linux/lib/assoc_array.c
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   1/* Generic associative array implementation.
   2 *
   3 * See Documentation/assoc_array.txt for information.
   4 *
   5 * Copyright (C) 2013 Red Hat, Inc. All Rights Reserved.
   6 * Written by David Howells (dhowells@redhat.com)
   7 *
   8 * This program is free software; you can redistribute it and/or
   9 * modify it under the terms of the GNU General Public Licence
  10 * as published by the Free Software Foundation; either version
  11 * 2 of the Licence, or (at your option) any later version.
  12 */
  13//#define DEBUG
  14#include <linux/rcupdate.h>
  15#include <linux/slab.h>
  16#include <linux/err.h>
  17#include <linux/assoc_array_priv.h>
  18
  19/*
  20 * Iterate over an associative array.  The caller must hold the RCU read lock
  21 * or better.
  22 */
  23static int assoc_array_subtree_iterate(const struct assoc_array_ptr *root,
  24                                       const struct assoc_array_ptr *stop,
  25                                       int (*iterator)(const void *leaf,
  26                                                       void *iterator_data),
  27                                       void *iterator_data)
  28{
  29        const struct assoc_array_shortcut *shortcut;
  30        const struct assoc_array_node *node;
  31        const struct assoc_array_ptr *cursor, *ptr, *parent;
  32        unsigned long has_meta;
  33        int slot, ret;
  34
  35        cursor = root;
  36
  37begin_node:
  38        if (assoc_array_ptr_is_shortcut(cursor)) {
  39                /* Descend through a shortcut */
  40                shortcut = assoc_array_ptr_to_shortcut(cursor);
  41                smp_read_barrier_depends();
  42                cursor = ACCESS_ONCE(shortcut->next_node);
  43        }
  44
  45        node = assoc_array_ptr_to_node(cursor);
  46        smp_read_barrier_depends();
  47        slot = 0;
  48
  49        /* We perform two passes of each node.
  50         *
  51         * The first pass does all the leaves in this node.  This means we
  52         * don't miss any leaves if the node is split up by insertion whilst
  53         * we're iterating over the branches rooted here (we may, however, see
  54         * some leaves twice).
  55         */
  56        has_meta = 0;
  57        for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
  58                ptr = ACCESS_ONCE(node->slots[slot]);
  59                has_meta |= (unsigned long)ptr;
  60                if (ptr && assoc_array_ptr_is_leaf(ptr)) {
  61                        /* We need a barrier between the read of the pointer
  62                         * and dereferencing the pointer - but only if we are
  63                         * actually going to dereference it.
  64                         */
  65                        smp_read_barrier_depends();
  66
  67                        /* Invoke the callback */
  68                        ret = iterator(assoc_array_ptr_to_leaf(ptr),
  69                                       iterator_data);
  70                        if (ret)
  71                                return ret;
  72                }
  73        }
  74
  75        /* The second pass attends to all the metadata pointers.  If we follow
  76         * one of these we may find that we don't come back here, but rather go
  77         * back to a replacement node with the leaves in a different layout.
  78         *
  79         * We are guaranteed to make progress, however, as the slot number for
  80         * a particular portion of the key space cannot change - and we
  81         * continue at the back pointer + 1.
  82         */
  83        if (!(has_meta & ASSOC_ARRAY_PTR_META_TYPE))
  84                goto finished_node;
  85        slot = 0;
  86
  87continue_node:
  88        node = assoc_array_ptr_to_node(cursor);
  89        smp_read_barrier_depends();
  90
  91        for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
  92                ptr = ACCESS_ONCE(node->slots[slot]);
  93                if (assoc_array_ptr_is_meta(ptr)) {
  94                        cursor = ptr;
  95                        goto begin_node;
  96                }
  97        }
  98
  99finished_node:
 100        /* Move up to the parent (may need to skip back over a shortcut) */
 101        parent = ACCESS_ONCE(node->back_pointer);
 102        slot = node->parent_slot;
 103        if (parent == stop)
 104                return 0;
 105
 106        if (assoc_array_ptr_is_shortcut(parent)) {
 107                shortcut = assoc_array_ptr_to_shortcut(parent);
 108                smp_read_barrier_depends();
 109                cursor = parent;
 110                parent = ACCESS_ONCE(shortcut->back_pointer);
 111                slot = shortcut->parent_slot;
 112                if (parent == stop)
 113                        return 0;
 114        }
 115
 116        /* Ascend to next slot in parent node */
 117        cursor = parent;
 118        slot++;
 119        goto continue_node;
 120}
 121
 122/**
 123 * assoc_array_iterate - Pass all objects in the array to a callback
 124 * @array: The array to iterate over.
 125 * @iterator: The callback function.
 126 * @iterator_data: Private data for the callback function.
 127 *
 128 * Iterate over all the objects in an associative array.  Each one will be
 129 * presented to the iterator function.
 130 *
 131 * If the array is being modified concurrently with the iteration then it is
 132 * possible that some objects in the array will be passed to the iterator
 133 * callback more than once - though every object should be passed at least
 134 * once.  If this is undesirable then the caller must lock against modification
 135 * for the duration of this function.
 136 *
 137 * The function will return 0 if no objects were in the array or else it will
 138 * return the result of the last iterator function called.  Iteration stops
 139 * immediately if any call to the iteration function results in a non-zero
 140 * return.
 141 *
 142 * The caller should hold the RCU read lock or better if concurrent
 143 * modification is possible.
 144 */
 145int assoc_array_iterate(const struct assoc_array *array,
 146                        int (*iterator)(const void *object,
 147                                        void *iterator_data),
 148                        void *iterator_data)
 149{
 150        struct assoc_array_ptr *root = ACCESS_ONCE(array->root);
 151
 152        if (!root)
 153                return 0;
 154        return assoc_array_subtree_iterate(root, NULL, iterator, iterator_data);
 155}
 156
 157enum assoc_array_walk_status {
 158        assoc_array_walk_tree_empty,
 159        assoc_array_walk_found_terminal_node,
 160        assoc_array_walk_found_wrong_shortcut,
 161};
 162
 163struct assoc_array_walk_result {
 164        struct {
 165                struct assoc_array_node *node;  /* Node in which leaf might be found */
 166                int             level;
 167                int             slot;
 168        } terminal_node;
 169        struct {
 170                struct assoc_array_shortcut *shortcut;
 171                int             level;
 172                int             sc_level;
 173                unsigned long   sc_segments;
 174                unsigned long   dissimilarity;
 175        } wrong_shortcut;
 176};
 177
 178/*
 179 * Navigate through the internal tree looking for the closest node to the key.
 180 */
 181static enum assoc_array_walk_status
 182assoc_array_walk(const struct assoc_array *array,
 183                 const struct assoc_array_ops *ops,
 184                 const void *index_key,
 185                 struct assoc_array_walk_result *result)
 186{
 187        struct assoc_array_shortcut *shortcut;
 188        struct assoc_array_node *node;
 189        struct assoc_array_ptr *cursor, *ptr;
 190        unsigned long sc_segments, dissimilarity;
 191        unsigned long segments;
 192        int level, sc_level, next_sc_level;
 193        int slot;
 194
 195        pr_devel("-->%s()\n", __func__);
 196
 197        cursor = ACCESS_ONCE(array->root);
 198        if (!cursor)
 199                return assoc_array_walk_tree_empty;
 200
 201        level = 0;
 202
 203        /* Use segments from the key for the new leaf to navigate through the
 204         * internal tree, skipping through nodes and shortcuts that are on
 205         * route to the destination.  Eventually we'll come to a slot that is
 206         * either empty or contains a leaf at which point we've found a node in
 207         * which the leaf we're looking for might be found or into which it
 208         * should be inserted.
 209         */
 210jumped:
 211        segments = ops->get_key_chunk(index_key, level);
 212        pr_devel("segments[%d]: %lx\n", level, segments);
 213
 214        if (assoc_array_ptr_is_shortcut(cursor))
 215                goto follow_shortcut;
 216
 217consider_node:
 218        node = assoc_array_ptr_to_node(cursor);
 219        smp_read_barrier_depends();
 220
 221        slot = segments >> (level & ASSOC_ARRAY_KEY_CHUNK_MASK);
 222        slot &= ASSOC_ARRAY_FAN_MASK;
 223        ptr = ACCESS_ONCE(node->slots[slot]);
 224
 225        pr_devel("consider slot %x [ix=%d type=%lu]\n",
 226                 slot, level, (unsigned long)ptr & 3);
 227
 228        if (!assoc_array_ptr_is_meta(ptr)) {
 229                /* The node doesn't have a node/shortcut pointer in the slot
 230                 * corresponding to the index key that we have to follow.
 231                 */
 232                result->terminal_node.node = node;
 233                result->terminal_node.level = level;
 234                result->terminal_node.slot = slot;
 235                pr_devel("<--%s() = terminal_node\n", __func__);
 236                return assoc_array_walk_found_terminal_node;
 237        }
 238
 239        if (assoc_array_ptr_is_node(ptr)) {
 240                /* There is a pointer to a node in the slot corresponding to
 241                 * this index key segment, so we need to follow it.
