xref: /openbmc/linux/lib/btree.c (revision ff7b437f)
1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * lib/btree.c	- Simple In-memory B+Tree
4  *
5  * Copyright (c) 2007-2008 Joern Engel <joern@purestorage.com>
6  * Bits and pieces stolen from Peter Zijlstra's code, which is
7  * Copyright 2007, Red Hat Inc. Peter Zijlstra
8  *
9  * see http://programming.kicks-ass.net/kernel-patches/vma_lookup/btree.patch
10  *
11  * A relatively simple B+Tree implementation.  I have written it as a learning
12  * exercise to understand how B+Trees work.  Turned out to be useful as well.
13  *
14  * B+Trees can be used similar to Linux radix trees (which don't have anything
15  * in common with textbook radix trees, beware).  Prerequisite for them working
16  * well is that access to a random tree node is much faster than a large number
17  * of operations within each node.
18  *
19  * Disks have fulfilled the prerequisite for a long time.  More recently DRAM
20  * has gained similar properties, as memory access times, when measured in cpu
21  * cycles, have increased.  Cacheline sizes have increased as well, which also
22  * helps B+Trees.
23  *
24  * Compared to radix trees, B+Trees are more efficient when dealing with a
25  * sparsely populated address space.  Between 25% and 50% of the memory is
26  * occupied with valid pointers.  When densely populated, radix trees contain
27  * ~98% pointers - hard to beat.  Very sparse radix trees contain only ~2%
28  * pointers.
29  *
30  * This particular implementation stores pointers identified by a long value.
31  * Storing NULL pointers is illegal, lookup will return NULL when no entry
32  * was found.
33  *
34  * A tricks was used that is not commonly found in textbooks.  The lowest
35  * values are to the right, not to the left.  All used slots within a node
36  * are on the left, all unused slots contain NUL values.  Most operations
37  * simply loop once over all slots and terminate on the first NUL.
38  */
39 
40 #include <linux/btree.h>
41 #include <linux/cache.h>
42 #include <linux/kernel.h>
43 #include <linux/slab.h>
44 #include <linux/module.h>
45 
46 #define MAX(a, b) ((a) > (b) ? (a) : (b))
47 #define NODESIZE MAX(L1_CACHE_BYTES, 128)
48 
49 struct btree_geo {
50 	int keylen;
51 	int no_pairs;
52 	int no_longs;
53 };
54 
55 struct btree_geo btree_geo32 = {
56 	.keylen = 1,
57 	.no_pairs = NODESIZE / sizeof(long) / 2,
58 	.no_longs = NODESIZE / sizeof(long) / 2,
59 };
60 EXPORT_SYMBOL_GPL(btree_geo32);
61 
62 #define LONG_PER_U64 (64 / BITS_PER_LONG)
63 struct btree_geo btree_geo64 = {
64 	.keylen = LONG_PER_U64,
65 	.no_pairs = NODESIZE / sizeof(long) / (1 + LONG_PER_U64),
66 	.no_longs = LONG_PER_U64 * (NODESIZE / sizeof(long) / (1 + LONG_PER_U64)),
67 };
68 EXPORT_SYMBOL_GPL(btree_geo64);
69 
70 struct btree_geo btree_geo128 = {
71 	.keylen = 2 * LONG_PER_U64,
72 	.no_pairs = NODESIZE / sizeof(long) / (1 + 2 * LONG_PER_U64),
