summaryrefslogtreecommitdiff
path: root/net/dccp/ackvec.c
blob: c4bbac99740d8eabd9e59615503c7e623aa97d73 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
// SPDX-License-Identifier: GPL-2.0-only
/*
 *  net/dccp/ackvec.c
 *
 *  An implementation of Ack Vectors for the DCCP protocol
 *  Copyright (c) 2007 University of Aberdeen, Scotland, UK
 *  Copyright (c) 2005 Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
 */
#include "dccp.h"
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/export.h>

static struct kmem_cache *dccp_ackvec_slab;
static struct kmem_cache *dccp_ackvec_record_slab;

struct dccp_ackvec *dccp_ackvec_alloc(const gfp_t priority)
{
	struct dccp_ackvec *av = kmem_cache_zalloc(dccp_ackvec_slab, priority);

	if (av != NULL) {
		av->av_buf_head	= av->av_buf_tail = DCCPAV_MAX_ACKVEC_LEN - 1;
		INIT_LIST_HEAD(&av->av_records);
	}
	return av;
}

static void dccp_ackvec_purge_records(struct dccp_ackvec *av)
{
	struct dccp_ackvec_record *cur, *next;

	list_for_each_entry_safe(cur, next, &av->av_records, avr_node)
		kmem_cache_free(dccp_ackvec_record_slab, cur);
	INIT_LIST_HEAD(&av->av_records);
}

void dccp_ackvec_free(struct dccp_ackvec *av)
{
	if (likely(av != NULL)) {
		dccp_ackvec_purge_records(av);
		kmem_cache_free(dccp_ackvec_slab, av);
	}
}

/**
 * dccp_ackvec_update_records  -  Record information about sent Ack Vectors
 * @av:		Ack Vector records to update
 * @seqno:	Sequence number of the packet carrying the Ack Vector just sent
 * @nonce_sum:	The sum of all buffer nonces contained in the Ack Vector
 */
int dccp_ackvec_update_records(struct dccp_ackvec *av, u64 seqno, u8 nonce_sum)
{
	struct dccp_ackvec_record *avr;

	avr = kmem_cache_alloc(dccp_ackvec_record_slab, GFP_ATOMIC);
	if (avr == NULL)
		return -ENOBUFS;

	avr->avr_ack_seqno  = seqno;
	avr->avr_ack_ptr    = av->av_buf_head;
	avr->avr_ack_ackno  = av->av_buf_ackno;
	avr->avr_ack_nonce  = nonce_sum;
	avr->avr_ack_runlen = dccp_ackvec_runlen(av->av_buf + av->av_buf_head);
	/*
	 * When the buffer overflows, we keep no more than one record. This is
	 * the simplest way of disambiguating sender-Acks dating from before the
	 * overflow from sender-Acks which refer to after the overflow; a simple
	 * solution is preferable here since we are handling an exception.
	 */
	if (av->av_overflow)
		dccp_ackvec_purge_records(av);
	/*
	 * Since GSS is incremented for each packet, the list is automatically
	 * arranged in descending order of @ack_seqno.
	 */
	list_add(&avr->avr_node, &av->av_records);

	dccp_pr_debug("Added Vector, ack_seqno=%llu, ack_ackno=%llu (rl=%u)\n",
		      (unsigned long long)avr->avr_ack_seqno,
		      (unsigned long long)avr->avr_ack_ackno,
		      avr->avr_ack_runlen);
	return 0;
}

static struct dccp_ackvec_record *dccp_ackvec_lookup(struct list_head *av_list,
						     const u64 ackno)
{
	struct dccp_ackvec_record *avr;
	/*
	 * Exploit that records are inserted in descending order of sequence
	 * number, start with the oldest record first. If @ackno is `before'
	 * the earliest ack_ackno, the packet is too old to be considered.
	 */
	list_for_each_entry_reverse(avr, av_list, avr_node) {
		if (avr->avr_ack_seqno == ackno)
			return avr;
		if (before48(ackno, avr->avr_ack_seqno))
			break;
	}
	return NULL;
}

