root/lib/assoc_array.c

DEFINITIONS

1. assoc_array_subtree_iterate
2. assoc_array_iterate
3. assoc_array_walk
4. assoc_array_find
5. assoc_array_destroy_subtree
6. assoc_array_destroy
7. assoc_array_insert_in_empty_tree
8. assoc_array_insert_into_terminal_node
9. assoc_array_insert_mid_shortcut
10. assoc_array_insert
11. assoc_array_insert_set_object
12. assoc_array_delete_collapse_iterator
13. assoc_array_delete
14. assoc_array_clear
15. assoc_array_rcu_cleanup
16. assoc_array_apply_edit
17. assoc_array_cancel_edit
18. assoc_array_gc

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /* Generic associative array implementation.
   3  *
   4  * See Documentation/core-api/assoc_array.rst for information.
   5  *
   6  * Copyright (C) 2013 Red Hat, Inc. All Rights Reserved.
   7  * Written by David Howells (dhowells@redhat.com)
   8  */
   9 //#define DEBUG
  10 #include <linux/rcupdate.h>
  11 #include <linux/slab.h>
  12 #include <linux/err.h>
  13 #include <linux/assoc_array_priv.h>
  14 
  15 /*
  16  * Iterate over an associative array.  The caller must hold the RCU read lock
  17  * or better.
  18  */
  19 static int assoc_array_subtree_iterate(const struct assoc_array_ptr *root,
  20                                        const struct assoc_array_ptr *stop,
  21                                        int (*iterator)(const void *leaf,
  22                                                        void *iterator_data),
  23                                        void *iterator_data)
  24 {
  25         const struct assoc_array_shortcut *shortcut;
  26         const struct assoc_array_node *node;
  27         const struct assoc_array_ptr *cursor, *ptr, *parent;
  28         unsigned long has_meta;
  29         int slot, ret;
  30 
  31         cursor = root;
  32 
  33 begin_node:
  34         if (assoc_array_ptr_is_shortcut(cursor)) {
  35                 /* Descend through a shortcut */
  36                 shortcut = assoc_array_ptr_to_shortcut(cursor);
  37                 cursor = READ_ONCE(shortcut->next_node); /* Address dependency. */
  38         }
  39 
  40         node = assoc_array_ptr_to_node(cursor);
  41         slot = 0;
  42 
  43         /* We perform two passes of each node.
  44          *
  45          * The first pass does all the leaves in this node.  This means we
  46          * don't miss any leaves if the node is split up by insertion whilst
  47          * we're iterating over the branches rooted here (we may, however, see
  48          * some leaves twice).
  49          */
  50         has_meta = 0;
  51         for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
  52                 ptr = READ_ONCE(node->slots[slot]); /* Address dependency. */
  53                 has_meta |= (unsigned long)ptr;
  54                 if (ptr && assoc_array_ptr_is_leaf(ptr)) {
  55                         /* We need a barrier between the read of the pointer,
  56                          * which is supplied by the above READ_ONCE().
  57                          */
  58                         /* Invoke the callback */
  59                         ret = iterator(assoc_array_ptr_to_leaf(ptr),
  60                                        iterator_data);
  61                         if (ret)
  62                                 return ret;
  63                 }
  64         }
  65 
  66         /* The second pass attends to all the metadata pointers.  If we follow
  67          * one of these we may find that we don't come back here, but rather go
  68          * back to a replacement node with the leaves in a different layout.
  69          *
  70          * We are guaranteed to make progress, however, as the slot number for
  71          * a particular portion of the key space cannot change - and we
  72          * continue at the back pointer + 1.
  73          */
  74         if (!(has_meta & ASSOC_ARRAY_PTR_META_TYPE))
  75                 goto finished_node;
  76         slot = 0;
  77 
  78 continue_node:
  79         node = assoc_array_ptr_to_node(cursor);
  80         for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
  81                 ptr = READ_ONCE(node->slots[slot]); /* Address dependency. */
  82                 if (assoc_array_ptr_is_meta(ptr)) {
  83                         cursor = ptr;
  84                         goto begin_node;
  85                 }
  86         }
  87 
  88 finished_node:
  89         /* Move up to the parent (may need to skip back over a shortcut) */
  90         parent = READ_ONCE(node->back_pointer); /* Address dependency. */
  91         slot = node->parent_slot;
  92         if (parent == stop)
  93                 return 0;
  94 
  95         if (assoc_array_ptr_is_shortcut(parent)) {
  96                 shortcut = assoc_array_ptr_to_shortcut(parent);
  97                 cursor = parent;
  98                 parent = READ_ONCE(shortcut->back_pointer); /* Address dependency. */
  99                 slot = shortcut->parent_slot;
 100                 if (parent == stop)
 101                         return 0;
 102         }
 103 
 104         /* Ascend to next slot in parent node */
 105         cursor = parent;
 106         slot++;
 107         goto continue_node;
 108 }
 109 
 110 /**
 111  * assoc_array_iterate - Pass all objects in the array to a callback
 112  * @array: The array to iterate over.
 113  * @iterator: The callback function.
 114  * @iterator_data: Private data for the callback function.
 115  *
 116  * Iterate over all the objects in an associative array.  Each one will be
 117  * presented to the iterator function.
 118  *
 119  * If the array is being modified concurrently with the iteration then it is
 120  * possible that some objects in the array will be passed to the iterator
 121  * callback more than once - though every object should be passed at least
 122  * once.  If this is undesirable then the caller must lock against modification
 123  * for the duration of this function.
 124  *
 125  * The function will return 0 if no objects were in the array or else it will
 126  * return the result of the last iterator function called.  Iteration stops
 127  * immediately if any call to the iteration function results in a non-zero
 128  * return.
 129  *
 130  * The caller should hold the RCU read lock or better if concurrent
 131  * modification is possible.
 132  */
 133 int assoc_array_iterate(const struct assoc_array *array,
 134                         int (*iterator)(const void *object,
 135                                         void *iterator_data),
 136                         void *iterator_data)
 137 {
 138         struct assoc_array_ptr *root = READ_ONCE(array->root); /* Address dependency. */
 139 
 140         if (!root)
 141                 return 0;
 142         return assoc_array_subtree_iterate(root, NULL, iterator, iterator_data);
 143 }
 144 
 145 enum assoc_array_walk_status {
 146         assoc_array_walk_tree_empty,
 147         assoc_array_walk_found_terminal_node,
 148         assoc_array_walk_found_wrong_shortcut,
 149 };
 150 
 151 struct assoc_array_walk_result {
 152         struct {
 153                 struct assoc_array_node *node;  /* Node in which leaf might be found */
 154                 int             level;
 155                 int             slot;
 156         } terminal_node;
 157         struct {
 158                 struct assoc_array_shortcut *shortcut;
 159                 int             level;
 160                 int             sc_level;
 161                 unsigned long   sc_segments;
 162                 unsigned long   dissimilarity;
 163         } wrong_shortcut;
 164 };
 165 
 166 /*
 167  * Navigate through the internal tree looking for the closest node to the key.
 168  */
 169 static enum assoc_array_walk_status
 170 assoc_array_walk(const struct assoc_array *array,
 171                  const struct assoc_array_ops *ops,
 172                  const void *index_key,
 173                  struct assoc_array_walk_result *result)
 174 {
 175         struct assoc_array_shortcut *shortcut;
 176         struct assoc_array_node *node;
 177         struct assoc_array_ptr *cursor, *ptr;
 178         unsigned long sc_segments, dissimilarity;
 179         unsigned long segments;
 180         int level, sc_level, next_sc_level;
 181         int slot;
 182 
 183         pr_devel("-->%s()\n", __func__);
 184 
 185         cursor = READ_ONCE(array->root);  /* Address dependency. */
 186         if (!cursor)
 187                 return assoc_array_walk_tree_empty;
 188 
 189         level = 0;
 190 
 191         /* Use segments from the key for the new leaf to navigate through the
 192          * internal tree, skipping through nodes and shortcuts that are on
 193          * route to the destination.  Eventually we'll come to a slot that is
 194          * either empty or contains a leaf at which point we've found a node in
 195          * which the leaf we're looking for might be found or into which it
 196          * should be inserted.
 197          */
 198 jumped:
 199         segments = ops->get_key_chunk(index_key, level);
 200         pr_devel("segments[%d]: %lx\n", level, segments);
 201 
 202         if (assoc_array_ptr_is_shortcut(cursor))
 203                 goto follow_shortcut;
 204 
 205 consider_node:
 206         node = assoc_array_ptr_to_node(cursor);
 207         slot = segments >> (level & ASSOC_ARRAY_KEY_CHUNK_MASK);
 208         slot &= ASSOC_ARRAY_FAN_MASK;
 209         ptr = READ_ONCE(node->slots[slot]); /* Address dependency. */
 210 
 211         pr_devel("consider slot %x [ix=%d type=%lu]\n",
 212                  slot, level, (unsigned long)ptr & 3);
 213 
 214         if (!assoc_array_ptr_is_meta(ptr)) {
 215                 /* The node doesn't have a node/shortcut pointer in the slot
 216                  * corresponding to the index key that we have to follow.