73 	.no_longs = 2 * LONG_PER_U64 * (NODESIZE / sizeof(long) / (1 + 2 * LONG_PER_U64)),
74 };
75 EXPORT_SYMBOL_GPL(btree_geo128);
76 
77 #define MAX_KEYLEN	(2 * LONG_PER_U64)
78 
79 static struct kmem_cache *btree_cachep;
80 
81 void *btree_alloc(gfp_t gfp_mask, void *pool_data)
82 {
83 	return kmem_cache_alloc(btree_cachep, gfp_mask);
84 }
85 EXPORT_SYMBOL_GPL(btree_alloc);
86 
87 void btree_free(void *element, void *pool_data)
88 {
89 	kmem_cache_free(btree_cachep, element);
90 }
91 EXPORT_SYMBOL_GPL(btree_free);
92 
93 static unsigned long *btree_node_alloc(struct btree_head *head, gfp_t gfp)
94 {
95 	unsigned long *node;
96 
97 	node = mempool_alloc(head->mempool, gfp);
98 	if (likely(node))
99 		memset(node, 0, NODESIZE);
100 	return node;
101 }
102 
103 static int longcmp(const unsigned long *l1, const unsigned long *l2, size_t n)
104 {
105 	size_t i;
106 
107 	for (i = 0; i < n; i++) {
108 		if (l1[i] < l2[i])
109 			return -1;
110 		if (l1[i] > l2[i])
111 			return 1;
112 	}
113 	return 0;
114 }
115 
116 static unsigned long *longcpy(unsigned long *dest, const unsigned long *src,
117 		size_t n)
118 {
119 	size_t i;
120 
121 	for (i = 0; i < n; i++)
122 		dest[i] = src[i];
123 	return dest;
124 }
125 
126 static unsigned long *longset(unsigned long *s, unsigned long c, size_t n)
127 {
128 	size_t i;
129 
130 	for (i = 0; i < n; i++)
131 		s[i] = c;
132 	return s;
133 }
134 
135 static void dec_key(struct btree_geo *geo, unsigned long *key)
136 {
137 	unsigned long val;
138 	int i;
139 
140 	for (i = geo->keylen - 1; i >= 0; i--) {
141 		val = key[i];
142 		key[i] = val - 1;
143 		if (val)
144 			break;
145 	}
146 }
147 
148 static unsigned long *bkey(struct btree_geo *geo, unsigned long *node, int n)
149 {
150 	return &node[n * geo->keylen];
151 }
152 
153 static void *bval(struct btree_geo *geo, unsigned long *node, int n)
154 {
155 	return (void *)node[geo->no_longs + n];
156 }
157 
158 static void setkey(struct btree_geo *geo, unsigned long *node, int n,
159 		   unsigned long *key)
160 {
161 	longcpy(bkey(geo, node, n), key, geo->keylen);
162 }
163 
164 static void setval(struct btree_geo *geo, unsigned long *node, int n,
165 		   void *val)
166 {
167 	node[geo->no_longs + n] = (unsigned long) val;
168 }
169 
170 static void clearpair(struct btree_geo *geo, unsigned long *node, int n)
171 {
172 	longset(bkey(geo, node, n), 0, geo->keylen);
173 	node[geo->no_longs + n] = 0;
174 }
175 
176 static inline void __btree_init(struct btree_head *head)
177 {
178 	head->node = NULL;
179 	head->height = 0;
180 }
181 
182 void btree_init_mempool(struct btree_head *head, mempool_t *mempool)
183 {
184 	__btree_init(head);
185 	head->mempool = mempool;
186 }
187 EXPORT_SYMBOL_GPL(btree_init_mempool);
188 
189 int btree_init(struct btree_head *head)
190 {
191 	__btree_init(head);
192 	head->mempool = mempool_create(0, btree_alloc, btree_free, NULL);
193 	if (!head->mempool)
194 		return -ENOMEM;
195 	return 0;
196 }
197 EXPORT_SYMBOL_GPL(btree_init);
198 
