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 */
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 /*
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
48 struct kfifo_rec_ptr_1 test;
49 
50 #else
51 typedef STRUCT_KFIFO_REC_1(FIFO_SIZE) mytest;
52 
53 static mytest test;
54 #endif
55 
56 static 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 
69 static 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 
120 static 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_lock))
127 		return -ERESTARTSYS;
128 
129 	ret = kfifo_from_user(&test, buf, count, &copied);
130 
131 	mutex_unlock(&write_lock);
132 	if (ret)
133 		return ret;
134 
135 	return copied;
136 }
137 
138 static 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_lock))
145 		return -ERESTARTSYS;
146 
147 	ret = kfifo_to_user(&test, buf, count, &copied);
148 
149 	mutex_unlock(&read_lock);
150 	if (ret)
151 		return ret;
152 
153 	return copied;
154 }
155 
156 static const struct proc_ops fifo_proc_ops = {
157 	.proc_read	= fifo_read,
158 	.proc_write	= fifo_write,
159 	.proc_lseek	= noop_llseek,
160 };
161 
162 static 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 
191 static void __exit example_exit(void)
192 {
193 	remove_proc_entry(PROC_FIFO, NULL);
194 #ifdef DYNAMIC
195 	kfifo_free(&test);
196 #endif
197 }
198 
199 module_init(example_init);
200 module_exit(example_exit);
201 MODULE_LICENSE("GPL");
202 MODULE_AUTHOR("Stefani Seibold <stefani@seibold.net>");
203