1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 *  Copyright (c) 2007   The University of Aberdeen, Scotland, UK
4 *  Copyright (c) 2005-7 The University of Waikato, Hamilton, New Zealand.
5 *  Copyright (c) 2005-7 Ian McDonald <ian.mcdonald@jandi.co.nz>
6 *  Copyright (c) 2005 Arnaldo Carvalho de Melo <acme@conectiva.com.br>
7 */
8#include <net/sock.h>
9#include "tfrc.h"
10
11static struct kmem_cache  *tfrc_lh_slab  __read_mostly;
12/* Loss Interval weights from [RFC 3448, 5.4], scaled by 10 */
13static const int tfrc_lh_weights[NINTERVAL] = { 10, 10, 10, 10, 8, 6, 4, 2 };
14
15/* implements LIFO semantics on the array */
16static inline u8 LIH_INDEX(const u8 ctr)
17{
18	return LIH_SIZE - 1 - (ctr % LIH_SIZE);
19}
20
21/* the `counter' index always points at the next entry to be populated */
22static inline struct tfrc_loss_interval *tfrc_lh_peek(struct tfrc_loss_hist *lh)
23{
24	return lh->counter ? lh->ring[LIH_INDEX(lh->counter - 1)] : NULL;
25}
26
27/* given i with 0 <= i <= k, return I_i as per the rfc3448bis notation */
28static inline u32 tfrc_lh_get_interval(struct tfrc_loss_hist *lh, const u8 i)
29{
30	BUG_ON(i >= lh->counter);
31	return lh->ring[LIH_INDEX(lh->counter - i - 1)]->li_length;
32}
33
34/*
35 *	On-demand allocation and de-allocation of entries
36 */
37static struct tfrc_loss_interval *tfrc_lh_demand_next(struct tfrc_loss_hist *lh)
38{
39	if (lh->ring[LIH_INDEX(lh->counter)] == NULL)
40		lh->ring[LIH_INDEX(lh->counter)] = kmem_cache_alloc(tfrc_lh_slab,
41								    GFP_ATOMIC);
42	return lh->ring[LIH_INDEX(lh->counter)];
43}
44
45void tfrc_lh_cleanup(struct tfrc_loss_hist *lh)
46{
47	if (!tfrc_lh_is_initialised(lh))
48		return;
49
50	for (lh->counter = 0; lh->counter < LIH_SIZE; lh->counter++)
51		if (lh->ring[LIH_INDEX(lh->counter)] != NULL) {
52			kmem_cache_free(tfrc_lh_slab,
53					lh->ring[LIH_INDEX(lh->counter)]);
54			lh->ring[LIH_INDEX(lh->counter)] = NULL;
55		}
56}
57
58static void tfrc_lh_calc_i_mean(struct tfrc_loss_hist *lh)
59{
60	u32 i_i, i_tot0 = 0, i_tot1 = 0, w_tot = 0;
61	int i, k = tfrc_lh_length(lh) - 1; /* k is as in rfc3448bis, 5.4 */
62
63	if (k <= 0)
64		return;
65
66	for (i = 0; i <= k; i++) {
67		i_i = tfrc_lh_get_interval(lh, i);
68
69		if (i < k) {
70			i_tot0 += i_i * tfrc_lh_weights[i];
71			w_tot  += tfrc_lh_weights[i];
72		}
73		if (i > 0)
74			i_tot1 += i_i * tfrc_lh_weights[i-1];
75	}
76
77	lh->i_mean = max(i_tot0, i_tot1) / w_tot;
78}
79
80/**
81 * tfrc_lh_update_i_mean  -  Update the `open' loss interval I_0
82 * @lh: histogram to update
83 * @skb: received socket triggering loss interval update
84 *
85 * For recomputing p: returns `true' if p > p_prev  <=>  1/p < 1/p_prev
86 */
87u8 tfrc_lh_update_i_mean(struct tfrc_loss_hist *lh, struct sk_buff *skb)
88{
89	struct tfrc_loss_interval *cur = tfrc_lh_peek(lh);
90	u32 old_i_mean = lh->i_mean;
91	s64 len;
92
93	if (cur == NULL)			/* not initialised */
94		return 0;
95
96	len = dccp_delta_seqno(cur->li_seqno, DCCP_SKB_CB(skb)->dccpd_seq) + 1;
97
98	if (len - (s64)cur->li_length <= 0)	/* duplicate or reordered */
99		return 0;
100
101	if (SUB16(dccp_hdr(skb)->dccph_ccval, cur->li_ccval) > 4)
102		/*
103		 * Implements RFC 4342, 10.2:
104		 * If a packet S (skb) exists whose seqno comes `after' the one
105		 * starting the current loss interval (cur) and if the modulo-16
106		 * distance from C(cur) to C(S) is greater than 4, consider all
107		 * subsequent packets as belonging to a new loss interval. This
108		 * test is necessary since CCVal may wrap between intervals.
