// SPDX-License-Identifier: GPL-2.0-only/* * Sample dynamic sized record fifo 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 variable sized record fifo. */ /* fifo size in elements (bytes) */#define FIFO_SIZE	128 /* name of the proc entry */#define	PROC_FIFO	"record-fifo" /* lock for procfs read access */static DEFINE_MUTEX(read_lock); /* lock for procfs write access */static DEFINE_MUTEX(write_lock); /* * 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 /* * struct kfifo_rec_ptr_1 and  STRUCT_KFIFO_REC_1 can handle records of a * length between 0 and 255 bytes. * * struct kfifo_rec_ptr_2 and  STRUCT_KFIFO_REC_2 can handle records of a * length between 0 and 65535 bytes. */ #ifdef DYNAMICstruct kfifo_rec_ptr_1 test; #elsetypedef STRUCT_KFIFO_REC_1(FIFO_SIZE) mytest; static mytest test;#endif static const char *expected_result[] = {	"a",	"bb",	"ccc",	"dddd",	"eeeee",	"ffffff",	"ggggggg",	"hhhhhhhh",	"iiiiiiiii",	"jjjjjjjjjj",}; static int __init testfunc(void){	char		buf[100];	unsigned int	i;	unsigned int	ret;	struct { unsigned char buf[6]; } hello = { "hello" }; 	printk(KERN_INFO "record fifo test start\n"); 	kfifo_in(&test, &hello, sizeof(hello)); 	/* show the size of the next record in the fifo */	printk(KERN_INFO "fifo peek len: %u\n", kfifo_peek_len(&test)); 	/* put in variable length data */	for (i = 0; i < 10; i++) {		memset(buf, 'a' + i, i + 1);		kfifo_in(&test, buf, i + 1);	} 	/* skip first element of the fifo */	printk(KERN_INFO "skip 1st element\n");	kfifo_skip(&test); 	printk(KERN_INFO "fifo len: %u\n", kfifo_len(&test)); 	/* show the first record without removing from the fifo */	ret = kfifo_out_peek(&test, buf, sizeof(buf));	if (ret)		printk(KERN_INFO "%.*s\n", ret, buf); 	/* check the correctness of all values in the fifo */	i = 0;	while (!kfifo_is_empty(&test)) {		ret = kfifo_out(&test, buf, sizeof(buf));		buf[ret] = '\0';		printk(KERN_INFO "item = %.*s\n", ret, buf);		if (strcmp(buf, expected_result[i++])) {			printk(KERN_WARNING "value mismatch: test failed\n");			return -EIO;		}	}	if (i != 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_lock))		return -ERESTARTSYS; 	ret = kfifo_from_user(&test, buf, count, &copied); 	mutex_unlock(&write_lock); 	return ret ? ret : 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_lock))		return -ERESTARTSYS; 	ret = kfifo_to_user(&test, buf, count, &copied); 	mutex_unlock(&read_lock); 	return ret ? ret : copied;} static const struct file_operations fifo_fops = {	.owner		= THIS_MODULE,	.read		= fifo_read,	.write		= fifo_write,	.llseek		= 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_fops) == 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_LICENSE("GPL");MODULE_AUTHOR("Stefani Seibold <stefani@seibold.net>");