 217                  */
 218                 result->terminal_node.node = node;
 219                 result->terminal_node.level = level;
 220                 result->terminal_node.slot = slot;
 221                 pr_devel("<--%s() = terminal_node\n", __func__);
 222                 return assoc_array_walk_found_terminal_node;
 223         }
 224 
 225         if (assoc_array_ptr_is_node(ptr)) {
 226                 /* There is a pointer to a node in the slot corresponding to
 227                  * this index key segment, so we need to follow it.
 228                  */
 229                 cursor = ptr;
 230                 level += ASSOC_ARRAY_LEVEL_STEP;
 231                 if ((level & ASSOC_ARRAY_KEY_CHUNK_MASK) != 0)
 232                         goto consider_node;
 233                 goto jumped;
 234         }
 235 
 236         /* There is a shortcut in the slot corresponding to the index key
 237          * segment.  We follow the shortcut if its partial index key matches
 238          * this leaf's.  Otherwise we need to split the shortcut.
 239          */
 240         cursor = ptr;
 241 follow_shortcut:
 242         shortcut = assoc_array_ptr_to_shortcut(cursor);
 243         pr_devel("shortcut to %d\n", shortcut->skip_to_level);
 244         sc_level = level + ASSOC_ARRAY_LEVEL_STEP;
 245         BUG_ON(sc_level > shortcut->skip_to_level);
 246 
 247         do {
 248                 /* Check the leaf against the shortcut's index key a word at a
 249                  * time, trimming the final word (the shortcut stores the index
 250                  * key completely from the root to the shortcut's target).
 251                  */
 252                 if ((sc_level & ASSOC_ARRAY_KEY_CHUNK_MASK) == 0)
 253                         segments = ops->get_key_chunk(index_key, sc_level);
 254 
 255                 sc_segments = shortcut->index_key[sc_level >> ASSOC_ARRAY_KEY_CHUNK_SHIFT];
 256                 dissimilarity = segments ^ sc_segments;
 257 
 258                 if (round_up(sc_level, ASSOC_ARRAY_KEY_CHUNK_SIZE) > shortcut->skip_to_level) {
 259                         /* Trim segments that are beyond the shortcut */
 260                         int shift = shortcut->skip_to_level & ASSOC_ARRAY_KEY_CHUNK_MASK;
 261                         dissimilarity &= ~(ULONG_MAX << shift);
 262                         next_sc_level = shortcut->skip_to_level;
 263                 } else {
 264                         next_sc_level = sc_level + ASSOC_ARRAY_KEY_CHUNK_SIZE;
 265                         next_sc_level = round_down(next_sc_level, ASSOC_ARRAY_KEY_CHUNK_SIZE);
 266                 }
 267 
 268                 if (dissimilarity != 0) {
 269                         /* This shortcut points elsewhere */
 270                         result->wrong_shortcut.shortcut = shortcut;
 271                         result->wrong_shortcut.level = level;
 272                         result->wrong_shortcut.sc_level = sc_level;
 273                         result->wrong_shortcut.sc_segments = sc_segments;
 274                         result->wrong_shortcut.dissimilarity = dissimilarity;
 275                         return assoc_array_walk_found_wrong_shortcut;
 276                 }
 277 
 278                 sc_level = next_sc_level;
 279         } while (sc_level < shortcut->skip_to_level);
 280 
 281         /* The shortcut matches the leaf's index to this point. */
 282         cursor = READ_ONCE(shortcut->next_node); /* Address dependency. */
 283         if (((level ^ sc_level) & ~ASSOC_ARRAY_KEY_CHUNK_MASK) != 0) {
 284                 level = sc_level;
 285                 goto jumped;
 286         } else {
 287                 level = sc_level;
 288                 goto consider_node;
 289         }
 290 }
 291 
 292 /**
 293  * assoc_array_find - Find an object by index key
 294  * @array: The associative array to search.
 295  * @ops: The operations to use.
 296  * @index_key: The key to the object.
 297  *
 298  * Find an object in an associative array by walking through the internal tree
 299  * to the node that should contain the object and then searching the leaves
 300  * there.  NULL is returned if the requested object was not found in the array.
 301  *
 302  * The caller must hold the RCU read lock or better.
 303  */
 304 void *assoc_array_find(const struct assoc_array *array,
 305                        const struct assoc_array_ops *ops,
 306                        const void *index_key)
 307 {
 308         struct assoc_array_walk_result result;
 309         const struct assoc_array_node *node;
 310         const struct assoc_array_ptr *ptr;
 311         const void *leaf;
 312         int slot;
 313 
 314         if (assoc_array_walk(array, ops, index_key, &result) !=
 315             assoc_array_walk_found_terminal_node)
 316                 return NULL;
 317 
 318         node = result.terminal_node.node;
 319 
 320         /* If the target key is available to us, it's has to be pointed to by
 321          * the terminal node.
 322          */
 323         for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
 324                 ptr = READ_ONCE(node->slots[slot]); /* Address dependency. */
 325                 if (ptr && assoc_array_ptr_is_leaf(ptr)) {
 326                         /* We need a barrier between the read of the pointer
 327                          * and dereferencing the pointer - but only if we are
 328                          * actually going to dereference it.
 329                          */
 330                         leaf = assoc_array_ptr_to_leaf(ptr);
 331                         if (ops->compare_object(leaf, index_key))
 332                                 return (void *)leaf;
 333                 }
 334         }
 335 
 336         return NULL;
 337 }
 338 
 339 /*
 340  * Destructively iterate over an associative array.  The caller must prevent
 341  * other simultaneous accesses.
 342  */
 343 static void assoc_array_destroy_subtree(struct assoc_array_ptr *root,
 344                                         const struct assoc_array_ops *ops)
 345 {
 346         struct assoc_array_shortcut *shortcut;
 347         struct assoc_array_node *node;
 348         struct assoc_array_ptr *cursor, *parent = NULL;
 349         int slot = -1;
 350 
 351         pr_devel("-->%s()\n", __func__);
 352 
 353         cursor = root;
 354         if (!cursor) {
 355                 pr_devel("empty\n");
 356                 return;
 357         }
 358 
 359 move_to_meta:
 360         if (assoc_array_ptr_is_shortcut(cursor)) {
 361                 /* Descend through a shortcut */
 362                 pr_devel("[%d] shortcut\n", slot);
 363                 BUG_ON(!assoc_array_ptr_is_shortcut(cursor));
 364                 shortcut = assoc_array_ptr_to_shortcut(cursor);
 365                 BUG_ON(shortcut->back_pointer != parent);
 366                 BUG_ON(slot != -1 && shortcut->parent_slot != slot);
 367                 parent = cursor;
 368                 cursor = shortcut->next_node;
 369                 slot = -1;
 370                 BUG_ON(!assoc_array_ptr_is_node(cursor));
 371         }
 372 
 373         pr_devel("[%d] node\n", slot);
 374         node = assoc_array_ptr_to_node(cursor);
 375         BUG_ON(node->back_pointer != parent);
 376         BUG_ON(slot != -1 && node->parent_slot != slot);
 377         slot = 0;
 378 
 379 continue_node:
 380         pr_devel("Node %p [back=%p]\n", node, node->back_pointer);
 381         for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
 382                 struct assoc_array_ptr *ptr = node->slots[slot];
 383                 if (!ptr)
 384                         continue;
 385                 if (assoc_array_ptr_is_meta(ptr)) {
 386                         parent = cursor;
 387                         cursor = ptr;
 388                         goto move_to_meta;
 389                 }
 390 
 391                 if (ops) {
 392                         pr_devel("[%d] free leaf\n", slot);
 393                         ops->free_object(assoc_array_ptr_to_leaf(ptr));
 394                 }
 395         }
 396 
 397         parent = node->back_pointer;
 398         slot = node->parent_slot;
 399         pr_devel("free node\n");
 400         kfree(node);
 401         if (!parent)
 402                 return; /* Done */
 403 
 404         /* Move back up to the parent (may need to free a shortcut on
 405          * the way up) */
 406         if (assoc_array_ptr_is_shortcut(parent)) {
 407                 shortcut = assoc_array_ptr_to_shortcut(parent);
 408                 BUG_ON(shortcut->next_node != cursor);
 409                 cursor = parent;
 410                 parent = shortcut->back_pointer;
 411                 slot = shortcut->parent_slot;
 412                 pr_devel("free shortcut\n");
 413                 kfree(shortcut);
 414                 if (!parent)
 415                         return;
 416 
 417                 BUG_ON(!assoc_array_ptr_is_node(parent));
 418         }
 419 
 420         /* Ascend to next slot in parent node */
 421         pr_devel("ascend to %p[%d]\n", parent, slot);
 422         cursor = parent;
 423         node = assoc_array_ptr_to_node(cursor);
 424         slot++;
 425         goto continue_node;
 426 }
 427 
 428 /**
 429  * assoc_array_destroy - Destroy an associative array
 430  * @array: The array to destroy.
 431  * @ops: The operations to use.
 432  *
 433  * Discard all metadata and free all objects in an associative array.  The
 434  * array will be empty and ready to use again upon completion.  This function
 435  * cannot fail.
 436  *
 437  * The caller must prevent all other accesses whilst this takes place as no
 438  * attempt is made to adjust pointers gracefully to permit RCU readlock-holding
 439  * accesses to continue.  On the other hand, no memory allocation is required.
