/*
 *  net/dccp/packet_history.c
 *
 *  Copyright (c) 2007   The University of Aberdeen, Scotland, UK
 *  Copyright (c) 2005-7 The University of Waikato, Hamilton, New Zealand.
 *
 *  An implementation of the DCCP protocol
 *
 *  This code has been developed by the University of Waikato WAND
 *  research group. For further information please see http://www.wand.net.nz/
 *  or e-mail Ian McDonald - ian.mcdonald@jandi.co.nz
 *
 *  This code also uses code from Lulea University, rereleased as GPL by its
 *  authors:
 *  Copyright (c) 2003 Nils-Erik Mattsson, Joacim Haggmark, Magnus Erixzon
 *
 *  Changes to meet Linux coding standards, to make it meet latest ccid3 draft
 *  and to make it work as a loadable module in the DCCP stack written by
 *  Arnaldo Carvalho de Melo <acme@conectiva.com.br>.
 *
 *  Copyright (c) 2005 Arnaldo Carvalho de Melo <acme@conectiva.com.br>
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  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., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

#include <linux/string.h>
#include "packet_history.h"

/**
 *  tfrc_tx_hist_entry  -  Simple singly-linked TX history list
 *  @next:  next oldest entry (LIFO order)
 *  @seqno: sequence number of this entry
 *  @stamp: send time of packet with sequence number @seqno
 */
struct tfrc_tx_hist_entry {
	struct tfrc_tx_hist_entry *next;
	u64			  seqno;
	ktime_t			  stamp;
};

/*
 * Transmitter History Routines
 */
static struct kmem_cache *tfrc_tx_hist_slab;

static struct tfrc_tx_hist_entry *
	tfrc_tx_hist_find_entry(struct tfrc_tx_hist_entry *head, u64 seqno)
{
	while (head != NULL && head->seqno != seqno)
		head = head->next;

	return head;
}

int tfrc_tx_hist_add(struct tfrc_tx_hist_entry **headp, u64 seqno)
{
	struct tfrc_tx_hist_entry *entry = kmem_cache_alloc(tfrc_tx_hist_slab, gfp_any());

	if (entry == NULL)
		return -ENOBUFS;
	entry->seqno = seqno;
	entry->stamp = ktime_get_real();
	entry->next  = *headp;
	*headp	     = entry;
	return 0;
}
EXPORT_SYMBOL_GPL(tfrc_tx_hist_add);

void tfrc_tx_hist_purge(struct tfrc_tx_hist_entry **headp)
{
	struct tfrc_tx_hist_entry *head = *headp;

	while (head != NULL) {
		struct tfrc_tx_hist_entry *next = head->next;

		kmem_cache_free(tfrc_tx_hist_slab, head);
		head = next;
	}

	*headp = NULL;
}
EXPORT_SYMBOL_GPL(tfrc_tx_hist_purge);

u32 tfrc_tx_hist_rtt(struct tfrc_tx_hist_entry *head, const u64 seqno,
		     const ktime_t now)
{
	u32 rtt = 0;
	struct tfrc_tx_hist_entry *packet = tfrc_tx_hist_find_entry(head, seqno);

	if (packet != NULL) {
		rtt = ktime_us_delta(now, packet->stamp);
		/*
		 * Garbage-collect older (irrelevant) entries:
		 */
		tfrc_tx_hist_purge(&packet->next);
	}

	return rtt;
}
EXPORT_SYMBOL_GPL(tfrc_tx_hist_rtt);

/*
 * 	Receiver History Routines
 */
static struct kmem_cache *tfrc_rx_hist_slab;

struct tfrc_rx_hist_entry *tfrc_rx_hist_entry_new(const u32 ndp,
						  const struct sk_buff *skb,
						  const gfp_t prio)
{
	struct tfrc_rx_hist_entry *entry = kmem_cache_alloc(tfrc_rx_hist_slab,
							    prio);

	if (entry != NULL) {
		const struct dccp_hdr *dh = dccp_hdr(skb);

		entry->tfrchrx_seqno = DCCP_SKB_CB(skb)->dccpd_seq;
		entry->tfrchrx_ccval = dh->dccph_ccval;
		entry->tfrchrx_type  = dh->dccph_type;
		entry->tfrchrx_ndp   = ndp;
		entry->tfrchrx_tstamp = ktime_get_real();
	}

	return entry;
}
EXPORT_SYMBOL_GPL(tfrc_rx_hist_entry_new);

static inline void tfrc_rx_hist_entry_delete(struct tfrc_rx_hist_entry *entry)
{
	kmem_cache_free(tfrc_rx_hist_slab, entry);
}

int tfrc_rx_hist_find_entry(const struct list_head *list, const u64 seq,
			    u8 *ccval)
{
	struct tfrc_rx_hist_entry *packet = NULL, *entry;

