1 /*
2 * net/tipc/ref.c: TIPC object registry code
3 *
4 * Copyright (c) 1991-2006, Ericsson AB
5 * Copyright (c) 2004-2007, Wind River Systems
6 * All rights reserved.
7 *
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions are met:
10 *
11 * 1. Redistributions of source code must retain the above copyright
12 * notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 * notice, this list of conditions and the following disclaimer in the
15 * documentation and/or other materials provided with the distribution.
16 * 3. Neither the names of the copyright holders nor the names of its
17 * contributors may be used to endorse or promote products derived from
18 * this software without specific prior written permission.
19 *
20 * Alternatively, this software may be distributed under the terms of the
21 * GNU General Public License ("GPL") version 2 as published by the Free
22 * Software Foundation.
23 *
24 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
25 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
26 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
27 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
28 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
29 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
30 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
31 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
32 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
33 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
34 * POSSIBILITY OF SUCH DAMAGE.
35 */
36
37 #include "core.h"
38 #include "ref.h"
39
40 /**
41 * struct reference - TIPC object reference entry
42 * @object: pointer to object associated with reference entry
43 * @lock: spinlock controlling access to object
44 * @ref: reference value for object (combines instance & array index info)
45 */
46
47 struct reference {
48 void *object;
49 spinlock_t lock;
50 u32 ref;
51 };
52
53 /**
54 * struct tipc_ref_table - table of TIPC object reference entries
55 * @entries: pointer to array of reference entries
56 * @capacity: array index of first unusable entry
57 * @init_point: array index of first uninitialized entry
58 * @first_free: array index of first unused object reference entry
59 * @last_free: array index of last unused object reference entry
60 * @index_mask: bitmask for array index portion of reference values
61 * @start_mask: initial value for instance value portion of reference values
62 */
63
64 struct ref_table {
65 struct reference *entries;
66 u32 capacity;
67 u32 init_point;
68 u32 first_free;
69 u32 last_free;
70 u32 index_mask;
71 u32 start_mask;
72 };
73
74 /*
75 * Object reference table consists of 2**N entries.
76 *
77 * State Object ptr Reference
78 * ----- ---------- ---------
79 * In use non-NULL XXXX|own index
80 * (XXXX changes each time entry is acquired)
81 * Free NULL YYYY|next free index
82 * (YYYY is one more than last used XXXX)
83 * Uninitialized NULL 0
84 *
85 * Entry 0 is not used; this allows index 0 to denote the end of the free list.
86 *
87 * Note that a reference value of 0 does not necessarily indicate that an
88 * entry is uninitialized, since the last entry in the free list could also
89 * have a reference value of 0 (although this is unlikely).
90 */
91
92 static struct ref_table tipc_ref_table;
93
94 static DEFINE_RWLOCK(ref_table_lock);
95
96 /**
97 * tipc_ref_table_init - create reference table for objects
98 */
99
tipc_ref_table_init(u32 requested_size,u32 start)100 int tipc_ref_table_init(u32 requested_size, u32 start)
101 {
102 struct reference *table;
103 u32 actual_size;
104
105 /* account for unused entry, then round up size to a power of 2 */
106
107 requested_size++;
108 for (actual_size = 16; actual_size < requested_size; actual_size <<= 1)
109 /* do nothing */ ;
110
111 /* allocate table & mark all entries as uninitialized */
112
113 table = vzalloc(actual_size * sizeof(struct reference));
114 if (table == NULL)
115 return -ENOMEM;
116
117 tipc_ref_table.entries = table;
118 tipc_ref_table.capacity = requested_size;
119 tipc_ref_table.init_point = 1;
120 tipc_ref_table.first_free = 0;
121 tipc_ref_table.last_free = 0;
122 tipc_ref_table.index_mask = actual_size - 1;
123 tipc_ref_table.start_mask = start & ~tipc_ref_table.index_mask;
124
125 return 0;
126 }
127
128 /**
129 * tipc_ref_table_stop - destroy reference table for objects
130 */
131
tipc_ref_table_stop(void)132 void tipc_ref_table_stop(void)
133 {
134 if (!tipc_ref_table.entries)
135 return;
136
137 vfree(tipc_ref_table.entries);
138 tipc_ref_table.entries = NULL;
139 }
140
141 /**
142 * tipc_ref_acquire - create reference to an object
143 *
144 * Register an object pointer in reference table and lock the object.
145 * Returns a unique reference value that is used from then on to retrieve the
146 * object pointer, or to determine that the object has been deregistered.
147 *
148 * Note: The object is returned in the locked state so that the caller can
149 * register a partially initialized object, without running the risk that
150 * the object will be accessed before initialization is complete.