/*
 * Buffer index and length computation using modulo-buffersize arithmetic.
 * Note that, as pointers move from right to left, head is `before' tail.
 */
static inline u16 __ackvec_idx_add(const u16 a, const u16 b)
{
	return (a + b) % DCCPAV_MAX_ACKVEC_LEN;
}

static inline u16 __ackvec_idx_sub(const u16 a, const u16 b)
{
	return __ackvec_idx_add(a, DCCPAV_MAX_ACKVEC_LEN - b);
}

u16 dccp_ackvec_buflen(const struct dccp_ackvec *av)
{
	if (unlikely(av->av_overflow))
		return DCCPAV_MAX_ACKVEC_LEN;
	return __ackvec_idx_sub(av->av_buf_tail, av->av_buf_head);
}

/**
 * dccp_ackvec_update_old  -  Update previous state as per RFC 4340, 11.4.1
 * @av:		non-empty buffer to update
 * @distance:   negative or zero distance of @seqno from buf_ackno downward
 * @seqno:	the (old) sequence number whose record is to be updated
 * @state:	state in which packet carrying @seqno was received
 */
static void dccp_ackvec_update_old(struct dccp_ackvec *av, s64 distance,
				   u64 seqno, enum dccp_ackvec_states state)
{
	u16 ptr = av->av_buf_head;

	BUG_ON(distance > 0);
	if (unlikely(dccp_ackvec_is_empty(av)))
		return;

	do {
		u8 runlen = dccp_ackvec_runlen(av->av_buf + ptr);

		if (distance + runlen >= 0) {
			/*
			 * Only update the state if packet has not been received
			 * yet. This is OK as per the second table in RFC 4340,
			 * 11.4.1; i.e. here we are using the following table:
			 *                     RECEIVED
			 *                      0   1   3
			 *              S     +---+---+---+
			 *              T   0 | 0 | 0 | 0 |
			 *              O     +---+---+---+
			 *              R   1 | 1 | 1 | 1 |
			 *              E     +---+---+---+
			 *              D   3 | 0 | 1 | 3 |
			 *                    +---+---+---+
			 * The "Not Received" state was set by reserve_seats().
			 */
			if (av->av_buf[ptr] == DCCPAV_NOT_RECEIVED)
				av->av_buf[ptr] = state;
			else
				dccp_pr_debug("Not changing %llu state to %u\n",
					      (unsigned long long)seqno, state);
			break;
		}

		distance += runlen + 1;
		ptr	  = __ackvec_idx_add(ptr, 1);

	} while (ptr != av->av_buf_tail);
}

/* Mark @num entries after buf_head as "Not yet received". */
static void dccp_ackvec_reserve_seats(struct dccp_ackvec *av, u16 num)
{
	u16 start = __ackvec_idx_add(av->av_buf_head, 1),
	    len	  = DCCPAV_MAX_ACKVEC_LEN - start;

	/* check for buffer wrap-around */
	if (num > len) {
		memset(av->av_buf + start, DCCPAV_NOT_RECEIVED, len);
		start = 0;
		num  -= len;
	}
	if (num)
		memset(av->av_buf + start, DCCPAV_NOT_RECEIVED, num);
}

/**
 * dccp_ackvec_add_new  -  Record one or more new entries in Ack Vector buffer
 * @av:		 container of buffer to update (can be empty or non-empty)
 * @num_packets: number of packets to register (must be >= 1)
 * @seqno:	 sequence number of the first packet in @num_packets
 * @state:	 state in which packet carrying @seqno was received
 */
static void dccp_ackvec_add_new(struct dccp_ackvec *av, u32 num_packets,
				u64 seqno, enum dccp_ackvec_states state)
{
	u32 num_cells = num_packets;

	if (num_packets > DCCPAV_BURST_THRESH) {
		u32 lost_packets = num_packets - 1;

