Linux Kernel  3.7.1
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bytestream-example.c
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1 /*
2  * Sample kfifo byte stream implementation
3  *
4  * Copyright (C) 2010 Stefani Seibold <[email protected]>
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 
122  return -ERESTARTSYS;
123 
124  ret = kfifo_from_user(&test, buf, count, &copied);
125 
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 
138  return -ERESTARTSYS;
139 
140  ret = kfifo_to_user(&test, buf, count, &copied);
141 
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 
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 {
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 <[email protected]>");