/*
 * linux/net/netfilter/xt_IDLETIMER.c
 *
 * Netfilter module to trigger a timer when packet matches.
 * After timer expires a kevent will be sent.
 *
 * Copyright (C) 2004, 2010 Nokia Corporation
 * Written by Timo Teras <ext-timo.teras@nokia.com>
 *
 * Converted to x_tables and reworked for upstream inclusion
 * by Luciano Coelho <luciano.coelho@nokia.com>
 *
 * Contact: Luciano Coelho <luciano.coelho@nokia.com>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * version 2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
 * 02110-1301 USA
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/module.h>
#include <linux/timer.h>
#include <linux/list.h>
#include <linux/mutex.h>
#include <linux/netfilter.h>
#include <linux/netfilter/x_tables.h>
#include <linux/netfilter/xt_IDLETIMER.h>
#include <linux/kdev_t.h>
#include <linux/kobject.h>
#include <linux/workqueue.h>
#include <linux/sysfs.h>

struct idletimer_tg_attr {
        struct attribute attr;
        ssize_t (*show)(struct kobject *kobj,
                        struct attribute *attr, char *buf);
};

struct idletimer_tg {
        struct list_head entry;
        struct timer_list timer;
        struct work_struct work;

        struct kobject *kobj;
        struct idletimer_tg_attr attr;

        unsigned int refcnt;
};

static LIST_HEAD(idletimer_tg_list);
static DEFINE_MUTEX(list_mutex);

static struct kobject *idletimer_tg_kobj;

static
struct idletimer_tg *__idletimer_tg_find_by_label(const char *label)
{
        struct idletimer_tg *entry;

        BUG_ON(!label);

        list_for_each_entry(entry, &idletimer_tg_list, entry) {
                if (!strcmp(label, entry->attr.attr.name))
                        return entry;
        }

        return NULL;
}

static ssize_t idletimer_tg_show(struct kobject *kobj, struct attribute *attr,
                                 char *buf)
{
        struct idletimer_tg *timer;
        unsigned long expires = 0;

        mutex_lock(&list_mutex);

        timer = __idletimer_tg_find_by_label(attr->name);
        if (timer)
                expires = timer->timer.expires;

        mutex_unlock(&list_mutex);

        if (time_after(expires, jiffies))
                return sprintf(buf, "%u\n",
                               jiffies_to_msecs(expires - jiffies) / 1000);

        return sprintf(buf, "0\n");
}

static void idletimer_tg_work(struct work_struct *work)
{
        struct idletimer_tg *timer = container_of(work, struct idletimer_tg,
                                                  work);

        sysfs_notify(idletimer_tg_kobj, NULL, timer->attr.attr.name);
}

static void idletimer_tg_expired(unsigned long data)
{
        struct idletimer_tg *timer = (struct idletimer_tg *) data;

        pr_debug("timer %s expired\n", timer->attr.attr.name);

        schedule_work(&timer->work);
}

static int idletimer_tg_create(struct idletimer_tg_info *info)
{
        int ret;

        info->timer = kmalloc(sizeof(*info->timer), GFP_KERNEL);
        if (!info->timer) {
                ret = -ENOMEM;
                goto out;
        }

        sysfs_attr_init(&info->timer->attr.attr);
        info->timer->attr.attr.name = kstrdup(info->label, GFP_KERNEL);
        if (!info->timer->attr.attr.name) {
                ret = -ENOMEM;
                goto out_free_timer;
        }
        info->timer->attr.attr.mode = S_IRUGO;
        info->timer->attr.show = idletimer_tg_show;

        ret = sysfs_create_file(idletimer_tg_kobj, &info->timer->attr.attr);
        if (ret < 0) {
                pr_debug("couldn't add file to sysfs");
                goto out_free_attr;
        }

        list_add(&info->timer->entry, &idletimer_tg_list);

        setup_timer(&info->timer->timer, idletimer_tg_expired,
                    (unsigned long) info->timer);
        info->timer->refcnt = 1;

        mod_timer(&info->timer->timer,
                  msecs_to_jiffies(info->timeout * 1000) + jiffies);

        INIT_WORK(&info->timer->work, idletimer_tg_work);

        return 0;

out_free_attr:
        kfree(info->timer->attr.attr.name);
out_free_timer:
        kfree(info->timer);
out:
        return ret;
}

/*
 * The actual xt_tables plugin.
 */
static unsigned int idletimer_tg_target(struct sk_buff *skb,
                                         const struct xt_action_param *par)
{
        const struct idletimer_tg_info *info = par->targinfo;

        pr_debug("resetting timer %s, timeout period %u\n",
                 info->label, info->timeout);

