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
49struct btree_geo {
50	int keylen;
51	int no_pairs;
52	int no_longs;
53};
54
55struct btree_geo btree_geo32 = {
56	.keylen = 1,
57	.no_pairs = NODESIZE / sizeof(long) / 2,
58	.no_longs = NODESIZE / sizeof(long) / 2,
59};
60EXPORT_SYMBOL_GPL(btree_geo32);
61
62#define LONG_PER_U64 (64 / BITS_PER_LONG)
63struct 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};
68EXPORT_SYMBOL_GPL(btree_geo64);
69
70struct 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};
75EXPORT_SYMBOL_GPL(btree_geo128);
76
77#define MAX_KEYLEN	(2 * LONG_PER_U64)
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_free(head->node, head->mempool);
202	mempool_destroy(head->mempool);
203	head->mempool = NULL;
204}
205EXPORT_SYMBOL_GPL(btree_destroy);
206
207void *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}
222EXPORT_SYMBOL_GPL(btree_last);
223
224static 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
230static 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
241static void *btree_lookup_node(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	return node;
261}
262
263void *btree_lookup(struct btree_head *head, struct btree_geo *geo,
264		unsigned long *key)
265{
266	int i;
267	unsigned long *node;
268
269	node = btree_lookup_node(head, geo, key);
270	if (!node)
271		return NULL;
272
273	for (i = 0; i < geo->no_pairs; i++)
274		if (keycmp(geo, node, i, key) == 0)
275			return bval(geo, node, i);
276	return NULL;
277}
278EXPORT_SYMBOL_GPL(btree_lookup);
279
280int btree_update(struct btree_head *head, struct btree_geo *geo,
281		 unsigned long *key, void *val)
282{
283	int i;
284	unsigned long *node;
285
286	node = btree_lookup_node(head, geo, key);
287	if (!node)
288		return -ENOENT;
289
290	for (i = 0; i < geo->no_pairs; i++)
291		if (keycmp(geo, node, i, key) == 0) {
292			setval(geo, node, i, val);
293			return 0;
294		}
295	return -ENOENT;
296}
297EXPORT_SYMBOL_GPL(btree_update);
298
299/*
300 * Usually this function is quite similar to normal lookup.  But the key of
301 * a parent node may be smaller than the smallest key of all its siblings.
302 * In such a case we cannot just return NULL, as we have only proven that no
303 * key smaller than __key, but larger than this parent key exists.
304 * So we set __key to the parent key and retry.  We have to use the smallest
305 * such parent key, which is the last parent key we encountered.
306 */
307void *btree_get_prev(struct btree_head *head, struct btree_geo *geo,
308		     unsigned long *__key)
309{
310	int i, height;
311	unsigned long *node, *oldnode;
312	unsigned long *retry_key = NULL, key[MAX_KEYLEN];
313
314	if (keyzero(geo, __key))
315		return NULL;
316
317	if (head->height == 0)
318		return NULL;
319	longcpy(key, __key, geo->keylen);
320retry:
321	dec_key(geo, key);
322
323	node = head->node;
324	for (height = head->height ; height > 1; height--) {
325		for (i = 0; i < geo->no_pairs; i++)
326			if (keycmp(geo, node, i, key) <= 0)
327				break;
328		if (i == geo->no_pairs)
329			goto miss;
330		oldnode = node;
331		node = bval(geo, node, i);
332		if (!node)
333			goto miss;
334		retry_key = bkey(geo, oldnode, i);
335	}
336
337	if (!node)
338		goto miss;
339
340	for (i = 0; i < geo->no_pairs; i++) {
341		if (keycmp(geo, node, i, key) <= 0) {
342			if (bval(geo, node, i)) {
343				longcpy(__key, bkey(geo, node, i), geo->keylen);
344				return bval(geo, node, i);
345			} else
346				goto miss;
347		}
348	}
349miss:
350	if (retry_key) {
351		longcpy(key, retry_key, geo->keylen);
352		retry_key = NULL;
353		goto retry;
354	}
355	return NULL;
356}
357EXPORT_SYMBOL_GPL(btree_get_prev);
358
359static int getpos(struct btree_geo *geo, unsigned long *node,
360		unsigned long *key)
361{
362	int i;
363
364	for (i = 0; i < geo->no_pairs; i++) {
365		if (keycmp(geo, node, i, key) <= 0)
366			break;
367	}
368	return i;
369}
370
371static int getfill(struct btree_geo *geo, unsigned long *node, int start)
372{
373	int i;
374
375	for (i = start; i < geo->no_pairs; i++)
376		if (!bval(geo, node, i))
377			break;
378	return i;
379}
380
381/*
382 * locate the correct leaf node in the btree
383 */
384static unsigned long *find_level(struct btree_head *head, struct btree_geo *geo,
385		unsigned long *key, int level)
386{
387	unsigned long *node = head->node;
388	int i, height;
389
390	for (height = head->height; height > level; height--) {
391		for (i = 0; i < geo->no_pairs; i++)
