/*
 * 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) {
		pr_debug("couldn't alloc timer\n");
		ret = -ENOMEM;
		goto out;
	}

	info->timer->attr.attr.name = kstrdup(info->label, GFP_KERNEL);
	if (!info->timer->attr.attr.name) {
		pr_debug("couldn't alloc attribute name\n");
		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);
		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");