record-example.c

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/*
 * Sample dynamic sized record fifo implementation
 *
 * Copyright (C) 2010 Stefani Seibold <[email protected]>
 *
 * Released under the GPL version 2 only.
 *
 */

#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 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_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 <[email protected]>");