 242                 */
 243                cursor = ptr;
 244                level += ASSOC_ARRAY_LEVEL_STEP;
 245                if ((level & ASSOC_ARRAY_KEY_CHUNK_MASK) != 0)
 246                        goto consider_node;
 247                goto jumped;
 248        }
 249
 250        /* There is a shortcut in the slot corresponding to the index key
 251         * segment.  We follow the shortcut if its partial index key matches
 252         * this leaf's.  Otherwise we need to split the shortcut.
 253         */
 254        cursor = ptr;
 255follow_shortcut:
 256        shortcut = assoc_array_ptr_to_shortcut(cursor);
 257        smp_read_barrier_depends();
 258        pr_devel("shortcut to %d\n", shortcut->skip_to_level);
 259        sc_level = level + ASSOC_ARRAY_LEVEL_STEP;
 260        BUG_ON(sc_level > shortcut->skip_to_level);
 261
 262        do {
 263                /* Check the leaf against the shortcut's index key a word at a
 264                 * time, trimming the final word (the shortcut stores the index
 265                 * key completely from the root to the shortcut's target).
 266                 */
 267                if ((sc_level & ASSOC_ARRAY_KEY_CHUNK_MASK) == 0)
 268                        segments = ops->get_key_chunk(index_key, sc_level);
 269
 270                sc_segments = shortcut->index_key[sc_level >> ASSOC_ARRAY_KEY_CHUNK_SHIFT];
 271                dissimilarity = segments ^ sc_segments;
 272
 273                if (round_up(sc_level, ASSOC_ARRAY_KEY_CHUNK_SIZE) > shortcut->skip_to_level) {
 274                        /* Trim segments that are beyond the shortcut */
 275                        int shift = shortcut->skip_to_level & ASSOC_ARRAY_KEY_CHUNK_MASK;
 276                        dissimilarity &= ~(ULONG_MAX << shift);
 277                        next_sc_level = shortcut->skip_to_level;
 278                } else {
 279                        next_sc_level = sc_level + ASSOC_ARRAY_KEY_CHUNK_SIZE;
 280                        next_sc_level = round_down(next_sc_level, ASSOC_ARRAY_KEY_CHUNK_SIZE);
 281                }
 282
 283                if (dissimilarity != 0) {
 284                        /* This shortcut points elsewhere */
 285                        result->wrong_shortcut.shortcut = shortcut;
 286                        result->wrong_shortcut.level = level;
 287                        result->wrong_shortcut.sc_level = sc_level;
 288                        result->wrong_shortcut.sc_segments = sc_segments;
 289                        result->wrong_shortcut.dissimilarity = dissimilarity;
 290                        return assoc_array_walk_found_wrong_shortcut;
 291                }
 292
 293                sc_level = next_sc_level;
 294        } while (sc_level < shortcut->skip_to_level);
 295
 296        /* The shortcut matches the leaf's index to this point. */
 297        cursor = ACCESS_ONCE(shortcut->next_node);
 298        if (((level ^ sc_level) & ~ASSOC_ARRAY_KEY_CHUNK_MASK) != 0) {
 299                level = sc_level;
 300                goto jumped;
 301        } else {
 302                level = sc_level;
 303                goto consider_node;
 304        }
 305}
 306
 307/**
 308 * assoc_array_find - Find an object by index key
 309 * @array: The associative array to search.
 310 * @ops: The operations to use.
 311 * @index_key: The key to the object.
 312 *
 313 * Find an object in an associative array by walking through the internal tree
 314 * to the node that should contain the object and then searching the leaves
 315 * there.  NULL is returned if the requested object was not found in the array.
 316 *
 317 * The caller must hold the RCU read lock or better.
 318 */
 319void *assoc_array_find(const struct assoc_array *array,
 320                       const struct assoc_array_ops *ops,
 321                       const void *index_key)
 322{
 323        struct assoc_array_walk_result result;
 324        const struct assoc_array_node *node;
 325        const struct assoc_array_ptr *ptr;
 326        const void *leaf;
 327        int slot;
 328
 329        if (assoc_array_walk(array, ops, index_key, &result) !=
 330            assoc_array_walk_found_terminal_node)
 331                return NULL;
 332
 333        node = result.terminal_node.node;
 334        smp_read_barrier_depends();
 335
 336        /* If the target key is available to us, it's has to be pointed to by
 337         * the terminal node.
 338         */
 339        for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
 340                ptr = ACCESS_ONCE(node->slots[slot]);
 341                if (ptr && assoc_array_ptr_is_leaf(ptr)) {
 342                        /* We need a barrier between the read of the pointer
 343                         * and dereferencing the pointer - but only if we are
 344                         * actually going to dereference it.
 345                         */
 346                        leaf = assoc_array_ptr_to_leaf(ptr);
 347                        smp_read_barrier_depends();
 348                        if (ops->compare_object(leaf, index_key))
 349                                return (void *)leaf;
 350                }
 351        }
 352
 353        return NULL;
 354}
 355
 356/*
 357 * Destructively iterate over an associative array.  The caller must prevent
 358 * other simultaneous accesses.
 359 */
 360static void assoc_array_destroy_subtree(struct assoc_array_ptr *root,
 361                                        const struct assoc_array_ops *ops)
 362{
 363        struct assoc_array_shortcut *shortcut;
 364        struct assoc_array_node *node;
 365        struct assoc_array_ptr *cursor, *parent = NULL;
 366        int slot = -1;
 367
 368        pr_devel("-->%s()\n", __func__);
 369
 370        cursor = root;
 371        if (!cursor) {
 372                pr_devel("empty\n");
 373                return;
 374        }
 375
 376move_to_meta:
 377        if (assoc_array_ptr_is_shortcut(cursor)) {
 378                /* Descend through a shortcut */
 379                pr_devel("[%d] shortcut\n", slot);
 380                BUG_ON(!assoc_array_ptr_is_shortcut(cursor));
 381                shortcut = assoc_array_ptr_to_shortcut(cursor);
 382                BUG_ON(shortcut->back_pointer != parent);
 383                BUG_ON(slot != -1 && shortcut->parent_slot != slot);
 384                parent = cursor;
 385                cursor = shortcut->next_node;
 386                slot = -1;
 387                BUG_ON(!assoc_array_ptr_is_node(cursor));
 388        }
 389
 390        pr_devel("[%d] node\n", slot);
 391        node = assoc_array_ptr_to_node(cursor);
 392        BUG_ON(node->back_pointer != parent);
 393        BUG_ON(slot != -1 && node->parent_slot != slot);
 394        slot = 0;
 395
 396continue_node:
 397        pr_devel("Node %p [back=%p]\n", node, node->back_pointer);
 398        for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
 399                struct assoc_array_ptr *ptr = node->slots[slot];
 400                if (!ptr)
 401                        continue;
 402                if (assoc_array_ptr_is_meta(ptr)) {
 403                        parent = cursor;
 404                        cursor = ptr;
 405                        goto move_to_meta;
 406                }
 407
 408                if (ops) {
 409                        pr_devel("[%d] free leaf\n", slot);
 410                        ops->free_object(assoc_array_ptr_to_leaf(ptr));
 411                }
 412        }
 413
 414        parent = node->back_pointer;
 415        slot = node->parent_slot;
 416        pr_devel("free node\n");
 417        kfree(node);
 418        if (!parent)
 419                return; /* Done */
 420
 421        /* Move back up to the parent (may need to free a shortcut on
 422         * the way up) */
 423        if (assoc_array_ptr_is_shortcut(parent)) {
 424                shortcut = assoc_array_ptr_to_shortcut(parent);
 425                BUG_ON(shortcut->next_node != cursor);
 426                cursor = parent;
 427                parent = shortcut->back_pointer;
 428                slot = shortcut->parent_slot;
 429                pr_devel("free shortcut\n");
 430                kfree(shortcut);
 431                if (!parent)
 432                        return;
 433
 434                BUG_ON(!assoc_array_ptr_is_node(parent));
 435        }
 436
 437        /* Ascend to next slot in parent node */
 438        pr_devel("ascend to %p[%d]\n", parent, slot);
 439        cursor = parent;
 440        node = assoc_array_ptr_to_node(cursor);
 441        slot++;
 442        goto continue_node;
 443}
 444
 445/**
 446 * assoc_array_destroy - Destroy an associative array
 447 * @array: The array to destroy.
 448 * @ops: The operations to use.
 449 *
 450 * Discard all metadata and free all objects in an associative array.  The
 451 * array will be empty and ready to use again upon completion.  This function
 452 * cannot fail.
 453 *
 454 * The caller must prevent all other accesses whilst this takes place as no
 455 * attempt is made to adjust pointers gracefully to permit RCU readlock-holding
 456 * accesses to continue.  On the other hand, no memory allocation is required.
 457 */
 458void assoc_array_destroy(struct assoc_array *array,
 459                         const struct assoc_array_ops *ops)
 460{
 461        assoc_array_destroy_subtree(array->root, ops);
 462        array->root = NULL;
 463}
 464
 465/*
 466 * Handle insertion into an empty tree.
