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 int __init
testfunc(void)
53 printk(KERN_INFO
"byte stream fifo test start\n");
55 /* put string into the fifo */
56 kfifo_in(&test
, "hello", 5);
58 /* put values into the fifo */
59 for (i
= 0; i
!= 10; i
++)
62 /* show the number of used elements */
63 printk(KERN_INFO
"fifo len: %u\n", kfifo_len(&test
));
65 /* get max of 5 bytes from the fifo */
66 i
= kfifo_out(&test
, buf
, 5);
67 printk(KERN_INFO
"buf: %.*s\n", i
, buf
);
69 /* get max of 2 elements from the fifo */
70 ret
= kfifo_out(&test
, buf
, 2);
71 printk(KERN_INFO
"ret: %d\n", ret
);
72 /* and put it back to the end of the fifo */
73 ret
= kfifo_in(&test
, buf
, ret
);
74 printk(KERN_INFO
"ret: %d\n", ret
);
76 /* put values into the fifo until is full */
77 for (i
= 20; kfifo_put(&test
, &i
); i
++)
80 printk(KERN_INFO
"queue len: %u\n", kfifo_len(&test
));
82 /* print out all values in the fifo */
83 while (kfifo_get(&test
, &i
))
90 static ssize_t
fifo_write(struct file
*file
, const char __user
*buf
,
91 size_t count
, loff_t
*ppos
)
96 if (mutex_lock_interruptible(&write_lock
))
99 ret
= kfifo_from_user(&test
, buf
, count
, &copied
);
101 mutex_unlock(&write_lock
);
103 return ret
? ret
: copied
;
106 static ssize_t
fifo_read(struct file
*file
, char __user
*buf
,
107 size_t count
, loff_t
*ppos
)
112 if (mutex_lock_interruptible(&read_lock
))
115 ret
= kfifo_to_user(&test
, buf
, count
, &copied
);
117 mutex_unlock(&read_lock
);
119 return ret
? ret
: copied
;
122 static const struct file_operations fifo_fops
= {
123 .owner
= THIS_MODULE
,
128 static int __init
example_init(void)
133 ret
= kfifo_alloc(&test
, FIFO_SIZE
, GFP_KERNEL
);
135 printk(KERN_ERR
"error kfifo_alloc\n");
143 if (proc_create(PROC_FIFO
, 0, NULL
, &fifo_fops
) == NULL
) {
152 static void __exit
example_exit(void)
154 remove_proc_entry(PROC_FIFO
, NULL
);
160 module_init(example_init
);
161 module_exit(example_exit
);
162 MODULE_LICENSE("GPL");
163 MODULE_AUTHOR("Stefani Seibold <stefani@seibold.net>");