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TOMOYO Linux Cross Reference
Linux/lib/btree.c

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  1 /*
  2  * lib/btree.c  - Simple In-memory B+Tree
  3  *
  4  * As should be obvious for Linux kernel code, license is GPLv2
  5  *
  6  * Copyright (c) 2007-2008 Joern Engel <joern@logfs.org>
  7  * Bits and pieces stolen from Peter Zijlstra's code, which is
  8  * Copyright 2007, Red Hat Inc. Peter Zijlstra
  9  * GPLv2
 10  *
 11  * see http://programming.kicks-ass.net/kernel-patches/vma_lookup/btree.patch
 12  *
 13  * A relatively simple B+Tree implementation.  I have written it as a learning
 14  * exercise to understand how B+Trees work.  Turned out to be useful as well.
 15  *
 16  * B+Trees can be used similar to Linux radix trees (which don't have anything
 17  * in common with textbook radix trees, beware).  Prerequisite for them working
 18  * well is that access to a random tree node is much faster than a large number
 19  * of operations within each node.
 20  *
 21  * Disks have fulfilled the prerequisite for a long time.  More recently DRAM
 22  * has gained similar properties, as memory access times, when measured in cpu
 23  * cycles, have increased.  Cacheline sizes have increased as well, which also
 24  * helps B+Trees.
 25  *
 26  * Compared to radix trees, B+Trees are more efficient when dealing with a
 27  * sparsely populated address space.  Between 25% and 50% of the memory is
 28  * occupied with valid pointers.  When densely populated, radix trees contain
 29  * ~98% pointers - hard to beat.  Very sparse radix trees contain only ~2%
 30  * pointers.
 31  *
 32  * This particular implementation stores pointers identified by a long value.
 33  * Storing NULL pointers is illegal, lookup will return NULL when no entry
 34  * was found.
 35  *
 36  * A tricks was used that is not commonly found in textbooks.  The lowest
 37  * values are to the right, not to the left.  All used slots within a node
 38  * are on the left, all unused slots contain NUL values.  Most operations
 39  * simply loop once over all slots and terminate on the first NUL.
 40  */
 41 
 42 #include <linux/btree.h>
 43 #include <linux/cache.h>
 44 #include <linux/kernel.h>
 45 #include <linux/slab.h>
 46 #include <linux/module.h>
 47 
 48 #define MAX(a, b) ((a) > (b) ? (a) : (b))
 49 #define NODESIZE MAX(L1_CACHE_BYTES, 128)
 50 
 51 struct btree_geo {
 52         int keylen;
 53         int no_pairs;
 54         int no_longs;
 55 };
 56 
 57 struct btree_geo btree_geo32 = {
 58         .keylen = 1,
 59         .no_pairs = NODESIZE / sizeof(long) / 2,
 60         .no_longs = NODESIZE / sizeof(long) / 2,
 61 };
 62 EXPORT_SYMBOL_GPL(btree_geo32);
 63 
 64 #define LONG_PER_U64 (64 / BITS_PER_LONG)
 65 struct btree_geo btree_geo64 = {
 66         .keylen = LONG_PER_U64,
 67         .no_pairs = NODESIZE / sizeof(long) / (1 + LONG_PER_U64),
 68         .no_longs = LONG_PER_U64 * (NODESIZE / sizeof(long) / (1 + LONG_PER_U64)),
 69 };
 70 EXPORT_SYMBOL_GPL(btree_geo64);
 71 
 72 struct btree_geo btree_geo128 = {
 73         .keylen = 2 * LONG_PER_U64,
 74         .no_pairs = NODESIZE / sizeof(long) / (1 + 2 * LONG_PER_U64),
 75         .no_longs = 2 * LONG_PER_U64 * (NODESIZE / sizeof(long) / (1 + 2 * LONG_PER_U64)),
 76 };
 77 EXPORT_SYMBOL_GPL(btree_geo128);
 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[geo->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[geo->keylen];
643         unsigned long dup[geo->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 

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