2 * Sample kfifo byte stream 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 byte stream fifo.
20 /* fifo size in elements (bytes) */
23 /* name of the proc entry */
24 #define PROC_FIFO "bytestream-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 static struct kfifo test
;
44 static DECLARE_KFIFO(test
, unsigned char, FIFO_SIZE
);
47 static const unsigned char expected_result
[FIFO_SIZE
] = {
48 3, 4, 5, 6, 7, 8, 9, 0,
49 1, 20, 21, 22, 23, 24, 25, 26,
50 27, 28, 29, 30, 31, 32, 33, 34,
51 35, 36, 37, 38, 39, 40, 41, 42,
54 static int __init
testfunc(void)
60 printk(KERN_INFO
"byte stream fifo test start\n");
62 /* put string into the fifo */
63 kfifo_in(&test
, "hello", 5);
65 /* put values into the fifo */
66 for (i
= 0; i
!= 10; i
++)
69 /* show the number of used elements */
70 printk(KERN_INFO
"fifo len: %u\n", kfifo_len(&test
));
72 /* get max of 5 bytes from the fifo */
73 i
= kfifo_out(&test
, buf
, 5);
74 printk(KERN_INFO
"buf: %.*s\n", i
, buf
);
76 /* get max of 2 elements from the fifo */
77 ret
= kfifo_out(&test
, buf
, 2);
78 printk(KERN_INFO
"ret: %d\n", ret
);
79 /* and put it back to the end of the fifo */
80 ret
= kfifo_in(&test
, buf
, ret
);
81 printk(KERN_INFO
"ret: %d\n", ret
);
83 /* skip first element of the fifo */
84 printk(KERN_INFO
"skip 1st element\n");
87 /* put values into the fifo until is full */
88 for (i
= 20; kfifo_put(&test
, &i
); i
++)
91 printk(KERN_INFO
"queue len: %u\n", kfifo_len(&test
));
93 /* show the first value without removing from the fifo */
94 if (kfifo_peek(&test
, &i
))
95 printk(KERN_INFO
"%d\n", i
);
97 /* check the correctness of all values in the fifo */
99 while (kfifo_get(&test
, &i
)) {
100 printk(KERN_INFO
"item = %d\n", i
);
101 if (i
!= expected_result
[j
++]) {
102 printk(KERN_WARNING
"value mismatch: test failed\n");
106 if (j
!= ARRAY_SIZE(expected_result
)) {
107 printk(KERN_WARNING
"size mismatch: test failed\n");
110 printk(KERN_INFO
"test passed\n");
115 static ssize_t
fifo_write(struct file
*file
, const char __user
*buf
,
116 size_t count
, loff_t
*ppos
)
121 if (mutex_lock_interruptible(&write_lock
))
124 ret
= kfifo_from_user(&test
, buf
, count
, &copied
);
126 mutex_unlock(&write_lock
);
128 return ret
? ret
: copied
;
131 static ssize_t
fifo_read(struct file
*file
, char __user
*buf
,
132 size_t count
, loff_t
*ppos
)
137 if (mutex_lock_interruptible(&read_lock
))
140 ret
= kfifo_to_user(&test
, buf
, count
, &copied
);
142 mutex_unlock(&read_lock
);
144 return ret
? ret
: copied
;
147 static const struct file_operations fifo_fops
= {
148 .owner
= THIS_MODULE
,
153 static int __init
example_init(void)
158 ret
= kfifo_alloc(&test
, FIFO_SIZE
, GFP_KERNEL
);
160 printk(KERN_ERR
"error kfifo_alloc\n");
166 if (testfunc() < 0) {
173 if (proc_create(PROC_FIFO
, 0, NULL
, &fifo_fops
) == NULL
) {
182 static void __exit
example_exit(void)
184 remove_proc_entry(PROC_FIFO
, NULL
);
190 module_init(example_init
);
191 module_exit(example_exit
);
192 MODULE_LICENSE("GPL");
193 MODULE_AUTHOR("Stefani Seibold <stefani@seibold.net>");