linux/samples/kfifo/record-example.c
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   1/*
   2 * Sample dynamic sized record fifo 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 variable sized record fifo.
  18 */
  19
  20/* fifo size in elements (bytes) */
  21#define FIFO_SIZE       128
  22
  23/* name of the proc entry */
  24#define PROC_FIFO       "record-fifo"
  25
  26/* lock for procfs read access */
  27static DEFINE_MUTEX(read_lock);
  28
  29/* lock for procfs write access */
  30static 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/*
  42 * struct kfifo_rec_ptr_1 and  STRUCT_KFIFO_REC_1 can handle records of a
  43 * length between 0 and 255 bytes.
  44 *
  45 * struct kfifo_rec_ptr_2 and  STRUCT_KFIFO_REC_2 can handle records of a
  46 * length between 0 and 65535 bytes.
  47 */
  48
  49#ifdef DYNAMIC
  50struct kfifo_rec_ptr_1 test;
  51
  52#else
  53typedef STRUCT_KFIFO_REC_1(FIFO_SIZE) mytest;
  54
  55static mytest test;
  56#endif
  57
  58static const char *expected_result[] = {
  59        "a",
  60        "bb",
  61        "ccc",
  62        "dddd",
  63        "eeeee",
  64        "ffffff",
  65        "ggggggg",
  66        "hhhhhhhh",
  67        "iiiiiiiii",
  68        "jjjjjjjjjj",
  69};
  70
  71static int __init testfunc(void)
  72{
  73        char            buf[100];
  74        unsigned int    i;
  75        unsigned int    ret;
  76        struct { unsigned char buf[6]; } hello = { "hello" };
  77
  78        printk(KERN_INFO "record fifo test start\n");
  79
  80        kfifo_in(&test, &hello, sizeof(hello));
  81
  82        /* show the size of the next record in the fifo */
  83        printk(KERN_INFO "fifo peek len: %u\n", kfifo_peek_len(&test));
  84
  85        /* put in variable length data */
  86        for (i = 0; i < 10; i++) {
  87                memset(buf, 'a' + i, i + 1);
  88                kfifo_in(&test, buf, i + 1);
  89        }
  90
  91        /* skip first element of the fifo */
  92        printk(KERN_INFO "skip 1st element\n");
  93        kfifo_skip(&test);
  94
  95        printk(KERN_INFO "fifo len: %u\n", kfifo_len(&test));
  96
  97        /* show the first record without removing from the fifo */
  98        ret = kfifo_out_peek(&test, buf, sizeof(buf));
  99        if (ret)
 100                printk(KERN_INFO "%.*s\n", ret, buf);
 101
 102        /* check the correctness of all values in the fifo */
 103        i = 0;
 104        while (!kfifo_is_empty(&test)) {
 105                ret = kfifo_out(&test, buf, sizeof(buf));
 106                buf[ret] = '\0';
 107                printk(KERN_INFO "item = %.*s\n", ret, buf);
 108                if (strcmp(buf, expected_result[i++])) {
 109                        printk(KERN_WARNING "value mismatch: test failed\n");
 110                        return -EIO;
 111                }
 112        }
 113        if (i != ARRAY_SIZE(expected_result)) {
 114                printk(KERN_WARNING "size mismatch: test failed\n");
 115                return -EIO;
 116        }
 117        printk(KERN_INFO "test passed\n");
 118
 119        return 0;
 120}
 121
 122static ssize_t fifo_write(struct file *file, const char __user *buf,
 123                                                size_t count, loff_t *ppos)
 124{
 125        int ret;
 126        unsigned int copied;
 127
 128        if (mutex_lock_interruptible(&write_lock))
 129                return -ERESTARTSYS;
 130
 131        ret = kfifo_from_user(&test, buf, count, &copied);
 132
 133        mutex_unlock(&write_lock);
 134
 135        return ret ? ret : copied;
 136}
 137
 138static ssize_t fifo_read(struct file *file, char __user *buf,
 139                                                size_t count, loff_t *ppos)
 140{
 141        int ret;
 142        unsigned int copied;
 143
 144        if (mutex_lock_interruptible(&read_lock))
 145                return -ERESTARTSYS;
 146
 147        ret = kfifo_to_user(&test, buf, count, &copied);
 148
 149        mutex_unlock(&read_lock);
 150
 151        return ret ? ret : copied;
 152}
 153
 154static const struct file_operations fifo_fops = {
 155        .owner          = THIS_MODULE,
 156        .read           = fifo_read,
 157        .write          = fifo_write,
 158        .llseek         = noop_llseek,
 159};
 160
 161static int __init example_init(void)
 162{
 163#ifdef DYNAMIC
 164        int ret;
 165
 166        ret = kfifo_alloc(&test, FIFO_SIZE, GFP_KERNEL);
 167        if (ret) {
 168                printk(KERN_ERR "error kfifo_alloc\n");
 169                return ret;
 170        }
 171#else
 172        INIT_KFIFO(test);
 173#endif
 174        if (testfunc() < 0) {
 175#ifdef DYNAMIC
 176                kfifo_free(&test);
 177#endif
 178                return -EIO;
 179        }
 180
 181        if (proc_create(PROC_FIFO, 0, NULL, &fifo_fops) == NULL) {
 182#ifdef DYNAMIC
 183                kfifo_free(&test);
 184#endif
 185                return -ENOMEM;
 186        }
 187        return 0;
 188}
 189
 190static void __exit example_exit(void)
 191{
 192        remove_proc_entry(PROC_FIFO, NULL);
 193#ifdef DYNAMIC
 194        kfifo_free(&test);
 195#endif
 196}
 197
 198module_init(example_init);
 199module_exit(example_exit);
 200MODULE_LICENSE("GPL");
 201MODULE_AUTHOR("Stefani Seibold <stefani@seibold.net>");
 202
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