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;
  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 = 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
 132void 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
 153u32 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
 215void 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
 257exit:
 258        write_unlock_bh(&ref_table_lock);
 259}
 260
 261/**
 262 * tipc_ref_lock - lock referenced object and return pointer to it
 263 */
 264
 265void *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
 287void *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