Root/lib/btree.c

Source at commit b386be689295730688885552666ea40b2e639b14 created 8 years 11 months ago.
By Maarten ter Huurne, Revert "MIPS: JZ4740: reset: Initialize hibernate wakeup counters."
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 <pzijlstr@redhat.com>
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
51struct btree_geo {
52    int keylen;
53    int no_pairs;
54    int no_longs;
55};
56
57struct btree_geo btree_geo32 = {
58    .keylen = 1,
59    .no_pairs = NODESIZE / sizeof(long) / 2,
60    .no_longs = NODESIZE / sizeof(long) / 2,
61};
62EXPORT_SYMBOL_GPL(btree_geo32);
63
64#define LONG_PER_U64 (64 / BITS_PER_LONG)
65struct 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};
70EXPORT_SYMBOL_GPL(btree_geo64);
71
72struct 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};
77EXPORT_SYMBOL_GPL(btree_geo128);
78
79static struct kmem_cache *btree_cachep;
80
81void *btree_alloc(gfp_t gfp_mask, void *pool_data)
82{
83    return kmem_cache_alloc(btree_cachep, gfp_mask);
84}
85EXPORT_SYMBOL_GPL(btree_alloc);
86
87void btree_free(void *element, void *pool_data)
88{
89    kmem_cache_free(btree_cachep, element);
90}
91EXPORT_SYMBOL_GPL(btree_free);
92
93static 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
103static 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
116static 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
126static 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
135static 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
148static unsigned long *bkey(struct btree_geo *geo, unsigned long *node, int n)
149{
150    return &node[n * geo->keylen];
151}
152
153static void *bval(struct btree_geo *geo, unsigned long *node, int n)
154{
155    return (void *)node[geo->no_longs + n];
156}
157
158static 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
164static 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
170static 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
176static inline void __btree_init(struct btree_head *head)
177{
178    head->node = NULL;
179    head->height = 0;
180}
181
182void btree_init_mempool(struct btree_head *head, mempool_t *mempool)
183{
184    __btree_init(head);
185    head->mempool = mempool;
186}
187EXPORT_SYMBOL_GPL(btree_init_mempool);
188
189int 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}
197EXPORT_SYMBOL_GPL(btree_init);
198
199void btree_destroy(struct btree_head *head)
200{
201    mempool_destroy(head->mempool);
202    head->mempool = NULL;
203}
204EXPORT_SYMBOL_GPL(btree_destroy);
205
206void *btree_last(struct btree_head *head, struct btree_geo *geo,
207         unsigned long *key)
208{
209    int height = head->height;
210    unsigned long *node = head->node;
211
212    if (height == 0)
213        return NULL;
214
215    for ( ; height > 1; height--)
216        node = bval(geo, node, 0);
217
218    longcpy(key, bkey(geo, node, 0), geo->keylen);
219    return bval(geo, node, 0);
220}
221EXPORT_SYMBOL_GPL(btree_last);
222
223static int keycmp(struct btree_geo *geo, unsigned long *node, int pos,
224          unsigned long *key)
225{
226    return longcmp(bkey(geo, node, pos), key, geo->keylen);
227}
228
229static int keyzero(struct btree_geo *geo, unsigned long *key)
230{
231    int i;
232
233    for (i = 0; i < geo->keylen; i++)
234        if (key[i])
235            return 0;
236
237    return 1;
238}
239
240void *btree_lookup(struct btree_head *head, struct btree_geo *geo,
241        unsigned long *key)
242{
243    int i, height = head->height;
244    unsigned long *node = head->node;
245
246    if (height == 0)
247        return NULL;
248
249    for ( ; height > 1; height--) {
250        for (i = 0; i < geo->no_pairs; i++)
251            if (keycmp(geo, node, i, key) <= 0)
252                break;
253        if (i == geo->no_pairs)
254            return NULL;
255        node = bval(geo, node, i);
256        if (!node)
257            return NULL;
258    }
259
260    if (!node)
261        return NULL;
262
263    for (i = 0; i < geo->no_pairs; i++)
264        if (keycmp(geo, node, i, key) == 0)
265            return bval(geo, node, i);
266    return NULL;
267}
268EXPORT_SYMBOL_GPL(btree_lookup);
269
270int btree_update(struct btree_head *head, struct btree_geo *geo,
271         unsigned long *key, void *val)
272{
273    int i, height = head->height;
274    unsigned long *node = head->node;
275
276    if (height == 0)
277        return -ENOENT;
278
279    for ( ; height > 1; height--) {
280        for (i = 0; i < geo->no_pairs; i++)
281            if (keycmp(geo, node, i, key) <= 0)
282                break;
283        if (i == geo->no_pairs)
284            return -ENOENT;
285        node = bval(geo, node, i);
286        if (!node)
287            return -ENOENT;
288    }
289
290    if (!node)
291        return -ENOENT;
292
293    for (i = 0; i < geo->no_pairs; i++)
294        if (keycmp(geo, node, i, key) == 0) {
295            setval(geo, node, i, val);
296            return 0;
297        }
298    return -ENOENT;
299}
300EXPORT_SYMBOL_GPL(btree_update);
301
302/*
303 * Usually this function is quite similar to normal lookup. But the key of
304 * a parent node may be smaller than the smallest key of all its siblings.
