aboutsummaryrefslogtreecommitdiffstats
path: root/net/tipc/ref.c
blob: a101de86824d2b1db6e485775d1d1def6bf2c1b7 (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
/*
 * net/tipc/ref.c: TIPC object registry code
 *
 * Copyright (c) 1991-2006, Ericsson AB
 * Copyright (c) 2004-2007, Wind River Systems
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the names of the copyright holders nor the names of its
 *    contributors may be used to endorse or promote products derived from
 *    this software without specific prior written permission.
 *
 * Alternatively, this software may be distributed under the terms of the
 * GNU General Public License ("GPL") version 2 as published by the Free
 * Software Foundation.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

#include "core.h"
#include "ref.h"

/**
 * struct reference - TIPC object reference entry
 * @object: pointer to object associated with reference entry
 * @lock: spinlock controlling access to object
 * @ref: reference value for object (combines instance & array index info)
 */

struct reference {
	void *object;
	spinlock_t lock;
	u32 ref;
};

/**
 * struct tipc_ref_table - table of TIPC object reference entries
 * @entries: pointer to array of reference entries
 * @capacity: array index of first unusable entry
 * @init_point: array index of first uninitialized entry
 * @first_free: array index of first unused object reference entry
 * @last_free: array index of last unused object reference entry
 * @index_mask: bitmask for array index portion of reference values
 * @start_mask: initial value for instance value portion of reference values
 */

struct ref_table {
	struct reference *entries;
	u32 capacity;
	u32 init_point;
	u32 first_free;
	u32 last_free;
	u32 index_mask;
	u32 start_mask;
};

/*
 * Object reference table consists of 2**N entries.
 *
 * State	Object ptr	Reference
 * -----        ----------      ---------
 * In use        non-NULL       XXXX|own index
 *				(XXXX changes each time entry is acquired)
 * Free            NULL         YYYY|next free index
 *				(YYYY is one more than last used XXXX)
 * Uninitialized   NULL         0
 *
 * Entry 0 is not used; this allows index 0 to denote the end of the free list.
 *
 * Note that a reference value of 0 does not necessarily indicate that an
 * entry is uninitialized, since the last entry in the free list could also
 * have a reference value of 0 (although this is unlikely).
 */

static struct ref_table tipc_ref_table = { NULL };

static DEFINE_RWLOCK(ref_table_lock);

/**
 * tipc_ref_table_init - create reference table for objects
 */

int tipc_ref_table_init(u32 requested_size, u32 start)
{
	struct reference *table;
	u32 actual_size;

	/* account for unused entry, then round up size to a power of 2 */

	requested_size++;
	for (actual_size = 16; actual_size < requested_size; actual_size <<= 1)
		/* do nothing */ ;

	/* allocate table & mark all entries as uninitialized */

	table = __vmalloc(actual_size * sizeof(struct reference),
			  GFP_KERNEL | __GFP_HIGHMEM | __GFP_ZERO, PAGE_KERNEL);
	if (table == NULL)
		return -ENOMEM;

	tipc_ref_table.entries = table;
	tipc_ref_table.capacity = requested_size;
	tipc_ref_table.init_point = 1;
	tipc_ref_table.first_free = 0;
	tipc_ref_table.last_free = 0;
	tipc_ref_table.index_mask = actual_size - 1;
	tipc_ref_table.start_mask = start & ~tipc_ref_table.index_mask;

	return TIPC_OK;
}

/**
 * tipc_ref_table_stop - destroy reference table for objects
 */

void tipc_ref_table_stop(void)
{
	if (!tipc_ref_table.entries)
		return;

	vfree(tipc_ref_table.entries);
	tipc_ref_table.entries = NULL;
}

/**
 * tipc_ref_acquire - create reference to an object
 *
 * Register an object pointer in reference table and lock the object.
 * Returns a unique reference value that is used from then on to retrieve the
 * object pointer, or to determine that the object has been deregistered.
 *
 * Note: The object is returned in the locked state so that the caller can
 * register a partially initialized object, without running the risk that
 * the object will be accessed before initialization is complete.
 */

u32 tipc_ref_acquire(void *object, spinlock_t **lock)
{
	struct reference *entry;
	u32 index;
	u32 index_mask;
	u32 next_plus_upper;
	u32 ref;

	if (!object) {
		err("Attempt to acquire reference to non-existent object\n");
		return 0;
	}
	if (!tipc_ref_table.entries) {
		err("Reference table not found during acquisition attempt\n");
		return 0;
	}

