44 
45 static 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 
52 static 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 
113 static 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 
131 static 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 
149 static const struct proc_ops fifo_proc_ops = {
150 	.proc_read	= fifo_read,
151 	.proc_write	= fifo_write,
152 	.proc_lseek	= noop_llseek,
153 };
154 
155 static 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 
184 static void __exit example_exit(void)
185 {
186 	remove_proc_entry(PROC_FIFO, NULL);
187 #ifdef DYNAMIC
188 	kfifo_free(&test);
189 #endif
190 }
191 
192 module_init(example_init);
193 module_exit(example_exit);
194 MODULE_LICENSE("GPL");
195 MODULE_AUTHOR("Stefani Seibold <stefani@seibold.net>");
196