305 * In such a case we cannot just return NULL, as we have only proven that no
306 * key smaller than __key, but larger than this parent key exists.
307 * So we set __key to the parent key and retry. We have to use the smallest
308 * such parent key, which is the last parent key we encountered.
309 */
310void *btree_get_prev(struct btree_head *head, struct btree_geo *geo,
311             unsigned long *__key)
312{
313    int i, height;
314    unsigned long *node, *oldnode;
315    unsigned long *retry_key = NULL, key[geo->keylen];
316
317    if (keyzero(geo, __key))
318        return NULL;
319
320    if (head->height == 0)
321        return NULL;
322retry:
323    longcpy(key, __key, geo->keylen);
324    dec_key(geo, key);
325
326    node = head->node;
327    for (height = head->height ; height > 1; height--) {
328        for (i = 0; i < geo->no_pairs; i++)
329            if (keycmp(geo, node, i, key) <= 0)
330                break;
331        if (i == geo->no_pairs)
332            goto miss;
333        oldnode = node;
334        node = bval(geo, node, i);
335        if (!node)
336            goto miss;
337        retry_key = bkey(geo, oldnode, i);
338    }
339
340    if (!node)
341        goto miss;
342
343    for (i = 0; i < geo->no_pairs; i++) {
344        if (keycmp(geo, node, i, key) <= 0) {
345            if (bval(geo, node, i)) {
346                longcpy(__key, bkey(geo, node, i), geo->keylen);
347                return bval(geo, node, i);
348            } else
349                goto miss;
350        }
351    }
352miss:
353    if (retry_key) {
354        __key = retry_key;
355        retry_key = NULL;
356        goto retry;
357    }
358    return NULL;
359}
360EXPORT_SYMBOL_GPL(btree_get_prev);
361
362static int getpos(struct btree_geo *geo, unsigned long *node,
363        unsigned long *key)
364{
365    int i;
366
367    for (i = 0; i < geo->no_pairs; i++) {
368        if (keycmp(geo, node, i, key) <= 0)
369            break;
370    }
371    return i;
372}
373
374static int getfill(struct btree_geo *geo, unsigned long *node, int start)
375{
376    int i;
377
378    for (i = start; i < geo->no_pairs; i++)
379        if (!bval(geo, node, i))
380            break;
381    return i;
382}
383
384/*
385 * locate the correct leaf node in the btree
386 */
387static unsigned long *find_level(struct btree_head *head, struct btree_geo *geo,
388        unsigned long *key, int level)
389{
390    unsigned long *node = head->node;
391    int i, height;
392
393    for (height = head->height; height > level; height--) {
394        for (i = 0; i < geo->no_pairs; i++)
395            if (keycmp(geo, node, i, key) <= 0)
396                break;
397
398        if ((i == geo->no_pairs) || !bval(geo, node, i)) {
399            /* right-most key is too large, update it */
400            /* FIXME: If the right-most key on higher levels is
401             * always zero, this wouldn't be necessary. */
402            i--;
403            setkey(geo, node, i, key);
404        }
405        BUG_ON(i < 0);
406        node = bval(geo, node, i);
407    }
408    BUG_ON(!node);
409    return node;
410}
411
412static int btree_grow(struct btree_head *head, struct btree_geo *geo,
413              gfp_t gfp)
414{
415    unsigned long *node;
416    int fill;
417
418    node = btree_node_alloc(head, gfp);
419    if (!node)
420        return -ENOMEM;
421    if (head->node) {
422        fill = getfill(geo, head->node, 0);
423        setkey(geo, node, 0, bkey(geo, head->node, fill - 1));
424        setval(geo, node, 0, head->node);
425    }
426    head->node = node;
427    head->height++;
428    return 0;
429}
430
431static void btree_shrink(struct btree_head *head, struct btree_geo *geo)
432{
433    unsigned long *node;
434    int fill;
435
436    if (head->height <= 1)
437        return;
438
