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 
11 static struct kmem_cache  *tfrc_lh_slab  __read_mostly;
12 /* Loss Interval weights from [RFC 3448, 5.4], scaled by 10 */
13 static const int tfrc_lh_weights[NINTERVAL] = { 10, 10, 10, 10, 8, 6, 4, 2 };
14 
15 /* implements LIFO semantics on the array */
LIH_INDEX(const u8 ctr)16 static 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 */
tfrc_lh_peek(struct tfrc_loss_hist * lh)22 static 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 */
tfrc_lh_get_interval(struct tfrc_loss_hist * lh,const u8 i)28 static 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  */
tfrc_lh_demand_next(struct tfrc_loss_hist * lh)37 static 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 
tfrc_lh_cleanup(struct tfrc_loss_hist * lh)45 void 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 
tfrc_lh_calc_i_mean(struct tfrc_loss_hist * lh)58 static 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  */
tfrc_lh_update_i_mean(struct tfrc_loss_hist * lh,struct sk_buff * skb)87 u8 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] */
tfrc_lh_is_new_loss(struct tfrc_loss_interval * cur,struct tfrc_rx_hist_entry * new_loss)122 static 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  */
tfrc_lh_interval_add(struct tfrc_loss_hist * lh,struct tfrc_rx_hist * rh,u32 (* calc_first_li)(struct sock *),struct sock * sk)138 int 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 
tfrc_li_init(void)170 int __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 
tfrc_li_exit(void)178 void 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