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 struct 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  */
  62 struct 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
  90 static struct ref_table tipc_ref_table;
  91
  92 static DEFINE_RWLOCK(ref_table_lock);
  93
  94 /**
  95  * tipc_ref_table_init - create reference table for objects
  96  */
  97 int 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  */
 127 void 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  */
 147 u32 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  */
 207 void 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
 247 exit:
 248         write_unlock_bh(&ref_table_lock);
 249 }
 250
 251 /**
 252  * tipc_ref_lock - lock referenced object and return pointer to it
 253  */
 254 void *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  */
 275 void *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 }