 467 */
 468static bool assoc_array_insert_in_empty_tree(struct assoc_array_edit *edit)
 469{
 470        struct assoc_array_node *new_n0;
 471
 472        pr_devel("-->%s()\n", __func__);
 473
 474        new_n0 = kzalloc(sizeof(struct assoc_array_node), GFP_KERNEL);
 475        if (!new_n0)
 476                return false;
 477
 478        edit->new_meta[0] = assoc_array_node_to_ptr(new_n0);
 479        edit->leaf_p = &new_n0->slots[0];
 480        edit->adjust_count_on = new_n0;
 481        edit->set[0].ptr = &edit->array->root;
 482        edit->set[0].to = assoc_array_node_to_ptr(new_n0);
 483
 484        pr_devel("<--%s() = ok [no root]\n", __func__);
 485        return true;
 486}
 487
 488/*
 489 * Handle insertion into a terminal node.
 490 */
 491static bool assoc_array_insert_into_terminal_node(struct assoc_array_edit *edit,
 492                                                  const struct assoc_array_ops *ops,
 493                                                  const void *index_key,
 494                                                  struct assoc_array_walk_result *result)
 495{
 496        struct assoc_array_shortcut *shortcut, *new_s0;
 497        struct assoc_array_node *node, *new_n0, *new_n1, *side;
 498        struct assoc_array_ptr *ptr;
 499        unsigned long dissimilarity, base_seg, blank;
 500        size_t keylen;
 501        bool have_meta;
 502        int level, diff;
 503        int slot, next_slot, free_slot, i, j;
 504
 505        node    = result->terminal_node.node;
 506        level   = result->terminal_node.level;
 507        edit->segment_cache[ASSOC_ARRAY_FAN_OUT] = result->terminal_node.slot;
 508
 509        pr_devel("-->%s()\n", __func__);
 510
 511        /* We arrived at a node which doesn't have an onward node or shortcut
 512         * pointer that we have to follow.  This means that (a) the leaf we
 513         * want must go here (either by insertion or replacement) or (b) we
 514         * need to split this node and insert in one of the fragments.
 515         */
 516        free_slot = -1;
 517
 518        /* Firstly, we have to check the leaves in this node to see if there's
 519         * a matching one we should replace in place.
 520         */
 521        for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
 522                ptr = node->slots[i];
 523                if (!ptr) {
 524                        free_slot = i;
 525                        continue;
 526                }
 527                if (assoc_array_ptr_is_leaf(ptr) &&
 528                    ops->compare_object(assoc_array_ptr_to_leaf(ptr),
 529                                        index_key)) {
 530                        pr_devel("replace in slot %d\n", i);
 531                        edit->leaf_p = &node->slots[i];
 532                        edit->dead_leaf = node->slots[i];
 533                        pr_devel("<--%s() = ok [replace]\n", __func__);
 534                        return true;
 535                }
 536        }
 537
 538        /* If there is a free slot in this node then we can just insert the
 539         * leaf here.
 540         */
 541        if (free_slot >= 0) {
 542                pr_devel("insert in free slot %d\n", free_slot);
 543                edit->leaf_p = &node->slots[free_slot];
 544                edit->adjust_count_on = node;
 545                pr_devel("<--%s() = ok [insert]\n", __func__);
 546                return true;
 547        }
 548
 549        /* The node has no spare slots - so we're either going to have to split
 550         * it or insert another node before it.
 551         *
 552         * Whatever, we're going to need at least two new nodes - so allocate
 553         * those now.  We may also need a new shortcut, but we deal with that
 554         * when we need it.
 555         */
 556        new_n0 = kzalloc(sizeof(struct assoc_array_node), GFP_KERNEL);
 557        if (!new_n0)
 558                return false;
 559        edit->new_meta[0] = assoc_array_node_to_ptr(new_n0);
 560        new_n1 = kzalloc(sizeof(struct assoc_array_node), GFP_KERNEL);
 561        if (!new_n1)
 562                return false;
 563        edit->new_meta[1] = assoc_array_node_to_ptr(new_n1);
 564
 565        /* We need to find out how similar the leaves are. */
 566        pr_devel("no spare slots\n");
 567        have_meta = false;
 568        for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
 569                ptr = node->slots[i];
 570                if (assoc_array_ptr_is_meta(ptr)) {
 571                        edit->segment_cache[i] = 0xff;
 572                        have_meta = true;
 573                        continue;
 574                }
 575                base_seg = ops->get_object_key_chunk(
 576                        assoc_array_ptr_to_leaf(ptr), level);
 577                base_seg >>= level & ASSOC_ARRAY_KEY_CHUNK_MASK;
 578                edit->segment_cache[i] = base_seg & ASSOC_ARRAY_FAN_MASK;
 579        }
 580
 581        if (have_meta) {
 582                pr_devel("have meta\n");
 583                goto split_node;
 584        }
 585
 586        /* The node contains only leaves */
 587        dissimilarity = 0;
 588        base_seg = edit->segment_cache[0];
 589        for (i = 1; i < ASSOC_ARRAY_FAN_OUT; i++)
 590                dissimilarity |= edit->segment_cache[i] ^ base_seg;
 591
 592        pr_devel("only leaves; dissimilarity=%lx\n", dissimilarity);
 593
 594        if ((dissimilarity & ASSOC_ARRAY_FAN_MASK) == 0) {
 595                /* The old leaves all cluster in the same slot.  We will need
 596                 * to insert a shortcut if the new node wants to cluster with them.
 597                 */
 598                if ((edit->segment_cache[ASSOC_ARRAY_FAN_OUT] ^ base_seg) == 0)
 599                        goto all_leaves_cluster_together;
 600
 601                /* Otherwise we can just insert a new node ahead of the old
 602                 * one.
 603                 */
 604                goto present_leaves_cluster_but_not_new_leaf;
 605        }
 606
 607split_node:
 608        pr_devel("split node\n");
 609
 610        /* We need to split the current node; we know that the node doesn't
 611         * simply contain a full set of leaves that cluster together (it
 612         * contains meta pointers and/or non-clustering leaves).
 613         *
 614         * We need to expel at least two leaves out of a set consisting of the
 615         * leaves in the node and the new leaf.
 616         *
 617         * We need a new node (n0) to replace the current one and a new node to
 618         * take the expelled nodes (n1).
 619         */
 620        edit->set[0].to = assoc_array_node_to_ptr(new_n0);
 621        new_n0->back_pointer = node->back_pointer;
 622        new_n0->parent_slot = node->parent_slot;
 623        new_n1->back_pointer = assoc_array_node_to_ptr(new_n0);
 624        new_n1->parent_slot = -1; /* Need to calculate this */
 625
 626do_split_node:
 627        pr_devel("do_split_node\n");
 628
 629        new_n0->nr_leaves_on_branch = node->nr_leaves_on_branch;
 630        new_n1->nr_leaves_on_branch = 0;
 631
 632        /* Begin by finding two matching leaves.  There have to be at least two
 633         * that match - even if there are meta pointers - because any leaf that
 634         * would match a slot with a meta pointer in it must be somewhere
 635         * behind that meta pointer and cannot be here.  Further, given N
 636         * remaining leaf slots, we now have N+1 leaves to go in them.
 637         */
 638        for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
 639                slot = edit->segment_cache[i];
 640                if (slot != 0xff)
 641                        for (j = i + 1; j < ASSOC_ARRAY_FAN_OUT + 1; j++)
 642                                if (edit->segment_cache[j] == slot)
 643                                        goto found_slot_for_multiple_occupancy;
 644        }
 645found_slot_for_multiple_occupancy:
 646        pr_devel("same slot: %x %x [%02x]\n", i, j, slot);
 647        BUG_ON(i >= ASSOC_ARRAY_FAN_OUT);
 648        BUG_ON(j >= ASSOC_ARRAY_FAN_OUT + 1);
 649        BUG_ON(slot >= ASSOC_ARRAY_FAN_OUT);
 650
 651        new_n1->parent_slot = slot;
 652
 653        /* Metadata pointers cannot change slot */
 654        for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++)
 655                if (assoc_array_ptr_is_meta(node->slots[i]))
 656                        new_n0->slots[i] = node->slots[i];
 657                else
 658                        new_n0->slots[i] = NULL;
 659        BUG_ON(new_n0->slots[slot] != NULL);
 660        new_n0->slots[slot] = assoc_array_node_to_ptr(new_n1);
 661
 662        /* Filter the leaf pointers between the new nodes */
 663        free_slot = -1;
 664        next_slot = 0;
 665        for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
 666                if (assoc_array_ptr_is_meta(node->slots[i]))
 667                        continue;
 668                if (edit->segment_cache[i] == slot) {
 669                        new_n1->slots[next_slot++] = node->slots[i];
 670                        new_n1->nr_leaves_on_branch++;
 671                } else {
 672                        do {
 673                                free_slot++;
 674                        } while (new_n0->slots[free_slot] != NULL);
 675                        new_n0->slots[free_slot] = node->slots[i];
 676                }
 677        }
 678
 679        pr_devel("filtered: f=%x n=%x\n", free_slot, next_slot);
 680
 681        if (edit->segment_cache[ASSOC_ARRAY_FAN_OUT] != slot) {
 682                do {
 683                        free_slot++;
 684                } while (new_n0->slots[free_slot] != NULL);
 685                edit->leaf_p = &new_n0->slots[free_slot];
 686                edit->adjust_count_on = new_n0;
 687        } else {
 688                edit->leaf_p = &new_n1->slots[next_slot++];
 689                edit->adjust_count_on = new_n1;
 690        }
 691
 692        BUG_ON(next_slot <= 1);
 693
 694        edit->set_backpointers_to = assoc_array_node_to_ptr(new_n0);
 695        for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
 696                if (edit->segment_cache[i] == 0xff) {
 697                        ptr = node->slots[i];
 698                        BUG_ON(assoc_array_ptr_is_leaf(ptr));
 699                        if (assoc_array_ptr_is_node(ptr)) {
 700                                side = assoc_array_ptr_to_node(ptr);
 701                                edit->set_backpointers[i] = &side->back_pointer;
 702                        } else {
 703                                shortcut = assoc_array_ptr_to_shortcut(ptr);
 704                                edit->set_backpointers[i] = &shortcut->back_pointer;
 705                        }
 706                }
 707        }
 708
 709        ptr = node->back_pointer;
 710        if (!ptr)
 711                edit->set[0].ptr = &edit->array->root;
 712        else if (assoc_array_ptr_is_node(ptr))
 713                edit->set[0].ptr = &assoc_array_ptr_to_node(ptr)->slots[node->parent_slot];
 714        else
 715                edit->set[0].ptr = &assoc_array_ptr_to_shortcut(ptr)->next_node;
 716        edit->excised_meta[0] = assoc_array_node_to_ptr(node);
 717        pr_devel("<--%s() = ok [split node]\n", __func__);
 718        return true;
 719
 720present_leaves_cluster_but_not_new_leaf:
 721        /* All the old leaves cluster in the same slot, but the new leaf wants
 722         * to go into a different slot, so we create a new node to hold the new
 723         * leaf and a pointer to a new node holding all the old leaves.