439    node = head->node;
440    fill = getfill(geo, node, 0);
441    BUG_ON(fill > 1);
442    head->node = bval(geo, node, 0);
443    head->height--;
444    mempool_free(node, head->mempool);
445}
446
447static int btree_insert_level(struct btree_head *head, struct btree_geo *geo,
448                  unsigned long *key, void *val, int level,
449                  gfp_t gfp)
450{
451    unsigned long *node;
452    int i, pos, fill, err;
453
454    BUG_ON(!val);
455    if (head->height < level) {
456        err = btree_grow(head, geo, gfp);
457        if (err)
458            return err;
459    }
460
461retry:
462    node = find_level(head, geo, key, level);
463    pos = getpos(geo, node, key);
464    fill = getfill(geo, node, pos);
465    /* two identical keys are not allowed */
466    BUG_ON(pos < fill && keycmp(geo, node, pos, key) == 0);
467
468    if (fill == geo->no_pairs) {
469        /* need to split node */
470        unsigned long *new;
471
472        new = btree_node_alloc(head, gfp);
473        if (!new)
474            return -ENOMEM;
475        err = btree_insert_level(head, geo,
476                bkey(geo, node, fill / 2 - 1),
477                new, level + 1, gfp);
478        if (err) {
479            mempool_free(new, head->mempool);
480            return err;
481        }
482        for (i = 0; i < fill / 2; i++) {
483            setkey(geo, new, i, bkey(geo, node, i));
484            setval(geo, new, i, bval(geo, node, i));
485            setkey(geo, node, i, bkey(geo, node, i + fill / 2));
486            setval(geo, node, i, bval(geo, node, i + fill / 2));
487            clearpair(geo, node, i + fill / 2);
488        }
489        if (fill & 1) {
490            setkey(geo, node, i, bkey(geo, node, fill - 1));
491            setval(geo, node, i, bval(geo, node, fill - 1));
492            clearpair(geo, node, fill - 1);
493        }
494        goto retry;
495    }
496    BUG_ON(fill >= geo->no_pairs);
497
498    /* shift and insert */
499    for (i = fill; i > pos; i--) {
500        setkey(geo, node, i, bkey(geo, node, i - 1));
501        setval(geo, node, i, bval(geo, node, i - 1));
502    }
503    setkey(geo, node, pos, key);
504    setval(geo, node, pos, val);
505
506    return 0;
507}
508
509int btree_insert(struct btree_head *head, struct btree_geo *geo,
510        unsigned long *key, void *val, gfp_t gfp)
511{
512    return btree_insert_level(head, geo, key, val, 1, gfp);
513}
514EXPORT_SYMBOL_GPL(btree_insert);
515
516static void *btree_remove_level(struct btree_head *head, struct btree_geo *geo,
517        unsigned long *key, int level);
518static void merge(struct btree_head *head, struct btree_geo *geo, int level,
519        unsigned long *left, int lfill,
520        unsigned long *right, int rfill,
521        unsigned long *parent, int lpos)
522{
523    int i;
524
525    for (i = 0; i < rfill; i++) {
526        /* Move all keys to the left */
527        setkey(geo, left, lfill + i, bkey(geo, right, i));
528        setval(geo, left, lfill + i, bval(geo, right, i));
529    }
530    /* Exchange left and right child in parent */
531    setval(geo, parent, lpos, right);
532    setval(geo, parent, lpos + 1, left);
533    /* Remove left (formerly right) child from parent */
534    btree_remove_level(head, geo, bkey(geo, parent, lpos), level + 1);
535    mempool_free(right, head->mempool);
536}
537
538static void rebalance(struct btree_head *head, struct btree_geo *geo,
539        unsigned long *key, int level, unsigned long *child, int fill)
540{
541    unsigned long *parent, *left = NULL, *right = NULL;
542    int i, no_left, no_right;
543
544    if (fill == 0) {
545        /* Because we don't steal entries from a neighbour, this case
546         * can happen. Parent node contains a single child, this
547         * node, so merging with a sibling never happens.