109		 */
110		cur->li_is_closed = 1;
111
112	if (tfrc_lh_length(lh) == 1)		/* due to RFC 3448, 6.3.1 */
113		return 0;
114
115	cur->li_length = len;
116	tfrc_lh_calc_i_mean(lh);
117
118	return lh->i_mean < old_i_mean;
119}
120
121/* Determine if `new_loss' does begin a new loss interval [RFC 4342, 10.2] */
122static inline u8 tfrc_lh_is_new_loss(struct tfrc_loss_interval *cur,
123				     struct tfrc_rx_hist_entry *new_loss)
124{
125	return	dccp_delta_seqno(cur->li_seqno, new_loss->tfrchrx_seqno) > 0 &&
126		(cur->li_is_closed || SUB16(new_loss->tfrchrx_ccval, cur->li_ccval) > 4);
127}
128
129/**
130 * tfrc_lh_interval_add  -  Insert new record into the Loss Interval database
131 * @lh:		   Loss Interval database
132 * @rh:		   Receive history containing a fresh loss event
133 * @calc_first_li: Caller-dependent routine to compute length of first interval
134 * @sk:		   Used by @calc_first_li in caller-specific way (subtyping)
135 *
136 * Updates I_mean and returns 1 if a new interval has in fact been added to @lh.
137 */
138int tfrc_lh_interval_add(struct tfrc_loss_hist *lh, struct tfrc_rx_hist *rh,
139			 u32 (*calc_first_li)(struct sock *), struct sock *sk)
140{
141	struct tfrc_loss_interval *cur = tfrc_lh_peek(lh), *new;
142
143	if (cur != NULL && !tfrc_lh_is_new_loss(cur, tfrc_rx_hist_loss_prev(rh)))
144		return 0;
145
146	new = tfrc_lh_demand_next(lh);
147	if (unlikely(new == NULL)) {
148		DCCP_CRIT("Cannot allocate/add loss record.");
149		return 0;
150	}
151
152	new->li_seqno	  = tfrc_rx_hist_loss_prev(rh)->tfrchrx_seqno;
153	new->li_ccval	  = tfrc_rx_hist_loss_prev(rh)->tfrchrx_ccval;
154	new->li_is_closed = 0;
155
156	if (++lh->counter == 1)
157		lh->i_mean = new->li_length = (*calc_first_li)(sk);
158	else {
159		cur->li_length = dccp_delta_seqno(cur->li_seqno, new->li_seqno);
160		new->li_length = dccp_delta_seqno(new->li_seqno,
161				  tfrc_rx_hist_last_rcv(rh)->tfrchrx_seqno) + 1;
162		if (lh->counter > (2*LIH_SIZE))
163			lh->counter -= LIH_SIZE;
164
165		tfrc_lh_calc_i_mean(lh);
166	}
167	return 1;
168}
169
170int __init tfrc_li_init(void)
171{
172	tfrc_lh_slab = kmem_cache_create("tfrc_li_hist",
173					 sizeof(struct tfrc_loss_interval), 0,
174					 SLAB_HWCACHE_ALIGN, NULL);
175	return tfrc_lh_slab == NULL ? -ENOBUFS : 0;
176}
177
178void tfrc_li_exit(void)
179{
180	if (tfrc_lh_slab != NULL) {
181		kmem_cache_destroy(tfrc_lh_slab);
182		tfrc_lh_slab = NULL;
183	}
184}
185