 724         */
 725        pr_devel("present leaves cluster but not new leaf\n");
 726
 727        new_n0->back_pointer = node->back_pointer;
 728        new_n0->parent_slot = node->parent_slot;
 729        new_n0->nr_leaves_on_branch = node->nr_leaves_on_branch;
 730        new_n1->back_pointer = assoc_array_node_to_ptr(new_n0);
 731        new_n1->parent_slot = edit->segment_cache[0];
 732        new_n1->nr_leaves_on_branch = node->nr_leaves_on_branch;
 733        edit->adjust_count_on = new_n0;
 734
 735        for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++)
 736                new_n1->slots[i] = node->slots[i];
 737
 738        new_n0->slots[edit->segment_cache[0]] = assoc_array_node_to_ptr(new_n0);
 739        edit->leaf_p = &new_n0->slots[edit->segment_cache[ASSOC_ARRAY_FAN_OUT]];
 740
 741        edit->set[0].ptr = &assoc_array_ptr_to_node(node->back_pointer)->slots[node->parent_slot];
 742        edit->set[0].to = assoc_array_node_to_ptr(new_n0);
 743        edit->excised_meta[0] = assoc_array_node_to_ptr(node);
 744        pr_devel("<--%s() = ok [insert node before]\n", __func__);
 745        return true;
 746
 747all_leaves_cluster_together:
 748        /* All the leaves, new and old, want to cluster together in this node
 749         * in the same slot, so we have to replace this node with a shortcut to
 750         * skip over the identical parts of the key and then place a pair of
 751         * nodes, one inside the other, at the end of the shortcut and
 752         * distribute the keys between them.
 753         *
 754         * Firstly we need to work out where the leaves start diverging as a
 755         * bit position into their keys so that we know how big the shortcut
 756         * needs to be.
 757         *
 758         * We only need to make a single pass of N of the N+1 leaves because if
 759         * any keys differ between themselves at bit X then at least one of
 760         * them must also differ with the base key at bit X or before.
 761         */
 762        pr_devel("all leaves cluster together\n");
 763        diff = INT_MAX;
 764        for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
 765                int x = ops->diff_objects(assoc_array_ptr_to_leaf(node->slots[i]),
 766                                          index_key);
 767                if (x < diff) {
 768                        BUG_ON(x < 0);
 769                        diff = x;
 770                }
 771        }
 772        BUG_ON(diff == INT_MAX);
 773        BUG_ON(diff < level + ASSOC_ARRAY_LEVEL_STEP);
 774
 775        keylen = round_up(diff, ASSOC_ARRAY_KEY_CHUNK_SIZE);
 776        keylen >>= ASSOC_ARRAY_KEY_CHUNK_SHIFT;
 777
 778        new_s0 = kzalloc(sizeof(struct assoc_array_shortcut) +
 779                         keylen * sizeof(unsigned long), GFP_KERNEL);
 780        if (!new_s0)
 781                return false;
 782        edit->new_meta[2] = assoc_array_shortcut_to_ptr(new_s0);
 783
 784        edit->set[0].to = assoc_array_shortcut_to_ptr(new_s0);
 785        new_s0->back_pointer = node->back_pointer;
 786        new_s0->parent_slot = node->parent_slot;
 787        new_s0->next_node = assoc_array_node_to_ptr(new_n0);
 788        new_n0->back_pointer = assoc_array_shortcut_to_ptr(new_s0);
 789        new_n0->parent_slot = 0;
 790        new_n1->back_pointer = assoc_array_node_to_ptr(new_n0);
 791        new_n1->parent_slot = -1; /* Need to calculate this */
 792
 793        new_s0->skip_to_level = level = diff & ~ASSOC_ARRAY_LEVEL_STEP_MASK;
 794        pr_devel("skip_to_level = %d [diff %d]\n", level, diff);
 795        BUG_ON(level <= 0);
 796
 797        for (i = 0; i < keylen; i++)
 798                new_s0->index_key[i] =
 799                        ops->get_key_chunk(index_key, i * ASSOC_ARRAY_KEY_CHUNK_SIZE);
 800
 801        blank = ULONG_MAX << (level & ASSOC_ARRAY_KEY_CHUNK_MASK);
 802        pr_devel("blank off [%zu] %d: %lx\n", keylen - 1, level, blank);
 803        new_s0->index_key[keylen - 1] &= ~blank;
 804
 805        /* This now reduces to a node splitting exercise for which we'll need
 806         * to regenerate the disparity table.
 807         */
 808        for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
 809                ptr = node->slots[i];
 810                base_seg = ops->get_object_key_chunk(assoc_array_ptr_to_leaf(ptr),
 811                                                     level);
 812                base_seg >>= level & ASSOC_ARRAY_KEY_CHUNK_MASK;
 813                edit->segment_cache[i] = base_seg & ASSOC_ARRAY_FAN_MASK;
 814        }
 815
 816        base_seg = ops->get_key_chunk(index_key, level);
 817        base_seg >>= level & ASSOC_ARRAY_KEY_CHUNK_MASK;
 818        edit->segment_cache[ASSOC_ARRAY_FAN_OUT] = base_seg & ASSOC_ARRAY_FAN_MASK;
 819        goto do_split_node;
 820}
 821
 822/*
 823 * Handle insertion into the middle of a shortcut.
 824 */
 825static bool assoc_array_insert_mid_shortcut(struct assoc_array_edit *edit,
 826                                            const struct assoc_array_ops *ops,
 827                                            struct assoc_array_walk_result *result)
 828{
 829        struct assoc_array_shortcut *shortcut, *new_s0, *new_s1;
 830        struct assoc_array_node *node, *new_n0, *side;
 831        unsigned long sc_segments, dissimilarity, blank;
 832        size_t keylen;
 833        int level, sc_level, diff;
 834        int sc_slot;
 835
 836        shortcut        = result->wrong_shortcut.shortcut;
 837        level           = result->wrong_shortcut.level;
 838        sc_level        = result->wrong_shortcut.sc_level;
 839        sc_segments     = result->wrong_shortcut.sc_segments;
 840        dissimilarity   = result->wrong_shortcut.dissimilarity;
 841
 842        pr_devel("-->%s(ix=%d dis=%lx scix=%d)\n",
 843                 __func__, level, dissimilarity, sc_level);
 844
 845        /* We need to split a shortcut and insert a node between the two
 846         * pieces.  Zero-length pieces will be dispensed with entirely.
 847         *
 848         * First of all, we need to find out in which level the first
 849         * difference was.
 850         */
 851        diff = __ffs(dissimilarity);
 852        diff &= ~ASSOC_ARRAY_LEVEL_STEP_MASK;
 853        diff += sc_level & ~ASSOC_ARRAY_KEY_CHUNK_MASK;
 854        pr_devel("diff=%d\n", diff);
 855
 856        if (!shortcut->back_pointer) {
 857                edit->set[0].ptr = &edit->array->root;
 858        } else if (assoc_array_ptr_is_node(shortcut->back_pointer)) {
 859                node = assoc_array_ptr_to_node(shortcut->back_pointer);
 860                edit->set[0].ptr = &node->slots[shortcut->parent_slot];
 861        } else {
 862                BUG();
 863        }
 864
 865        edit->excised_meta[0] = assoc_array_shortcut_to_ptr(shortcut);
 866
 867        /* Create a new node now since we're going to need it anyway */
 868        new_n0 = kzalloc(sizeof(struct assoc_array_node), GFP_KERNEL);
 869        if (!new_n0)
 870                return false;
 871        edit->new_meta[0] = assoc_array_node_to_ptr(new_n0);
 872        edit->adjust_count_on = new_n0;
 873
 874        /* Insert a new shortcut before the new node if this segment isn't of
 875         * zero length - otherwise we just connect the new node directly to the
 876         * parent.