199 void btree_destroy(struct btree_head *head)
200 {
201 	mempool_free(head->node, head->mempool);
202 	mempool_destroy(head->mempool);
203 	head->mempool = NULL;
204 }
205 EXPORT_SYMBOL_GPL(btree_destroy);
206 
207 void *btree_last(struct btree_head *head, struct btree_geo *geo,
208 		 unsigned long *key)
209 {
210 	int height = head->height;
211 	unsigned long *node = head->node;
212 
213 	if (height == 0)
214 		return NULL;
215 
216 	for ( ; height > 1; height--)
217 		node = bval(geo, node, 0);
218 
219 	longcpy(key, bkey(geo, node, 0), geo->keylen);
220 	return bval(geo, node, 0);
221 }
222 EXPORT_SYMBOL_GPL(btree_last);
223 
224 static int keycmp(struct btree_geo *geo, unsigned long *node, int pos,
225 		  unsigned long *key)
226 {
227 	return longcmp(bkey(geo, node, pos), key, geo->keylen);
228 }
229 
230 static int keyzero(struct btree_geo *geo, unsigned long *key)
231 {
232 	int i;
233 
234 	for (i = 0; i < geo->keylen; i++)
235 		if (key[i])
236 			return 0;
237 
238 	return 1;
239 }
240 
241 void *btree_lookup(struct btree_head *head, struct btree_geo *geo,
242 		unsigned long *key)
243 {
244 	int i, height = head->height;
245 	unsigned long *node = head->node;
246 
247 	if (height == 0)
248 		return NULL;
249 
250 	for ( ; height > 1; height--) {
251 		for (i = 0; i < geo->no_pairs; i++)
252 			if (keycmp(geo, node, i, key) <= 0)
253 				break;
254 		if (i == geo->no_pairs)
255 			return NULL;
256 		node = bval(geo, node, i);
257 		if (!node)
258 			return NULL;
259 	}
260 
261 	if (!node)
262 		return NULL;
263 
264 	for (i = 0; i < geo->no_pairs; i++)
265 		if (keycmp(geo, node, i, key) == 0)
266 			return bval(geo, node, i);
267 	return NULL;
268 }
269 EXPORT_SYMBOL_GPL(btree_lookup);
270 
271 int btree_update(struct btree_head *head, struct btree_geo *geo,
272 		 unsigned long *key, void *val)
273 {
274 	int i, height = head->height;
275 	unsigned long *node = head->node;
276 
277 	if (height == 0)
278 		return -ENOENT;
279 
280 	for ( ; height > 1; height--) {
281 		for (i = 0; i < geo->no_pairs; i++)
282 			if (keycmp(geo, node, i, key) <= 0)
283 				break;
284 		if (i == geo->no_pairs)
285 			return -ENOENT;
286 		node = bval(geo, node, i);
287 		if (!node)
288 			return -ENOENT;
289 	}
290 
291 	if (!node)
292 		return -ENOENT;
293 
294 	for (i = 0; i < geo->no_pairs; i++)
295 		if (keycmp(geo, node, i, key) == 0) {
296 			setval(geo, node, i, val);
297 			return 0;
298 		}
299 	return -ENOENT;
300 }
301 EXPORT_SYMBOL_GPL(btree_update);
302 
303 /*
304  * Usually this function is quite similar to normal lookup.  But the key of
305  * a parent node may be smaller than the smallest key of all its siblings.
306  * In such a case we cannot just return NULL, as we have only proven that no
307  * key smaller than __key, but larger than this parent key exists.
308  * So we set __key to the parent key and retry.  We have to use the smallest
309  * such parent key, which is the last parent key we encountered.
