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1// SPDX-License-Identifier: GPL-2.0-only2/*3 * Sample kfifo byte stream implementation4 *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 byte stream fifo.16 */17 18/* fifo size in elements (bytes) */19#define FIFO_SIZE 3220 21/* name of the proc entry */22#define PROC_FIFO "bytestream-fifo"23 24/* lock for procfs read access */25static DEFINE_MUTEX(read_access);26 27/* lock for procfs write access */28static DEFINE_MUTEX(write_access);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 036#define DYNAMIC37#endif38 39#ifdef DYNAMIC40static struct kfifo test;41#else42static DECLARE_KFIFO(test, unsigned char, FIFO_SIZE);43#endif44 45static const unsigned char expected_result[FIFO_SIZE] = {46 3, 4, 5, 6, 7, 8, 9, 0,47 1, 20, 21, 22, 23, 24, 25, 26,48 27, 28, 29, 30, 31, 32, 33, 34,49 35, 36, 37, 38, 39, 40, 41, 42,50};51 52static int __init testfunc(void)53{54 unsigned char buf[6];55 unsigned char i, j;56 unsigned int ret;57 58 printk(KERN_INFO "byte stream fifo test start\n");59 60 /* put string into the fifo */61 kfifo_in(&test, "hello", 5);62 63 /* put values into the fifo */64 for (i = 0; i != 10; i++)65 kfifo_put(&test, i);66 67 /* show the number of used elements */68 printk(KERN_INFO "fifo len: %u\n", kfifo_len(&test));69 70 /* get max of 5 bytes from the fifo */71 i = kfifo_out(&test, buf, 5);72 printk(KERN_INFO "buf: %.*s\n", i, buf);73 74 /* get max of 2 elements from the fifo */75 ret = kfifo_out(&test, buf, 2);76 printk(KERN_INFO "ret: %d\n", ret);77 /* and put it back to the end of the fifo */78 ret = kfifo_in(&test, buf, ret);79 printk(KERN_INFO "ret: %d\n", ret);80 81 /* skip first element of the fifo */82 printk(KERN_INFO "skip 1st element\n");83 kfifo_skip(&test);84 85 /* put values into the fifo until is full */86 for (i = 20; kfifo_put(&test, i); i++)87 ;88 89 printk(KERN_INFO "queue len: %u\n", kfifo_len(&test));90 91 /* show the first value without removing from the fifo */92 if (kfifo_peek(&test, &i))93 printk(KERN_INFO "%d\n", i);94 95 /* check the correctness of all values in the fifo */96 j = 0;97 while (kfifo_get(&test, &i)) {98 printk(KERN_INFO "item = %d\n", i);99 if (i != expected_result[j++]) {100 printk(KERN_WARNING "value mismatch: test failed\n");101 return -EIO;102 }103 }104 if (j != ARRAY_SIZE(expected_result)) {105 printk(KERN_WARNING "size mismatch: test failed\n");106 return -EIO;107 }108 printk(KERN_INFO "test passed\n");109 110 return 0;111}112 113static ssize_t fifo_write(struct file *file, const char __user *buf,114 size_t count, loff_t *ppos)115{116 int ret;117 unsigned int copied;118 119 if (mutex_lock_interruptible(&write_access))120 return -ERESTARTSYS;121 122 ret = kfifo_from_user(&test, buf, count, &copied);123 124 mutex_unlock(&write_access);125 if (ret)126 return ret;127 128 return copied;129}130 131static 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_access))138 return -ERESTARTSYS;139 140 ret = kfifo_to_user(&test, buf, count, &copied);141 142 mutex_unlock(&read_access);143 if (ret)144 return ret;145 146 return copied;147}148 149static const struct proc_ops fifo_proc_ops = {150 .proc_read = fifo_read,151 .proc_write = fifo_write,152 .proc_lseek = noop_llseek,153};154 155static int __init example_init(void)156{157#ifdef DYNAMIC158 int ret;159 160 ret = kfifo_alloc(&test, FIFO_SIZE, GFP_KERNEL);161 if (ret) {162 printk(KERN_ERR "error kfifo_alloc\n");163 return ret;164 }165#else166 INIT_KFIFO(test);167#endif168 if (testfunc() < 0) {169#ifdef DYNAMIC170 kfifo_free(&test);171#endif172 return -EIO;173 }174 175 if (proc_create(PROC_FIFO, 0, NULL, &fifo_proc_ops) == NULL) {176#ifdef DYNAMIC177 kfifo_free(&test);178#endif179 return -ENOMEM;180 }181 return 0;182}183 184static void __exit example_exit(void)185{186 remove_proc_entry(PROC_FIFO, NULL);187#ifdef DYNAMIC188 kfifo_free(&test);189#endif190}191 192module_init(example_init);193module_exit(example_exit);194MODULE_DESCRIPTION("Sample kfifo byte stream implementation");195MODULE_LICENSE("GPL");196MODULE_AUTHOR("Stefani Seibold <stefani@seibold.net>");197