392			if (keycmp(geo, node, i, key) <= 0)
393				break;
394
395		if ((i == geo->no_pairs) || !bval(geo, node, i)) {
396			/* right-most key is too large, update it */
397			/* FIXME: If the right-most key on higher levels is
398			 * always zero, this wouldn't be necessary. */
399			i--;
400			setkey(geo, node, i, key);
401		}
402		BUG_ON(i < 0);
403		node = bval(geo, node, i);
404	}
405	BUG_ON(!node);
406	return node;
407}
408
409static int btree_grow(struct btree_head *head, struct btree_geo *geo,
410		      gfp_t gfp)
411{
412	unsigned long *node;
413	int fill;
414
415	node = btree_node_alloc(head, gfp);
416	if (!node)
417		return -ENOMEM;
418	if (head->node) {
419		fill = getfill(geo, head->node, 0);
420		setkey(geo, node, 0, bkey(geo, head->node, fill - 1));
421		setval(geo, node, 0, head->node);
422	}
423	head->node = node;
424	head->height++;
425	return 0;
426}
427
428static void btree_shrink(struct btree_head *head, struct btree_geo *geo)
429{
430	unsigned long *node;
431	int fill;
432
433	if (head->height <= 1)
434		return;
435
436	node = head->node;
437	fill = getfill(geo, node, 0);
438	BUG_ON(fill > 1);
439	head->node = bval(geo, node, 0);
440	head->height--;
441	mempool_free(node, head->mempool);
442}
443
444static int btree_insert_level(struct btree_head *head, struct btree_geo *geo,
445			      unsigned long *key, void *val, int level,
446			      gfp_t gfp)
447{
448	unsigned long *node;
449	int i, pos, fill, err;
450
451	BUG_ON(!val);
452	if (head->height < level) {
453		err = btree_grow(head, geo, gfp);
454		if (err)
455			return err;
456	}
457
458retry:
459	node = find_level(head, geo, key, level);
460	pos = getpos(geo, node, key);
461	fill = getfill(geo, node, pos);
462	/* two identical keys are not allowed */
463	BUG_ON(pos < fill && keycmp(geo, node, pos, key) == 0);
464
465	if (fill == geo->no_pairs) {
466		/* need to split node */
467		unsigned long *new;
468
469		new = btree_node_alloc(head, gfp);
470		if (!new)
471			return -ENOMEM;
472		err = btree_insert_level(head, geo,
473				bkey(geo, node, fill / 2 - 1),
474				new, level + 1, gfp);
475		if (err) {
476			mempool_free(new, head->mempool);
477			return err;
478		}
479		for (i = 0; i < fill / 2; i++) {
480			setkey(geo, new, i, bkey(geo, node, i));
481			setval(geo, new, i, bval(geo, node, i));
482			setkey(geo, node, i, bkey(geo, node, i + fill / 2));
483			setval(geo, node, i, bval(geo, node, i + fill / 2));
484			clearpair(geo, node, i + fill / 2);
485		}
486		if (fill & 1) {
487			setkey(geo, node, i, bkey(geo, node, fill - 1));
488			setval(geo, node, i, bval(geo, node, fill - 1));
489			clearpair(geo, node, fill - 1);
490		}
491		goto retry;
492	}
493	BUG_ON(fill >= geo->no_pairs);
494
495	/* shift and insert */
496	for (i = fill; i > pos; i--) {
497		setkey(geo, node, i, bkey(geo, node, i - 1));
498		setval(geo, node, i, bval(geo, node, i - 1));
499	}
500	setkey(geo, node, pos, key);
501	setval(geo, node, pos, val);
502
503	return 0;
504}
505
506int btree_insert(struct btree_head *head, struct btree_geo *geo,
507		unsigned long *key, void *val, gfp_t gfp)
508{
509	BUG_ON(!val);
510	return btree_insert_level(head, geo, key, val, 1, gfp);
511}
512EXPORT_SYMBOL_GPL(btree_insert);
513
514static void *btree_remove_level(struct btree_head *head, struct btree_geo *geo,
515		unsigned long *key, int level);
516static void merge(struct btree_head *head, struct btree_geo *geo, int level,
517		unsigned long *left, int lfill,
518		unsigned long *right, int rfill,
519		unsigned long *parent, int lpos)
520{
521	int i;
522
523	for (i = 0; i < rfill; i++) {
524		/* Move all keys to the left */
525		setkey(geo, left, lfill + i, bkey(geo, right, i));
526		setval(geo, left, lfill + i, bval(geo, right, i));
527	}
528	/* Exchange left and right child in parent */
529	setval(geo, parent, lpos, right);
530	setval(geo, parent, lpos + 1, left);
531	/* Remove left (formerly right) child from parent */
532	btree_remove_level(head, geo, bkey(geo, parent, lpos), level + 1);
533	mempool_free(right, head->mempool);
534}
535
536static void rebalance(struct btree_head *head, struct btree_geo *geo,
537		unsigned long *key, int level, unsigned long *child, int fill)
538{
539	unsigned long *parent, *left = NULL, *right = NULL;
540	int i, no_left, no_right;
541
542	if (fill == 0) {
543		/* Because we don't steal entries from a neighbour, this case
544		 * can happen.  Parent node contains a single child, this
545		 * node, so merging with a sibling never happens.