		DCCP_WARN("Warning: large burst loss (%u)\n", lost_packets);
		/*
		 * We received 1 packet and have a loss of size "num_packets-1"
		 * which we squeeze into num_cells-1 rather than reserving an
		 * entire byte for each lost packet.
		 * The reason is that the vector grows in O(burst_length); when
		 * it grows too large there will no room left for the payload.
		 * This is a trade-off: if a few packets out of the burst show
		 * up later, their state will not be changed; it is simply too
		 * costly to reshuffle/reallocate/copy the buffer each time.
		 * Should such problems persist, we will need to switch to a
		 * different underlying data structure.
		 */
		for (num_packets = num_cells = 1; lost_packets; ++num_cells) {
			u8 len = min_t(u32, lost_packets, DCCPAV_MAX_RUNLEN);

			av->av_buf_head = __ackvec_idx_sub(av->av_buf_head, 1);
			av->av_buf[av->av_buf_head] = DCCPAV_NOT_RECEIVED | len;

			lost_packets -= len;
		}
	}

	if (num_cells + dccp_ackvec_buflen(av) >= DCCPAV_MAX_ACKVEC_LEN) {
		DCCP_CRIT("Ack Vector buffer overflow: dropping old entries");
		av->av_overflow = true;
	}

	av->av_buf_head = __ackvec_idx_sub(av->av_buf_head, num_packets);
	if (av->av_overflow)
		av->av_buf_tail = av->av_buf_head;

	av->av_buf[av->av_buf_head] = state;
	av->av_buf_ackno	    = seqno;

	if (num_packets > 1)
		dccp_ackvec_reserve_seats(av, num_packets - 1);
}

/**
 * dccp_ackvec_input  -  Register incoming packet in the buffer
 * @av: Ack Vector to register packet to
 * @skb: Packet to register
 */
void dccp_ackvec_input(struct dccp_ackvec *av, struct sk_buff *skb)
{
	u64 seqno = DCCP_SKB_CB(skb)->dccpd_seq;
	enum dccp_ackvec_states state = DCCPAV_RECEIVED;

	if (dccp_ackvec_is_empty(av)) {
		dccp_ackvec_add_new(av, 1, seqno, state);
		av->av_tail_ackno = seqno;

	} else {
		s64 num_packets = dccp_delta_seqno(av->av_buf_ackno, seqno);
		u8 *current_head = av->av_buf + av->av_buf_head;

		if (num_packets == 1 &&
		    dccp_ackvec_state(current_head) == state &&
		    dccp_ackvec_runlen(current_head) < DCCPAV_MAX_RUNLEN) {

			*current_head   += 1;
			av->av_buf_ackno = seqno;

		} else if (num_packets > 0) {
			dccp_ackvec_add_new(av, num_packets, seqno, state);
		} else {
			dccp_ackvec_update_old(av, num_packets, seqno, state);
		}
	}
}

/**
 * dccp_ackvec_clear_state  -  Perform house-keeping / garbage-collection
 * @av: Ack Vector record to clean
 * @ackno: last Ack Vector which has been acknowledged
 *
 * This routine is called when the peer acknowledges the receipt of Ack Vectors
 * up to and including @ackno. While based on section A.3 of RFC 4340, here
 * are additional precautions to prevent corrupted buffer state. In particular,
 * we use tail_ackno to identify outdated records; it always marks the earliest
 * packet of group (2) in 11.4.2.
 */
void dccp_ackvec_clear_state(struct dccp_ackvec *av, const u64 ackno)
{
	struct dccp_ackvec_record *avr, *next;
	u8 runlen_now, eff_runlen;
	s64 delta;

	avr = dccp_ackvec_lookup(&av->av_records, ackno);
	if (avr == NULL)
		return;
	/*
	 * Deal with outdated acknowledgments: this arises when e.g. there are
	 * several old records and the acks from the peer come in slowly. In
	 * that case we may still have records that pre-date tail_ackno.
	 */
	delta = dccp_delta_seqno(av->av_tail_ackno, avr->avr_ack_ackno);
	if (delta < 0)
		goto free_records;
	/*
	 * Deal with overlapping Ack Vectors: don't subtract more than the
	 * number of packets between tail_ackno and ack_ackno.
	 */
	eff_runlen = delta < avr->avr_ack_runlen ? delta : avr->avr_ack_runlen;