 877         */
 878        level += ASSOC_ARRAY_LEVEL_STEP;
 879        if (diff > level) {
 880                pr_devel("pre-shortcut %d...%d\n", level, diff);
 881                keylen = round_up(diff, ASSOC_ARRAY_KEY_CHUNK_SIZE);
 882                keylen >>= ASSOC_ARRAY_KEY_CHUNK_SHIFT;
 883
 884                new_s0 = kzalloc(sizeof(struct assoc_array_shortcut) +
 885                                 keylen * sizeof(unsigned long), GFP_KERNEL);
 886                if (!new_s0)
 887                        return false;
 888                edit->new_meta[1] = assoc_array_shortcut_to_ptr(new_s0);
 889                edit->set[0].to = assoc_array_shortcut_to_ptr(new_s0);
 890                new_s0->back_pointer = shortcut->back_pointer;
 891                new_s0->parent_slot = shortcut->parent_slot;
 892                new_s0->next_node = assoc_array_node_to_ptr(new_n0);
 893                new_s0->skip_to_level = diff;
 894
 895                new_n0->back_pointer = assoc_array_shortcut_to_ptr(new_s0);
 896                new_n0->parent_slot = 0;
 897
 898                memcpy(new_s0->index_key, shortcut->index_key,
 899                       keylen * sizeof(unsigned long));
 900
 901                blank = ULONG_MAX << (diff & ASSOC_ARRAY_KEY_CHUNK_MASK);
 902                pr_devel("blank off [%zu] %d: %lx\n", keylen - 1, diff, blank);
 903                new_s0->index_key[keylen - 1] &= ~blank;
 904        } else {
 905                pr_devel("no pre-shortcut\n");
 906                edit->set[0].to = assoc_array_node_to_ptr(new_n0);
 907                new_n0->back_pointer = shortcut->back_pointer;
 908                new_n0->parent_slot = shortcut->parent_slot;
 909        }
 910
 911        side = assoc_array_ptr_to_node(shortcut->next_node);
 912        new_n0->nr_leaves_on_branch = side->nr_leaves_on_branch;
 913
 914        /* We need to know which slot in the new node is going to take a
 915         * metadata pointer.
 916         */
 917        sc_slot = sc_segments >> (diff & ASSOC_ARRAY_KEY_CHUNK_MASK);
 918        sc_slot &= ASSOC_ARRAY_FAN_MASK;
 919
 920        pr_devel("new slot %lx >> %d -> %d\n",
 921                 sc_segments, diff & ASSOC_ARRAY_KEY_CHUNK_MASK, sc_slot);
 922
 923        /* Determine whether we need to follow the new node with a replacement
 924         * for the current shortcut.  We could in theory reuse the current
 925         * shortcut if its parent slot number doesn't change - but that's a
 926         * 1-in-16 chance so not worth expending the code upon.
 927         */
 928        level = diff + ASSOC_ARRAY_LEVEL_STEP;
 929        if (level < shortcut->skip_to_level) {
 930                pr_devel("post-shortcut %d...%d\n", level, shortcut->skip_to_level);
 931                keylen = round_up(shortcut->skip_to_level, ASSOC_ARRAY_KEY_CHUNK_SIZE);
 932                keylen >>= ASSOC_ARRAY_KEY_CHUNK_SHIFT;
 933
 934                new_s1 = kzalloc(sizeof(struct assoc_array_shortcut) +
 935                                 keylen * sizeof(unsigned long), GFP_KERNEL);
 936                if (!new_s1)
 937                        return false;
 938                edit->new_meta[2] = assoc_array_shortcut_to_ptr(new_s1);
 939
 940                new_s1->back_pointer = assoc_array_node_to_ptr(new_n0);
 941                new_s1->parent_slot = sc_slot;
 942                new_s1->next_node = shortcut->next_node;
 943                new_s1->skip_to_level = shortcut->skip_to_level;
 944
 945                new_n0->slots[sc_slot] = assoc_array_shortcut_to_ptr(new_s1);
 946
 947                memcpy(new_s1->index_key, shortcut->index_key,
 948                       keylen * sizeof(unsigned long));
 949
 950                edit->set[1].ptr = &side->back_pointer;
 951                edit->set[1].to = assoc_array_shortcut_to_ptr(new_s1);
 952        } else {
 953                pr_devel("no post-shortcut\n");
 954
 955                /* We don't have to replace the pointed-to node as long as we
 956                 * use memory barriers to make sure the parent slot number is
 957                 * changed before the back pointer (the parent slot number is
 958                 * irrelevant to the old parent shortcut).
 959                 */
 960                new_n0->slots[sc_slot] = shortcut->next_node;
 961                edit->set_parent_slot[0].p = &side->parent_slot;
 962                edit->set_parent_slot[0].to = sc_slot;
 963                edit->set[1].ptr = &side->back_pointer;
 964                edit->set[1].to = assoc_array_node_to_ptr(new_n0);
 965        }
 966
 967        /* Install the new leaf in a spare slot in the new node. */
 968        if (sc_slot == 0)
 969                edit->leaf_p = &new_n0->slots[1];
 970        else
 971                edit->leaf_p = &new_n0->slots[0];
 972
 973        pr_devel("<--%s() = ok [split shortcut]\n", __func__);
 974        return edit;
 975}
 976
 977/**
 978 * assoc_array_insert - Script insertion of an object into an associative array
 979 * @array: The array to insert into.
 980 * @ops: The operations to use.
 981 * @index_key: The key to insert at.
 982 * @object: The object to insert.
 983 *
 984 * Precalculate and preallocate a script for the insertion or replacement of an
 985 * object in an associative array.  This results in an edit script that can
 986 * either be applied or cancelled.
 987 *
 988 * The function returns a pointer to an edit script or -ENOMEM.
 989 *
 990 * The caller should lock against other modifications and must continue to hold
 991 * the lock until assoc_array_apply_edit() has been called.
 992 *
 993 * Accesses to the tree may take place concurrently with this function,
 994 * provided they hold the RCU read lock.
 995 */
 996struct assoc_array_edit *assoc_array_insert(struct assoc_array *array,
 997                                            const struct assoc_array_ops *ops,
 998                                            const void *index_key,
 999                                            void *object)
1000{
1001        struct assoc_array_walk_result result;
1002        struct assoc_array_edit *edit;
1003
1004        pr_devel("-->%s()\n", __func__);
1005
1006        /* The leaf pointer we're given must not have the bottom bit set as we
1007         * use those for type-marking the pointer.  NULL pointers are also not
1008         * allowed as they indicate an empty slot but we have to allow them
1009         * here as they can be updated later.
1010         */
1011        BUG_ON(assoc_array_ptr_is_meta(object));
1012
1013        edit = kzalloc(sizeof(struct assoc_array_edit), GFP_KERNEL);
1014        if (!edit)
1015                return ERR_PTR(-ENOMEM);
1016        edit->array = array;
1017        edit->ops = ops;
1018        edit->leaf = assoc_array_leaf_to_ptr(object);
1019        edit->adjust_count_by = 1;
1020
1021        switch (assoc_array_walk(array, ops, index_key, &result)) {
1022        case assoc_array_walk_tree_empty:
1023                /* Allocate a root node if there isn't one yet */
1024                if (!assoc_array_insert_in_empty_tree(edit))
1025                        goto enomem;
1026                return edit;
1027
1028        case assoc_array_walk_found_terminal_node:
1029                /* We found a node that doesn't have a node/shortcut pointer in
1030                 * the slot corresponding to the index key that we have to
1031                 * follow.
1032                 */
1033                if (!assoc_array_insert_into_terminal_node(edit, ops, index_key,
1034                                                           &result))
1035                        goto enomem;
1036                return edit;
1037
1038        case assoc_array_walk_found_wrong_shortcut:
1039                /* We found a shortcut that didn't match our key in a slot we
1040                 * needed to follow.
1041                 */
1042                if (!assoc_array_insert_mid_shortcut(edit, ops, &result))
1043                        goto enomem;
1044                return edit;
1045        }
1046
1047enomem:
1048        /* Clean up after an out of memory error */
1049        pr_devel("enomem\n");
1050        assoc_array_cancel_edit(edit);
1051        return ERR_PTR(-ENOMEM);
1052}
1053
1054/**
1055 * assoc_array_insert_set_object - Set the new object pointer in an edit script
1056 * @edit: The edit script to modify.
1057 * @object: The object pointer to set.
1058 *
1059 * Change the object to be inserted in an edit script.  The object pointed to
1060 * by the old object is not freed.  This must be done prior to applying the
1061 * script.