 440  */
 441 void assoc_array_destroy(struct assoc_array *array,
 442                          const struct assoc_array_ops *ops)
 443 {
 444         assoc_array_destroy_subtree(array->root, ops);
 445         array->root = NULL;
 446 }
 447 
 448 /*
 449  * Handle insertion into an empty tree.
 450  */
 451 static bool assoc_array_insert_in_empty_tree(struct assoc_array_edit *edit)
 452 {
 453         struct assoc_array_node *new_n0;
 454 
 455         pr_devel("-->%s()\n", __func__);
 456 
 457         new_n0 = kzalloc(sizeof(struct assoc_array_node), GFP_KERNEL);
 458         if (!new_n0)
 459                 return false;
 460 
 461         edit->new_meta[0] = assoc_array_node_to_ptr(new_n0);
 462         edit->leaf_p = &new_n0->slots[0];
 463         edit->adjust_count_on = new_n0;
 464         edit->set[0].ptr = &edit->array->root;
 465         edit->set[0].to = assoc_array_node_to_ptr(new_n0);
 466 
 467         pr_devel("<--%s() = ok [no root]\n", __func__);
 468         return true;
 469 }
 470 
 471 /*
 472  * Handle insertion into a terminal node.
 473  */
 474 static bool assoc_array_insert_into_terminal_node(struct assoc_array_edit *edit,
 475                                                   const struct assoc_array_ops *ops,
 476                                                   const void *index_key,
 477                                                   struct assoc_array_walk_result *result)
 478 {
 479         struct assoc_array_shortcut *shortcut, *new_s0;
 480         struct assoc_array_node *node, *new_n0, *new_n1, *side;
 481         struct assoc_array_ptr *ptr;
 482         unsigned long dissimilarity, base_seg, blank;
 483         size_t keylen;
 484         bool have_meta;
 485         int level, diff;
 486         int slot, next_slot, free_slot, i, j;
 487 
 488         node    = result->terminal_node.node;
 489         level   = result->terminal_node.level;
 490         edit->segment_cache[ASSOC_ARRAY_FAN_OUT] = result->terminal_node.slot;
 491 
 492         pr_devel("-->%s()\n", __func__);
 493 
 494         /* We arrived at a node which doesn't have an onward node or shortcut
 495          * pointer that we have to follow.  This means that (a) the leaf we
 496          * want must go here (either by insertion or replacement) or (b) we
 497          * need to split this node and insert in one of the fragments.
 498          */
 499         free_slot = -1;
 500 
 501         /* Firstly, we have to check the leaves in this node to see if there's
 502          * a matching one we should replace in place.
 503          */
 504         for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
 505                 ptr = node->slots[i];
 506                 if (!ptr) {
 507                         free_slot = i;
 508                         continue;
 509                 }
 510                 if (assoc_array_ptr_is_leaf(ptr) &&
 511                     ops->compare_object(assoc_array_ptr_to_leaf(ptr),
 512                                         index_key)) {
 513                         pr_devel("replace in slot %d\n", i);
 514                         edit->leaf_p = &node->slots[i];
 515                         edit->dead_leaf = node->slots[i];
 516                         pr_devel("<--%s() = ok [replace]\n", __func__);
 517                         return true;
 518                 }
 519         }
 520 
 521         /* If there is a free slot in this node then we can just insert the
 522          * leaf here.
 523          */
 524         if (free_slot >= 0) {
 525                 pr_devel("insert in free slot %d\n", free_slot);
 526                 edit->leaf_p = &node->slots[free_slot];
 527                 edit->adjust_count_on = node;
 528                 pr_devel("<--%s() = ok [insert]\n", __func__);
 529                 return true;
 530         }
 531 
 532         /* The node has no spare slots - so we're either going to have to split
 533          * it or insert another node before it.
 534          *
 535          * Whatever, we're going to need at least two new nodes - so allocate
 536          * those now.  We may also need a new shortcut, but we deal with that
 537          * when we need it.
 538          */
 539         new_n0 = kzalloc(sizeof(struct assoc_array_node), GFP_KERNEL);
 540         if (!new_n0)
 541                 return false;
 542         edit->new_meta[0] = assoc_array_node_to_ptr(new_n0);
 543         new_n1 = kzalloc(sizeof(struct assoc_array_node), GFP_KERNEL);
 544         if (!new_n1)
 545                 return false;
 546         edit->new_meta[1] = assoc_array_node_to_ptr(new_n1);
 547 
 548         /* We need to find out how similar the leaves are. */
 549         pr_devel("no spare slots\n");
 550         have_meta = false;
 551         for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
 552                 ptr = node->slots[i];
 553                 if (assoc_array_ptr_is_meta(ptr)) {
 554                         edit->segment_cache[i] = 0xff;
 555                         have_meta = true;
 556                         continue;
 557                 }
 558                 base_seg = ops->get_object_key_chunk(
 559                         assoc_array_ptr_to_leaf(ptr), level);
 560                 base_seg >>= level & ASSOC_ARRAY_KEY_CHUNK_MASK;
 561                 edit->segment_cache[i] = base_seg & ASSOC_ARRAY_FAN_MASK;
 562         }
 563 
 564         if (have_meta) {
 565                 pr_devel("have meta\n");
 566                 goto split_node;
 567         }
 568 
 569         /* The node contains only leaves */
 570         dissimilarity = 0;
 571         base_seg = edit->segment_cache[0];
 572         for (i = 1; i < ASSOC_ARRAY_FAN_OUT; i++)
 573                 dissimilarity |= edit->segment_cache[i] ^ base_seg;
 574 
 575         pr_devel("only leaves; dissimilarity=%lx\n", dissimilarity);
 576 
 577         if ((dissimilarity & ASSOC_ARRAY_FAN_MASK) == 0) {
 578                 /* The old leaves all cluster in the same slot.  We will need
 579                  * to insert a shortcut if the new node wants to cluster with them.
 580                  */
 581                 if ((edit->segment_cache[ASSOC_ARRAY_FAN_OUT] ^ base_seg) == 0)
 582                         goto all_leaves_cluster_together;
 583 
 584                 /* Otherwise all the old leaves cluster in the same slot, but
 585                  * the new leaf wants to go into a different slot - so we
 586                  * create a new node (n0) to hold the new leaf and a pointer to
 587                  * a new node (n1) holding all the old leaves.
 588                  *
 589                  * This can be done by falling through to the node splitting
 590                  * path.
 591                  */
 592                 pr_devel("present leaves cluster but not new leaf\n");
 593         }
 594 
 595 split_node:
 596         pr_devel("split node\n");
 597 
 598         /* We need to split the current node.  The node must contain anything
 599          * from a single leaf (in the one leaf case, this leaf will cluster
 600          * with the new leaf) and the rest meta-pointers, to all leaves, some
 601          * of which may cluster.
 602          *
 603          * It won't contain the case in which all the current leaves plus the
 604          * new leaves want to cluster in the same slot.
 605          *
 606          * We need to expel at least two leaves out of a set consisting of the
 607          * leaves in the node and the new leaf.  The current meta pointers can
 608          * just be copied as they shouldn't cluster with any of the leaves.
 609          *
 610          * We need a new node (n0) to replace the current one and a new node to
 611          * take the expelled nodes (n1).
 612          */
 613         edit->set[0].to = assoc_array_node_to_ptr(new_n0);
 614         new_n0->back_pointer = node->back_pointer;
 615         new_n0->parent_slot = node->parent_slot;
 616         new_n1->back_pointer = assoc_array_node_to_ptr(new_n0);
 617         new_n1->parent_slot = -1; /* Need to calculate this */
 618 
 619 do_split_node:
 620         pr_devel("do_split_node\n");
 621 
 622         new_n0->nr_leaves_on_branch = node->nr_leaves_on_branch;
 623         new_n1->nr_leaves_on_branch = 0;
 624 
 625         /* Begin by finding two matching leaves.  There have to be at least two
 626          * that match - even if there are meta pointers - because any leaf that
 627          * would match a slot with a meta pointer in it must be somewhere
 628          * behind that meta pointer and cannot be here.  Further, given N
 629          * remaining leaf slots, we now have N+1 leaves to go in them.