310  */
311 void *btree_get_prev(struct btree_head *head, struct btree_geo *geo,
312 		     unsigned long *__key)
313 {
314 	int i, height;
315 	unsigned long *node, *oldnode;
316 	unsigned long *retry_key = NULL, key[MAX_KEYLEN];
317 
318 	if (keyzero(geo, __key))
319 		return NULL;
320 
321 	if (head->height == 0)
322 		return NULL;
323 	longcpy(key, __key, geo->keylen);
324 retry:
325 	dec_key(geo, key);
326 
327 	node = head->node;
328 	for (height = head->height ; height > 1; height--) {
329 		for (i = 0; i < geo->no_pairs; i++)
330 			if (keycmp(geo, node, i, key) <= 0)
331 				break;
332 		if (i == geo->no_pairs)
333 			goto miss;
334 		oldnode = node;
335 		node = bval(geo, node, i);
336 		if (!node)
337 			goto miss;
338 		retry_key = bkey(geo, oldnode, i);
339 	}
340 
341 	if (!node)
342 		goto miss;
343 
344 	for (i = 0; i < geo->no_pairs; i++) {
345 		if (keycmp(geo, node, i, key) <= 0) {
346 			if (bval(geo, node, i)) {
347 				longcpy(__key, bkey(geo, node, i), geo->keylen);
348 				return bval(geo, node, i);
349 			} else
350 				goto miss;
351 		}
352 	}
353 miss:
354 	if (retry_key) {
355 		longcpy(key, retry_key, geo->keylen);
356 		retry_key = NULL;
357 		goto retry;
358 	}
359 	return NULL;
360 }
361 EXPORT_SYMBOL_GPL(btree_get_prev);
362 
363 static int getpos(struct btree_geo *geo, unsigned long *node,
364 		unsigned long *key)
365 {
366 	int i;
367 
368 	for (i = 0; i < geo->no_pairs; i++) {
369 		if (keycmp(geo, node, i, key) <= 0)
370 			break;
371 	}
372 	return i;
373 }
374 
375 static int getfill(struct btree_geo *geo, unsigned long *node, int start)
376 {
377 	int i;
378 
379 	for (i = start; i < geo->no_pairs; i++)
380 		if (!bval(geo, node, i))
381 			break;
382 	return i;
383 }
384 
385 /*
386  * locate the correct leaf node in the btree
387  */
388 static unsigned long *find_level(struct btree_head *head, struct btree_geo *geo,
389 		unsigned long *key, int level)
390 {
391 	unsigned long *node = head->node;
392 	int i, height;
393 
394 	for (height = head->height; height > level; height--) {
395 		for (i = 0; i < geo->no_pairs; i++)
396 			if (keycmp(geo, node, i, key) <= 0)
397 				break;
398 
399 		if ((i == geo->no_pairs) || !bval(geo, node, i)) {
400 			/* right-most key is too large, update it */
401 			/* FIXME: If the right-most key on higher levels is
402 			 * always zero, this wouldn't be necessary. */
403 			i--;
404 			setkey(geo, node, i, key);
405 		}
406 		BUG_ON(i < 0);
407 		node = bval(geo, node, i);
408 	}
409 	BUG_ON(!node);
410 	return node;
411 }
412 
413 static int btree_grow(struct btree_head *head, struct btree_geo *geo,
414 		      gfp_t gfp)
415 {
416 	unsigned long *node;
417 	int fill;
418 
419 	node = btree_node_alloc(head, gfp);
420 	if (!node)
421 		return -ENOMEM;
422 	if (head->node) {
423 		fill = getfill(geo, head->node, 0);
424 		setkey(geo, node, 0, bkey(geo, head->node, fill - 1));
425 		setval(geo, node, 0, head->node);
426 	}
427 	head->node = node;
428 	head->height++;
429 	return 0;
430 }
431 
432 static void btree_shrink(struct btree_head *head, struct btree_geo *geo)
433 {
434 	unsigned long *node;
435 	int fill;
436 
437 	if (head->height <= 1)
438 		return;
439 
440 	node = head->node;
441 	fill = getfill(geo, node, 0);
442 	BUG_ON(fill > 1);
443 	head->node = bval(geo, node, 0);
444 	head->height--;
445 	mempool_free(node, head->mempool);
