/*

 *  net/dccp/ccids/lib/loss_interval.c

 *

 *  Copyright (c) 2007   The University of Aberdeen, Scotland, UK

 *  Copyright (c) 2005-7 The University of Waikato, Hamilton, New Zealand.

 *  Copyright (c) 2005-7 Ian McDonald <ian.mcdonald@jandi.co.nz>

 *  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.

 */

#include <net/sock.h>

#include "tfrc.h"

static struct kmem_cache  *tfrc_lh_slab  __read_mostly;

/* Loss Interval weights from [RFC 3448, 5.4], scaled by 10 */

static const int tfrc_lh_weights[NINTERVAL] = { 10, 10, 10, 10, 8, 6, 4, 2 };

/* implements LIFO semantics on the array */

static inline u8 LIH_INDEX(const u8 ctr)

{

	return (LIH_SIZE - 1 - (ctr % LIH_SIZE));

}

/* the `counter' index always points at the next entry to be populated */

static inline struct tfrc_loss_interval *tfrc_lh_peek(struct tfrc_loss_hist *lh)

{

	return lh->counter ? lh->ring[LIH_INDEX(lh->counter - 1)] : NULL;

}

/* given i with 0 <= i <= k, return I_i as per the rfc3448bis notation */

static inline u32 tfrc_lh_get_interval(struct tfrc_loss_hist *lh, const u8 i)

{

	BUG_ON(i >= lh->counter);

	return lh->ring[LIH_INDEX(lh->counter - i - 1)]->li_length;

}

/*

 *	On-demand allocation and de-allocation of entries

 */

static struct tfrc_loss_interval *tfrc_lh_demand_next(struct tfrc_loss_hist *lh)

{

	if (lh->ring[LIH_INDEX(lh->counter)] == NULL)

		lh->ring[LIH_INDEX(lh->counter)] = kmem_cache_alloc(tfrc_lh_slab,

								    GFP_ATOMIC);

	return lh->ring[LIH_INDEX(lh->counter)];

}

void tfrc_lh_cleanup(struct tfrc_loss_hist *lh)

{

	if (!tfrc_lh_is_initialised(lh))

		return;

	for (lh->counter = 0; lh->counter < LIH_SIZE; lh->counter++)

		if (lh->ring[LIH_INDEX(lh->counter)] != NULL) {

			kmem_cache_free(tfrc_lh_slab,

					lh->ring[LIH_INDEX(lh->counter)]);

			lh->ring[LIH_INDEX(lh->counter)] = NULL;

		}

}

static void tfrc_lh_calc_i_mean(struct tfrc_loss_hist *lh)

{

	u32 i_i, i_tot0 = 0, i_tot1 = 0, w_tot = 0;

	int i, k = tfrc_lh_length(lh) - 1; /* k is as in rfc3448bis, 5.4 */

	if (k <= 0)

		return;

	for (i = 0; i <= k; i++) {

		i_i = tfrc_lh_get_interval(lh, i);

		if (i < k) {

			i_tot0 += i_i * tfrc_lh_weights[i];

			w_tot  += tfrc_lh_weights[i];

		}

		if (i > 0)

			i_tot1 += i_i * tfrc_lh_weights[i-1];

	}

	lh->i_mean = max(i_tot0, i_tot1) / w_tot;

}

/**

 * tfrc_lh_update_i_mean  -  Update the `open' loss interval I_0

 * For recomputing p: returns `true' if p > p_prev  <=>  1/p < 1/p_prev

 */

u8 tfrc_lh_update_i_mean(struct tfrc_loss_hist *lh, struct sk_buff *skb)

{

	struct tfrc_loss_interval *cur = tfrc_lh_peek(lh);

	u32 old_i_mean = lh->i_mean;

	s64 len;

	if (cur == NULL)			/* not initialised */

		return 0;

	len = dccp_delta_seqno(cur->li_seqno, DCCP_SKB_CB(skb)->dccpd_seq) + 1;

	if (len - (s64)cur->li_length <= 0)	/* duplicate or reordered */

		return 0;

	if (SUB16(dccp_hdr(skb)->dccph_ccval, cur->li_ccval) > 4)

		/*

		 * Implements RFC 4342, 10.2:

		 * If a packet S (skb) exists whose seqno comes `after' the one

		 * starting the current loss interval (cur) and if the modulo-16

		 * distance from C(cur) to C(S) is greater than 4, consider all

		 * subsequent packets as belonging to a new loss interval. This

		 * test is necessary since CCVal may wrap between intervals.

		 */

		cur->li_is_closed = 1;

	if (tfrc_lh_length(lh) == 1)		/* due to RFC 3448, 6.3.1 */

		return 0;

	cur->li_length = len;

	tfrc_lh_calc_i_mean(lh);

	return (lh->i_mean < old_i_mean);

}

/* Determine if `new_loss' does begin a new loss interval [RFC 4342, 10.2] */

static inline u8 tfrc_lh_is_new_loss(struct tfrc_loss_interval *cur,

				     struct tfrc_rx_hist_entry *new_loss)

{

	return	dccp_delta_seqno(cur->li_seqno, new_loss->tfrchrx_seqno) > 0 &&

		(cur->li_is_closed || SUB16(new_loss->tfrchrx_ccval, cur->li_ccval) > 4);

}

/** tfrc_lh_interval_add  -  Insert new record into the Loss Interval database

 * @lh:		   Loss Interval database

 * @rh:		   Receive history containing a fresh loss event

 * @calc_first_li: Caller-dependent routine to compute length of first interval

 * @sk:		   Used by @calc_first_li in caller-specific way (subtyping)

 * Updates I_mean and returns 1 if a new interval has in fact been added to @lh.

 */

int tfrc_lh_interval_add(struct tfrc_loss_hist *lh, struct tfrc_rx_hist *rh,

			 u32 (*calc_first_li)(struct sock *), struct sock *sk)

{

	struct tfrc_loss_interval *cur = tfrc_lh_peek(lh), *new;

	if (cur != NULL && !tfrc_lh_is_new_loss(cur, tfrc_rx_hist_loss_prev(rh)))

		return 0;

	new = tfrc_lh_demand_next(lh);

	if (unlikely(new == NULL)) {

		DCCP_CRIT("Cannot allocate/add loss record.");

		return 0;

	}

	new->li_seqno	  = tfrc_rx_hist_loss_prev(rh)->tfrchrx_seqno;

	new->li_ccval	  = tfrc_rx_hist_loss_prev(rh)->tfrchrx_ccval;

	new->li_is_closed = 0;

	if (++lh->counter == 1)

		lh->i_mean = new->li_length = (*calc_first_li)(sk);

	else {

		cur->li_length = dccp_delta_seqno(cur->li_seqno, new->li_seqno);

		new->li_length = dccp_delta_seqno(new->li_seqno,

				  tfrc_rx_hist_last_rcv(rh)->tfrchrx_seqno) + 1;

		if (lh->counter > (2*LIH_SIZE))

			lh->counter -= LIH_SIZE;

		tfrc_lh_calc_i_mean(lh);

	}

	return 1;

}

int __init tfrc_li_init(void)

{

	tfrc_lh_slab = kmem_cache_create("tfrc_li_hist",

					 sizeof(struct tfrc_loss_interval), 0,

					 SLAB_HWCACHE_ALIGN, NULL);

	return tfrc_lh_slab == NULL ? -ENOBUFS : 0;

}

void tfrc_li_exit(void)

{

	if (tfrc_lh_slab != NULL) {

		kmem_cache_destroy(tfrc_lh_slab);

		tfrc_lh_slab = NULL;

	}

}