 630          */
 631         for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
 632                 slot = edit->segment_cache[i];
 633                 if (slot != 0xff)
 634                         for (j = i + 1; j < ASSOC_ARRAY_FAN_OUT + 1; j++)
 635                                 if (edit->segment_cache[j] == slot)
 636                                         goto found_slot_for_multiple_occupancy;
 637         }
 638 found_slot_for_multiple_occupancy:
 639         pr_devel("same slot: %x %x [%02x]\n", i, j, slot);
 640         BUG_ON(i >= ASSOC_ARRAY_FAN_OUT);
 641         BUG_ON(j >= ASSOC_ARRAY_FAN_OUT + 1);
 642         BUG_ON(slot >= ASSOC_ARRAY_FAN_OUT);
 643 
 644         new_n1->parent_slot = slot;
 645 
 646         /* Metadata pointers cannot change slot */
 647         for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++)
 648                 if (assoc_array_ptr_is_meta(node->slots[i]))
 649                         new_n0->slots[i] = node->slots[i];
 650                 else
 651                         new_n0->slots[i] = NULL;
 652         BUG_ON(new_n0->slots[slot] != NULL);
 653         new_n0->slots[slot] = assoc_array_node_to_ptr(new_n1);
 654 
 655         /* Filter the leaf pointers between the new nodes */
 656         free_slot = -1;
 657         next_slot = 0;
 658         for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
 659                 if (assoc_array_ptr_is_meta(node->slots[i]))
 660                         continue;
 661                 if (edit->segment_cache[i] == slot) {
 662                         new_n1->slots[next_slot++] = node->slots[i];
 663                         new_n1->nr_leaves_on_branch++;
 664                 } else {
 665                         do {
 666                                 free_slot++;
 667                         } while (new_n0->slots[free_slot] != NULL);
 668                         new_n0->slots[free_slot] = node->slots[i];
 669                 }
 670         }
 671 
 672         pr_devel("filtered: f=%x n=%x\n", free_slot, next_slot);
 673 
 674         if (edit->segment_cache[ASSOC_ARRAY_FAN_OUT] != slot) {
 675                 do {
 676                         free_slot++;
 677                 } while (new_n0->slots[free_slot] != NULL);
 678                 edit->leaf_p = &new_n0->slots[free_slot];
 679                 edit->adjust_count_on = new_n0;
 680         } else {
 681                 edit->leaf_p = &new_n1->slots[next_slot++];
 682                 edit->adjust_count_on = new_n1;
 683         }
 684 
 685         BUG_ON(next_slot <= 1);
 686 
 687         edit->set_backpointers_to = assoc_array_node_to_ptr(new_n0);
 688         for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
 689                 if (edit->segment_cache[i] == 0xff) {
 690                         ptr = node->slots[i];
 691                         BUG_ON(assoc_array_ptr_is_leaf(ptr));
 692                         if (assoc_array_ptr_is_node(ptr)) {
 693                                 side = assoc_array_ptr_to_node(ptr);
 694                                 edit->set_backpointers[i] = &side->back_pointer;
 695                         } else {
 696                                 shortcut = assoc_array_ptr_to_shortcut(ptr);
 697                                 edit->set_backpointers[i] = &shortcut->back_pointer;
 698                         }
 699                 }
 700         }
 701 
 702         ptr = node->back_pointer;
 703         if (!ptr)
 704                 edit->set[0].ptr = &edit->array->root;
 705         else if (assoc_array_ptr_is_node(ptr))
 706                 edit->set[0].ptr = &assoc_array_ptr_to_node(ptr)->slots[node->parent_slot];
 707         else
 708                 edit->set[0].ptr = &assoc_array_ptr_to_shortcut(ptr)->next_node;
 709         edit->excised_meta[0] = assoc_array_node_to_ptr(node);
 710         pr_devel("<--%s() = ok [split node]\n", __func__);
 711         return true;
 712 
 713 all_leaves_cluster_together:
 714         /* All the leaves, new and old, want to cluster together in this node
 715          * in the same slot, so we have to replace this node with a shortcut to
 716          * skip over the identical parts of the key and then place a pair of
 717          * nodes, one inside the other, at the end of the shortcut and
 718          * distribute the keys between them.
 719          *
 720          * Firstly we need to work out where the leaves start diverging as a
 721          * bit position into their keys so that we know how big the shortcut
 722          * needs to be.
 723          *
 724          * We only need to make a single pass of N of the N+1 leaves because if
 725          * any keys differ between themselves at bit X then at least one of
 726          * them must also differ with the base key at bit X or before.
 727          */
 728         pr_devel("all leaves cluster together\n");
 729         diff = INT_MAX;
 730         for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
 731                 int x = ops->diff_objects(assoc_array_ptr_to_leaf(node->slots[i]),
 732                                           index_key);
 733                 if (x < diff) {
 734                         BUG_ON(x < 0);
 735                         diff = x;
 736                 }
 737         }
 738         BUG_ON(diff == INT_MAX);
 739         BUG_ON(diff < level + ASSOC_ARRAY_LEVEL_STEP);
 740 
 741         keylen = round_up(diff, ASSOC_ARRAY_KEY_CHUNK_SIZE);
 742         keylen >>= ASSOC_ARRAY_KEY_CHUNK_SHIFT;
 743 
 744         new_s0 = kzalloc(sizeof(struct assoc_array_shortcut) +
 745                          keylen * sizeof(unsigned long), GFP_KERNEL);
 746         if (!new_s0)
 747                 return false;
 748         edit->new_meta[2] = assoc_array_shortcut_to_ptr(new_s0);
 749 
 750         edit->set[0].to = assoc_array_shortcut_to_ptr(new_s0);
 751         new_s0->back_pointer = node->back_pointer;
 752         new_s0->parent_slot = node->parent_slot;
 753         new_s0->next_node = assoc_array_node_to_ptr(new_n0);
 754         new_n0->back_pointer = assoc_array_shortcut_to_ptr(new_s0);
 755         new_n0->parent_slot = 0;
 756         new_n1->back_pointer = assoc_array_node_to_ptr(new_n0);
 757         new_n1->parent_slot = -1; /* Need to calculate this */
 758 
 759         new_s0->skip_to_level = level = diff & ~ASSOC_ARRAY_LEVEL_STEP_MASK;
 760         pr_devel("skip_to_level = %d [diff %d]\n", level, diff);
 761         BUG_ON(level <= 0);
 762 
 763         for (i = 0; i < keylen; i++)
 764                 new_s0->index_key[i] =
 765                         ops->get_key_chunk(index_key, i * ASSOC_ARRAY_KEY_CHUNK_SIZE);
 766 
 767         if (level & ASSOC_ARRAY_KEY_CHUNK_MASK) {
 768                 blank = ULONG_MAX << (level & ASSOC_ARRAY_KEY_CHUNK_MASK);
 769                 pr_devel("blank off [%zu] %d: %lx\n", keylen - 1, level, blank);
 770                 new_s0->index_key[keylen - 1] &= ~blank;
 771         }
 772 
 773         /* This now reduces to a node splitting exercise for which we'll need
 774          * to regenerate the disparity table.
 775          */
 776         for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
 777                 ptr = node->slots[i];
 778                 base_seg = ops->get_object_key_chunk(assoc_array_ptr_to_leaf(ptr),
 779                                                      level);
 780                 base_seg >>= level & ASSOC_ARRAY_KEY_CHUNK_MASK;
 781                 edit->segment_cache[i] = base_seg & ASSOC_ARRAY_FAN_MASK;
 782         }
 783 
 784         base_seg = ops->get_key_chunk(index_key, level);
 785         base_seg >>= level & ASSOC_ARRAY_KEY_CHUNK_MASK;
 786         edit->segment_cache[ASSOC_ARRAY_FAN_OUT] = base_seg & ASSOC_ARRAY_FAN_MASK;
 787         goto do_split_node;
 788 }
 789 
 790 /*
 791  * Handle insertion into the middle of a shortcut.
 792  */
 793 static bool assoc_array_insert_mid_shortcut(struct assoc_array_edit *edit,
 794                                             const struct assoc_array_ops *ops,
 795                                             struct assoc_array_walk_result *result)
 796 {
 797         struct assoc_array_shortcut *shortcut, *new_s0, *new_s1;
 798         struct assoc_array_node *node, *new_n0, *side;
 799         unsigned long sc_segments, dissimilarity, blank;
 800         size_t keylen;
 801         int level, sc_level, diff;
 802         int sc_slot;
 803 
 804         shortcut        = result->wrong_shortcut.shortcut;
 805         level           = result->wrong_shortcut.level;
 806         sc_level        = result->wrong_shortcut.sc_level;
 807         sc_segments     = result->wrong_shortcut.sc_segments;
 808         dissimilarity   = result->wrong_shortcut.dissimilarity;
 809 
 810         pr_devel("-->%s(ix=%d dis=%lx scix=%d)\n",
 811                  __func__, level, dissimilarity, sc_level);
 812 
 813         /* We need to split a shortcut and insert a node between the two
 814          * pieces.  Zero-length pieces will be dispensed with entirely.
 815          *
 816          * First of all, we need to find out in which level the first
 817          * difference was.
 818          */
 819         diff = __ffs(dissimilarity);
 820         diff &= ~ASSOC_ARRAY_LEVEL_STEP_MASK;
 821         diff += sc_level & ~ASSOC_ARRAY_KEY_CHUNK_MASK;
 822         pr_devel("diff=%d\n", diff);
 823 
 824         if (!shortcut->back_pointer) {
 825                 edit->set[0].ptr = &edit->array->root;
 826         } else if (assoc_array_ptr_is_node(shortcut->back_pointer)) {
 827                 node = assoc_array_ptr_to_node(shortcut->back_pointer);
 828                 edit->set[0].ptr = &node->slots[shortcut->parent_slot];
 829         } else {
 830                 BUG();
 831         }
 832 
 833         edit->excised_meta[0] = assoc_array_shortcut_to_ptr(shortcut);
 834 
 835         /* Create a new node now since we're going to need it anyway */
 836         new_n0 = kzalloc(sizeof(struct assoc_array_node), GFP_KERNEL);
 837         if (!new_n0)
 838                 return false;
 839         edit->new_meta[0] = assoc_array_node_to_ptr(new_n0);
 840         edit->adjust_count_on = new_n0;
 841 
 842         /* Insert a new shortcut before the new node if this segment isn't of
 843          * zero length - otherwise we just connect the new node directly to the
 844          * parent.
