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 */
  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
 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
 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
 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
 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
 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
 183 static void __exit example_exit(void)
 184 {
 185         remove_proc_entry(PROC_FIFO, NULL);
 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 <stefani@seibold.net>");