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_SPINLOCK(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         vfree(tipc_ref_table.entries);
 130         tipc_ref_table.entries = NULL;
 131 }
 132
 133 /**
 134  * tipc_ref_acquire - create reference to an object
 135  *
 136  * Register an object pointer in reference table and lock the object.
 137  * Returns a unique reference value that is used from then on to retrieve the
 138  * object pointer, or to determine that the object has been deregistered.
 139  *
 140  * Note: The object is returned in the locked state so that the caller can
 141  * register a partially initialized object, without running the risk that
 142  * the object will be accessed before initialization is complete.
 143  */
 144 u32 tipc_ref_acquire(void *object, spinlock_t **lock)
 145 {
 146         u32 index;
 147         u32 index_mask;
 148         u32 next_plus_upper;
 149         u32 ref;
 150         struct reference *entry = NULL;
 151
 152         if (!object) {
 153                 pr_err("Attempt to acquire ref. to non-existent obj\n");
 154                 return 0;
 155         }
 156         if (!tipc_ref_table.entries) {
 157                 pr_err("Ref. table not found in acquisition attempt\n");
 158                 return 0;
 159         }
 160
 161         /* take a free entry, if available; otherwise initialize a new entry */
 162         spin_lock_bh(&ref_table_lock);
 163         if (tipc_ref_table.first_free) {
 164                 index = tipc_ref_table.first_free;
 165                 entry = &(tipc_ref_table.entries[index]);
 166                 index_mask = tipc_ref_table.index_mask;
 167                 next_plus_upper = entry->ref;
 168                 tipc_ref_table.first_free = next_plus_upper & index_mask;
 169                 ref = (next_plus_upper & ~index_mask) + index;
 170         } else if (tipc_ref_table.init_point < tipc_ref_table.capacity) {
 171                 index = tipc_ref_table.init_point++;
 172                 entry = &(tipc_ref_table.entries[index]);
 173                 spin_lock_init(&entry->lock);
 174                 ref = tipc_ref_table.start_mask + index;
 175         } else {
 176                 ref = 0;
 177         }
 178         spin_unlock_bh(&ref_table_lock);
 179
 180         /*
 181          * Grab the lock so no one else can modify this entry
 182          * While we assign its ref value & object pointer
 183          */
 184         if (entry) {
 185                 spin_lock_bh(&entry->lock);
 186                 entry->ref = ref;
 187                 entry->object = object;
 188                 *lock = &entry->lock;
 189                 /*
 190                  * keep it locked, the caller is responsible
 191                  * for unlocking this when they're done with it
 192                  */
 193         }
 194
 195         return ref;
 196 }
 197
 198 /**
 199  * tipc_ref_discard - invalidate references to an object
 200  *
 201  * Disallow future references to an object and free up the entry for re-use.
 202  * Note: The entry's spin_lock may still be busy after discard
 203  */
 204 void tipc_ref_discard(u32 ref)
 205 {
 206         struct reference *entry;
 207         u32 index;
 208         u32 index_mask;
 209
 210         if (!tipc_ref_table.entries) {
 211                 pr_err("Ref. table not found during discard attempt\n");
 212                 return;
 213         }
 214
 215         index_mask = tipc_ref_table.index_mask;
 216         index = ref & index_mask;
 217         entry = &(tipc_ref_table.entries[index]);
 218
 219         spin_lock_bh(&ref_table_lock);
 220
 221         if (!entry->object) {
 222                 pr_err("Attempt to discard ref. to non-existent obj\n");
 223                 goto exit;
 224         }
 225         if (entry->ref != ref) {
 226                 pr_err("Attempt to discard non-existent reference\n");
 227                 goto exit;
 228         }
 229
 230         /*
 231          * mark entry as unused; increment instance part of entry's reference
 232          * to invalidate any subsequent references
 233          */
 234         entry->object = NULL;
 235         entry->ref = (ref & ~index_mask) + (index_mask + 1);
 236
 237         /* append entry to free entry list */
 238         if (tipc_ref_table.first_free == 0)
 239                 tipc_ref_table.first_free = index;
 240         else
 241                 tipc_ref_table.entries[tipc_ref_table.last_free].ref |= index;
 242         tipc_ref_table.last_free = index;
 243
 244 exit:
 245         spin_unlock_bh(&ref_table_lock);
 246 }
 247
 248 /**
 249  * tipc_ref_lock - lock referenced object and return pointer to it
 250  */
 251 void *tipc_ref_lock(u32 ref)
 252 {
 253         if (likely(tipc_ref_table.entries)) {
 254                 struct reference *entry;
 255
 256                 entry = &tipc_ref_table.entries[ref &
 257                                                 tipc_ref_table.index_mask];
 258                 if (likely(entry->ref != 0)) {
 259                         spin_lock_bh(&entry->lock);
 260                         if (likely((entry->ref == ref) && (entry->object)))
 261                                 return entry->object;
 262                         spin_unlock_bh(&entry->lock);
 263                 }
 264         }
 265         return NULL;
 266 }