/* SPDX-License-Identifier: GPL-2.0-or-later */
/*
 *  Packet RX/TX history data structures and routines for TFRC-based protocols.
 *
 *  Copyright (c) 2007   The University of Aberdeen, Scotland, UK
 *  Copyright (c) 2005-6 The University of Waikato, Hamilton, New Zealand.
 *
 *  This code has been developed by the University of Waikato WAND
 *  research group. For further information please see https://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>
 */

#ifndef _DCCP_PKT_HIST_
#define _DCCP_PKT_HIST_

#include <linux/list.h>
#include <linux/slab.h>
#include "tfrc.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;
};

static inline 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);
void tfrc_tx_hist_purge(struct tfrc_tx_hist_entry **headp);

/* Subtraction a-b modulo-16, respects circular wrap-around */
#define SUB16(a, b) (((a) + 16 - (b)) & 0xF)

/* Number of packets to wait after a missing packet (RFC 4342, 6.1) */
#define TFRC_NDUPACK 3

/**
 * tfrc_rx_hist_entry - Store information about a single received packet
 * @tfrchrx_seqno:	DCCP packet sequence number
 * @tfrchrx_ccval:	window counter value of packet (RFC 4342, 8.1)
 * @tfrchrx_ndp:	the NDP count (if any) of the packet
 * @tfrchrx_tstamp:	actual receive time of packet
 */
struct tfrc_rx_hist_entry {
	u64		 tfrchrx_seqno:48,
			 tfrchrx_ccval:4,
			 tfrchrx_type:4;
	u64		 tfrchrx_ndp:48;
	ktime_t		 tfrchrx_tstamp;
};

/**
 * tfrc_rx_hist  -  RX history structure for TFRC-based protocols
 * @ring:		Packet history for RTT sampling and loss detection
 * @loss_count:		Number of entries in circular history
 * @loss_start:		Movable index (for loss detection)
 * @rtt_sample_prev:	Used during RTT sampling, points to candidate entry
 */
struct tfrc_rx_hist {
	struct tfrc_rx_hist_entry *ring[TFRC_NDUPACK + 1];
	u8			  loss_count:2,
				  loss_start:2;
#define rtt_sample_prev		  loss_start
};

/**
 * tfrc_rx_hist_index - index to reach n-th entry after loss_start
 */
static inline u8 tfrc_rx_hist_index(const struct tfrc_rx_hist *h, const u8 n)
{
	return (h->loss_start + n) & TFRC_NDUPACK;
}

/**
 * tfrc_rx_hist_last_rcv - entry with highest-received-seqno so far
 */
static inline struct tfrc_rx_hist_entry *
			tfrc_rx_hist_last_rcv(const struct tfrc_rx_hist *h)
{
	return h->ring[tfrc_rx_hist_index(h, h->loss_count)];
}

/**
 * tfrc_rx_hist_entry - return the n-th history entry after loss_start
 */
static inline struct tfrc_rx_hist_entry *
			tfrc_rx_hist_entry(const struct tfrc_rx_hist *h, const u8 n)
{
	return h->ring[tfrc_rx_hist_index(h, n)];
}

/**
 * tfrc_rx_hist_loss_prev - entry with highest-received-seqno before loss was detected
 */
static inline struct tfrc_rx_hist_entry *
			tfrc_rx_hist_loss_prev(const struct tfrc_rx_hist *h)
{
	return h->ring[h->loss_start];
}

/* indicate whether previously a packet was detected missing */
static inline bool tfrc_rx_hist_loss_pending(const struct tfrc_rx_hist *h)
{
	return h->loss_count > 0;
}

void tfrc_rx_hist_add_packet(struct tfrc_rx_hist *h, const struct sk_buff *skb,
			     const u64 ndp);

int tfrc_rx_hist_duplicate(struct tfrc_rx_hist *h, struct sk_buff *skb);

struct tfrc_loss_hist;
int tfrc_rx_handle_loss(struct tfrc_rx_hist *h, struct tfrc_loss_hist *lh,
			struct sk_buff *skb, const u64 ndp,
			u32 (*first_li)(struct sock *sk), struct sock *sk);
u32 tfrc_rx_hist_sample_rtt(struct tfrc_rx_hist *h, const struct sk_buff *skb);
int tfrc_rx_hist_alloc(struct tfrc_rx_hist *h);
void tfrc_rx_hist_purge(struct tfrc_rx_hist *h);

#endif /* _DCCP_PKT_HIST_ */