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 int __init testfunc(void)
  48 {
  49         unsigned char   buf[6];
  50         unsigned char   i;
  51         unsigned int    ret;
  52
  53         printk(KERN_INFO "byte stream fifo test start\n");
  54
  55         /* put string into the fifo */
  56         kfifo_in(&test, "hello", 5);
  57
  58         /* put values into the fifo */
  59         for (i = 0; i != 10; i++)
  60                 kfifo_put(&test, &i);
  61
  62         /* show the number of used elements */
  63         printk(KERN_INFO "fifo len: %u\n", kfifo_len(&test));
  64
  65         /* get max of 5 bytes from the fifo */
  66         i = kfifo_out(&test, buf, 5);
  67         printk(KERN_INFO "buf: %.*s\n", i, buf);
  68
  69         /* get max of 2 elements from the fifo */
  70         ret = kfifo_out(&test, buf, 2);
  71         printk(KERN_INFO "ret: %d\n", ret);
  72         /* and put it back to the end of the fifo */
  73         ret = kfifo_in(&test, buf, ret);
  74         printk(KERN_INFO "ret: %d\n", ret);
  75
  76         /* put values into the fifo until is full */
  77         for (i = 20; kfifo_put(&test, &i); i++)
  78                 ;
  79
  80         printk(KERN_INFO "queue len: %u\n", kfifo_len(&test));
  81
  82         /* print out all values in the fifo */
  83         while (kfifo_get(&test, &i))
  84                 printk("%d ", i);
  85         printk("\n");
  86
  87         return 0;
  88 }
  89
  90 static ssize_t fifo_write(struct file *file, const char __user *buf,
  91                                                 size_t count, loff_t *ppos)
  92 {
  93         int ret;
  94         unsigned int copied;
  95
  96         if (mutex_lock_interruptible(&write_lock))
  97                 return -ERESTARTSYS;
  98
  99         ret = kfifo_from_user(&test, buf, count, &copied);
 100
 101         mutex_unlock(&write_lock);
 102
 103         return ret ? ret : copied;
 104 }
 105
 106 static ssize_t fifo_read(struct file *file, char __user *buf,
 107                                                 size_t count, loff_t *ppos)
 108 {
 109         int ret;
 110         unsigned int copied;
 111
 112         if (mutex_lock_interruptible(&read_lock))
 113                 return -ERESTARTSYS;
 114
 115         ret = kfifo_to_user(&test, buf, count, &copied);
 116
 117         mutex_unlock(&read_lock);
 118
 119         return ret ? ret : copied;
 120 }
 121
 122 static const struct file_operations fifo_fops = {
 123         .owner          = THIS_MODULE,
 124         .read           = fifo_read,
 125         .write          = fifo_write,
 126 };
 127
 128 static int __init example_init(void)
 129 {
 130 #ifdef DYNAMIC
 131         int ret;
 132
 133         ret = kfifo_alloc(&test, FIFO_SIZE, GFP_KERNEL);
 134         if (ret) {
 135                 printk(KERN_ERR "error kfifo_alloc\n");
 136                 return ret;
 137         }
 138 #else
 139         INIT_KFIFO(test);
 140 #endif
 141         testfunc();
 142
 143         if (proc_create(PROC_FIFO, 0, NULL, &fifo_fops) == NULL) {
 144 #ifdef DYNAMIC
 145                 kfifo_free(&test);
 146 #endif
 147                 return -ENOMEM;
 148         }
 149         return 0;
 150 }
 151
 152 static void __exit example_exit(void)
 153 {
 154         remove_proc_entry(PROC_FIFO, NULL);
 155 #ifdef DYNAMIC
 156         kfifo_free(&test);
 157 #endif
 158 }
 159
 160 module_init(example_init);
 161 module_exit(example_exit);
 162 MODULE_LICENSE("GPL");
 163 MODULE_AUTHOR("Stefani Seibold <stefani@seibold.net>");