samples/kfifo/record-example.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Sample dynamic sized record fifo 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 variable sized record fifo.
  16  */
  17
  18 /* fifo size in elements (bytes) */
  19 #define FIFO_SIZE       128
  20
  21 /* name of the proc entry */
  22 #define PROC_FIFO       "record-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 /*
  40  * struct kfifo_rec_ptr_1 and  STRUCT_KFIFO_REC_1 can handle records of a
  41  * length between 0 and 255 bytes.
  42  *
  43  * struct kfifo_rec_ptr_2 and  STRUCT_KFIFO_REC_2 can handle records of a
  44  * length between 0 and 65535 bytes.
  45  */
  46
  47 #ifdef DYNAMIC
  48 struct kfifo_rec_ptr_1 test;
  49
  50 #else
  51 typedef STRUCT_KFIFO_REC_1(FIFO_SIZE) mytest;
  52
  53 static mytest test;
  54 #endif
  55
  56 static const char *expected_result[] = {
  57         "a",
  58         "bb",
  59         "ccc",
  60         "dddd",
  61         "eeeee",
  62         "ffffff",
  63         "ggggggg",
  64         "hhhhhhhh",
  65         "iiiiiiiii",
  66         "jjjjjjjjjj",
  67 };
  68
  69 static int __init testfunc(void)
  70 {
  71         char            buf[100];
  72         unsigned int    i;
  73         unsigned int    ret;
  74         struct { unsigned char buf[6]; } hello = { "hello" };
  75
  76         printk(KERN_INFO "record fifo test start\n");
  77
  78         kfifo_in(&test, &hello, sizeof(hello));
  79
  80         /* show the size of the next record in the fifo */
  81         printk(KERN_INFO "fifo peek len: %u\n", kfifo_peek_len(&test));
  82
  83         /* put in variable length data */
  84         for (i = 0; i < 10; i++) {
  85                 memset(buf, 'a' + i, i + 1);
  86                 kfifo_in(&test, buf, i + 1);
  87         }
  88
  89         /* skip first element of the fifo */
  90         printk(KERN_INFO "skip 1st element\n");
  91         kfifo_skip(&test);
  92
  93         printk(KERN_INFO "fifo len: %u\n", kfifo_len(&test));
  94
  95         /* show the first record without removing from the fifo */
  96         ret = kfifo_out_peek(&test, buf, sizeof(buf));
  97         if (ret)
  98                 printk(KERN_INFO "%.*s\n", ret, buf);
  99
 100         /* check the correctness of all values in the fifo */
 101         i = 0;
 102         while (!kfifo_is_empty(&test)) {
 103                 ret = kfifo_out(&test, buf, sizeof(buf));
 104                 buf[ret] = '\0';
 105                 printk(KERN_INFO "item = %.*s\n", ret, buf);
 106                 if (strcmp(buf, expected_result[i++])) {
 107                         printk(KERN_WARNING "value mismatch: test failed\n");
 108                         return -EIO;
 109                 }
 110         }
 111         if (i != ARRAY_SIZE(expected_result)) {
 112                 printk(KERN_WARNING "size mismatch: test failed\n");
 113                 return -EIO;
 114         }
 115         printk(KERN_INFO "test passed\n");
 116
 117         return 0;
 118 }
 119
 120 static ssize_t fifo_write(struct file *file, const char __user *buf,
 121                                                 size_t count, loff_t *ppos)
 122 {
 123         int ret;
 124         unsigned int copied;
 125
 126         if (mutex_lock_interruptible(&write_lock))
 127                 return -ERESTARTSYS;
 128
 129         ret = kfifo_from_user(&test, buf, count, &copied);
 130
 131         mutex_unlock(&write_lock);
 132
 133         return ret ? ret : copied;
 134 }
 135
 136 static ssize_t fifo_read(struct file *file, char __user *buf,
 137                                                 size_t count, loff_t *ppos)
 138 {
 139         int ret;
 140         unsigned int copied;
 141
 142         if (mutex_lock_interruptible(&read_lock))
 143                 return -ERESTARTSYS;
 144
 145         ret = kfifo_to_user(&test, buf, count, &copied);
 146
 147         mutex_unlock(&read_lock);
 148
 149         return ret ? ret : copied;
 150 }
 151
 152 static const struct file_operations fifo_fops = {
 153         .owner          = THIS_MODULE,
 154         .read           = fifo_read,
 155         .write          = fifo_write,
 156         .llseek         = noop_llseek,
 157 };
 158
 159 static int __init example_init(void)
 160 {
 161 #ifdef DYNAMIC
 162         int ret;
 163
 164         ret = kfifo_alloc(&test, FIFO_SIZE, GFP_KERNEL);
 165         if (ret) {
 166                 printk(KERN_ERR "error kfifo_alloc\n");
 167                 return ret;
 168         }
 169 #else
 170         INIT_KFIFO(test);
 171 #endif
 172         if (testfunc() < 0) {
 173 #ifdef DYNAMIC
 174                 kfifo_free(&test);
 175 #endif
 176                 return -EIO;
 177         }
 178
 179         if (proc_create(PROC_FIFO, 0, NULL, &fifo_fops) == NULL) {
 180 #ifdef DYNAMIC
 181                 kfifo_free(&test);
 182 #endif
 183                 return -ENOMEM;
 184         }
 185         return 0;
 186 }
 187
 188 static void __exit example_exit(void)
 189 {
 190         remove_proc_entry(PROC_FIFO, NULL);
 191 #ifdef DYNAMIC
 192         kfifo_free(&test);
 193 #endif
 194 }
 195
 196 module_init(example_init);
 197 module_exit(example_exit);
 198 MODULE_LICENSE("GPL");
 199 MODULE_AUTHOR("Stefani Seibold <stefani@seibold.net>");