        BUG_ON(!info->timer);

        mod_timer(&info->timer->timer,
                  msecs_to_jiffies(info->timeout * 1000) + jiffies);

        return XT_CONTINUE;
}

static int idletimer_tg_checkentry(const struct xt_tgchk_param *par)
{
        struct idletimer_tg_info *info = par->targinfo;
        int ret;

        pr_debug("checkentry targinfo%s\n", info->label);

        if (info->timeout == 0) {
                pr_debug("timeout value is zero\n");
                return -EINVAL;
        }

        if (info->label[0] == '\0' ||
            strnlen(info->label,
                    MAX_IDLETIMER_LABEL_SIZE) == MAX_IDLETIMER_LABEL_SIZE) {
                pr_debug("label is empty or not nul-terminated\n");
                return -EINVAL;
        }

        mutex_lock(&list_mutex);

        info->timer = __idletimer_tg_find_by_label(info->label);
        if (info->timer) {
                info->timer->refcnt++;
                mod_timer(&info->timer->timer,
                          msecs_to_jiffies(info->timeout * 1000) + jiffies);

                pr_debug("increased refcnt of timer %s to %u\n",
                         info->label, info->timer->refcnt);
        } else {
                ret = idletimer_tg_create(info);
                if (ret < 0) {
                        pr_debug("failed to create timer\n");
                        mutex_unlock(&list_mutex);
                        return ret;
                }
        }

        mutex_unlock(&list_mutex);
        return 0;
}

static void idletimer_tg_destroy(const struct xt_tgdtor_param *par)
{
        const struct idletimer_tg_info *info = par->targinfo;

        pr_debug("destroy targinfo %s\n", info->label);

        mutex_lock(&list_mutex);

        if (--info->timer->refcnt == 0) {
                pr_debug("deleting timer %s\n", info->label);

                list_del(&info->timer->entry);
                del_timer_sync(&info->timer->timer);
                cancel_work_sync(&info->timer->work);
                sysfs_remove_file(idletimer_tg_kobj, &info->timer->attr.attr);
                kfree(info->timer->attr.attr.name);
                kfree(info->timer);
        } else {
                pr_debug("decreased refcnt of timer %s to %u\n",
                         info->label, info->timer->refcnt);
        }

        mutex_unlock(&list_mutex);
}

static struct xt_target idletimer_tg __read_mostly = {
        .name           = "IDLETIMER",
        .family         = NFPROTO_UNSPEC,
        .target         = idletimer_tg_target,
        .targetsize     = sizeof(struct idletimer_tg_info),
        .checkentry     = idletimer_tg_checkentry,
        .destroy        = idletimer_tg_destroy,
        .me             = THIS_MODULE,
};

static struct class *idletimer_tg_class;

static struct device *idletimer_tg_device;

static int __init idletimer_tg_init(void)
{
        int err;

        idletimer_tg_class = class_create(THIS_MODULE, "xt_idletimer");
        err = PTR_ERR(idletimer_tg_class);
        if (IS_ERR(idletimer_tg_class)) {
                pr_debug("couldn't register device class\n");
                goto out;
        }

        idletimer_tg_device = device_create(idletimer_tg_class, NULL,
                                            MKDEV(0, 0), NULL, "timers");
        err = PTR_ERR(idletimer_tg_device);
        if (IS_ERR(idletimer_tg_device)) {
                pr_debug("couldn't register system device\n");
                goto out_class;
        }

        idletimer_tg_kobj = &idletimer_tg_device->kobj;

        err =  xt_register_target(&idletimer_tg);
        if (err < 0) {
                pr_debug("couldn't register xt target\n");
                goto out_dev;
        }

        return 0;
out_dev:
        device_destroy(idletimer_tg_class, MKDEV(0, 0));
out_class:
        class_destroy(idletimer_tg_class);
out:
        return err;
}

static void __exit idletimer_tg_exit(void)
{
        xt_unregister_target(&idletimer_tg);

        device_destroy(idletimer_tg_class, MKDEV(0, 0));
        class_destroy(idletimer_tg_class);
}

module_init(idletimer_tg_init);
module_exit(idletimer_tg_exit);

MODULE_AUTHOR("Timo Teras <ext-timo.teras@nokia.com>");
MODULE_AUTHOR("Luciano Coelho <luciano.coelho@nokia.com>");
MODULE_DESCRIPTION("Xtables: idle time monitor");
MODULE_LICENSE("GPL v2");
MODULE_ALIAS("ipt_IDLETIMER");
MODULE_ALIAS("ip6t_IDLETIMER");