1062 */
1063void assoc_array_insert_set_object(struct assoc_array_edit *edit, void *object)
1064{
1065        BUG_ON(!object);
1066        edit->leaf = assoc_array_leaf_to_ptr(object);
1067}
1068
1069struct assoc_array_delete_collapse_context {
1070        struct assoc_array_node *node;
1071        const void              *skip_leaf;
1072        int                     slot;
1073};
1074
1075/*
1076 * Subtree collapse to node iterator.
1077 */
1078static int assoc_array_delete_collapse_iterator(const void *leaf,
1079                                                void *iterator_data)
1080{
1081        struct assoc_array_delete_collapse_context *collapse = iterator_data;
1082
1083        if (leaf == collapse->skip_leaf)
1084                return 0;
1085
1086        BUG_ON(collapse->slot >= ASSOC_ARRAY_FAN_OUT);
1087
1088        collapse->node->slots[collapse->slot++] = assoc_array_leaf_to_ptr(leaf);
1089        return 0;
1090}
1091
1092/**
1093 * assoc_array_delete - Script deletion of an object from an associative array
1094 * @array: The array to search.
1095 * @ops: The operations to use.
1096 * @index_key: The key to the object.
1097 *
1098 * Precalculate and preallocate a script for the deletion of an object from an
1099 * associative array.  This results in an edit script that can either be
1100 * applied or cancelled.
1101 *
1102 * The function returns a pointer to an edit script if the object was found,
1103 * NULL if the object was not found or -ENOMEM.
1104 *
1105 * The caller should lock against other modifications and must continue to hold
1106 * the lock until assoc_array_apply_edit() has been called.
1107 *
1108 * Accesses to the tree may take place concurrently with this function,
1109 * provided they hold the RCU read lock.
1110 */
1111struct assoc_array_edit *assoc_array_delete(struct assoc_array *array,
1112                                            const struct assoc_array_ops *ops,
1113                                            const void *index_key)
1114{
1115        struct assoc_array_delete_collapse_context collapse;
1116        struct assoc_array_walk_result result;
1117        struct assoc_array_node *node, *new_n0;
1118        struct assoc_array_edit *edit;
1119        struct assoc_array_ptr *ptr;
1120        bool has_meta;
1121        int slot, i;
1122
1123        pr_devel("-->%s()\n", __func__);
1124
1125        edit = kzalloc(sizeof(struct assoc_array_edit), GFP_KERNEL);
1126        if (!edit)
1127                return ERR_PTR(-ENOMEM);
1128        edit->array = array;
1129        edit->ops = ops;
1130        edit->adjust_count_by = -1;
1131
1132        switch (assoc_array_walk(array, ops, index_key, &result)) {
1133        case assoc_array_walk_found_terminal_node:
1134                /* We found a node that should contain the leaf we've been
1135                 * asked to remove - *if* it's in the tree.
1136                 */
1137                pr_devel("terminal_node\n");
1138                node = result.terminal_node.node;
1139
1140                for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
1141                        ptr = node->slots[slot];
1142                        if (ptr &&
1143                            assoc_array_ptr_is_leaf(ptr) &&
1144                            ops->compare_object(assoc_array_ptr_to_leaf(ptr),
1145                                                index_key))
1146                                goto found_leaf;
1147                }
1148        case assoc_array_walk_tree_empty:
1149        case assoc_array_walk_found_wrong_shortcut:
1150        default:
1151                assoc_array_cancel_edit(edit);
1152                pr_devel("not found\n");
1153                return NULL;
1154        }
1155
1156found_leaf:
1157        BUG_ON(array->nr_leaves_on_tree <= 0);
1158
1159        /* In the simplest form of deletion we just clear the slot and release
1160         * the leaf after a suitable interval.
1161         */
1162        edit->dead_leaf = node->slots[slot];
1163        edit->set[0].ptr = &node->slots[slot];
1164        edit->set[0].to = NULL;
1165        edit->adjust_count_on = node;
1166
1167        /* If that concludes erasure of the last leaf, then delete the entire
1168         * internal array.
1169         */
1170        if (array->nr_leaves_on_tree == 1) {
1171                edit->set[1].ptr = &array->root;
1172                edit->set[1].to = NULL;
1173                edit->adjust_count_on = NULL;
1174                edit->excised_subtree = array->root;
1175                pr_devel("all gone\n");
1176                return edit;
1177        }
1178
1179        /* However, we'd also like to clear up some metadata blocks if we
1180         * possibly can.
1181         *
1182         * We go for a simple algorithm of: if this node has FAN_OUT or fewer
1183         * leaves in it, then attempt to collapse it - and attempt to
1184         * recursively collapse up the tree.
1185         *
1186         * We could also try and collapse in partially filled subtrees to take
1187         * up space in this node.
1188         */
1189        if (node->nr_leaves_on_branch <= ASSOC_ARRAY_FAN_OUT + 1) {
1190                struct assoc_array_node *parent, *grandparent;
1191                struct assoc_array_ptr *ptr;
1192
1193                /* First of all, we need to know if this node has metadata so
1194                 * that we don't try collapsing if all the leaves are already
1195                 * here.
1196                 */
1197                has_meta = false;
1198                for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
1199                        ptr = node->slots[i];
1200                        if (assoc_array_ptr_is_meta(ptr)) {
1201                                has_meta = true;
1202                                break;
1203                        }
1204                }
1205
1206                pr_devel("leaves: %ld [m=%d]\n",
1207                         node->nr_leaves_on_branch - 1, has_meta);
1208
1209                /* Look further up the tree to see if we can collapse this node
1210                 * into a more proximal node too.
1211                 */
1212                parent = node;
1213        collapse_up:
1214                pr_devel("collapse subtree: %ld\n", parent->nr_leaves_on_branch);
1215
1216                ptr = parent->back_pointer;
1217                if (!ptr)
1218                        goto do_collapse;
1219                if (assoc_array_ptr_is_shortcut(ptr)) {
1220                        struct assoc_array_shortcut *s = assoc_array_ptr_to_shortcut(ptr);
1221                        ptr = s->back_pointer;
1222                        if (!ptr)
1223                                goto do_collapse;
1224                }
1225
1226                grandparent = assoc_array_ptr_to_node(ptr);
1227                if (grandparent->nr_leaves_on_branch <= ASSOC_ARRAY_FAN_OUT + 1) {
1228                        parent = grandparent;
1229                        goto collapse_up;
1230                }
1231
1232        do_collapse:
1233                /* There's no point collapsing if the original node has no meta
1234                 * pointers to discard and if we didn't merge into one of that
1235                 * node's ancestry.
1236                 */
1237                if (has_meta || parent != node) {
1238                        node = parent;
1239
1240                        /* Create a new node to collapse into */
1241                        new_n0 = kzalloc(sizeof(struct assoc_array_node), GFP_KERNEL);
1242                        if (!new_n0)
1243                                goto enomem;
1244                        edit->new_meta[0] = assoc_array_node_to_ptr(new_n0);
1245
1246                        new_n0->back_pointer = node->back_pointer;
1247                        new_n0->parent_slot = node->parent_slot;
1248                        new_n0->nr_leaves_on_branch = node->nr_leaves_on_branch;
1249                        edit->adjust_count_on = new_n0;
1250
1251                        collapse.node = new_n0;
1252                        collapse.skip_leaf = assoc_array_ptr_to_leaf(edit->dead_leaf);
1253                        collapse.slot = 0;
1254                        assoc_array_subtree_iterate(assoc_array_node_to_ptr(node),
1255                                                    node->back_pointer,
1256                                                    assoc_array_delete_collapse_iterator,
1257                                                    &collapse);
1258                        pr_devel("collapsed %d,%lu\n", collapse.slot, new_n0->nr_leaves_on_branch);
1259                        BUG_ON(collapse.slot != new_n0->nr_leaves_on_branch - 1);
1260
1261                        if (!node->back_pointer) {
1262                                edit->set[1].ptr = &array->root;
1263                        } else if (assoc_array_ptr_is_leaf(node->back_pointer)) {
1264                                BUG();
1265                        } else if (assoc_array_ptr_is_node(node->back_pointer)) {
1266                                struct assoc_array_node *p =
1267                                        assoc_array_ptr_to_node(node->back_pointer);
1268                                edit->set[1].ptr = &p->slots[node->parent_slot];
1269                        } else if (assoc_array_ptr_is_shortcut(node->back_pointer)) {
1270                                struct assoc_array_shortcut *s =
1271                                        assoc_array_ptr_to_shortcut(node->back_pointer);
1272                                edit->set[1].ptr = &s->next_node;
1273                        }
1274                        edit->set[1].to = assoc_array_node_to_ptr(new_n0);
1275                        edit->excised_subtree = assoc_array_node_to_ptr(node);
1276                }
1277        }
1278
1279        return edit;
1280
1281enomem:
1282        /* Clean up after an out of memory error */
1283        pr_devel("enomem\n");
1284        assoc_array_cancel_edit(edit);
1285        return ERR_PTR(-ENOMEM);
1286}
1287
1288/**
1289 * assoc_array_clear - Script deletion of all objects from an associative array
1290 * @array: The array to clear.
1291 * @ops: The operations to use.
1292 *
1293 * Precalculate and preallocate a script for the deletion of all the objects
1294 * from an associative array.  This results in an edit script that can either
1295 * be applied or cancelled.
