// 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 DYNAMIC
static struct kfifo test;
#else
static 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>");