// SPDX-License-Identifier: GPL-2.0-only/* * Sample kfifo byte stream implementation * * Copyright (C) 2010 Stefani Seibold <stefani@seibold.net> */ #include <linux/init.h>#include <linux/module.h>#include <linux/proc_fs.h>#include <linux/mutex.h>#include <linux/kfifo.h> /* * This module shows how to create a byte stream fifo. */ /* fifo size in elements (bytes) */#define FIFO_SIZE	32 /* name of the proc entry */#define	PROC_FIFO	"bytestream-fifo" /* lock for procfs read access */static DEFINE_MUTEX(read_access); /* lock for procfs write access */static DEFINE_MUTEX(write_access); /* * define DYNAMIC in this example for a dynamically allocated fifo. * * Otherwise the fifo storage will be a part of the fifo structure. */#if 0#define DYNAMIC#endif #ifdef DYNAMICstatic struct kfifo test;#elsestatic DECLARE_KFIFO(test, unsigned char, FIFO_SIZE);#endif static const unsigned char expected_result[FIFO_SIZE] = {	 3,  4,  5,  6,  7,  8,  9,  0,	 1, 20, 21, 22, 23, 24, 25, 26,	27, 28, 29, 30, 31, 32, 33, 34,	35, 36, 37, 38, 39, 40, 41, 42,}; static int __init testfunc(void){	unsigned char	buf[6];	unsigned char	i, j;	unsigned int	ret; 	printk(KERN_INFO "byte stream fifo test start\n"); 	/* put string into the fifo */	kfifo_in(&test, "hello", 5); 	/* put values into the fifo */	for (i = 0; i != 10; i++)		kfifo_put(&test, i); 	/* show the number of used elements */	printk(KERN_INFO "fifo len: %u\n", kfifo_len(&test)); 	/* get max of 5 bytes from the fifo */	i = kfifo_out(&test, buf, 5);	printk(KERN_INFO "buf: %.*s\n", i, buf); 	/* get max of 2 elements from the fifo */	ret = kfifo_out(&test, buf, 2);	printk(KERN_INFO "ret: %d\n", ret);	/* and put it back to the end of the fifo */	ret = kfifo_in(&test, buf, ret);	printk(KERN_INFO "ret: %d\n", ret); 	/* skip first element of the fifo */	printk(KERN_INFO "skip 1st element\n");	kfifo_skip(&test); 	/* put values into the fifo until is full */	for (i = 20; kfifo_put(&test, i); i++)		; 	printk(KERN_INFO "queue len: %u\n", kfifo_len(&test)); 	/* show the first value without removing from the fifo */	if (kfifo_peek(&test, &i))		printk(KERN_INFO "%d\n", i); 	/* check the correctness of all values in the fifo */	j = 0;	while (kfifo_get(&test, &i)) {		printk(KERN_INFO "item = %d\n", i);		if (i != expected_result[j++]) {			printk(KERN_WARNING "value mismatch: test failed\n");			return -EIO;		}	}	if (j != ARRAY_SIZE(expected_result)) {		printk(KERN_WARNING "size mismatch: test failed\n");		return -EIO;	}	printk(KERN_INFO "test passed\n"); 	return 0;} static ssize_t fifo_write(struct file *file, const char __user *buf,						size_t count, loff_t *ppos){	int ret;	unsigned int copied; 	if (mutex_lock_interruptible(&write_access))		return -ERESTARTSYS; 	ret = kfifo_from_user(&test, buf, count, &copied); 	mutex_unlock(&write_access);	if (ret)		return ret; 	return copied;} static ssize_t fifo_read(struct file *file, char __user *buf,						size_t count, loff_t *ppos){	int ret;	unsigned int copied; 	if (mutex_lock_interruptible(&read_access))		return -ERESTARTSYS; 	ret = kfifo_to_user(&test, buf, count, &copied); 	mutex_unlock(&read_access);	if (ret)		return ret; 	return copied;} static const struct proc_ops fifo_proc_ops = {	.proc_read	= fifo_read,	.proc_write	= fifo_write,	.proc_lseek	= noop_llseek,}; static int __init example_init(void){#ifdef DYNAMIC	int ret; 	ret = kfifo_alloc(&test, FIFO_SIZE, GFP_KERNEL);	if (ret) {		printk(KERN_ERR "error kfifo_alloc\n");		return ret;	}#else	INIT_KFIFO(test);#endif	if (testfunc() < 0) {#ifdef DYNAMIC		kfifo_free(&test);#endif		return -EIO;	} 	if (proc_create(PROC_FIFO, 0, NULL, &fifo_proc_ops) == NULL) {#ifdef DYNAMIC		kfifo_free(&test);#endif		return -ENOMEM;	}	return 0;} static void __exit example_exit(void){	remove_proc_entry(PROC_FIFO, NULL);#ifdef DYNAMIC	kfifo_free(&test);#endif} module_init(example_init);module_exit(example_exit);MODULE_DESCRIPTION("Sample kfifo byte stream implementation");MODULE_LICENSE("GPL");MODULE_AUTHOR("Stefani Seibold <stefani@seibold.net>");