1296 *
1297 * The function returns a pointer to an edit script if there are objects to be
1298 * deleted, NULL if there are no objects in the array or -ENOMEM.
1299 *
1300 * The caller should lock against other modifications and must continue to hold
1301 * the lock until assoc_array_apply_edit() has been called.
1302 *
1303 * Accesses to the tree may take place concurrently with this function,
1304 * provided they hold the RCU read lock.
1305 */
1306struct assoc_array_edit *assoc_array_clear(struct assoc_array *array,
1307                                           const struct assoc_array_ops *ops)
1308{
1309        struct assoc_array_edit *edit;
1310
1311        pr_devel("-->%s()\n", __func__);
1312
1313        if (!array->root)
1314                return NULL;
1315
1316        edit = kzalloc(sizeof(struct assoc_array_edit), GFP_KERNEL);
1317        if (!edit)
1318                return ERR_PTR(-ENOMEM);
1319        edit->array = array;
1320        edit->ops = ops;
1321        edit->set[1].ptr = &array->root;
1322        edit->set[1].to = NULL;
1323        edit->excised_subtree = array->root;
1324        edit->ops_for_excised_subtree = ops;
1325        pr_devel("all gone\n");
1326        return edit;
1327}
1328
1329/*
1330 * Handle the deferred destruction after an applied edit.
1331 */
1332static void assoc_array_rcu_cleanup(struct rcu_head *head)
1333{
1334        struct assoc_array_edit *edit =
1335                container_of(head, struct assoc_array_edit, rcu);
1336        int i;
1337
1338        pr_devel("-->%s()\n", __func__);
1339
1340        if (edit->dead_leaf)
1341                edit->ops->free_object(assoc_array_ptr_to_leaf(edit->dead_leaf));
1342        for (i = 0; i < ARRAY_SIZE(edit->excised_meta); i++)
1343                if (edit->excised_meta[i])
1344                        kfree(assoc_array_ptr_to_node(edit->excised_meta[i]));
1345
1346        if (edit->excised_subtree) {
1347                BUG_ON(assoc_array_ptr_is_leaf(edit->excised_subtree));
1348                if (assoc_array_ptr_is_node(edit->excised_subtree)) {
1349                        struct assoc_array_node *n =
1350                                assoc_array_ptr_to_node(edit->excised_subtree);
1351                        n->back_pointer = NULL;
1352                } else {
1353                        struct assoc_array_shortcut *s =
1354                                assoc_array_ptr_to_shortcut(edit->excised_subtree);
1355                        s->back_pointer = NULL;
1356                }
1357                assoc_array_destroy_subtree(edit->excised_subtree,
1358                                            edit->ops_for_excised_subtree);
1359        }
1360
1361        kfree(edit);
1362}
1363
1364/**
1365 * assoc_array_apply_edit - Apply an edit script to an associative array
1366 * @edit: The script to apply.
1367 *
1368 * Apply an edit script to an associative array to effect an insertion,
1369 * deletion or clearance.  As the edit script includes preallocated memory,
1370 * this is guaranteed not to fail.
1371 *
1372 * The edit script, dead objects and dead metadata will be scheduled for
1373 * destruction after an RCU grace period to permit those doing read-only
1374 * accesses on the array to continue to do so under the RCU read lock whilst
1375 * the edit is taking place.
1376 */
1377void assoc_array_apply_edit(struct assoc_array_edit *edit)
1378{
1379        struct assoc_array_shortcut *shortcut;
1380        struct assoc_array_node *node;
1381        struct assoc_array_ptr *ptr;
1382        int i;
1383
1384        pr_devel("-->%s()\n", __func__);
1385
1386        smp_wmb();
1387        if (edit->leaf_p)
1388                *edit->leaf_p = edit->leaf;
1389
1390        smp_wmb();
1391        for (i = 0; i < ARRAY_SIZE(edit->set_parent_slot); i++)
1392                if (edit->set_parent_slot[i].p)
1393                        *edit->set_parent_slot[i].p = edit->set_parent_slot[i].to;
1394
1395        smp_wmb();
1396        for (i = 0; i < ARRAY_SIZE(edit->set_backpointers); i++)
1397                if (edit->set_backpointers[i])
1398                        *edit->set_backpointers[i] = edit->set_backpointers_to;
1399
1400        smp_wmb();
1401        for (i = 0; i < ARRAY_SIZE(edit->set); i++)
1402                if (edit->set[i].ptr)
1403                        *edit->set[i].ptr = edit->set[i].to;
1404
1405        if (edit->array->root == NULL) {
1406                edit->array->nr_leaves_on_tree = 0;
1407        } else if (edit->adjust_count_on) {
1408                node = edit->adjust_count_on;
1409                for (;;) {
1410                        node->nr_leaves_on_branch += edit->adjust_count_by;
1411
1412                        ptr = node->back_pointer;
1413                        if (!ptr)
1414                                break;
1415                        if (assoc_array_ptr_is_shortcut(ptr)) {
1416                                shortcut = assoc_array_ptr_to_shortcut(ptr);
1417                                ptr = shortcut->back_pointer;
1418                                if (!ptr)
1419                                        break;
1420                        }
1421                        BUG_ON(!assoc_array_ptr_is_node(ptr));
1422                        node = assoc_array_ptr_to_node(ptr);
1423                }
1424
1425                edit->array->nr_leaves_on_tree += edit->adjust_count_by;
1426        }
1427
1428        call_rcu(&edit->rcu, assoc_array_rcu_cleanup);
1429}
1430
1431/**
1432 * assoc_array_cancel_edit - Discard an edit script.
1433 * @edit: The script to discard.
1434 *
1435 * Free an edit script and all the preallocated data it holds without making
1436 * any changes to the associative array it was intended for.
1437 *
1438 * NOTE!  In the case of an insertion script, this does _not_ release the leaf
1439 * that was to be inserted.  That is left to the caller.
1440 */
1441void assoc_array_cancel_edit(struct assoc_array_edit *edit)
1442{
1443        struct assoc_array_ptr *ptr;
1444        int i;
1445
1446        pr_devel("-->%s()\n", __func__);
1447
1448        /* Clean up after an out of memory error */
1449        for (i = 0; i < ARRAY_SIZE(edit->new_meta); i++) {
1450                ptr = edit->new_meta[i];
1451                if (ptr) {
1452                        if (assoc_array_ptr_is_node(ptr))
1453                                kfree(assoc_array_ptr_to_node(ptr));
1454                        else
1455                                kfree(assoc_array_ptr_to_shortcut(ptr));
1456                }
1457        }
1458        kfree(edit);
1459}
1460
1461/**
1462 * assoc_array_gc - Garbage collect an associative array.
1463 * @array: The array to clean.
1464 * @ops: The operations to use.
1465 * @iterator: A callback function to pass judgement on each object.
1466 * @iterator_data: Private data for the callback function.
1467 *
1468 * Collect garbage from an associative array and pack down the internal tree to
1469 * save memory.
1470 *
1471 * The iterator function is asked to pass judgement upon each object in the
1472 * array.  If it returns false, the object is discard and if it returns true,
1473 * the object is kept.  If it returns true, it must increment the object's
1474 * usage count (or whatever it needs to do to retain it) before returning.
1475 *
1476 * This function returns 0 if successful or -ENOMEM if out of memory.  In the
1477 * latter case, the array is not changed.
1478 *
1479 * The caller should lock against other modifications and must continue to hold
1480 * the lock until assoc_array_apply_edit() has been called.
1481 *
1482 * Accesses to the tree may take place concurrently with this function,
1483 * provided they hold the RCU read lock.
1484 */
1485int assoc_array_gc(struct assoc_array *array,
1486                   const struct assoc_array_ops *ops,
1487                   bool (*iterator)(void *object, void *iterator_data),
1488                   void *iterator_data)
1489{
1490        struct assoc_array_shortcut *shortcut, *new_s;
1491        struct assoc_array_node *node, *new_n;
1492        struct assoc_array_edit *edit;
1493        struct assoc_array_ptr *cursor, *ptr;
1494        struct assoc_array_ptr *new_root, *new_parent, **new_ptr_pp;
1495        unsigned long nr_leaves_on_tree;
1496        int keylen, slot, nr_free, next_slot, i;
1497
1498        pr_devel("-->%s()\n", __func__);
1499
1500        if (!array->root)
1501                return 0;
1502
1503        edit = kzalloc(sizeof(struct assoc_array_edit), GFP_KERNEL);
1504        if (!edit)
1505                return -ENOMEM;
1506        edit->array = array;
1507        edit->ops = ops;
1508        edit->ops_for_excised_subtree = ops;
1509        edit->set[0].ptr = &array->root;
1510        edit->excised_subtree = array->root;
1511
1512        new_root = new_parent = NULL;
1513        new_ptr_pp = &new_root;
1514        cursor = array->root;
1515
1516descend:
1517        /* If this point is a shortcut, then we need to duplicate it and
1518         * advance the target cursor.