 845          */
 846         level += ASSOC_ARRAY_LEVEL_STEP;
 847         if (diff > level) {
 848                 pr_devel("pre-shortcut %d...%d\n", level, diff);
 849                 keylen = round_up(diff, ASSOC_ARRAY_KEY_CHUNK_SIZE);
 850                 keylen >>= ASSOC_ARRAY_KEY_CHUNK_SHIFT;
 851 
 852                 new_s0 = kzalloc(sizeof(struct assoc_array_shortcut) +
 853                                  keylen * sizeof(unsigned long), GFP_KERNEL);
 854                 if (!new_s0)
 855                         return false;
 856                 edit->new_meta[1] = assoc_array_shortcut_to_ptr(new_s0);
 857                 edit->set[0].to = assoc_array_shortcut_to_ptr(new_s0);
 858                 new_s0->back_pointer = shortcut->back_pointer;
 859                 new_s0->parent_slot = shortcut->parent_slot;
 860                 new_s0->next_node = assoc_array_node_to_ptr(new_n0);
 861                 new_s0->skip_to_level = diff;
 862 
 863                 new_n0->back_pointer = assoc_array_shortcut_to_ptr(new_s0);
 864                 new_n0->parent_slot = 0;
 865 
 866                 memcpy(new_s0->index_key, shortcut->index_key,
 867                        keylen * sizeof(unsigned long));
 868 
 869                 blank = ULONG_MAX << (diff & ASSOC_ARRAY_KEY_CHUNK_MASK);
 870                 pr_devel("blank off [%zu] %d: %lx\n", keylen - 1, diff, blank);
 871                 new_s0->index_key[keylen - 1] &= ~blank;
 872         } else {
 873                 pr_devel("no pre-shortcut\n");
 874                 edit->set[0].to = assoc_array_node_to_ptr(new_n0);
 875                 new_n0->back_pointer = shortcut->back_pointer;
 876                 new_n0->parent_slot = shortcut->parent_slot;
 877         }
 878 
 879         side = assoc_array_ptr_to_node(shortcut->next_node);
 880         new_n0->nr_leaves_on_branch = side->nr_leaves_on_branch;
 881 
 882         /* We need to know which slot in the new node is going to take a
 883          * metadata pointer.
 884          */
 885         sc_slot = sc_segments >> (diff & ASSOC_ARRAY_KEY_CHUNK_MASK);
 886         sc_slot &= ASSOC_ARRAY_FAN_MASK;
 887 
 888         pr_devel("new slot %lx >> %d -> %d\n",
 889                  sc_segments, diff & ASSOC_ARRAY_KEY_CHUNK_MASK, sc_slot);
 890 
 891         /* Determine whether we need to follow the new node with a replacement
 892          * for the current shortcut.  We could in theory reuse the current
 893          * shortcut if its parent slot number doesn't change - but that's a
 894          * 1-in-16 chance so not worth expending the code upon.
 895          */
 896         level = diff + ASSOC_ARRAY_LEVEL_STEP;
 897         if (level < shortcut->skip_to_level) {
 898                 pr_devel("post-shortcut %d...%d\n", level, shortcut->skip_to_level);
 899                 keylen = round_up(shortcut->skip_to_level, ASSOC_ARRAY_KEY_CHUNK_SIZE);
 900                 keylen >>= ASSOC_ARRAY_KEY_CHUNK_SHIFT;
 901 
 902                 new_s1 = kzalloc(sizeof(struct assoc_array_shortcut) +
 903                                  keylen * sizeof(unsigned long), GFP_KERNEL);
 904                 if (!new_s1)
 905                         return false;
 906                 edit->new_meta[2] = assoc_array_shortcut_to_ptr(new_s1);
 907 
 908                 new_s1->back_pointer = assoc_array_node_to_ptr(new_n0);
 909                 new_s1->parent_slot = sc_slot;
 910                 new_s1->next_node = shortcut->next_node;
 911                 new_s1->skip_to_level = shortcut->skip_to_level;
 912 
 913                 new_n0->slots[sc_slot] = assoc_array_shortcut_to_ptr(new_s1);
 914 
 915                 memcpy(new_s1->index_key, shortcut->index_key,
 916                        keylen * sizeof(unsigned long));
 917 
 918                 edit->set[1].ptr = &side->back_pointer;
 919                 edit->set[1].to = assoc_array_shortcut_to_ptr(new_s1);
 920         } else {
 921                 pr_devel("no post-shortcut\n");
 922 
 923                 /* We don't have to replace the pointed-to node as long as we
 924                  * use memory barriers to make sure the parent slot number is
 925                  * changed before the back pointer (the parent slot number is
 926                  * irrelevant to the old parent shortcut).
 927                  */
 928                 new_n0->slots[sc_slot] = shortcut->next_node;
 929                 edit->set_parent_slot[0].p = &side->parent_slot;
 930                 edit->set_parent_slot[0].to = sc_slot;
 931                 edit->set[1].ptr = &side->back_pointer;
 932                 edit->set[1].to = assoc_array_node_to_ptr(new_n0);
 933         }
 934 
 935         /* Install the new leaf in a spare slot in the new node. */
 936         if (sc_slot == 0)
 937                 edit->leaf_p = &new_n0->slots[1];
 938         else
 939                 edit->leaf_p = &new_n0->slots[0];
 940 
 941         pr_devel("<--%s() = ok [split shortcut]\n", __func__);
 942         return edit;
 943 }
 944 
 945 /**
 946  * assoc_array_insert - Script insertion of an object into an associative array
 947  * @array: The array to insert into.
 948  * @ops: The operations to use.
 949  * @index_key: The key to insert at.
 950  * @object: The object to insert.
 951  *
 952  * Precalculate and preallocate a script for the insertion or replacement of an
 953  * object in an associative array.  This results in an edit script that can
 954  * either be applied or cancelled.
 955  *
 956  * The function returns a pointer to an edit script or -ENOMEM.
 957  *
 958  * The caller should lock against other modifications and must continue to hold
 959  * the lock until assoc_array_apply_edit() has been called.
 960  *
 961  * Accesses to the tree may take place concurrently with this function,
 962  * provided they hold the RCU read lock.
 963  */
 964 struct assoc_array_edit *assoc_array_insert(struct assoc_array *array,
 965                                             const struct assoc_array_ops *ops,
 966                                             const void *index_key,
 967                                             void *object)
 968 {
 969         struct assoc_array_walk_result result;
 970         struct assoc_array_edit *edit;
 971 
 972         pr_devel("-->%s()\n", __func__);
 973 
 974         /* The leaf pointer we're given must not have the bottom bit set as we
 975          * use those for type-marking the pointer.  NULL pointers are also not
 976          * allowed as they indicate an empty slot but we have to allow them
 977          * here as they can be updated later.
 978          */
 979         BUG_ON(assoc_array_ptr_is_meta(object));
 980 
 981         edit = kzalloc(sizeof(struct assoc_array_edit), GFP_KERNEL);
 982         if (!edit)
 983                 return ERR_PTR(-ENOMEM);
 984         edit->array = array;
 985         edit->ops = ops;
 986         edit->leaf = assoc_array_leaf_to_ptr(object);
 987         edit->adjust_count_by = 1;
 988 
 989         switch (assoc_array_walk(array, ops, index_key, &result)) {
 990         case assoc_array_walk_tree_empty:
 991                 /* Allocate a root node if there isn't one yet */
 992                 if (!assoc_array_insert_in_empty_tree(edit))
 993                         goto enomem;
 994                 return edit;
 995 
 996         case assoc_array_walk_found_terminal_node:
 997                 /* We found a node that doesn't have a node/shortcut pointer in
 998                  * the slot corresponding to the index key that we have to
 999                  * follow.
1000                  */
1001                 if (!assoc_array_insert_into_terminal_node(edit, ops, index_key,
1002                                                            &result))
1003                         goto enomem;
1004                 return edit;
1005 
1006         case assoc_array_walk_found_wrong_shortcut:
1007                 /* We found a shortcut that didn't match our key in a slot we
1008                  * needed to follow.
1009                  */
1010                 if (!assoc_array_insert_mid_shortcut(edit, ops, &result))
1011                         goto enomem;
1012                 return edit;
1013         }
1014 
1015 enomem:
1016         /* Clean up after an out of memory error */
1017         pr_devel("enomem\n");
1018         assoc_array_cancel_edit(edit);
1019         return ERR_PTR(-ENOMEM);
1020 }
1021 
1022 /**
1023  * assoc_array_insert_set_object - Set the new object pointer in an edit script
1024  * @edit: The edit script to modify.
1025  * @object: The object pointer to set.
1026  *
1027  * Change the object to be inserted in an edit script.  The object pointed to
1028  * by the old object is not freed.  This must be done prior to applying the
1029  * script.
1030  */
1031 void assoc_array_insert_set_object(struct assoc_array_edit *edit, void *object)
1032 {
1033         BUG_ON(!object);
1034         edit->leaf = assoc_array_leaf_to_ptr(object);
1035 }
1036 
1037 struct assoc_array_delete_collapse_context {
1038         struct assoc_array_node *node;
1039         const void              *skip_leaf;
1040         int                     slot;
1041 };
1042 
1043 /*
1044  * Subtree collapse to node iterator.
