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
  47 struct 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
  64 struct 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
  92 static struct ref_table tipc_ref_table;
  93
  94 static DEFINE_RWLOCK(ref_table_lock);
  95
  96 /**
  97  * tipc_ref_table_init - create reference table for objects
  98  */
  99
 100 int 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
 132 void 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
 153 u32 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
 215 void 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
 257 exit:
 258         write_unlock_bh(&ref_table_lock);
 259 }
 260
 261 /**
 262  * tipc_ref_lock - lock referenced object and return pointer to it
 263  */
 264
 265 void *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
 287 void *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