	runlen_now = dccp_ackvec_runlen(av->av_buf + avr->avr_ack_ptr);
	/*
	 * The run length of Ack Vector cells does not decrease over time. If
	 * the run length is the same as at the time the Ack Vector was sent, we
	 * free the ack_ptr cell. That cell can however not be freed if the run
	 * length has increased: in this case we need to move the tail pointer
	 * backwards (towards higher indices), to its next-oldest neighbour.
	 */
	if (runlen_now > eff_runlen) {

		av->av_buf[avr->avr_ack_ptr] -= eff_runlen + 1;
		av->av_buf_tail = __ackvec_idx_add(avr->avr_ack_ptr, 1);

		/* This move may not have cleared the overflow flag. */
		if (av->av_overflow)
			av->av_overflow = (av->av_buf_head == av->av_buf_tail);
	} else {
		av->av_buf_tail	= avr->avr_ack_ptr;
		/*
		 * We have made sure that avr points to a valid cell within the
		 * buffer. This cell is either older than head, or equals head
		 * (empty buffer): in both cases we no longer have any overflow.
		 */
		av->av_overflow	= 0;
	}

	/*
	 * The peer has acknowledged up to and including ack_ackno. Hence the
	 * first packet in group (2) of 11.4.2 is the successor of ack_ackno.
	 */
	av->av_tail_ackno = ADD48(avr->avr_ack_ackno, 1);

free_records:
	list_for_each_entry_safe_from(avr, next, &av->av_records, avr_node) {
		list_del(&avr->avr_node);
		kmem_cache_free(dccp_ackvec_record_slab, avr);
	}
}

/*
 *	Routines to keep track of Ack Vectors received in an skb
 */
int dccp_ackvec_parsed_add(struct list_head *head, u8 *vec, u8 len, u8 nonce)
{
	struct dccp_ackvec_parsed *new = kmalloc(sizeof(*new), GFP_ATOMIC);

	if (new == NULL)
		return -ENOBUFS;
	new->vec   = vec;
	new->len   = len;
	new->nonce = nonce;

	list_add_tail(&new->node, head);
	return 0;
}
EXPORT_SYMBOL_GPL(dccp_ackvec_parsed_add);

void dccp_ackvec_parsed_cleanup(struct list_head *parsed_chunks)
{
	struct dccp_ackvec_parsed *cur, *next;

	list_for_each_entry_safe(cur, next, parsed_chunks, node)
		kfree(cur);
	INIT_LIST_HEAD(parsed_chunks);
}
EXPORT_SYMBOL_GPL(dccp_ackvec_parsed_cleanup);

int __init dccp_ackvec_init(void)
{
	dccp_ackvec_slab = kmem_cache_create("dccp_ackvec",
					     sizeof(struct dccp_ackvec), 0,
					     SLAB_HWCACHE_ALIGN, NULL);
	if (dccp_ackvec_slab == NULL)
		goto out_err;

	dccp_ackvec_record_slab = kmem_cache_create("dccp_ackvec_record",
					     sizeof(struct dccp_ackvec_record),
					     0, SLAB_HWCACHE_ALIGN, NULL);
	if (dccp_ackvec_record_slab == NULL)
		goto out_destroy_slab;

	return 0;

out_destroy_slab:
	kmem_cache_destroy(dccp_ackvec_slab);
	dccp_ackvec_slab = NULL;
out_err:
	DCCP_CRIT("Unable to create Ack Vector slab cache");
	return -ENOBUFS;
}

void dccp_ackvec_exit(void)
{
	kmem_cache_destroy(dccp_ackvec_slab);
	dccp_ackvec_slab = NULL;
	kmem_cache_destroy(dccp_ackvec_record_slab);
	dccp_ackvec_record_slab = NULL;
}