linux/net/tipc/ref.c
<<
>>
Prefs
   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 */
  46struct reference {
  47        void *object;
  48        spinlock_t lock;
  49        u32 ref;
  50};
  51
  52/**
  53 * struct tipc_ref_table - table of TIPC object reference entries
  54 * @entries: pointer to array of reference entries
  55 * @capacity: array index of first unusable entry
  56 * @init_point: array index of first uninitialized entry
  57 * @first_free: array index of first unused object reference entry
  58 * @last_free: array index of last unused object reference entry
  59 * @index_mask: bitmask for array index portion of reference values
  60 * @start_mask: initial value for instance value portion of reference values
  61 */
  62struct ref_table {
  63        struct reference *entries;
  64        u32 capacity;
  65        u32 init_point;
  66        u32 first_free;
  67        u32 last_free;
  68        u32 index_mask;
  69        u32 start_mask;
  70};
  71
  72/*
  73 * Object reference table consists of 2**N entries.
  74 *
  75 * State        Object ptr      Reference
  76 * -----        ----------      ---------
  77 * In use        non-NULL       XXXX|own index
  78 *                              (XXXX changes each time entry is acquired)
  79 * Free            NULL         YYYY|next free index
  80 *                              (YYYY is one more than last used XXXX)
  81 * Uninitialized   NULL         0
  82 *
  83 * Entry 0 is not used; this allows index 0 to denote the end of the free list.
  84 *
  85 * Note that a reference value of 0 does not necessarily indicate that an
  86 * entry is uninitialized, since the last entry in the free list could also
  87 * have a reference value of 0 (although this is unlikely).
  88 */
  89
  90static struct ref_table tipc_ref_table;
  91
  92static DEFINE_RWLOCK(ref_table_lock);
  93
  94/**
  95 * tipc_ref_table_init - create reference table for objects
  96 */
  97int tipc_ref_table_init(u32 requested_size, u32 start)
  98{
  99        struct reference *table;
 100        u32 actual_size;
 101
 102        /* account for unused entry, then round up size to a power of 2 */
 103
 104        requested_size++;
 105        for (actual_size = 16; actual_size < requested_size; actual_size <<= 1)
 106                /* do nothing */ ;
 107
 108        /* allocate table & mark all entries as uninitialized */
 109        table = vzalloc(actual_size * sizeof(struct reference));
 110        if (table == NULL)
 111                return -ENOMEM;
 112
 113        tipc_ref_table.entries = table;
 114        tipc_ref_table.capacity = requested_size;
 115        tipc_ref_table.init_point = 1;
 116        tipc_ref_table.first_free = 0;
 117        tipc_ref_table.last_free = 0;
 118        tipc_ref_table.index_mask = actual_size - 1;
 119        tipc_ref_table.start_mask = start & ~tipc_ref_table.index_mask;
 120
 121        return 0;
 122}
 123
 124/**
 125 * tipc_ref_table_stop - destroy reference table for objects
 126 */
 127void tipc_ref_table_stop(void)
 128{
 129        if (!tipc_ref_table.entries)
 130                return;
 131
 132        vfree(tipc_ref_table.entries);
 133        tipc_ref_table.entries = NULL;
 134}
 135
 136/**
 137 * tipc_ref_acquire - create reference to an object
 138 *
 139 * Register an object pointer in reference table and lock the object.
 140 * Returns a unique reference value that is used from then on to retrieve the
 141 * object pointer, or to determine that the object has been deregistered.
 142 *
 143 * Note: The object is returned in the locked state so that the caller can
 144 * register a partially initialized object, without running the risk that
 145 * the object will be accessed before initialization is complete.