548         */
549        btree_remove_level(head, geo, key, level + 1);
550        mempool_free(child, head->mempool);
551        return;
552    }
553
554    parent = find_level(head, geo, key, level + 1);
555    i = getpos(geo, parent, key);
556    BUG_ON(bval(geo, parent, i) != child);
557
558    if (i > 0) {
559        left = bval(geo, parent, i - 1);
560        no_left = getfill(geo, left, 0);
561        if (fill + no_left <= geo->no_pairs) {
562            merge(head, geo, level,
563                    left, no_left,
564                    child, fill,
565                    parent, i - 1);
566            return;
567        }
568    }
569    if (i + 1 < getfill(geo, parent, i)) {
570        right = bval(geo, parent, i + 1);
571        no_right = getfill(geo, right, 0);
572        if (fill + no_right <= geo->no_pairs) {
573            merge(head, geo, level,
574                    child, fill,
575                    right, no_right,
576                    parent, i);
577            return;
578        }
579    }
580    /*
581     * We could also try to steal one entry from the left or right
582     * neighbor. By not doing so we changed the invariant from
583     * "all nodes are at least half full" to "no two neighboring
584     * nodes can be merged". Which means that the average fill of
585     * all nodes is still half or better.
586     */
587}
588
589static void *btree_remove_level(struct btree_head *head, struct btree_geo *geo,
590        unsigned long *key, int level)
591{
592    unsigned long *node;
593    int i, pos, fill;
594    void *ret;
595
596    if (level > head->height) {
597        /* we recursed all the way up */
598        head->height = 0;
599        head->node = NULL;
600        return NULL;
601    }
602
603    node = find_level(head, geo, key, level);
604    pos = getpos(geo, node, key);
605    fill = getfill(geo, node, pos);
606    if ((level == 1) && (keycmp(geo, node, pos, key) != 0))
607        return NULL;
608    ret = bval(geo, node, pos);
609
610    /* remove and shift */
611    for (i = pos; i < fill - 1; i++) {
612        setkey(geo, node, i, bkey(geo, node, i + 1));
613        setval(geo, node, i, bval(geo, node, i + 1));
614    }
615    clearpair(geo, node, fill - 1);
616
617    if (fill - 1 < geo->no_pairs / 2) {
618        if (level < head->height)
619            rebalance(head, geo, key, level, node, fill - 1);
620        else if (fill - 1 == 1)
621            btree_shrink(head, geo);
622    }
623
624    return ret;
625}
626
627void *btree_remove(struct btree_head *head, struct btree_geo *geo,
628        unsigned long *key)
629{
630    if (head->height == 0)
631        return NULL;
632
633    return btree_remove_level(head, geo, key, 1);
634}
635EXPORT_SYMBOL_GPL(btree_remove);
636
637int btree_merge(struct btree_head *target, struct btree_head *victim,
638        struct btree_geo *geo, gfp_t gfp)
639{
640    unsigned long key[geo->keylen];
641    unsigned long dup[geo->keylen];
642    void *val;
643    int err;
644
645    BUG_ON(target == victim);
646
647    if (!(target->node)) {
648        /* target is empty, just copy fields over */
649        target->node = victim->node;
650        target->height = victim->height;
651        __btree_init(victim);
652        return 0;
653    }
654
655    /* TODO: This needs some optimizations. Currently we do three tree
656     * walks to remove a single object from the victim.
