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
75static struct ref_table tipc_ref_table = { NULL };
76
77static DEFINE_RWLOCK(ref_table_lock);
78
79/**
80 * tipc_ref_table_init - create reference table for objects
81 */
82
83int tipc_ref_table_init(u32 requested_size, u32 start)
84{
85	struct reference *table;
86	u32 actual_size;
87
88	/* account for unused entry, then round up size to a power of 2 */
89
90	requested_size++;
91	for (actual_size = 16; actual_size < requested_size; actual_size <<= 1)
92		/* do nothing */ ;
93
94	/* allocate table & mark all entries as uninitialized */
95
96	table = __vmalloc(actual_size * sizeof(struct reference),
97			  GFP_KERNEL | __GFP_HIGHMEM | __GFP_ZERO, PAGE_KERNEL);
98	if (table == NULL)
99		return -ENOMEM;
100
101	tipc_ref_table.entries = table;
102	tipc_ref_table.capacity = requested_size;
103	tipc_ref_table.init_point = 1;
104	tipc_ref_table.first_free = 0;
105	tipc_ref_table.last_free = 0;
106	tipc_ref_table.index_mask = actual_size - 1;
107	tipc_ref_table.start_mask = start & ~tipc_ref_table.index_mask;
108
109	return 0;
110}
111
112/**
113 * tipc_ref_table_stop - destroy reference table for objects
114 */
115
116void tipc_ref_table_stop(void)
117{
118	if (!tipc_ref_table.entries)
119		return;
120
121	vfree(tipc_ref_table.entries);
122	tipc_ref_table.entries = NULL;
123}
124
125/**
126 * tipc_ref_acquire - create reference to an object
127 *
128 * Register an object pointer in reference table and lock the object.
129 * Returns a unique reference value that is used from then on to retrieve the
130 * object pointer, or to determine that the object has been deregistered.
131 *
132 * Note: The object is returned in the locked state so that the caller can
133 * register a partially initialized object, without running the risk that
134 * the object will be accessed before initialization is complete.
135 */
136
137u32 tipc_ref_acquire(void *object, spinlock_t **lock)
138{
139	u32 index;
140	u32 index_mask;
141	u32 next_plus_upper;
142	u32 ref;
143	struct reference *entry = NULL;
144
145	if (!object) {
146		err("Attempt to acquire reference to non-existent object\n");
147		return 0;
148	}
149	if (!tipc_ref_table.entries) {
150		err("Reference table not found during acquisition attempt\n");
151		return 0;
152	}
153
154	/* take a free entry, if available; otherwise initialize a new entry */
155
156	write_lock_bh(&ref_table_lock);
157	if (tipc_ref_table.first_free) {
158		index = tipc_ref_table.first_free;
159		entry = &(tipc_ref_table.entries[index]);
160		index_mask = tipc_ref_table.index_mask;
161		next_plus_upper = entry->ref;
162		tipc_ref_table.first_free = next_plus_upper & index_mask;
163		ref = (next_plus_upper & ~index_mask) + index;
164	}
165	else if (tipc_ref_table.init_point < tipc_ref_table.capacity) {
166		index = tipc_ref_table.init_point++;
167		entry = &(tipc_ref_table.entries[index]);
168		spin_lock_init(&entry->lock);
169		ref = tipc_ref_table.start_mask + index;
170	}
171	else {
172		ref = 0;
173	}
174	write_unlock_bh(&ref_table_lock);
175
176	/*
177	 * Grab the lock so no one else can modify this entry
178	 * While we assign its ref value & object pointer
179	 */
180	if (entry) {
181		spin_lock_bh(&entry->lock);
182		entry->ref = ref;
183		entry->object = object;
184		*lock = &entry->lock;
185		/*
186		 * keep it locked, the caller is responsible
187		 * for unlocking this when they're done with it
188		 */
189	}
190
191	return ref;
192}
193
194/**
195 * tipc_ref_discard - invalidate references to an object
196 *
197 * Disallow future references to an object and free up the entry for re-use.
198 * Note: The entry's spin_lock may still be busy after discard
199 */
200
201void tipc_ref_discard(u32 ref)
202{
203	struct reference *entry;
204	u32 index;
205	u32 index_mask;
206
207	if (!tipc_ref_table.entries) {
208		err("Reference table not found during discard attempt\n");
209		return;
210	}
211
212	index_mask = tipc_ref_table.index_mask;
213	index = ref & index_mask;
214	entry = &(tipc_ref_table.entries[index]);
215
216	write_lock_bh(&ref_table_lock);
217
218	if (!entry->object) {
219		err("Attempt to discard reference to non-existent object\n");
220		goto exit;
221	}
222	if (entry->ref != ref) {
223		err("Attempt to discard non-existent reference\n");
224		goto exit;
225	}
226
227	/*
228	 * mark entry as unused; increment instance part of entry's reference
229	 * to invalidate any subsequent references
230	 */
231
232	entry->object = NULL;
233	entry->ref = (ref & ~index_mask) + (index_mask + 1);
234
235	/* append entry to free entry list */
236
237	if (tipc_ref_table.first_free == 0)
238		tipc_ref_table.first_free = index;
239	else
240		tipc_ref_table.entries[tipc_ref_table.last_free].ref |= index;
241	tipc_ref_table.last_free = index;
242
243exit:
244	write_unlock_bh(&ref_table_lock);
245}
246
247/**
248 * tipc_ref_lock - lock referenced object and return pointer to it
249 */
250
251void *tipc_ref_lock(u32 ref)
252{
253	if (likely(tipc_ref_table.entries)) {
254		struct reference *entry;
255
256		entry = &tipc_ref_table.entries[ref &
257						tipc_ref_table.index_mask];
258		if (likely(entry->ref != 0)) {
259			spin_lock_bh(&entry->lock);
260			if (likely((entry->ref == ref) && (entry->object)))
261				return entry->object;
262			spin_unlock_bh(&entry->lock);
263		}
264	}
265	return NULL;
266}
267
268/**
269 * tipc_ref_unlock - unlock referenced object
270 */
271
272void tipc_ref_unlock(u32 ref)
273{
274	if (likely(tipc_ref_table.entries)) {
275		struct reference *entry;
276
277		entry = &tipc_ref_table.entries[ref &
278						tipc_ref_table.index_mask];
279		if (likely((entry->ref == ref) && (entry->object)))
280			spin_unlock_bh(&entry->lock);
281		else
282			err("Attempt to unlock non-existent reference\n");
283	}
284}
285
286/**
287 * tipc_ref_deref - return pointer referenced object (without locking it)
288 */
289
290void *tipc_ref_deref(u32 ref)
291{
292	if (likely(tipc_ref_table.entries)) {
293		struct reference *entry;
294
295		entry = &tipc_ref_table.entries[ref &
296						tipc_ref_table.index_mask];
297		if (likely(entry->ref == ref))
298			return entry->object;
299	}
300	return NULL;
301}
302