1/*
2 *  Copyright (c) 2007   The University of Aberdeen, Scotland, UK
3 *  Copyright (c) 2005-7 The University of Waikato, Hamilton, New Zealand.
4 *  Copyright (c) 2005-7 Ian McDonald <ian.mcdonald@jandi.co.nz>
5 *  Copyright (c) 2005 Arnaldo Carvalho de Melo <acme@conectiva.com.br>
6 *
7 *  This program is free software; you can redistribute it and/or modify
8 *  it under the terms of the GNU General Public License as published by
9 *  the Free Software Foundation; either version 2 of the License, or
10 *  (at your option) any later version.
11 */
12#include <net/sock.h>
13#include "tfrc.h"
14
15static struct kmem_cache  *tfrc_lh_slab  __read_mostly;
16/* Loss Interval weights from [RFC 3448, 5.4], scaled by 10 */
17static const int tfrc_lh_weights[NINTERVAL] = { 10, 10, 10, 10, 8, 6, 4, 2 };
18
19/* implements LIFO semantics on the array */
20static inline u8 LIH_INDEX(const u8 ctr)
21{
22	return LIH_SIZE - 1 - (ctr % LIH_SIZE);
23}
24
25/* the `counter' index always points at the next entry to be populated */
26static inline struct tfrc_loss_interval *tfrc_lh_peek(struct tfrc_loss_hist *lh)
27{
28	return lh->counter ? lh->ring[LIH_INDEX(lh->counter - 1)] : NULL;
29}
30
31/* given i with 0 <= i <= k, return I_i as per the rfc3448bis notation */
32static inline u32 tfrc_lh_get_interval(struct tfrc_loss_hist *lh, const u8 i)
33{
34	BUG_ON(i >= lh->counter);
35	return lh->ring[LIH_INDEX(lh->counter - i - 1)]->li_length;
36}
37
38/*
39 *	On-demand allocation and de-allocation of entries
40 */
41static struct tfrc_loss_interval *tfrc_lh_demand_next(struct tfrc_loss_hist *lh)
42{
43	if (lh->ring[LIH_INDEX(lh->counter)] == NULL)
44		lh->ring[LIH_INDEX(lh->counter)] = kmem_cache_alloc(tfrc_lh_slab,
45								    GFP_ATOMIC);
46	return lh->ring[LIH_INDEX(lh->counter)];
47}
48
49void tfrc_lh_cleanup(struct tfrc_loss_hist *lh)
50{
51	if (!tfrc_lh_is_initialised(lh))
52		return;
53
54	for (lh->counter = 0; lh->counter < LIH_SIZE; lh->counter++)
55		if (lh->ring[LIH_INDEX(lh->counter)] != NULL) {
56			kmem_cache_free(tfrc_lh_slab,
57					lh->ring[LIH_INDEX(lh->counter)]);
58			lh->ring[LIH_INDEX(lh->counter)] = NULL;
59		}
60}
61
62static void tfrc_lh_calc_i_mean(struct tfrc_loss_hist *lh)
63{
64	u32 i_i, i_tot0 = 0, i_tot1 = 0, w_tot = 0;
65	int i, k = tfrc_lh_length(lh) - 1; /* k is as in rfc3448bis, 5.4 */
66
67	if (k <= 0)
68		return;
69
70	for (i = 0; i <= k; i++) {
71		i_i = tfrc_lh_get_interval(lh, i);
72
73		if (i < k) {
74			i_tot0 += i_i * tfrc_lh_weights[i];
75			w_tot  += tfrc_lh_weights[i];
76		}
77		if (i > 0)
78			i_tot1 += i_i * tfrc_lh_weights[i-1];
79	}
80
81	lh->i_mean = max(i_tot0, i_tot1) / w_tot;
82}
83
84/**
85 * tfrc_lh_update_i_mean  -  Update the `open' loss interval I_0
86 * For recomputing p: returns `true' if p > p_prev  <=>  1/p < 1/p_prev
87 */
88u8 tfrc_lh_update_i_mean(struct tfrc_loss_hist *lh, struct sk_buff *skb)
89{
90	struct tfrc_loss_interval *cur = tfrc_lh_peek(lh);
91	u32 old_i_mean = lh->i_mean;
92	s64 len;
93
94	if (cur == NULL)			/* not initialised */
95		return 0;
96
97	len = dccp_delta_seqno(cur->li_seqno, DCCP_SKB_CB(skb)->dccpd_seq) + 1;
98
99	if (len - (s64)cur->li_length <= 0)	/* duplicate or reordered */
100		return 0;
101
102	if (SUB16(dccp_hdr(skb)->dccph_ccval, cur->li_ccval) > 4)
103		/*
104		 * Implements RFC 4342, 10.2:
105		 * If a packet S (skb) exists whose seqno comes `after' the one
106		 * starting the current loss interval (cur) and if the modulo-16
107		 * distance from C(cur) to C(S) is greater than 4, consider all
108		 * subsequent packets as belonging to a new loss interval. This
109		 * test is necessary since CCVal may wrap between intervals.
