1 // SPDX-License-Identifier: GPL-2.0-only
3 * Sample dynamic sized record fifo implementation
5 * Copyright (C) 2010 Stefani Seibold <stefani@seibold.net>
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>
15 * This module shows how to create a variable sized record fifo.
18 /* fifo size in elements (bytes) */
21 /* name of the proc entry */
22 #define PROC_FIFO "record-fifo"
24 /* lock for procfs read access */
25 static DEFINE_MUTEX(read_access);
27 /* lock for procfs write access */
28 static DEFINE_MUTEX(write_access);
31 * define DYNAMIC in this example for a dynamically allocated fifo.
33 * Otherwise the fifo storage will be a part of the fifo structure.
40 * struct kfifo_rec_ptr_1 and STRUCT_KFIFO_REC_1 can handle records of a
41 * length between 0 and 255 bytes.
43 * struct kfifo_rec_ptr_2 and STRUCT_KFIFO_REC_2 can handle records of a
44 * length between 0 and 65535 bytes.
48 struct kfifo_rec_ptr_1 test;
51 typedef STRUCT_KFIFO_REC_1(FIFO_SIZE) mytest;
56 static const char *expected_result[] = {
69 static int __init testfunc(void)
74 struct { unsigned char buf[6]; } hello = { "hello" };
76 printk(KERN_INFO "record fifo test start\n");
78 kfifo_in(&test, &hello, sizeof(hello));
80 /* show the size of the next record in the fifo */
81 printk(KERN_INFO "fifo peek len: %u\n", kfifo_peek_len(&test));
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);
89 /* skip first element of the fifo */
90 printk(KERN_INFO "skip 1st element\n");
93 printk(KERN_INFO "fifo len: %u\n", kfifo_len(&test));
95 /* show the first record without removing from the fifo */
96 ret = kfifo_out_peek(&test, buf, sizeof(buf));
98 printk(KERN_INFO "%.*s\n", ret, buf);
100 /* check the correctness of all values in the fifo */
102 while (!kfifo_is_empty(&test)) {
103 ret = kfifo_out(&test, buf, sizeof(buf));
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");
111 if (i != ARRAY_SIZE(expected_result)) {
112 printk(KERN_WARNING "size mismatch: test failed\n");
115 printk(KERN_INFO "test passed\n");
120 static ssize_t fifo_write(struct file *file, const char __user *buf,
121 size_t count, loff_t *ppos)
126 if (mutex_lock_interruptible(&write_access))
129 ret = kfifo_from_user(&test, buf, count, &copied);
131 mutex_unlock(&write_access);
138 static ssize_t fifo_read(struct file *file, char __user *buf,
139 size_t count, loff_t *ppos)
144 if (mutex_lock_interruptible(&read_access))
147 ret = kfifo_to_user(&test, buf, count, &copied);
149 mutex_unlock(&read_access);
156 static const struct proc_ops fifo_proc_ops = {
157 .proc_read = fifo_read,
158 .proc_write = fifo_write,
159 .proc_lseek = noop_llseek,
162 static int __init example_init(void)
167 ret = kfifo_alloc(&test, FIFO_SIZE, GFP_KERNEL);
169 printk(KERN_ERR "error kfifo_alloc\n");
175 if (testfunc() < 0) {
182 if (proc_create(PROC_FIFO, 0, NULL, &fifo_proc_ops) == NULL) {
191 static void __exit example_exit(void)
193 remove_proc_entry(PROC_FIFO, NULL);
199 module_init(example_init);
200 module_exit(example_exit);
201 MODULE_LICENSE("GPL");
202 MODULE_AUTHOR("Stefani Seibold <stefani@seibold.net>");