root/samples/kfifo/bytestream-example.c

DEFINITIONS

1. testfunc
2. fifo_write
3. fifo_read
4. example_init
5. example_exit

   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 */
  25 static DEFINE_MUTEX(read_lock);
  26 
  27 /* lock for procfs write access */
  28 static 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
  40 static struct kfifo test;
  41 #else
  42 static DECLARE_KFIFO(test, unsigned char, FIFO_SIZE);
  43 #endif
  44 
  45 static 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 
  52 static 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 
 113 static 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 
 126         return ret ? ret : copied;
 127 }
 128 
 129 static ssize_t fifo_read(struct file *file, char __user *buf,
 130                                                 size_t count, loff_t *ppos)
 131 {
 132         int ret;
 133         unsigned int copied;
 134 
 135         if (mutex_lock_interruptible(&read_lock))
 136                 return -ERESTARTSYS;
 137 
 138         ret = kfifo_to_user(&test, buf, count, &copied);
 139 
 140         mutex_unlock(&read_lock);
 141 
 142         return ret ? ret : copied;
 143 }
 144 
 145 static const struct file_operations fifo_fops = {
 146         .owner          = THIS_MODULE,
 147         .read           = fifo_read,
 148         .write          = fifo_write,
 149         .llseek         = noop_llseek,
 150 };
 151 
 152 static int __init example_init(void)
 153 {
 154 #ifdef DYNAMIC
 155         int ret;
 156 
 157         ret = kfifo_alloc(&test, FIFO_SIZE, GFP_KERNEL);
 158         if (ret) {
 159                 printk(KERN_ERR "error kfifo_alloc\n");
 160                 return ret;
 161         }
 162 #else
 163         INIT_KFIFO(test);
 164 #endif
 165         if (testfunc() < 0) {
 166 #ifdef DYNAMIC
 167                 kfifo_free(&test);
 168 #endif
 169                 return -EIO;
 170         }
 171 
 172         if (proc_create(PROC_FIFO, 0, NULL, &fifo_fops) == NULL) {
 173 #ifdef DYNAMIC
 174                 kfifo_free(&test);
 175 #endif
 176                 return -ENOMEM;
 177         }
 178         return 0;
 179 }
 180 
 181 static void __exit example_exit(void)
 182 {
 183         remove_proc_entry(PROC_FIFO, NULL);
 184 #ifdef DYNAMIC
 185         kfifo_free(&test);
 186 #endif
 187 }
 188 
 189 module_init(example_init);
 190 module_exit(example_exit);
 191 MODULE_LICENSE("GPL");
 192 MODULE_AUTHOR("Stefani Seibold <stefani@seibold.net>");