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         /* skip first element of the fifo */
  77         printk(KERN_INFO "skip 1st element\n");
  78         kfifo_skip(&test);
  79
  80         /* put values into the fifo until is full */
  81         for (i = 20; kfifo_put(&test, &i); i++)
  82                 ;
  83
  84         printk(KERN_INFO "queue len: %u\n", kfifo_len(&test));
  85
  86         /* print out all values in the fifo */
  87         while (kfifo_get(&test, &i))
  88                 printk("%d ", i);
  89         printk("\n");
  90
  91         return 0;
  92 }
  93
  94 static ssize_t fifo_write(struct file *file, const char __user *buf,
  95                                                 size_t count, loff_t *ppos)
  96 {
  97         int ret;
  98         unsigned int copied;
  99
 100         if (mutex_lock_interruptible(&write_lock))
 101                 return -ERESTARTSYS;
 102
 103         ret = kfifo_from_user(&test, buf, count, &copied);
 104
 105         mutex_unlock(&write_lock);
 106
 107         return ret ? ret : copied;
 108 }
 109
 110 static ssize_t fifo_read(struct file *file, char __user *buf,
 111                                                 size_t count, loff_t *ppos)
 112 {
 113         int ret;
 114         unsigned int copied;
 115
 116         if (mutex_lock_interruptible(&read_lock))
 117                 return -ERESTARTSYS;
 118
 119         ret = kfifo_to_user(&test, buf, count, &copied);
 120
 121         mutex_unlock(&read_lock);
 122
 123         return ret ? ret : copied;
 124 }
 125
 126 static const struct file_operations fifo_fops = {
 127         .owner          = THIS_MODULE,
 128         .read           = fifo_read,
 129         .write          = fifo_write,
 130 };
 131
 132 static int __init example_init(void)
 133 {
 134 #ifdef DYNAMIC
 135         int ret;
 136
 137         ret = kfifo_alloc(&test, FIFO_SIZE, GFP_KERNEL);
 138         if (ret) {
 139                 printk(KERN_ERR "error kfifo_alloc\n");
 140                 return ret;
 141         }
 142 #else
 143         INIT_KFIFO(test);
 144 #endif
 145         testfunc();
 146
 147         if (proc_create(PROC_FIFO, 0, NULL, &fifo_fops) == NULL) {
 148 #ifdef DYNAMIC
 149                 kfifo_free(&test);
 150 #endif
 151                 return -ENOMEM;
 152         }
 153         return 0;
 154 }
 155
 156 static void __exit example_exit(void)
 157 {
 158         remove_proc_entry(PROC_FIFO, NULL);
 159 #ifdef DYNAMIC
 160         kfifo_free(&test);
 161 #endif
 162 }
 163
 164 module_init(example_init);
 165 module_exit(example_exit);
 166 MODULE_LICENSE("GPL");
 167 MODULE_AUTHOR("Stefani Seibold <stefani@seibold.net>");