	/* take a free entry, if available; otherwise initialize a new entry */

	write_lock_bh(&ref_table_lock);
	if (tipc_ref_table.first_free) {
		index = tipc_ref_table.first_free;
		entry = &(tipc_ref_table.entries[index]);
		index_mask = tipc_ref_table.index_mask;
		/* take lock in case a previous user of entry still holds it */
		spin_lock_bh(&entry->lock);
		next_plus_upper = entry->ref;
		tipc_ref_table.first_free = next_plus_upper & index_mask;
		ref = (next_plus_upper & ~index_mask) + index;
		entry->ref = ref;
		entry->object = object;
		*lock = &entry->lock;
	}
	else if (tipc_ref_table.init_point < tipc_ref_table.capacity) {
		index = tipc_ref_table.init_point++;
		entry = &(tipc_ref_table.entries[index]);
		spin_lock_init(&entry->lock);
		spin_lock_bh(&entry->lock);
		ref = tipc_ref_table.start_mask + index;
		entry->ref = ref;
		entry->object = object;
		*lock = &entry->lock;
	}
	else {
		ref = 0;
	}
	write_unlock_bh(&ref_table_lock);

	return ref;
}

/**
 * tipc_ref_discard - invalidate references to an object
 *
 * Disallow future references to an object and free up the entry for re-use.
 * Note: The entry's spin_lock may still be busy after discard
 */

void tipc_ref_discard(u32 ref)
{
	struct reference *entry;
	u32 index;
	u32 index_mask;

	if (!tipc_ref_table.entries) {
		err("Reference table not found during discard attempt\n");
		return;
	}

	index_mask = tipc_ref_table.index_mask;
	index = ref & index_mask;
	entry = &(tipc_ref_table.entries[index]);

	write_lock_bh(&ref_table_lock);

	if (!entry->object) {
		err("Attempt to discard reference to non-existent object\n");
		goto exit;
	}
	if (entry->ref != ref) {
		err("Attempt to discard non-existent reference\n");
		goto exit;
	}

	/*
	 * mark entry as unused; increment instance part of entry's reference
	 * to invalidate any subsequent references
	 */

	entry->object = NULL;
	entry->ref = (ref & ~index_mask) + (index_mask + 1);

	/* append entry to free entry list */

	if (tipc_ref_table.first_free == 0)
		tipc_ref_table.first_free = index;
	else
		tipc_ref_table.entries[tipc_ref_table.last_free].ref |= index;
	tipc_ref_table.last_free = index;

exit:
	write_unlock_bh(&ref_table_lock);
}

/**
 * tipc_ref_lock - lock referenced object and return pointer to it
 */

void *tipc_ref_lock(u32 ref)
{
	if (likely(tipc_ref_table.entries)) {
		struct reference *entry;

		entry = &tipc_ref_table.entries[ref &
						tipc_ref_table.index_mask];
		if (likely(entry->ref != 0)) {
			spin_lock_bh(&entry->lock);
			if (likely((entry->ref == ref) && (entry->object)))
				return entry->object;
			spin_unlock_bh(&entry->lock);
		}
	}
	return NULL;
}

/**
 * tipc_ref_unlock - unlock referenced object
 */

void tipc_ref_unlock(u32 ref)
{
	if (likely(tipc_ref_table.entries)) {
		struct reference *entry;

		entry = &tipc_ref_table.entries[ref &
						tipc_ref_table.index_mask];
		if (likely((entry->ref == ref) && (entry->object)))
			spin_unlock_bh(&entry->lock);
		else
			err("Attempt to unlock non-existent reference\n");
	}
}

/**
 * tipc_ref_deref - return pointer referenced object (without locking it)
 */

void *tipc_ref_deref(u32 ref)
{
	if (likely(tipc_ref_table.entries)) {
		struct reference *entry;

		entry = &tipc_ref_table.entries[ref &
						tipc_ref_table.index_mask];
		if (likely(entry->ref == ref))
			return entry->object;
	}
	return NULL;
}