Root/net/tipc/ref.c

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
47struct 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
64struct 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
92static struct ref_table tipc_ref_table = { NULL };
93
94static DEFINE_RWLOCK(ref_table_lock);
95
96/**
97 * tipc_ref_table_init - create reference table for objects
98 */
99
100int 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 = __vmalloc(actual_size * sizeof(struct reference),
114              GFP_KERNEL | __GFP_HIGHMEM | __GFP_ZERO, PAGE_KERNEL);
115    if (table == NULL)
116        return -ENOMEM;
117
118    tipc_ref_table.entries = table;
119    tipc_ref_table.capacity = requested_size;
120    tipc_ref_table.init_point = 1;
121    tipc_ref_table.first_free = 0;
122    tipc_ref_table.last_free = 0;
123    tipc_ref_table.index_mask = actual_size - 1;
124    tipc_ref_table.start_mask = start & ~tipc_ref_table.index_mask;
125
126    return 0;
127}
128
129/**
130 * tipc_ref_table_stop - destroy reference table for objects
131 */
132
133void tipc_ref_table_stop(void)
134{
135    if (!tipc_ref_table.entries)
136        return;
137
138    vfree(tipc_ref_table.entries);
139    tipc_ref_table.entries = NULL;
140}
141
142/**
143 * tipc_ref_acquire - create reference to an object
144 *
145 * Register an object pointer in reference table and lock the object.
146 * Returns a unique reference value that is used from then on to retrieve the
147 * object pointer, or to determine that the object has been deregistered.
148 *
149 * Note: The object is returned in the locked state so that the caller can
150 * register a partially initialized object, without running the risk that
151 * the object will be accessed before initialization is complete.
152 */
153
154u32 tipc_ref_acquire(void *object, spinlock_t **lock)
155{
156    struct reference *entry;
157    u32 index;
158    u32 index_mask;
159    u32 next_plus_upper;
160    u32 ref;
161
162    if (!object) {
163        err("Attempt to acquire reference to non-existent object\n");
164        return 0;
165    }
166    if (!tipc_ref_table.entries) {
167        err("Reference table not found during acquisition attempt\n");
168        return 0;
169    }
170
171    /* take a free entry, if available; otherwise initialize a new entry */
172
173    write_lock_bh(&ref_table_lock);
174    if (tipc_ref_table.first_free) {
175        index = tipc_ref_table.first_free;
176        entry = &(tipc_ref_table.entries[index]);
177        index_mask = tipc_ref_table.index_mask;
178        /* take lock in case a previous user of entry still holds it */
179        spin_lock_bh(&entry->lock);
180        next_plus_upper = entry->ref;
181        tipc_ref_table.first_free = next_plus_upper & index_mask;
182        ref = (next_plus_upper & ~index_mask) + index;
183        entry->ref = ref;
184        entry->object = object;
185        *lock = &entry->lock;
186    }
187    else if (tipc_ref_table.init_point < tipc_ref_table.capacity) {
188        index = tipc_ref_table.init_point++;
189        entry = &(tipc_ref_table.entries[index]);
190        spin_lock_init(&entry->lock);
191        spin_lock_bh(&entry->lock);
192        ref = tipc_ref_table.start_mask + index;
193        entry->ref = ref;
194        entry->object = object;
195        *lock = &entry->lock;
196    }
197    else {
198        ref = 0;
199    }
200    write_unlock_bh(&ref_table_lock);
201
202    return ref;
203}
204
205/**
206 * tipc_ref_discard - invalidate references to an object
207 *
208 * Disallow future references to an object and free up the entry for re-use.
209 * Note: The entry's spin_lock may still be busy after discard
210 */
211
212void tipc_ref_discard(u32 ref)
213{
214    struct reference *entry;
215    u32 index;
216    u32 index_mask;
217
218    if (!tipc_ref_table.entries) {
219        err("Reference table not found during discard attempt\n");
220        return;
221    }
222
223    index_mask = tipc_ref_table.index_mask;
224    index = ref & index_mask;
225    entry = &(tipc_ref_table.entries[index]);
226
227    write_lock_bh(&ref_table_lock);
228
229    if (!entry->object) {
230        err("Attempt to discard reference to non-existent object\n");
231        goto exit;
232    }
233    if (entry->ref != ref) {
234        err("Attempt to discard non-existent reference\n");
235        goto exit;
236    }
237
238    /*
239     * mark entry as unused; increment instance part of entry's reference
240     * to invalidate any subsequent references
241     */
242
243    entry->object = NULL;
244    entry->ref = (ref & ~index_mask) + (index_mask + 1);
245
246    /* append entry to free entry list */
247
248    if (tipc_ref_table.first_free == 0)
249        tipc_ref_table.first_free = index;
250    else
251        tipc_ref_table.entries[tipc_ref_table.last_free].ref |= index;
252    tipc_ref_table.last_free = index;
253
254exit:
255    write_unlock_bh(&ref_table_lock);
256}
257
258/**
259 * tipc_ref_lock - lock referenced object and return pointer to it
260 */
261
262void *tipc_ref_lock(u32 ref)
263{
264    if (likely(tipc_ref_table.entries)) {
265        struct reference *entry;
266
267        entry = &tipc_ref_table.entries[ref &
268                        tipc_ref_table.index_mask];
269        if (likely(entry->ref != 0)) {
270            spin_lock_bh(&entry->lock);
271            if (likely((entry->ref == ref) && (entry->object)))
272                return entry->object;
273            spin_unlock_bh(&entry->lock);
274        }
275    }
276    return NULL;
277}
278
279/**
280 * tipc_ref_unlock - unlock referenced object
281 */
282
283void tipc_ref_unlock(u32 ref)
284{
285    if (likely(tipc_ref_table.entries)) {
286        struct reference *entry;
287
288        entry = &tipc_ref_table.entries[ref &
289                        tipc_ref_table.index_mask];
290        if (likely((entry->ref == ref) && (entry->object)))
291            spin_unlock_bh(&entry->lock);
292        else
293            err("Attempt to unlock non-existent reference\n");
294    }
295}
296
297/**
298 * tipc_ref_deref - return pointer referenced object (without locking it)
299 */
300
301void *tipc_ref_deref(u32 ref)
302{
303    if (likely(tipc_ref_table.entries)) {
304        struct reference *entry;
305
306        entry = &tipc_ref_table.entries[ref &
307                        tipc_ref_table.index_mask];
308        if (likely(entry->ref == ref))
309            return entry->object;
310    }
311    return NULL;
312}
313
314

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