1045  */
1046 static int assoc_array_delete_collapse_iterator(const void *leaf,
1047                                                 void *iterator_data)
1048 {
1049         struct assoc_array_delete_collapse_context *collapse = iterator_data;
1050 
1051         if (leaf == collapse->skip_leaf)
1052                 return 0;
1053 
1054         BUG_ON(collapse->slot >= ASSOC_ARRAY_FAN_OUT);
1055 
1056         collapse->node->slots[collapse->slot++] = assoc_array_leaf_to_ptr(leaf);
1057         return 0;
1058 }
1059 
1060 /**
1061  * assoc_array_delete - Script deletion of an object from an associative array
1062  * @array: The array to search.
1063  * @ops: The operations to use.
1064  * @index_key: The key to the object.
1065  *
1066  * Precalculate and preallocate a script for the deletion of an object from an
1067  * associative array.  This results in an edit script that can either be
1068  * applied or cancelled.
1069  *
1070  * The function returns a pointer to an edit script if the object was found,
1071  * NULL if the object was not found or -ENOMEM.
1072  *
1073  * The caller should lock against other modifications and must continue to hold
1074  * the lock until assoc_array_apply_edit() has been called.
1075  *
1076  * Accesses to the tree may take place concurrently with this function,
1077  * provided they hold the RCU read lock.
1078  */
1079 struct assoc_array_edit *assoc_array_delete(struct assoc_array *array,
1080                                             const struct assoc_array_ops *ops,
1081                                             const void *index_key)
1082 {
1083         struct assoc_array_delete_collapse_context collapse;
1084         struct assoc_array_walk_result result;
1085         struct assoc_array_node *node, *new_n0;
1086         struct assoc_array_edit *edit;
1087         struct assoc_array_ptr *ptr;
1088         bool has_meta;
1089         int slot, i;
1090 
1091         pr_devel("-->%s()\n", __func__);
1092 
1093         edit = kzalloc(sizeof(struct assoc_array_edit), GFP_KERNEL);
1094         if (!edit)
1095                 return ERR_PTR(-ENOMEM);
1096         edit->array = array;
1097         edit->ops = ops;
1098         edit->adjust_count_by = -1;
1099 
1100         switch (assoc_array_walk(array, ops, index_key, &result)) {
1101         case assoc_array_walk_found_terminal_node:
1102                 /* We found a node that should contain the leaf we've been
1103                  * asked to remove - *if* it's in the tree.
1104                  */
1105                 pr_devel("terminal_node\n");
1106                 node = result.terminal_node.node;
1107 
1108                 for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
1109                         ptr = node->slots[slot];
1110                         if (ptr &&
1111                             assoc_array_ptr_is_leaf(ptr) &&
1112                             ops->compare_object(assoc_array_ptr_to_leaf(ptr),
1113                                                 index_key))
1114                                 goto found_leaf;
1115                 }
1116                 /* fall through */
1117         case assoc_array_walk_tree_empty:
1118         case assoc_array_walk_found_wrong_shortcut:
1119         default:
1120                 assoc_array_cancel_edit(edit);
1121                 pr_devel("not found\n");
1122                 return NULL;
1123         }
1124 
1125 found_leaf:
1126         BUG_ON(array->nr_leaves_on_tree <= 0);
1127 
1128         /* In the simplest form of deletion we just clear the slot and release
1129          * the leaf after a suitable interval.
1130          */
1131         edit->dead_leaf = node->slots[slot];
1132         edit->set[0].ptr = &node->slots[slot];
1133         edit->set[0].to = NULL;
1134         edit->adjust_count_on = node;
1135 
1136         /* If that concludes erasure of the last leaf, then delete the entire
1137          * internal array.
1138          */
1139         if (array->nr_leaves_on_tree == 1) {
1140                 edit->set[1].ptr = &array->root;
1141                 edit->set[1].to = NULL;
1142                 edit->adjust_count_on = NULL;
1143                 edit->excised_subtree = array->root;
1144                 pr_devel("all gone\n");
1145                 return edit;
1146         }
1147 
1148         /* However, we'd also like to clear up some metadata blocks if we
1149          * possibly can.
1150          *
1151          * We go for a simple algorithm of: if this node has FAN_OUT or fewer
1152          * leaves in it, then attempt to collapse it - and attempt to
1153          * recursively collapse up the tree.
1154          *
1155          * We could also try and collapse in partially filled subtrees to take
1156          * up space in this node.
1157          */
1158         if (node->nr_leaves_on_branch <= ASSOC_ARRAY_FAN_OUT + 1) {
1159                 struct assoc_array_node *parent, *grandparent;
1160                 struct assoc_array_ptr *ptr;
1161 
1162                 /* First of all, we need to know if this node has metadata so
1163                  * that we don't try collapsing if all the leaves are already
1164                  * here.
1165                  */
1166                 has_meta = false;
1167                 for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
1168                         ptr = node->slots[i];
1169                         if (assoc_array_ptr_is_meta(ptr)) {
1170                                 has_meta = true;
1171                                 break;
1172                         }
1173                 }
1174 
1175                 pr_devel("leaves: %ld [m=%d]\n",
1176                          node->nr_leaves_on_branch - 1, has_meta);
1177 
1178                 /* Look further up the tree to see if we can collapse this node
1179                  * into a more proximal node too.
1180                  */
1181                 parent = node;
1182         collapse_up:
1183                 pr_devel("collapse subtree: %ld\n", parent->nr_leaves_on_branch);
1184 
1185                 ptr = parent->back_pointer;
1186                 if (!ptr)
1187                         goto do_collapse;
1188                 if (assoc_array_ptr_is_shortcut(ptr)) {
1189                         struct assoc_array_shortcut *s = assoc_array_ptr_to_shortcut(ptr);
1190                         ptr = s->back_pointer;
1191                         if (!ptr)
1192                                 goto do_collapse;
1193                 }
1194 
1195                 grandparent = assoc_array_ptr_to_node(ptr);
1196                 if (grandparent->nr_leaves_on_branch <= ASSOC_ARRAY_FAN_OUT + 1) {
1197                         parent = grandparent;
1198                         goto collapse_up;
1199                 }
1200 
1201         do_collapse:
1202                 /* There's no point collapsing if the original node has no meta
1203                  * pointers to discard and if we didn't merge into one of that
1204                  * node's ancestry.
1205                  */
1206                 if (has_meta || parent != node) {
1207                         node = parent;
1208 
1209                         /* Create a new node to collapse into */
1210                         new_n0 = kzalloc(sizeof(struct assoc_array_node), GFP_KERNEL);
1211                         if (!new_n0)
1212                                 goto enomem;
1213                         edit->new_meta[0] = assoc_array_node_to_ptr(new_n0);
1214 
1215                         new_n0->back_pointer = node->back_pointer;
1216                         new_n0->parent_slot = node->parent_slot;
1217                         new_n0->nr_leaves_on_branch = node->nr_leaves_on_branch;
1218                         edit->adjust_count_on = new_n0;
1219 
1220                         collapse.node = new_n0;
1221                         collapse.skip_leaf = assoc_array_ptr_to_leaf(edit->dead_leaf);
1222                         collapse.slot = 0;
1223                         assoc_array_subtree_iterate(assoc_array_node_to_ptr(node),
1224                                                     node->back_pointer,
1225                                                     assoc_array_delete_collapse_iterator,
1226                                                     &collapse);
1227                         pr_devel("collapsed %d,%lu\n", collapse.slot, new_n0->nr_leaves_on_branch);
1228                         BUG_ON(collapse.slot != new_n0->nr_leaves_on_branch - 1);
1229 
1230                         if (!node->back_pointer) {
1231                                 edit->set[1].ptr = &array->root;
1232                         } else if (assoc_array_ptr_is_leaf(node->back_pointer)) {
1233                                 BUG();
1234                         } else if (assoc_array_ptr_is_node(node->back_pointer)) {
1235                                 struct assoc_array_node *p =
1236                                         assoc_array_ptr_to_node(node->back_pointer);
1237                                 edit->set[1].ptr = &p->slots[node->parent_slot];
1238                         } else if (assoc_array_ptr_is_shortcut(node->back_pointer)) {
1239                                 struct assoc_array_shortcut *s =
1240                                         assoc_array_ptr_to_shortcut(node->back_pointer);
1241                                 edit->set[1].ptr = &s->next_node;
1242                         }
1243                         edit->set[1].to = assoc_array_node_to_ptr(new_n0);
1244                         edit->excised_subtree = assoc_array_node_to_ptr(node);
1245                 }
1246         }
1247 
1248         return edit;
1249 
1250 enomem:
1251         /* Clean up after an out of memory error */
1252         pr_devel("enomem\n");
1253         assoc_array_cancel_edit(edit);
1254         return ERR_PTR(-ENOMEM);
1255 }
1256 
1257 /**
1258  * assoc_array_clear - Script deletion of all objects from an associative array
1259  * @array: The array to clear.
1260  * @ops: The operations to use.
1261  *
1262  * Precalculate and preallocate a script for the deletion of all the objects
1263  * from an associative array.  This results in an edit script that can either
1264  * be applied or cancelled.
1265  *
1266  * The function returns a pointer to an edit script if there are objects to be
1267  * deleted, NULL if there are no objects in the array or -ENOMEM.
1268  *
1269  * The caller should lock against other modifications and must continue to hold
1270  * the lock until assoc_array_apply_edit() has been called.