110		 */
111		cur->li_is_closed = 1;
112
113	if (tfrc_lh_length(lh) == 1)		/* due to RFC 3448, 6.3.1 */
114		return 0;
115
116	cur->li_length = len;
117	tfrc_lh_calc_i_mean(lh);
118
119	return lh->i_mean < old_i_mean;
120}
121
122/* Determine if `new_loss' does begin a new loss interval [RFC 4342, 10.2] */
123static inline u8 tfrc_lh_is_new_loss(struct tfrc_loss_interval *cur,
124				     struct tfrc_rx_hist_entry *new_loss)
125{
126	return	dccp_delta_seqno(cur->li_seqno, new_loss->tfrchrx_seqno) > 0 &&
127		(cur->li_is_closed || SUB16(new_loss->tfrchrx_ccval, cur->li_ccval) > 4);
128}
129
130/**
131 * tfrc_lh_interval_add  -  Insert new record into the Loss Interval database
132 * @lh:		   Loss Interval database
133 * @rh:		   Receive history containing a fresh loss event
134 * @calc_first_li: Caller-dependent routine to compute length of first interval
135 * @sk:		   Used by @calc_first_li in caller-specific way (subtyping)
136 *
137 * Updates I_mean and returns 1 if a new interval has in fact been added to @lh.
138 */
139int tfrc_lh_interval_add(struct tfrc_loss_hist *lh, struct tfrc_rx_hist *rh,
140			 u32 (*calc_first_li)(struct sock *), struct sock *sk)
141{
142	struct tfrc_loss_interval *cur = tfrc_lh_peek(lh), *new;
143
144	if (cur != NULL && !tfrc_lh_is_new_loss(cur, tfrc_rx_hist_loss_prev(rh)))
145		return 0;
146
147	new = tfrc_lh_demand_next(lh);
148	if (unlikely(new == NULL)) {
149		DCCP_CRIT("Cannot allocate/add loss record.");
150		return 0;
151	}
152
153	new->li_seqno	  = tfrc_rx_hist_loss_prev(rh)->tfrchrx_seqno;
154	new->li_ccval	  = tfrc_rx_hist_loss_prev(rh)->tfrchrx_ccval;
155	new->li_is_closed = 0;
156
157	if (++lh->counter == 1)
158		lh->i_mean = new->li_length = (*calc_first_li)(sk);
159	else {
160		cur->li_length = dccp_delta_seqno(cur->li_seqno, new->li_seqno);
161		new->li_length = dccp_delta_seqno(new->li_seqno,
162				  tfrc_rx_hist_last_rcv(rh)->tfrchrx_seqno) + 1;
163		if (lh->counter > (2*LIH_SIZE))
164			lh->counter -= LIH_SIZE;
165
166		tfrc_lh_calc_i_mean(lh);
167	}
168	return 1;
169}
170
171int __init tfrc_li_init(void)
172{
173	tfrc_lh_slab = kmem_cache_create("tfrc_li_hist",
174					 sizeof(struct tfrc_loss_interval), 0,
175					 SLAB_HWCACHE_ALIGN, NULL);
176	return tfrc_lh_slab == NULL ? -ENOBUFS : 0;
177}
178
179void tfrc_li_exit(void)
180{
181	if (tfrc_lh_slab != NULL) {
182		kmem_cache_destroy(tfrc_lh_slab);
183		tfrc_lh_slab = NULL;
184	}
185}
186