446 }
447 
448 static int btree_insert_level(struct btree_head *head, struct btree_geo *geo,
449 			      unsigned long *key, void *val, int level,
450 			      gfp_t gfp)
451 {
452 	unsigned long *node;
453 	int i, pos, fill, err;
454 
455 	BUG_ON(!val);
456 	if (head->height < level) {
457 		err = btree_grow(head, geo, gfp);
458 		if (err)
459 			return err;
460 	}
461 
462 retry:
463 	node = find_level(head, geo, key, level);
464 	pos = getpos(geo, node, key);
465 	fill = getfill(geo, node, pos);
466 	/* two identical keys are not allowed */
467 	BUG_ON(pos < fill && keycmp(geo, node, pos, key) == 0);
468 
469 	if (fill == geo->no_pairs) {
470 		/* need to split node */
471 		unsigned long *new;
472 
473 		new = btree_node_alloc(head, gfp);
474 		if (!new)
475 			return -ENOMEM;
476 		err = btree_insert_level(head, geo,
477 				bkey(geo, node, fill / 2 - 1),
478 				new, level + 1, gfp);
479 		if (err) {
480 			mempool_free(new, head->mempool);
481 			return err;
482 		}
483 		for (i = 0; i < fill / 2; i++) {
484 			setkey(geo, new, i, bkey(geo, node, i));
485 			setval(geo, new, i, bval(geo, node, i));
486 			setkey(geo, node, i, bkey(geo, node, i + fill / 2));
487 			setval(geo, node, i, bval(geo, node, i + fill / 2));
488 			clearpair(geo, node, i + fill / 2);
489 		}
490 		if (fill & 1) {
491 			setkey(geo, node, i, bkey(geo, node, fill - 1));
492 			setval(geo, node, i, bval(geo, node, fill - 1));
493 			clearpair(geo, node, fill - 1);
494 		}
495 		goto retry;
496 	}
497 	BUG_ON(fill >= geo->no_pairs);
498 
499 	/* shift and insert */
500 	for (i = fill; i > pos; i--) {
501 		setkey(geo, node, i, bkey(geo, node, i - 1));
502 		setval(geo, node, i, bval(geo, node, i - 1));
503 	}
504 	setkey(geo, node, pos, key);
505 	setval(geo, node, pos, val);
506 
507 	return 0;
508 }
509 
510 int btree_insert(struct btree_head *head, struct btree_geo *geo,
511 		unsigned long *key, void *val, gfp_t gfp)
512 {
513 	BUG_ON(!val);
514 	return btree_insert_level(head, geo, key, val, 1, gfp);
515 }
516 EXPORT_SYMBOL_GPL(btree_insert);
517 
518 static void *btree_remove_level(struct btree_head *head, struct btree_geo *geo,
519 		unsigned long *key, int level);
520 static void merge(struct btree_head *head, struct btree_geo *geo, int level,
521 		unsigned long *left, int lfill,
522 		unsigned long *right, int rfill,
523 		unsigned long *parent, int lpos)
524 {
525 	int i;
526 
527 	for (i = 0; i < rfill; i++) {
528 		/* Move all keys to the left */
529 		setkey(geo, left, lfill + i, bkey(geo, right, i));
530 		setval(geo, left, lfill + i, bval(geo, right, i));
531 	}
532 	/* Exchange left and right child in parent */
533 	setval(geo, parent, lpos, right);
534 	setval(geo, parent, lpos + 1, left);
535 	/* Remove left (formerly right) child from parent */
536 	btree_remove_level(head, geo, bkey(geo, parent, lpos), level + 1);
537 	mempool_free(right, head->mempool);
538 }
539 
540 static void rebalance(struct btree_head *head, struct btree_geo *geo,
541 		unsigned long *key, int level, unsigned long *child, int fill)
542 {
543 	unsigned long *parent, *left = NULL, *right = NULL;
544 	int i, no_left, no_right;
545 
546 	if (fill == 0) {
547 		/* Because we don't steal entries from a neighbour, this case
548 		 * can happen.  Parent node contains a single child, this
549 		 * node, so merging with a sibling never happens.