1271  *
1272  * Accesses to the tree may take place concurrently with this function,
1273  * provided they hold the RCU read lock.
1274  */
1275 struct assoc_array_edit *assoc_array_clear(struct assoc_array *array,
1276                                            const struct assoc_array_ops *ops)
1277 {
1278         struct assoc_array_edit *edit;
1279 
1280         pr_devel("-->%s()\n", __func__);
1281 
1282         if (!array->root)
1283                 return NULL;
1284 
1285         edit = kzalloc(sizeof(struct assoc_array_edit), GFP_KERNEL);
1286         if (!edit)
1287                 return ERR_PTR(-ENOMEM);
1288         edit->array = array;
1289         edit->ops = ops;
1290         edit->set[1].ptr = &array->root;
1291         edit->set[1].to = NULL;
1292         edit->excised_subtree = array->root;
1293         edit->ops_for_excised_subtree = ops;
1294         pr_devel("all gone\n");
1295         return edit;
1296 }
1297 
1298 /*
1299  * Handle the deferred destruction after an applied edit.
1300  */
1301 static void assoc_array_rcu_cleanup(struct rcu_head *head)
1302 {
1303         struct assoc_array_edit *edit =
1304                 container_of(head, struct assoc_array_edit, rcu);
1305         int i;
1306 
1307         pr_devel("-->%s()\n", __func__);
1308 
1309         if (edit->dead_leaf)
1310                 edit->ops->free_object(assoc_array_ptr_to_leaf(edit->dead_leaf));
1311         for (i = 0; i < ARRAY_SIZE(edit->excised_meta); i++)
1312                 if (edit->excised_meta[i])
1313                         kfree(assoc_array_ptr_to_node(edit->excised_meta[i]));
1314 
1315         if (edit->excised_subtree) {
1316                 BUG_ON(assoc_array_ptr_is_leaf(edit->excised_subtree));
1317                 if (assoc_array_ptr_is_node(edit->excised_subtree)) {
1318                         struct assoc_array_node *n =
1319                                 assoc_array_ptr_to_node(edit->excised_subtree);
1320                         n->back_pointer = NULL;
1321                 } else {
1322                         struct assoc_array_shortcut *s =
1323                                 assoc_array_ptr_to_shortcut(edit->excised_subtree);
1324                         s->back_pointer = NULL;
1325                 }
1326                 assoc_array_destroy_subtree(edit->excised_subtree,
1327                                             edit->ops_for_excised_subtree);
1328         }
1329 
1330         kfree(edit);
1331 }
1332 
1333 /**
1334  * assoc_array_apply_edit - Apply an edit script to an associative array
1335  * @edit: The script to apply.
1336  *
1337  * Apply an edit script to an associative array to effect an insertion,
1338  * deletion or clearance.  As the edit script includes preallocated memory,
1339  * this is guaranteed not to fail.
1340  *
1341  * The edit script, dead objects and dead metadata will be scheduled for
1342  * destruction after an RCU grace period to permit those doing read-only
1343  * accesses on the array to continue to do so under the RCU read lock whilst
1344  * the edit is taking place.
1345  */
1346 void assoc_array_apply_edit(struct assoc_array_edit *edit)
1347 {
1348         struct assoc_array_shortcut *shortcut;
1349         struct assoc_array_node *node;
1350         struct assoc_array_ptr *ptr;
1351         int i;
1352 
1353         pr_devel("-->%s()\n", __func__);
1354 
1355         smp_wmb();
1356         if (edit->leaf_p)
1357                 *edit->leaf_p = edit->leaf;
1358 
1359         smp_wmb();
1360         for (i = 0; i < ARRAY_SIZE(edit->set_parent_slot); i++)
1361                 if (edit->set_parent_slot[i].p)
1362                         *edit->set_parent_slot[i].p = edit->set_parent_slot[i].to;
1363 
1364         smp_wmb();
1365         for (i = 0; i < ARRAY_SIZE(edit->set_backpointers); i++)
1366                 if (edit->set_backpointers[i])
1367                         *edit->set_backpointers[i] = edit->set_backpointers_to;
1368 
1369         smp_wmb();
1370         for (i = 0; i < ARRAY_SIZE(edit->set); i++)
1371                 if (edit->set[i].ptr)
1372                         *edit->set[i].ptr = edit->set[i].to;
1373 
1374         if (edit->array->root == NULL) {
1375                 edit->array->nr_leaves_on_tree = 0;
1376         } else if (edit->adjust_count_on) {
1377                 node = edit->adjust_count_on;
1378                 for (;;) {
1379                         node->nr_leaves_on_branch += edit->adjust_count_by;
1380 
1381                         ptr = node->back_pointer;
1382                         if (!ptr)
1383                                 break;
1384                         if (assoc_array_ptr_is_shortcut(ptr)) {
1385                                 shortcut = assoc_array_ptr_to_shortcut(ptr);
1386                                 ptr = shortcut->back_pointer;
1387                                 if (!ptr)
1388                                         break;
1389                         }
1390                         BUG_ON(!assoc_array_ptr_is_node(ptr));
1391                         node = assoc_array_ptr_to_node(ptr);
1392                 }
1393 
1394                 edit->array->nr_leaves_on_tree += edit->adjust_count_by;
1395         }
1396 
1397         call_rcu(&edit->rcu, assoc_array_rcu_cleanup);
1398 }
1399 
1400 /**
1401  * assoc_array_cancel_edit - Discard an edit script.
1402  * @edit: The script to discard.
1403  *
1404  * Free an edit script and all the preallocated data it holds without making
1405  * any changes to the associative array it was intended for.
1406  *
1407  * NOTE!  In the case of an insertion script, this does _not_ release the leaf
1408  * that was to be inserted.  That is left to the caller.
1409  */
1410 void assoc_array_cancel_edit(struct assoc_array_edit *edit)
1411 {
1412         struct assoc_array_ptr *ptr;
1413         int i;
1414 
1415         pr_devel("-->%s()\n", __func__);
1416 
1417         /* Clean up after an out of memory error */
1418         for (i = 0; i < ARRAY_SIZE(edit->new_meta); i++) {
1419                 ptr = edit->new_meta[i];
1420                 if (ptr) {
1421                         if (assoc_array_ptr_is_node(ptr))
1422                                 kfree(assoc_array_ptr_to_node(ptr));
1423                         else
1424                                 kfree(assoc_array_ptr_to_shortcut(ptr));
1425                 }
1426         }
1427         kfree(edit);
1428 }
1429 
1430 /**
1431  * assoc_array_gc - Garbage collect an associative array.
1432  * @array: The array to clean.
1433  * @ops: The operations to use.
1434  * @iterator: A callback function to pass judgement on each object.
1435  * @iterator_data: Private data for the callback function.
1436  *
1437  * Collect garbage from an associative array and pack down the internal tree to
1438  * save memory.
1439  *
1440  * The iterator function is asked to pass judgement upon each object in the
1441  * array.  If it returns false, the object is discard and if it returns true,
1442  * the object is kept.  If it returns true, it must increment the object's
1443  * usage count (or whatever it needs to do to retain it) before returning.
1444  *
1445  * This function returns 0 if successful or -ENOMEM if out of memory.  In the
1446  * latter case, the array is not changed.
1447  *
1448  * The caller should lock against other modifications and must continue to hold
1449  * the lock until assoc_array_apply_edit() has been called.
1450  *
1451  * Accesses to the tree may take place concurrently with this function,
1452  * provided they hold the RCU read lock.
1453  */
1454 int assoc_array_gc(struct assoc_array *array,
1455                    const struct assoc_array_ops *ops,
1456                    bool (*iterator)(void *object, void *iterator_data),
1457                    void *iterator_data)
1458 {
1459         struct assoc_array_shortcut *shortcut, *new_s;
1460         struct assoc_array_node *node, *new_n;
1461         struct assoc_array_edit *edit;
1462         struct assoc_array_ptr *cursor, *ptr;
1463         struct assoc_array_ptr *new_root, *new_parent, **new_ptr_pp;
1464         unsigned long nr_leaves_on_tree;
1465         int keylen, slot, nr_free, next_slot, i;
1466 
1467         pr_devel("-->%s()\n", __func__);
1468 
1469         if (!array->root)
1470                 return 0;
1471 
1472         edit = kzalloc(sizeof(struct assoc_array_edit), GFP_KERNEL);
1473         if (!edit)
1474                 return -ENOMEM;
1475         edit->array = array;
1476         edit->ops = ops;
1477         edit->ops_for_excised_subtree = ops;
1478         edit->set[0].ptr = &array->root;
1479         edit->excised_subtree = array->root;
1480 
1481         new_root = new_parent = NULL;
1482         new_ptr_pp = &new_root;
1483         cursor = array->root;
1484 
1485 descend:
1486         /* If this point is a shortcut, then we need to duplicate it and
1487          * advance the target cursor.
