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}