linux/samples/kfifo/bytestream-example.c
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   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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