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