550 		 */
551 		btree_remove_level(head, geo, key, level + 1);
552 		mempool_free(child, head->mempool);
553 		return;
554 	}
555 
556 	parent = find_level(head, geo, key, level + 1);
557 	i = getpos(geo, parent, key);
558 	BUG_ON(bval(geo, parent, i) != child);
559 
560 	if (i > 0) {
561 		left = bval(geo, parent, i - 1);
562 		no_left = getfill(geo, left, 0);
563 		if (fill + no_left <= geo->no_pairs) {
564 			merge(head, geo, level,
565 					left, no_left,
566 					child, fill,
567 					parent, i - 1);
568 			return;
569 		}
570 	}
571 	if (i + 1 < getfill(geo, parent, i)) {
572 		right = bval(geo, parent, i + 1);
573 		no_right = getfill(geo, right, 0);
574 		if (fill + no_right <= geo->no_pairs) {
575 			merge(head, geo, level,
576 					child, fill,
577 					right, no_right,
578 					parent, i);
579 			return;
580 		}
581 	}
582 	/*
583 	 * We could also try to steal one entry from the left or right
584 	 * neighbor.  By not doing so we changed the invariant from
585 	 * "all nodes are at least half full" to "no two neighboring
586 	 * nodes can be merged".  Which means that the average fill of
587 	 * all nodes is still half or better.
588 	 */
589 }
590 
591 static void *btree_remove_level(struct btree_head *head, struct btree_geo *geo,
592 		unsigned long *key, int level)
593 {
594 	unsigned long *node;
595 	int i, pos, fill;
596 	void *ret;
597 
598 	if (level > head->height) {
599 		/* we recursed all the way up */
600 		head->height = 0;
601 		head->node = NULL;
602 		return NULL;
603 	}
604 
605 	node = find_level(head, geo, key, level);
606 	pos = getpos(geo, node, key);
607 	fill = getfill(geo, node, pos);
608 	if ((level == 1) && (keycmp(geo, node, pos, key) != 0))
609 		return NULL;
610 	ret = bval(geo, node, pos);
611 
612 	/* remove and shift */
613 	for (i = pos; i < fill - 1; i++) {
614 		setkey(geo, node, i, bkey(geo, node, i + 1));
615 		setval(geo, node, i, bval(geo, node, i + 1));
616 	}
617 	clearpair(geo, node, fill - 1);
618 
619 	if (fill - 1 < geo->no_pairs / 2) {
620 		if (level < head->height)
621 			rebalance(head, geo, key, level, node, fill - 1);
622 		else if (fill - 1 == 1)
623 			btree_shrink(head, geo);
624 	}
625 
626 	return ret;
627 }
628 
629 void *btree_remove(struct btree_head *head, struct btree_geo *geo,
630 		unsigned long *key)
631 {
632 	if (head->height == 0)
633 		return NULL;
634 
635 	return btree_remove_level(head, geo, key, 1);
636 }
637 EXPORT_SYMBOL_GPL(btree_remove);
638 
639 int btree_merge(struct btree_head *target, struct btree_head *victim,
640 		struct btree_geo *geo, gfp_t gfp)
641 {
642 	unsigned long key[MAX_KEYLEN];
643 	unsigned long dup[MAX_KEYLEN];
644 	void *val;
645 	int err;
646 
647 	BUG_ON(target == victim);
648 
649 	if (!(target->node)) {
650 		/* target is empty, just copy fields over */
651 		target->node = victim->node;
652 		target->height = victim->height;
653 		__btree_init(victim);
654 		return 0;
655 	}
656 
657 	/* TODO: This needs some optimizations.  Currently we do three tree
658 	 * walks to remove a single object from the victim.
