1 /*
2  * Sample kfifo byte stream implementation
3  *
4  * Copyright (C) 2010 Stefani Seibold <stefani@seibold.net>
5  *
6  * Released under the GPL version 2 only.
7  *
8  */
9 
10 #include <linux/init.h>
11 #include <linux/module.h>
12 #include <linux/proc_fs.h>
13 #include <linux/mutex.h>
14 #include <linux/kfifo.h>
15 
16 /*
17  * This module shows how to create a byte stream fifo.
18  */
19 
20 /* fifo size in elements (bytes) */
21 #define FIFO_SIZE	32
22 
23 /* name of the proc entry */
24 #define	PROC_FIFO	"bytestream-fifo"
25 
26 /* lock for procfs read access */
27 static DEFINE_MUTEX(read_lock);
28 
29 /* lock for procfs write access */
30 static DEFINE_MUTEX(write_lock);
31 
32 /*
33  * define DYNAMIC in this example for a dynamically allocated fifo.
34  *
35  * Otherwise the fifo storage will be a part of the fifo structure.
36  */
37 #if 0
38 #define DYNAMIC
39 #endif
40 
41 #ifdef DYNAMIC
42 static struct kfifo test;
43 #else
44 static DECLARE_KFIFO(test, unsigned char, FIFO_SIZE);
45 #endif
46 
47 static const unsigned char expected_result[FIFO_SIZE] = {
48 	 3,  4,  5,  6,  7,  8,  9,  0,
49 	 1, 20, 21, 22, 23, 24, 25, 26,
50 	27, 28, 29, 30, 31, 32, 33, 34,
51 	35, 36, 37, 38, 39, 40, 41, 42,
52 };
53 
54 static int __init testfunc(void)
55 {
56 	unsigned char	buf[6];
57 	unsigned char	i, j;
58 	unsigned int	ret;
59 
60 	printk(KERN_INFO "byte stream fifo test start\n");
61 
62 	/* put string into the fifo */
63 	kfifo_in(&test, "hello", 5);
64 
65 	/* put values into the fifo */
66 	for (i = 0; i != 10; i++)
67 		kfifo_put(&test, i);
68 
69 	/* show the number of used elements */
70 	printk(KERN_INFO "fifo len: %u\n", kfifo_len(&test));
71 
72 	/* get max of 5 bytes from the fifo */
73 	i = kfifo_out(&test, buf, 5);
74 	printk(KERN_INFO "buf: %.*s\n", i, buf);
75 
76 	/* get max of 2 elements from the fifo */
77 	ret = kfifo_out(&test, buf, 2);
78 	printk(KERN_INFO "ret: %d\n", ret);
79 	/* and put it back to the end of the fifo */
80 	ret = kfifo_in(&test, buf, ret);
81 	printk(KERN_INFO "ret: %d\n", ret);
82 
83 	/* skip first element of the fifo */
84 	printk(KERN_INFO "skip 1st element\n");
85 	kfifo_skip(&test);
86 
87 	/* put values into the fifo until is full */
88 	for (i = 20; kfifo_put(&test, i); i++)
89 		;
90 
91 	printk(KERN_INFO "queue len: %u\n", kfifo_len(&test));
92 
93 	/* show the first value without removing from the fifo */
94 	if (kfifo_peek(&test, &i))
95 		printk(KERN_INFO "%d\n", i);
96 
97 	/* check the correctness of all values in the fifo */
98 	j = 0;
99 	while (kfifo_get(&test, &i)) {
100 		printk(KERN_INFO "item = %d\n", i);
101 		if (i != expected_result[j++]) {
102 			printk(KERN_WARNING "value mismatch: test failed\n");
103 			return -EIO;
104 		}
105 	}
106 	if (j != ARRAY_SIZE(expected_result)) {
107 		printk(KERN_WARNING "size mismatch: test failed\n");
108 		return -EIO;
109 	}
110 	printk(KERN_INFO "test passed\n");
111 
112 	return 0;
113 }
114 
115 static ssize_t fifo_write(struct file *file, const char __user *buf,
116 						size_t count, loff_t *ppos)
117 {
118 	int ret;
119 	unsigned int copied;
120 
121 	if (mutex_lock_interruptible(&write_lock))
122 		return -ERESTARTSYS;
123 
124 	ret = kfifo_from_user(&test, buf, count, &copied);
125 
126 	mutex_unlock(&write_lock);
127 
128 	return ret ? ret : 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_lock))
138 		return -ERESTARTSYS;
139 
140 	ret = kfifo_to_user(&test, buf, count, &copied);
141 
142 	mutex_unlock(&read_lock);
143 
144 	return ret ? ret : copied;
145 }
146 
147 static const struct file_operations fifo_fops = {
148 	.owner		= THIS_MODULE,
149 	.read		= fifo_read,
150 	.write		= fifo_write,
151 	.llseek		= noop_llseek,
152 };
153 
154 static int __init example_init(void)
155 {
156 #ifdef DYNAMIC
157 	int ret;
158 
159 	ret = kfifo_alloc(&test, FIFO_SIZE, GFP_KERNEL);
160 	if (ret) {
161 		printk(KERN_ERR "error kfifo_alloc\n");
162 		return ret;
163 	}
164 #else
165 	INIT_KFIFO(test);
166 #endif
167 	if (testfunc() < 0) {
168 #ifdef DYNAMIC
169 		kfifo_free(&test);
170 #endif
171 		return -EIO;
172 	}
173 
174 	if (proc_create(PROC_FIFO, 0, NULL, &fifo_fops) == NULL) {
175 #ifdef DYNAMIC
176 		kfifo_free(&test);
177 #endif
178 		return -ENOMEM;
179 	}
180 	return 0;
181 }
182 
183 static void __exit example_exit(void)
184 {
185 	remove_proc_entry(PROC_FIFO, NULL);
186 #ifdef DYNAMIC
187 	kfifo_free(&test);
188 #endif
189 }
190 
191 module_init(example_init);
192 module_exit(example_exit);
193 MODULE_LICENSE("GPL");
194 MODULE_AUTHOR("Stefani Seibold <stefani@seibold.net>");
195