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 
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 
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 	if (ret)
119 		return ret;
120 
121 	return copied;
122 }
123 
124 static 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_lock))
131 		return -ERESTARTSYS;
132 
133 	ret = kfifo_to_user(&test, buf, count, &copied);
134 
135 	mutex_unlock(&read_lock);
136 	if (ret)
137 		return ret;
138 
139 	return copied;
140 }
141 
142 static const struct proc_ops fifo_proc_ops = {
143 	.proc_read	= fifo_read,
144 	.proc_write	= fifo_write,
145 	.proc_lseek	= noop_llseek,
146 };
147 
148 static 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 
175 static void __exit example_exit(void)
176 {
177 	remove_proc_entry(PROC_FIFO, NULL);
178 #ifdef DYNAMIC
179 	kfifo_free(&test);
180 #endif
181 }
182 
183 module_init(example_init);
184 module_exit(example_exit);
185 MODULE_LICENSE("GPL");
186 MODULE_AUTHOR("Stefani Seibold <stefani@seibold.net>");
187