LXR linux/samples/kfifo/bytestream-example.c

   1// SPDX-License-Identifier: GPL-2.0-only
   2/*
   3 * Sample kfifo byte stream 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 byte stream fifo.
  16 */
  17
  18/* fifo size in elements (bytes) */
  19#define FIFO_SIZE       32
  20
  21/* name of the proc entry */
  22#define PROC_FIFO       "bytestream-fifo"
  23
  24/* lock for procfs read access */
  25static DEFINE_MUTEX(read_lock);
  26
  27/* lock for procfs write access */
  28static 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#ifdef DYNAMIC
  40static struct kfifo test;
  41#else
  42static DECLARE_KFIFO(test, unsigned char, FIFO_SIZE);
  43#endif
  44
  45static const unsigned char expected_result[FIFO_SIZE] = {
  46         3,  4,  5,  6,  7,  8,  9,  0,
  47         1, 20, 21, 22, 23, 24, 25, 26,
  48        27, 28, 29, 30, 31, 32, 33, 34,
  49        35, 36, 37, 38, 39, 40, 41, 42,
  50};
  51
  52static int __init testfunc(void)
  53{
  54        unsigned char   buf[6];
  55        unsigned char   i, j;
  56        unsigned int    ret;
  57
  58        printk(KERN_INFO "byte stream fifo test start\n");
  59
  60        /* put string into the fifo */
  61        kfifo_in(&test, "hello", 5);
  62
  63        /* put values into the fifo */
  64        for (i = 0; i != 10; i++)
  65                kfifo_put(&test, i);
  66
  67        /* show the number of used elements */
  68        printk(KERN_INFO "fifo len: %u\n", kfifo_len(&test));
  69
  70        /* get max of 5 bytes from the fifo */
  71        i = kfifo_out(&test, buf, 5);
  72        printk(KERN_INFO "buf: %.*s\n", i, buf);
  73
  74        /* get max of 2 elements from the fifo */
  75        ret = kfifo_out(&test, buf, 2);
  76        printk(KERN_INFO "ret: %d\n", ret);
  77        /* and put it back to the end of the fifo */
  78        ret = kfifo_in(&test, buf, ret);
  79        printk(KERN_INFO "ret: %d\n", ret);
  80
  81        /* skip first element of the fifo */
  82        printk(KERN_INFO "skip 1st element\n");
  83        kfifo_skip(&test);
  84
  85        /* put values into the fifo until is full */
  86        for (i = 20; kfifo_put(&test, i); i++)
  87                ;
  88
  89        printk(KERN_INFO "queue len: %u\n", kfifo_len(&test));
  90
  91        /* show the first value without removing from the fifo */
  92        if (kfifo_peek(&test, &i))
  93                printk(KERN_INFO "%d\n", i);
  94
  95        /* check the correctness of all values in the fifo */
  96        j = 0;
  97        while (kfifo_get(&test, &i)) {
  98                printk(KERN_INFO "item = %d\n", i);
  99                if (i != expected_result[j++]) {
 100                        printk(KERN_WARNING "value mismatch: test failed\n");
 101                        return -EIO;
 102                }
 103        }
 104        if (j != ARRAY_SIZE(expected_result)) {
 105                printk(KERN_WARNING "size mismatch: test failed\n");
 106                return -EIO;
 107        }
 108        printk(KERN_INFO "test passed\n");
 109
 110        return 0;
 111}
 112
 113static ssize_t fifo_write(struct file *file, const char __user *buf,
 114                                                size_t count, loff_t *ppos)
 115{
 116        int ret;
 117        unsigned int copied;
 118
 119        if (mutex_lock_interruptible(&write_lock))
 120                return -ERESTARTSYS;
 121
 122        ret = kfifo_from_user(&test, buf, count, &copied);
 123
 124        mutex_unlock(&write_lock);
 125        if (ret)
 126                return ret;
 127
 128        return 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        if (ret)
 144                return ret;
 145
 146        return copied;
 147}
 148
 149static const struct proc_ops fifo_proc_ops = {
 150        .proc_read      = fifo_read,
 151        .proc_write     = fifo_write,
 152        .proc_lseek     = noop_llseek,
 153};
 154
 155static int __init example_init(void)
 156{
 157#ifdef DYNAMIC
 158        int ret;
 159
 160        ret = kfifo_alloc(&test, FIFO_SIZE, GFP_KERNEL);
 161        if (ret) {
 162                printk(KERN_ERR "error kfifo_alloc\n");
 163                return ret;
 164        }
 165#else
 166        INIT_KFIFO(test);
 167#endif
 168        if (testfunc() < 0) {
 169#ifdef DYNAMIC
 170                kfifo_free(&test);
 171#endif
 172                return -EIO;
 173        }
 174
 175        if (proc_create(PROC_FIFO, 0, NULL, &fifo_proc_ops) == NULL) {
 176#ifdef DYNAMIC
 177                kfifo_free(&test);
 178#endif
 179                return -ENOMEM;
 180        }
 181        return 0;
 182}
 183
 184static void __exit example_exit(void)
 185{
 186        remove_proc_entry(PROC_FIFO, NULL);
 187#ifdef DYNAMIC
 188        kfifo_free(&test);
 189#endif
 190}
 191
 192module_init(example_init);
 193module_exit(example_exit);
 194MODULE_LICENSE("GPL");
 195MODULE_AUTHOR("Stefani Seibold <stefani@seibold.net>");
 196