linux/net/tipc/ref.c
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   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        u32 index;
 157        u32 index_mask;
 158        u32 next_plus_upper;
 159        u32 ref;
 160        struct reference *entry = NULL;
 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                next_plus_upper = entry->ref;
 179                tipc_ref_table.first_free = next_plus_upper & index_mask;
 180                ref = (next_plus_upper & ~index_mask) + index;
 181        }
 182        else if (tipc_ref_table.init_point < tipc_ref_table.capacity) {
 183                index = tipc_ref_table.init_point++;
 184                entry = &(tipc_ref_table.entries[index]);
 185                spin_lock_init(&entry->lock);
 186                ref = tipc_ref_table.start_mask + index;
 187        }
 188        else {
 189                ref = 0;
 190        }
 191        write_unlock_bh(&ref_table_lock);
 192
 193        /*
 194         * Grab the lock so no one else can modify this entry
 195         * While we assign its ref value & object pointer
 196         */
 197        if (entry) {
 198                spin_lock_bh(&entry->lock);
 199                entry->ref = ref;
 200                entry->object = object;
 201                *lock = &entry->lock;
 202                /*
 203                 * keep it locked, the caller is responsible
 204                 * for unlocking this when they're done with it
 205                 */
 206        }
 207
 208        return ref;
 209}
 210
 211/**
 212 * tipc_ref_discard - invalidate references to an object
 213 *
 214 * Disallow future references to an object and free up the entry for re-use.
 215 * Note: The entry's spin_lock may still be busy after discard
 216 */
 217
 218void tipc_ref_discard(u32 ref)
 219{
 220        struct reference *entry;
 221        u32 index;
 222        u32 index_mask;
 223
 224        if (!tipc_ref_table.entries) {
 225                err("Reference table not found during discard attempt\n");
 226                return;
 227        }
 228
 229        index_mask = tipc_ref_table.index_mask;
 230        index = ref & index_mask;
 231        entry = &(tipc_ref_table.entries[index]);
 232
 233        write_lock_bh(&ref_table_lock);
 234
 235        if (!entry->object) {
 236                err("Attempt to discard reference to non-existent object\n");
 237                goto exit;
 238        }
 239        if (entry->ref != ref) {
 240                err("Attempt to discard non-existent reference\n");
 241                goto exit;
 242        }
 243
 244        /*
 245         * mark entry as unused; increment instance part of entry's reference
 246         * to invalidate any subsequent references
 247         */
 248
 249        entry->object = NULL;
 250        entry->ref = (ref & ~index_mask) + (index_mask + 1);
 251
 252        /* append entry to free entry list */
 253
 254        if (tipc_ref_table.first_free == 0)
 255                tipc_ref_table.first_free = index;
 256        else
 257                tipc_ref_table.entries[tipc_ref_table.last_free].ref |= index;
 258        tipc_ref_table.last_free = index;
 259
 260exit:
 261        write_unlock_bh(&ref_table_lock);
 262}
 263
 264/**
 265 * tipc_ref_lock - lock referenced object and return pointer to it
 266 */
 267
 268void *tipc_ref_lock(u32 ref)
 269{
 270        if (likely(tipc_ref_table.entries)) {
 271                struct reference *entry;
 272
 273                entry = &tipc_ref_table.entries[ref &
 274                                                tipc_ref_table.index_mask];
 275                if (likely(entry->ref != 0)) {
 276                        spin_lock_bh(&entry->lock);
 277                        if (likely((entry->ref == ref) && (entry->object)))
 278                                return entry->object;
 279                        spin_unlock_bh(&entry->lock);
 280                }
 281        }
 282        return NULL;
 283}
 284
 285/**
 286 * tipc_ref_unlock - unlock referenced object
 287 */
 288
 289void tipc_ref_unlock(u32 ref)
 290{
 291        if (likely(tipc_ref_table.entries)) {
 292                struct reference *entry;
 293
 294                entry = &tipc_ref_table.entries[ref &
 295                                                tipc_ref_table.index_mask];
 296                if (likely((entry->ref == ref) && (entry->object)))
 297                        spin_unlock_bh(&entry->lock);
 298                else
 299                        err("Attempt to unlock non-existent reference\n");
 300        }
 301}
 302
 303/**
 304 * tipc_ref_deref - return pointer referenced object (without locking it)
 305 */
 306
 307void *tipc_ref_deref(u32 ref)
 308{
 309        if (likely(tipc_ref_table.entries)) {
 310                struct reference *entry;
 311
 312                entry = &tipc_ref_table.entries[ref &
 313                                                tipc_ref_table.index_mask];
 314                if (likely(entry->ref == ref))
 315                        return entry->object;
 316        }
 317        return NULL;
 318}
 319
 320