1488          */
1489         if (assoc_array_ptr_is_shortcut(cursor)) {
1490                 shortcut = assoc_array_ptr_to_shortcut(cursor);
1491                 keylen = round_up(shortcut->skip_to_level, ASSOC_ARRAY_KEY_CHUNK_SIZE);
1492                 keylen >>= ASSOC_ARRAY_KEY_CHUNK_SHIFT;
1493                 new_s = kmalloc(sizeof(struct assoc_array_shortcut) +
1494                                 keylen * sizeof(unsigned long), GFP_KERNEL);
1495                 if (!new_s)
1496                         goto enomem;
1497                 pr_devel("dup shortcut %p -> %p\n", shortcut, new_s);
1498                 memcpy(new_s, shortcut, (sizeof(struct assoc_array_shortcut) +
1499                                          keylen * sizeof(unsigned long)));
1500                 new_s->back_pointer = new_parent;
1501                 new_s->parent_slot = shortcut->parent_slot;
1502                 *new_ptr_pp = new_parent = assoc_array_shortcut_to_ptr(new_s);
1503                 new_ptr_pp = &new_s->next_node;
1504                 cursor = shortcut->next_node;
1505         }
1506 
1507         /* Duplicate the node at this position */
1508         node = assoc_array_ptr_to_node(cursor);
1509         new_n = kzalloc(sizeof(struct assoc_array_node), GFP_KERNEL);
1510         if (!new_n)
1511                 goto enomem;
1512         pr_devel("dup node %p -> %p\n", node, new_n);
1513         new_n->back_pointer = new_parent;
1514         new_n->parent_slot = node->parent_slot;
1515         *new_ptr_pp = new_parent = assoc_array_node_to_ptr(new_n);
1516         new_ptr_pp = NULL;
1517         slot = 0;
1518 
1519 continue_node:
1520         /* Filter across any leaves and gc any subtrees */
1521         for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
1522                 ptr = node->slots[slot];
1523                 if (!ptr)
1524                         continue;
1525 
1526                 if (assoc_array_ptr_is_leaf(ptr)) {
1527                         if (iterator(assoc_array_ptr_to_leaf(ptr),
1528                                      iterator_data))
1529                                 /* The iterator will have done any reference
1530                                  * counting on the object for us.
1531                                  */
1532                                 new_n->slots[slot] = ptr;
1533                         continue;
1534                 }
1535 
1536                 new_ptr_pp = &new_n->slots[slot];
1537                 cursor = ptr;
1538                 goto descend;
1539         }
1540 
1541         pr_devel("-- compress node %p --\n", new_n);
1542 
1543         /* Count up the number of empty slots in this node and work out the
1544          * subtree leaf count.
1545          */
1546         new_n->nr_leaves_on_branch = 0;
1547         nr_free = 0;
1548         for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
1549                 ptr = new_n->slots[slot];
1550                 if (!ptr)
1551                         nr_free++;
1552                 else if (assoc_array_ptr_is_leaf(ptr))
1553                         new_n->nr_leaves_on_branch++;
1554         }
1555         pr_devel("free=%d, leaves=%lu\n", nr_free, new_n->nr_leaves_on_branch);
1556 
1557         /* See what we can fold in */
1558         next_slot = 0;
1559         for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
1560                 struct assoc_array_shortcut *s;
1561                 struct assoc_array_node *child;
1562 
1563                 ptr = new_n->slots[slot];
1564                 if (!ptr || assoc_array_ptr_is_leaf(ptr))
1565                         continue;
1566 
1567                 s = NULL;
1568                 if (assoc_array_ptr_is_shortcut(ptr)) {
1569                         s = assoc_array_ptr_to_shortcut(ptr);
1570                         ptr = s->next_node;
1571                 }
1572 
1573                 child = assoc_array_ptr_to_node(ptr);
1574                 new_n->nr_leaves_on_branch += child->nr_leaves_on_branch;
1575 
1576                 if (child->nr_leaves_on_branch <= nr_free + 1) {
1577                         /* Fold the child node into this one */
1578                         pr_devel("[%d] fold node %lu/%d [nx %d]\n",
1579                                  slot, child->nr_leaves_on_branch, nr_free + 1,
1580                                  next_slot);
1581 
1582                         /* We would already have reaped an intervening shortcut
1583                          * on the way back up the tree.
1584                          */
1585                         BUG_ON(s);
1586 
1587                         new_n->slots[slot] = NULL;
1588                         nr_free++;
1589                         if (slot < next_slot)
1590                                 next_slot = slot;
1591                         for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
1592                                 struct assoc_array_ptr *p = child->slots[i];
1593                                 if (!p)
1594                                         continue;
1595                                 BUG_ON(assoc_array_ptr_is_meta(p));
1596                                 while (new_n->slots[next_slot])
1597                                         next_slot++;
1598                                 BUG_ON(next_slot >= ASSOC_ARRAY_FAN_OUT);
1599                                 new_n->slots[next_slot++] = p;
1600                                 nr_free--;
1601                         }
1602                         kfree(child);
1603                 } else {
1604                         pr_devel("[%d] retain node %lu/%d [nx %d]\n",
1605                                  slot, child->nr_leaves_on_branch, nr_free + 1,
1606                                  next_slot);
1607                 }
1608         }
1609 
1610         pr_devel("after: %lu\n", new_n->nr_leaves_on_branch);
1611 
1612         nr_leaves_on_tree = new_n->nr_leaves_on_branch;
1613 
1614         /* Excise this node if it is singly occupied by a shortcut */
1615         if (nr_free == ASSOC_ARRAY_FAN_OUT - 1) {
1616                 for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++)
1617                         if ((ptr = new_n->slots[slot]))
1618                                 break;
1619 
1620                 if (assoc_array_ptr_is_meta(ptr) &&
1621                     assoc_array_ptr_is_shortcut(ptr)) {
1622                         pr_devel("excise node %p with 1 shortcut\n", new_n);
1623                         new_s = assoc_array_ptr_to_shortcut(ptr);
1624                         new_parent = new_n->back_pointer;
1625                         slot = new_n->parent_slot;
1626                         kfree(new_n);
1627                         if (!new_parent) {
1628                                 new_s->back_pointer = NULL;
1629                                 new_s->parent_slot = 0;
1630                                 new_root = ptr;
1631                                 goto gc_complete;
1632                         }
1633 
1634                         if (assoc_array_ptr_is_shortcut(new_parent)) {
1635                                 /* We can discard any preceding shortcut also */
1636                                 struct assoc_array_shortcut *s =
1637                                         assoc_array_ptr_to_shortcut(new_parent);
1638 
1639                                 pr_devel("excise preceding shortcut\n");
1640 
1641                                 new_parent = new_s->back_pointer = s->back_pointer;
1642                                 slot = new_s->parent_slot = s->parent_slot;
1643                                 kfree(s);
1644                                 if (!new_parent) {
1645                                         new_s->back_pointer = NULL;
1646                                         new_s->parent_slot = 0;
1647                                         new_root = ptr;
1648                                         goto gc_complete;
1649                                 }
1650                         }
1651 
1652                         new_s->back_pointer = new_parent;
1653                         new_s->parent_slot = slot;
1654                         new_n = assoc_array_ptr_to_node(new_parent);
1655                         new_n->slots[slot] = ptr;
1656                         goto ascend_old_tree;
1657                 }
1658         }
1659 
1660         /* Excise any shortcuts we might encounter that point to nodes that
1661          * only contain leaves.
1662          */
1663         ptr = new_n->back_pointer;
1664         if (!ptr)
1665                 goto gc_complete;
1666 
1667         if (assoc_array_ptr_is_shortcut(ptr)) {
1668                 new_s = assoc_array_ptr_to_shortcut(ptr);
1669                 new_parent = new_s->back_pointer;
1670                 slot = new_s->parent_slot;
1671 
1672                 if (new_n->nr_leaves_on_branch <= ASSOC_ARRAY_FAN_OUT) {
1673                         struct assoc_array_node *n;
1674 
1675                         pr_devel("excise shortcut\n");
1676                         new_n->back_pointer = new_parent;
1677                         new_n->parent_slot = slot;
1678                         kfree(new_s);
1679                         if (!new_parent) {
1680                                 new_root = assoc_array_node_to_ptr(new_n);
1681                                 goto gc_complete;
1682                         }
1683 
1684                         n = assoc_array_ptr_to_node(new_parent);
1685                         n->slots[slot] = assoc_array_node_to_ptr(new_n);
1686                 }
1687         } else {
1688                 new_parent = ptr;
1689         }
1690         new_n = assoc_array_ptr_to_node(new_parent);
1691 
1692 ascend_old_tree:
1693         ptr = node->back_pointer;
1694         if (assoc_array_ptr_is_shortcut(ptr)) {
1695                 shortcut = assoc_array_ptr_to_shortcut(ptr);
1696                 slot = shortcut->parent_slot;
1697                 cursor = shortcut->back_pointer;
1698                 if (!cursor)
1699                         goto gc_complete;
1700         } else {
1701                 slot = node->parent_slot;
1702                 cursor = ptr;
1703         }
1704         BUG_ON(!cursor);
1705         node = assoc_array_ptr_to_node(cursor);
1706         slot++;
1707         goto continue_node;
1708 
1709 gc_complete:
1710         edit->set[0].to = new_root;
1711         assoc_array_apply_edit(edit);
1712         array->nr_leaves_on_tree = nr_leaves_on_tree;
1713         return 0;
1714 
1715 enomem:
1716         pr_devel("enomem\n");
1717         assoc_array_destroy_subtree(new_root, edit->ops);
1718         kfree(edit);
1719         return -ENOMEM;
1720 }