// 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_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

/*
 * 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 DYNAMIC
struct kfifo_rec_ptr_1 test;

#else
typedef 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_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 dynamic sized record fifo implementation");
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Stefani Seibold <stefani@seibold.net>");