659 	 */
660 	for (;;) {
661 		if (!btree_last(victim, geo, key))
662 			break;
663 		val = btree_lookup(victim, geo, key);
664 		err = btree_insert(target, geo, key, val, gfp);
665 		if (err)
666 			return err;
667 		/* We must make a copy of the key, as the original will get
668 		 * mangled inside btree_remove. */
669 		longcpy(dup, key, geo->keylen);
670 		btree_remove(victim, geo, dup);
671 	}
672 	return 0;
673 }
674 EXPORT_SYMBOL_GPL(btree_merge);
675 
676 static size_t __btree_for_each(struct btree_head *head, struct btree_geo *geo,
677 			       unsigned long *node, unsigned long opaque,
678 			       void (*func)(void *elem, unsigned long opaque,
679 					    unsigned long *key, size_t index,
680 					    void *func2),
681 			       void *func2, int reap, int height, size_t count)
682 {
683 	int i;
684 	unsigned long *child;
685 
686 	for (i = 0; i < geo->no_pairs; i++) {
687 		child = bval(geo, node, i);
688 		if (!child)
689 			break;
690 		if (height > 1)
691 			count = __btree_for_each(head, geo, child, opaque,
692 					func, func2, reap, height - 1, count);
693 		else
694 			func(child, opaque, bkey(geo, node, i), count++,
695 					func2);
696 	}
697 	if (reap)
698 		mempool_free(node, head->mempool);
699 	return count;
700 }
701 
702 static void empty(void *elem, unsigned long opaque, unsigned long *key,
703 		  size_t index, void *func2)
704 {
705 }
706 
707 void visitorl(void *elem, unsigned long opaque, unsigned long *key,
708 	      size_t index, void *__func)
709 {
710 	visitorl_t func = __func;
711 
712 	func(elem, opaque, *key, index);
713 }
714 EXPORT_SYMBOL_GPL(visitorl);
715 
716 void visitor32(void *elem, unsigned long opaque, unsigned long *__key,
717 	       size_t index, void *__func)
718 {
719 	visitor32_t func = __func;
720 	u32 *key = (void *)__key;
721 
722 	func(elem, opaque, *key, index);
723 }
724 EXPORT_SYMBOL_GPL(visitor32);
725 
726 void visitor64(void *elem, unsigned long opaque, unsigned long *__key,
727 	       size_t index, void *__func)
728 {
729 	visitor64_t func = __func;
730 	u64 *key = (void *)__key;
731 
732 	func(elem, opaque, *key, index);
733 }
734 EXPORT_SYMBOL_GPL(visitor64);
735 
736 void visitor128(void *elem, unsigned long opaque, unsigned long *__key,
737 		size_t index, void *__func)
738 {
739 	visitor128_t func = __func;
740 	u64 *key = (void *)__key;
741 
742 	func(elem, opaque, key[0], key[1], index);
743 }
744 EXPORT_SYMBOL_GPL(visitor128);
745 
746 size_t btree_visitor(struct btree_head *head, struct btree_geo *geo,
747 		     unsigned long opaque,
748 		     void (*func)(void *elem, unsigned long opaque,
749 		     		  unsigned long *key,
750 		     		  size_t index, void *func2),
751 		     void *func2)
752 {
753 	size_t count = 0;
754 
755 	if (!func2)
756 		func = empty;
757 	if (head->node)
758 		count = __btree_for_each(head, geo, head->node, opaque, func,
759 				func2, 0, head->height, 0);
760 	return count;
761 }
762 EXPORT_SYMBOL_GPL(btree_visitor);
763 
764 size_t btree_grim_visitor(struct btree_head *head, struct btree_geo *geo,
765 			  unsigned long opaque,
766 			  void (*func)(void *elem, unsigned long opaque,
767 				       unsigned long *key,
768 				       size_t index, void *func2),
769 			  void *func2)
770 {
771 	size_t count = 0;
772 
773 	if (!func2)
774 		func = empty;
775 	if (head->node)
776 		count = __btree_for_each(head, geo, head->node, opaque, func,
777 				func2, 1, head->height, 0);
778 	__btree_init(head);
779 	return count;
780 }
781 EXPORT_SYMBOL_GPL(btree_grim_visitor);
782 
783 static int __init btree_module_init(void)
784 {
785 	btree_cachep = kmem_cache_create("btree_node", NODESIZE, 0,
786 			SLAB_HWCACHE_ALIGN, NULL);
787 	return 0;
788 }
789 
790 static void __exit btree_module_exit(void)
791 {
792 	kmem_cache_destroy(btree_cachep);
793 }
794 
795 /* If core code starts using btree, initialization should happen even earlier */
796 module_init(btree_module_init);
797 module_exit(btree_module_exit);
798 
799 MODULE_AUTHOR("Joern Engel <joern@logfs.org>");
800 MODULE_AUTHOR("Johannes Berg <johannes@sipsolutions.net>");
801 MODULE_LICENSE("GPL");
802