657     */
658    for (;;) {
659        if (!btree_last(victim, geo, key))
660            break;
661        val = btree_lookup(victim, geo, key);
662        err = btree_insert(target, geo, key, val, gfp);
663        if (err)
664            return err;
665        /* We must make a copy of the key, as the original will get
666         * mangled inside btree_remove. */
667        longcpy(dup, key, geo->keylen);
668        btree_remove(victim, geo, dup);
669    }
670    return 0;
671}
672EXPORT_SYMBOL_GPL(btree_merge);
673
674static size_t __btree_for_each(struct btree_head *head, struct btree_geo *geo,
675                   unsigned long *node, unsigned long opaque,
676                   void (*func)(void *elem, unsigned long opaque,
677                        unsigned long *key, size_t index,
678                        void *func2),
679                   void *func2, int reap, int height, size_t count)
680{
681    int i;
682    unsigned long *child;
683
684    for (i = 0; i < geo->no_pairs; i++) {
685        child = bval(geo, node, i);
686        if (!child)
687            break;
688        if (height > 1)
689            count = __btree_for_each(head, geo, child, opaque,
690                    func, func2, reap, height - 1, count);
691        else
692            func(child, opaque, bkey(geo, node, i), count++,
693                    func2);
694    }
695    if (reap)
696        mempool_free(node, head->mempool);
697    return count;
698}
699
700static void empty(void *elem, unsigned long opaque, unsigned long *key,
701          size_t index, void *func2)
702{
703}
704
705void visitorl(void *elem, unsigned long opaque, unsigned long *key,
706          size_t index, void *__func)
707{
708    visitorl_t func = __func;
709
710    func(elem, opaque, *key, index);
711}
712EXPORT_SYMBOL_GPL(visitorl);
713
714void visitor32(void *elem, unsigned long opaque, unsigned long *__key,
715           size_t index, void *__func)
716{
717    visitor32_t func = __func;
718    u32 *key = (void *)__key;
719
720    func(elem, opaque, *key, index);
721}
722EXPORT_SYMBOL_GPL(visitor32);
723
724void visitor64(void *elem, unsigned long opaque, unsigned long *__key,
725           size_t index, void *__func)
726{
727    visitor64_t func = __func;
728    u64 *key = (void *)__key;
729
730    func(elem, opaque, *key, index);
731}
732EXPORT_SYMBOL_GPL(visitor64);
733
734void visitor128(void *elem, unsigned long opaque, unsigned long *__key,
735        size_t index, void *__func)
736{
737    visitor128_t func = __func;
738    u64 *key = (void *)__key;
739
740    func(elem, opaque, key[0], key[1], index);
741}
742EXPORT_SYMBOL_GPL(visitor128);
743
744size_t btree_visitor(struct btree_head *head, struct btree_geo *geo,
745             unsigned long opaque,
746             void (*func)(void *elem, unsigned long opaque,
747                       unsigned long *key,
748                       size_t index, void *func2),
749             void *func2)
750{
751    size_t count = 0;
752
753    if (!func2)
754        func = empty;
755    if (head->node)
756        count = __btree_for_each(head, geo, head->node, opaque, func,
757                func2, 0, head->height, 0);
758    return count;
759}
760EXPORT_SYMBOL_GPL(btree_visitor);
761
762size_t btree_grim_visitor(struct btree_head *head, struct btree_geo *geo,
763              unsigned long opaque,
764              void (*func)(void *elem, unsigned long opaque,
765                       unsigned long *key,
766                       size_t index, void *func2),
767              void *func2)
768{
769    size_t count = 0;
770
771    if (!func2)
772        func = empty;
773    if (head->node)
774        count = __btree_for_each(head, geo, head->node, opaque, func,
775                func2, 1, head->height, 0);
776    __btree_init(head);
777    return count;
778}
779EXPORT_SYMBOL_GPL(btree_grim_visitor);
780
781static int __init btree_module_init(void)
782{
783    btree_cachep = kmem_cache_create("btree_node", NODESIZE, 0,
784            SLAB_HWCACHE_ALIGN, NULL);
785    return 0;
786}
787
788static void __exit btree_module_exit(void)
789{
790    kmem_cache_destroy(btree_cachep);
791}
792
793/* If core code starts using btree, initialization should happen even earlier */
794module_init(btree_module_init);
795module_exit(btree_module_exit);
796
797MODULE_AUTHOR("Joern Engel <joern@logfs.org>");
798MODULE_AUTHOR("Johannes Berg <johannes@sipsolutions.net>");
799MODULE_LICENSE("GPL");
800

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