Root/samples/kfifo/bytestream-example.c

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 */
27static DEFINE_MUTEX(read_lock);
28
29/* lock for procfs write access */
30static 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
42static struct kfifo test;
43#else
44static DECLARE_KFIFO(test, unsigned char, FIFO_SIZE);
45#endif
46
47static 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
54static 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
115static 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
131static 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
147static const struct file_operations fifo_fops = {
148    .owner = THIS_MODULE,
149    .read = fifo_read,
150    .write = fifo_write,
151    .llseek = noop_llseek,
152};
153
154static 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
183static void __exit example_exit(void)
184{
185    remove_proc_entry(PROC_FIFO, NULL);
186#ifdef DYNAMIC
187    kfifo_free(&test);
188#endif
189}
190
191module_init(example_init);
192module_exit(example_exit);
193MODULE_LICENSE("GPL");
194MODULE_AUTHOR("Stefani Seibold <stefani@seibold.net>");
195

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