	list_for_each_entry(entry, list, tfrchrx_node)
		if (entry->tfrchrx_seqno == seq) {
			packet = entry;
			break;
		}

	if (packet)
		*ccval = packet->tfrchrx_ccval;

	return packet != NULL;
}

EXPORT_SYMBOL_GPL(tfrc_rx_hist_find_entry);
struct tfrc_rx_hist_entry *
		tfrc_rx_hist_find_data_packet(const struct list_head *list)
{
	struct tfrc_rx_hist_entry *entry, *packet = NULL;

	list_for_each_entry(entry, list, tfrchrx_node)
		if (entry->tfrchrx_type == DCCP_PKT_DATA ||
		    entry->tfrchrx_type == DCCP_PKT_DATAACK) {
			packet = entry;
			break;
		}

	return packet;
}

EXPORT_SYMBOL_GPL(tfrc_rx_hist_find_data_packet);

void tfrc_rx_hist_add_packet(struct list_head *rx_list,
			     struct list_head *li_list,
			     struct tfrc_rx_hist_entry *packet,
			     u64 nonloss_seqno)
{
	struct tfrc_rx_hist_entry *entry, *next;
	u8 num_later = 0;

	list_add(&packet->tfrchrx_node, rx_list);

	num_later = TFRC_RECV_NUM_LATE_LOSS + 1;

	if (!list_empty(li_list)) {
		list_for_each_entry_safe(entry, next, rx_list, tfrchrx_node) {
			if (num_later == 0) {
				if (after48(nonloss_seqno,
				   entry->tfrchrx_seqno)) {
					list_del_init(&entry->tfrchrx_node);
					tfrc_rx_hist_entry_delete(entry);
				}
			} else if (tfrc_rx_hist_entry_data_packet(entry))
				--num_later;
		}
	} else {
		int step = 0;
		u8 win_count = 0; /* Not needed, but lets shut up gcc */
		int tmp;
		/*
		 * We have no loss interval history so we need at least one
		 * rtt:s of data packets to approximate rtt.
		 */
		list_for_each_entry_safe(entry, next, rx_list, tfrchrx_node) {
			if (num_later == 0) {
				switch (step) {
				case 0:
					step = 1;
					/* OK, find next data packet */
					num_later = 1;
					break;
				case 1:
					step = 2;
					/* OK, find next data packet */
					num_later = 1;
					win_count = entry->tfrchrx_ccval;
					break;
				case 2:
					tmp = win_count - entry->tfrchrx_ccval;
					if (tmp < 0)
						tmp += TFRC_WIN_COUNT_LIMIT;
					if (tmp > TFRC_WIN_COUNT_PER_RTT + 1) {
						/*
						 * We have found a packet older
						 * than one rtt remove the rest
						 */
						step = 3;
					} else /* OK, find next data packet */
						num_later = 1;
					break;
				case 3:
					list_del_init(&entry->tfrchrx_node);
					tfrc_rx_hist_entry_delete(entry);
					break;
				}
			} else if (tfrc_rx_hist_entry_data_packet(entry))
				--num_later;
		}
	}
}

EXPORT_SYMBOL_GPL(tfrc_rx_hist_add_packet);

void tfrc_rx_hist_purge(struct list_head *list)
{
	struct tfrc_rx_hist_entry *entry, *next;

	list_for_each_entry_safe(entry, next, list, tfrchrx_node) {
		list_del_init(&entry->tfrchrx_node);
		tfrc_rx_hist_entry_delete(entry);
	}
}

EXPORT_SYMBOL_GPL(tfrc_rx_hist_purge);

__init int packet_history_init(void)
{
	tfrc_tx_hist_slab = kmem_cache_create("tfrc_tx_hist",
					      sizeof(struct tfrc_tx_hist_entry), 0,
					      SLAB_HWCACHE_ALIGN, NULL);
	if (tfrc_tx_hist_slab == NULL)
		goto out_err;

	tfrc_rx_hist_slab = kmem_cache_create("tfrc_rx_hist",
					      sizeof(struct tfrc_rx_hist_entry), 0,
					      SLAB_HWCACHE_ALIGN, NULL);
	if (tfrc_rx_hist_slab == NULL)
		goto out_free_tx;

	return 0;

out_free_tx:
	kmem_cache_destroy(tfrc_tx_hist_slab);
	tfrc_tx_hist_slab = NULL;
out_err:
	return -ENOBUFS;
}

void packet_history_exit(void)
{
	if (tfrc_tx_hist_slab != NULL) {
		kmem_cache_destroy(tfrc_tx_hist_slab);
		tfrc_tx_hist_slab = NULL;
	}

	if (tfrc_rx_hist_slab != NULL) {
		kmem_cache_destroy(tfrc_rx_hist_slab);
		tfrc_rx_hist_slab = NULL;
	}
}