 146 */
 147u32 tipc_ref_acquire(void *object, spinlock_t **lock)
 148{
 149        u32 index;
 150        u32 index_mask;
 151        u32 next_plus_upper;
 152        u32 ref;
 153        struct reference *entry = NULL;
 154
 155        if (!object) {
 156                pr_err("Attempt to acquire ref. to non-existent obj\n");
 157                return 0;
 158        }
 159        if (!tipc_ref_table.entries) {
 160                pr_err("Ref. table not found in acquisition attempt\n");
 161                return 0;
 162        }
 163
 164        /* take a free entry, if available; otherwise initialize a new entry */
 165        write_lock_bh(&ref_table_lock);
 166        if (tipc_ref_table.first_free) {
 167                index = tipc_ref_table.first_free;
 168                entry = &(tipc_ref_table.entries[index]);
 169                index_mask = tipc_ref_table.index_mask;
 170                next_plus_upper = entry->ref;
 171                tipc_ref_table.first_free = next_plus_upper & index_mask;
 172                ref = (next_plus_upper & ~index_mask) + index;
 173        } else if (tipc_ref_table.init_point < tipc_ref_table.capacity) {
 174                index = tipc_ref_table.init_point++;
 175                entry = &(tipc_ref_table.entries[index]);
 176                spin_lock_init(&entry->lock);
 177                ref = tipc_ref_table.start_mask + index;
 178        } else {
 179                ref = 0;
 180        }
 181        write_unlock_bh(&ref_table_lock);
 182
 183        /*
 184         * Grab the lock so no one else can modify this entry
 185         * While we assign its ref value & object pointer
 186         */
 187        if (entry) {
 188                spin_lock_bh(&entry->lock);
 189                entry->ref = ref;
 190                entry->object = object;
 191                *lock = &entry->lock;
 192                /*
 193                 * keep it locked, the caller is responsible
 194                 * for unlocking this when they're done with it
 195                 */
 196        }
 197
 198        return ref;
 199}
 200
 201/**
 202 * tipc_ref_discard - invalidate references to an object
 203 *
 204 * Disallow future references to an object and free up the entry for re-use.
 205 * Note: The entry's spin_lock may still be busy after discard
 206 */
 207void tipc_ref_discard(u32 ref)
 208{
 209        struct reference *entry;
 210        u32 index;
 211        u32 index_mask;
 212
 213        if (!tipc_ref_table.entries) {
 214                pr_err("Ref. table not found during discard attempt\n");
 215                return;
 216        }
 217
 218        index_mask = tipc_ref_table.index_mask;
 219        index = ref & index_mask;
 220        entry = &(tipc_ref_table.entries[index]);
 221
 222        write_lock_bh(&ref_table_lock);
 223
 224        if (!entry->object) {
 225                pr_err("Attempt to discard ref. to non-existent obj\n");
 226                goto exit;
 227        }
 228        if (entry->ref != ref) {
 229                pr_err("Attempt to discard non-existent reference\n");
 230                goto exit;
 231        }
 232
 233        /*
 234         * mark entry as unused; increment instance part of entry's reference
 235         * to invalidate any subsequent references
 236         */
 237        entry->object = NULL;
 238        entry->ref = (ref & ~index_mask) + (index_mask + 1);
 239
 240        /* append entry to free entry list */
 241        if (tipc_ref_table.first_free == 0)
 242                tipc_ref_table.first_free = index;
 243        else
 244                tipc_ref_table.entries[tipc_ref_table.last_free].ref |= index;
 245        tipc_ref_table.last_free = index;
 246
 247exit:
 248        write_unlock_bh(&ref_table_lock);
 249}
 250
 251/**
 252 * tipc_ref_lock - lock referenced object and return pointer to it
 253 */
 254void *tipc_ref_lock(u32 ref)
 255{
 256        if (likely(tipc_ref_table.entries)) {
 257                struct reference *entry;
 258
 259                entry = &tipc_ref_table.entries[ref &
 260                                                tipc_ref_table.index_mask];
 261                if (likely(entry->ref != 0)) {
 262                        spin_lock_bh(&entry->lock);
 263                        if (likely((entry->ref == ref) && (entry->object)))
 264                                return entry->object;
 265                        spin_unlock_bh(&entry->lock);
 266                }
 267        }
 268        return NULL;
 269}
 270
 271
 272/**
 273 * tipc_ref_deref - return pointer referenced object (without locking it)
 274 */
 275void *tipc_ref_deref(u32 ref)
 276{
 277        if (likely(tipc_ref_table.entries)) {
 278                struct reference *entry;
 279
 280                entry = &tipc_ref_table.entries[ref &
 281                                                tipc_ref_table.index_mask];
 282                if (likely(entry->ref == ref))
 283                        return entry->object;
 284        }
 285        return NULL;
 286}
 287
lxr.linux.no kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.