151 */
152
tipc_ref_acquire(void * object,spinlock_t ** lock)153 u32 tipc_ref_acquire(void *object, spinlock_t **lock)
154 {
155 u32 index;
156 u32 index_mask;
157 u32 next_plus_upper;
158 u32 ref;
159 struct reference *entry = NULL;
160
161 if (!object) {
162 err("Attempt to acquire reference to non-existent object\n");
163 return 0;
164 }
165 if (!tipc_ref_table.entries) {
166 err("Reference table not found during acquisition attempt\n");
167 return 0;
168 }
169
170 /* take a free entry, if available; otherwise initialize a new entry */
171
172 write_lock_bh(&ref_table_lock);
173 if (tipc_ref_table.first_free) {
174 index = tipc_ref_table.first_free;
175 entry = &(tipc_ref_table.entries[index]);
176 index_mask = tipc_ref_table.index_mask;
177 next_plus_upper = entry->ref;
178 tipc_ref_table.first_free = next_plus_upper & index_mask;
179 ref = (next_plus_upper & ~index_mask) + index;
180 } else if (tipc_ref_table.init_point < tipc_ref_table.capacity) {
181 index = tipc_ref_table.init_point++;
182 entry = &(tipc_ref_table.entries[index]);
183 spin_lock_init(&entry->lock);
184 ref = tipc_ref_table.start_mask + index;
185 } else {
186 ref = 0;
187 }
188 write_unlock_bh(&ref_table_lock);
189
190 /*
191 * Grab the lock so no one else can modify this entry
192 * While we assign its ref value & object pointer
193 */
194 if (entry) {
195 spin_lock_bh(&entry->lock);
196 entry->ref = ref;
197 entry->object = object;
198 *lock = &entry->lock;
199 /*
200 * keep it locked, the caller is responsible
201 * for unlocking this when they're done with it
202 */
203 }
204
205 return ref;
206 }
207
208 /**
209 * tipc_ref_discard - invalidate references to an object
210 *
211 * Disallow future references to an object and free up the entry for re-use.
212 * Note: The entry's spin_lock may still be busy after discard
213 */
214
tipc_ref_discard(u32 ref)215 void tipc_ref_discard(u32 ref)
216 {
217 struct reference *entry;
218 u32 index;
219 u32 index_mask;
220
221 if (!tipc_ref_table.entries) {
222 err("Reference table not found during discard attempt\n");
223 return;
224 }
225
226 index_mask = tipc_ref_table.index_mask;
227 index = ref & index_mask;
228 entry = &(tipc_ref_table.entries[index]);
229
230 write_lock_bh(&ref_table_lock);
231
232 if (!entry->object) {
233 err("Attempt to discard reference to non-existent object\n");
234 goto exit;
235 }
236 if (entry->ref != ref) {
237 err("Attempt to discard non-existent reference\n");
238 goto exit;
239 }
240
241 /*
242 * mark entry as unused; increment instance part of entry's reference
243 * to invalidate any subsequent references
244 */
245
246 entry->object = NULL;
247 entry->ref = (ref & ~index_mask) + (index_mask + 1);
248
249 /* append entry to free entry list */
250
251 if (tipc_ref_table.first_free == 0)
252 tipc_ref_table.first_free = index;
253 else
254 tipc_ref_table.entries[tipc_ref_table.last_free].ref |= index;
255 tipc_ref_table.last_free = index;
256
257 exit:
258 write_unlock_bh(&ref_table_lock);
259 }
260
261 /**
262 * tipc_ref_lock - lock referenced object and return pointer to it
263 */
264
tipc_ref_lock(u32 ref)265 void *tipc_ref_lock(u32 ref)
266 {
267 if (likely(tipc_ref_table.entries)) {
268 struct reference *entry;
269
270 entry = &tipc_ref_table.entries[ref &
271 tipc_ref_table.index_mask];
272 if (likely(entry->ref != 0)) {
273 spin_lock_bh(&entry->lock);
274 if (likely((entry->ref == ref) && (entry->object)))
275 return entry->object;
276 spin_unlock_bh(&entry->lock);
277 }
278 }
279 return NULL;
280 }
281
282
283 /**
284 * tipc_ref_deref - return pointer referenced object (without locking it)
285 */
286
tipc_ref_deref(u32 ref)287 void *tipc_ref_deref(u32 ref)
288 {
289 if (likely(tipc_ref_table.entries)) {
290 struct reference *entry;
291
292 entry = &tipc_ref_table.entries[ref &
293 tipc_ref_table.index_mask];
294 if (likely(entry->ref == ref))
295 return entry->object;
296 }
297 return NULL;
298 }
299
300