2 * Sample dynamic sized record fifo implementation
4 * Copyright (C) 2010 Stefani Seibold <stefani@seibold.net>
6 * Released under the GPL version 2 only.
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>
17 * This module shows how to create a variable sized record fifo.
20 /* fifo size in elements (bytes) */
23 /* name of the proc entry */
24 #define PROC_FIFO "record-fifo"
26 /* lock for procfs read access */
27 static DEFINE_MUTEX(read_lock);
29 /* lock for procfs write access */
30 static DEFINE_MUTEX(write_lock);
33 * define DYNAMIC in this example for a dynamically allocated fifo.
35 * Otherwise the fifo storage will be a part of the fifo structure.
42 * struct kfifo_rec_ptr_1 and STRUCT_KFIFO_REC_1 can handle records of a
43 * length between 0 and 255 bytes.
45 * struct kfifo_rec_ptr_2 and STRUCT_KFIFO_REC_2 can handle records of a
46 * length between 0 and 65535 bytes.
50 struct kfifo_rec_ptr_1 test;
53 typedef STRUCT_KFIFO_REC_1(FIFO_SIZE) mytest;
58 static int __init testfunc(void)
63 struct { unsigned char buf[6]; } hello = { "hello" };
65 printk(KERN_INFO "record fifo test start\n");
67 kfifo_in(&test, &hello, sizeof(hello));
69 /* show the size of the next record in the fifo */
70 printk(KERN_INFO "fifo peek len: %u\n", kfifo_peek_len(&test));
72 /* put in variable length data */
73 for (i = 0; i < 10; i++) {
74 memset(buf, 'a' + i, i + 1);
75 kfifo_in(&test, buf, i + 1);
78 printk(KERN_INFO "fifo len: %u\n", kfifo_len(&test));
80 /* show the first record without removing from the fifo */
81 ret = kfifo_out_peek(&test, buf, sizeof(buf));
83 printk(KERN_INFO "%.*s\n", ret, buf);
85 /* print out all records in the fifo */
86 while (!kfifo_is_empty(&test)) {
87 ret = kfifo_out(&test, buf, sizeof(buf));
88 printk(KERN_INFO "%.*s\n", ret, buf);
94 static ssize_t fifo_write(struct file *file, const char __user *buf,
95 size_t count, loff_t *ppos)
100 if (mutex_lock_interruptible(&write_lock))
103 ret = kfifo_from_user(&test, buf, count, &copied);
105 mutex_unlock(&write_lock);
107 return ret ? ret : copied;
110 static ssize_t fifo_read(struct file *file, char __user *buf,
111 size_t count, loff_t *ppos)
116 if (mutex_lock_interruptible(&read_lock))
119 ret = kfifo_to_user(&test, buf, count, &copied);
121 mutex_unlock(&read_lock);
123 return ret ? ret : copied;
126 static const struct file_operations fifo_fops = {
127 .owner = THIS_MODULE,
132 static int __init example_init(void)
137 ret = kfifo_alloc(&test, FIFO_SIZE, GFP_KERNEL);
139 printk(KERN_ERR "error kfifo_alloc\n");
147 if (proc_create(PROC_FIFO, 0, NULL, &fifo_fops) == NULL) {
156 static void __exit example_exit(void)
158 remove_proc_entry(PROC_FIFO, NULL);
164 module_init(example_init);
165 module_exit(example_exit);
166 MODULE_LICENSE("GPL");
167 MODULE_AUTHOR("Stefani Seibold <stefani@seibold.net>");