1519         */
1520        if (assoc_array_ptr_is_shortcut(cursor)) {
1521                shortcut = assoc_array_ptr_to_shortcut(cursor);
1522                keylen = round_up(shortcut->skip_to_level, ASSOC_ARRAY_KEY_CHUNK_SIZE);
1523                keylen >>= ASSOC_ARRAY_KEY_CHUNK_SHIFT;
1524                new_s = kmalloc(sizeof(struct assoc_array_shortcut) +
1525                                keylen * sizeof(unsigned long), GFP_KERNEL);
1526                if (!new_s)
1527                        goto enomem;
1528                pr_devel("dup shortcut %p -> %p\n", shortcut, new_s);
1529                memcpy(new_s, shortcut, (sizeof(struct assoc_array_shortcut) +
1530                                         keylen * sizeof(unsigned long)));
1531                new_s->back_pointer = new_parent;
1532                new_s->parent_slot = shortcut->parent_slot;
1533                *new_ptr_pp = new_parent = assoc_array_shortcut_to_ptr(new_s);
1534                new_ptr_pp = &new_s->next_node;
1535                cursor = shortcut->next_node;
1536        }
1537
1538        /* Duplicate the node at this position */
1539        node = assoc_array_ptr_to_node(cursor);
1540        new_n = kzalloc(sizeof(struct assoc_array_node), GFP_KERNEL);
1541        if (!new_n)
1542                goto enomem;
1543        pr_devel("dup node %p -> %p\n", node, new_n);
1544        new_n->back_pointer = new_parent;
1545        new_n->parent_slot = node->parent_slot;
1546        *new_ptr_pp = new_parent = assoc_array_node_to_ptr(new_n);
1547        new_ptr_pp = NULL;
1548        slot = 0;
1549
1550continue_node:
1551        /* Filter across any leaves and gc any subtrees */
1552        for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
1553                ptr = node->slots[slot];
1554                if (!ptr)
1555                        continue;
1556
1557                if (assoc_array_ptr_is_leaf(ptr)) {
1558                        if (iterator(assoc_array_ptr_to_leaf(ptr),
1559                                     iterator_data))
1560                                /* The iterator will have done any reference
1561                                 * counting on the object for us.
1562                                 */
1563                                new_n->slots[slot] = ptr;
1564                        continue;
1565                }
1566
1567                new_ptr_pp = &new_n->slots[slot];
1568                cursor = ptr;
1569                goto descend;
1570        }
1571
1572        pr_devel("-- compress node %p --\n", new_n);
1573
1574        /* Count up the number of empty slots in this node and work out the
1575         * subtree leaf count.
1576         */
1577        new_n->nr_leaves_on_branch = 0;
1578        nr_free = 0;
1579        for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
1580                ptr = new_n->slots[slot];
1581                if (!ptr)
1582                        nr_free++;
1583                else if (assoc_array_ptr_is_leaf(ptr))
1584                        new_n->nr_leaves_on_branch++;
1585        }
1586        pr_devel("free=%d, leaves=%lu\n", nr_free, new_n->nr_leaves_on_branch);
1587
1588        /* See what we can fold in */
1589        next_slot = 0;
1590        for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
1591                struct assoc_array_shortcut *s;
1592                struct assoc_array_node *child;
1593
1594                ptr = new_n->slots[slot];
1595                if (!ptr || assoc_array_ptr_is_leaf(ptr))
1596                        continue;
1597
1598                s = NULL;
1599                if (assoc_array_ptr_is_shortcut(ptr)) {
1600                        s = assoc_array_ptr_to_shortcut(ptr);
1601                        ptr = s->next_node;
1602                }
1603
1604                child = assoc_array_ptr_to_node(ptr);
1605                new_n->nr_leaves_on_branch += child->nr_leaves_on_branch;
1606
1607                if (child->nr_leaves_on_branch <= nr_free + 1) {
1608                        /* Fold the child node into this one */
1609                        pr_devel("[%d] fold node %lu/%d [nx %d]\n",
1610                                 slot, child->nr_leaves_on_branch, nr_free + 1,
1611                                 next_slot);
1612
1613                        /* We would already have reaped an intervening shortcut
1614                         * on the way back up the tree.
1615                         */
1616                        BUG_ON(s);
1617
1618                        new_n->slots[slot] = NULL;
1619                        nr_free++;
1620                        if (slot < next_slot)
1621                                next_slot = slot;
1622                        for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
1623                                struct assoc_array_ptr *p = child->slots[i];
1624                                if (!p)
1625                                        continue;
1626                                BUG_ON(assoc_array_ptr_is_meta(p));
1627                                while (new_n->slots[next_slot])
1628                                        next_slot++;
1629                                BUG_ON(next_slot >= ASSOC_ARRAY_FAN_OUT);
1630                                new_n->slots[next_slot++] = p;
1631                                nr_free--;
1632                        }
1633                        kfree(child);
1634                } else {
1635                        pr_devel("[%d] retain node %lu/%d [nx %d]\n",
1636                                 slot, child->nr_leaves_on_branch, nr_free + 1,
1637                                 next_slot);
1638                }
1639        }
1640
1641        pr_devel("after: %lu\n", new_n->nr_leaves_on_branch);
1642
1643        nr_leaves_on_tree = new_n->nr_leaves_on_branch;
1644
1645        /* Excise this node if it is singly occupied by a shortcut */
1646        if (nr_free == ASSOC_ARRAY_FAN_OUT - 1) {
1647                for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++)
1648                        if ((ptr = new_n->slots[slot]))
1649                                break;
1650
1651                if (assoc_array_ptr_is_meta(ptr) &&
1652                    assoc_array_ptr_is_shortcut(ptr)) {
1653                        pr_devel("excise node %p with 1 shortcut\n", new_n);
1654                        new_s = assoc_array_ptr_to_shortcut(ptr);
1655                        new_parent = new_n->back_pointer;
1656                        slot = new_n->parent_slot;
1657                        kfree(new_n);
1658                        if (!new_parent) {
1659                                new_s->back_pointer = NULL;
1660                                new_s->parent_slot = 0;
1661                                new_root = ptr;
1662                                goto gc_complete;
1663                        }
1664
1665                        if (assoc_array_ptr_is_shortcut(new_parent)) {
1666                                /* We can discard any preceding shortcut also */
1667                                struct assoc_array_shortcut *s =
1668                                        assoc_array_ptr_to_shortcut(new_parent);
1669
1670                                pr_devel("excise preceding shortcut\n");
1671
1672                                new_parent = new_s->back_pointer = s->back_pointer;
1673                                slot = new_s->parent_slot = s->parent_slot;
1674                                kfree(s);
1675                                if (!new_parent) {
1676                                        new_s->back_pointer = NULL;
1677                                        new_s->parent_slot = 0;
1678                                        new_root = ptr;
1679                                        goto gc_complete;
1680                                }
1681                        }
1682
1683                        new_s->back_pointer = new_parent;
1684                        new_s->parent_slot = slot;
1685                        new_n = assoc_array_ptr_to_node(new_parent);
1686                        new_n->slots[slot] = ptr;
1687                        goto ascend_old_tree;
1688                }
1689        }
1690
1691        /* Excise any shortcuts we might encounter that point to nodes that
1692         * only contain leaves.
1693         */
1694        ptr = new_n->back_pointer;
1695        if (!ptr)
1696                goto gc_complete;
1697
1698        if (assoc_array_ptr_is_shortcut(ptr)) {
1699                new_s = assoc_array_ptr_to_shortcut(ptr);
1700                new_parent = new_s->back_pointer;
1701                slot = new_s->parent_slot;
1702
1703                if (new_n->nr_leaves_on_branch <= ASSOC_ARRAY_FAN_OUT) {
1704                        struct assoc_array_node *n;
1705
1706                        pr_devel("excise shortcut\n");
1707                        new_n->back_pointer = new_parent;
1708                        new_n->parent_slot = slot;
1709                        kfree(new_s);
1710                        if (!new_parent) {
1711                                new_root = assoc_array_node_to_ptr(new_n);
1712                                goto gc_complete;
1713                        }
1714
1715                        n = assoc_array_ptr_to_node(new_parent);
1716                        n->slots[slot] = assoc_array_node_to_ptr(new_n);
1717                }
1718        } else {
1719                new_parent = ptr;
1720        }
1721        new_n = assoc_array_ptr_to_node(new_parent);
1722
1723ascend_old_tree:
1724        ptr = node->back_pointer;
1725        if (assoc_array_ptr_is_shortcut(ptr)) {
1726                shortcut = assoc_array_ptr_to_shortcut(ptr);
1727                slot = shortcut->parent_slot;
1728                cursor = shortcut->back_pointer;
1729                if (!cursor)
1730                        goto gc_complete;
1731        } else {
1732                slot = node->parent_slot;
1733                cursor = ptr;
1734        }
1735        BUG_ON(!cursor);
1736        node = assoc_array_ptr_to_node(cursor);
1737        slot++;
1738        goto continue_node;
1739
1740gc_complete:
1741        edit->set[0].to = new_root;
1742        assoc_array_apply_edit(edit);
1743        array->nr_leaves_on_tree = nr_leaves_on_tree;
1744        return 0;
1745
1746enomem:
1747        pr_devel("enomem\n");
1748        assoc_array_destroy_subtree(new_root, edit->ops);
1749        kfree(edit);
1750        return -ENOMEM;
1751}
1752