546		 */
547		btree_remove_level(head, geo, key, level + 1);
548		mempool_free(child, head->mempool);
549		return;
550	}
551
552	parent = find_level(head, geo, key, level + 1);
553	i = getpos(geo, parent, key);
554	BUG_ON(bval(geo, parent, i) != child);
555
556	if (i > 0) {
557		left = bval(geo, parent, i - 1);
558		no_left = getfill(geo, left, 0);
559		if (fill + no_left <= geo->no_pairs) {
560			merge(head, geo, level,
561					left, no_left,
562					child, fill,
563					parent, i - 1);
564			return;
565		}
566	}
567	if (i + 1 < getfill(geo, parent, i)) {
568		right = bval(geo, parent, i + 1);
569		no_right = getfill(geo, right, 0);
570		if (fill + no_right <= geo->no_pairs) {
571			merge(head, geo, level,
572					child, fill,
573					right, no_right,
574					parent, i);
575			return;
576		}
577	}
578	/*
579	 * We could also try to steal one entry from the left or right
580	 * neighbor.  By not doing so we changed the invariant from
581	 * "all nodes are at least half full" to "no two neighboring
582	 * nodes can be merged".  Which means that the average fill of
583	 * all nodes is still half or better.
584	 */
585}
586
587static void *btree_remove_level(struct btree_head *head, struct btree_geo *geo,
588		unsigned long *key, int level)
589{
590	unsigned long *node;
591	int i, pos, fill;
592	void *ret;
593
594	if (level > head->height) {
595		/* we recursed all the way up */
596		head->height = 0;
597		head->node = NULL;
598		return NULL;
599	}
600
601	node = find_level(head, geo, key, level);
602	pos = getpos(geo, node, key);
603	fill = getfill(geo, node, pos);
604	if ((level == 1) && (keycmp(geo, node, pos, key) != 0))
605		return NULL;
606	ret = bval(geo, node, pos);
607
608	/* remove and shift */
609	for (i = pos; i < fill - 1; i++) {
610		setkey(geo, node, i, bkey(geo, node, i + 1));
611		setval(geo, node, i, bval(geo, node, i + 1));
612	}
613	clearpair(geo, node, fill - 1);
614
615	if (fill - 1 < geo->no_pairs / 2) {
616		if (level < head->height)
617			rebalance(head, geo, key, level, node, fill - 1);
618		else if (fill - 1 == 1)
619			btree_shrink(head, geo);
620	}
621
622	return ret;
623}
624
625void *btree_remove(struct btree_head *head, struct btree_geo *geo,
626		unsigned long *key)
627{
628	if (head->height == 0)
629		return NULL;
630
631	return btree_remove_level(head, geo, key, 1);
632}
633EXPORT_SYMBOL_GPL(btree_remove);
634
635int btree_merge(struct btree_head *target, struct btree_head *victim,
636		struct btree_geo *geo, gfp_t gfp)
637{
638	unsigned long key[MAX_KEYLEN];
639	unsigned long dup[MAX_KEYLEN];
640	void *val;
641	int err;
642
643	BUG_ON(target == victim);
644
645	if (!(target->node)) {
646		/* target is empty, just copy fields over */
647		target->node = victim->node;
648		target->height = victim->height;
649		__btree_init(victim);
650		return 0;
651	}
652
653	/* TODO: This needs some optimizations.  Currently we do three tree
654	 * walks to remove a single object from the victim.
655	 */
656	for (;;) {
657		if (!btree_last(victim, geo, key))
658			break;
659		val = btree_lookup(victim, geo, key);
660		err = btree_insert(target, geo, key, val, gfp);
661		if (err)
662			return err;
663		/* We must make a copy of the key, as the original will get
664		 * mangled inside btree_remove. */
665		longcpy(dup, key, geo->keylen);
666		btree_remove(victim, geo, dup);
667	}
668	return 0;
669}
670EXPORT_SYMBOL_GPL(btree_merge);
671
672static size_t __btree_for_each(struct btree_head *head, struct btree_geo *geo,
673			       unsigned long *node, unsigned long opaque,
674			       void (*func)(void *elem, unsigned long opaque,
675					    unsigned long *key, size_t index,
676					    void *func2),
677			       void *func2, int reap, int height, size_t count)
678{
679	int i;
680	unsigned long *child;
681
682	for (i = 0; i < geo->no_pairs; i++) {
683		child = bval(geo, node, i);
684		if (!child)
685			break;
686		if (height > 1)
687			count = __btree_for_each(head, geo, child, opaque,
688					func, func2, reap, height - 1, count);
689		else
690			func(child, opaque, bkey(geo, node, i), count++,
691					func2);
692	}
693	if (reap)
694		mempool_free(node, head->mempool);
695	return count;
696}
697
698static void empty(void *elem, unsigned long opaque, unsigned long *key,
699		  size_t index, void *func2)
700{
701}
702
703void visitorl(void *elem, unsigned long opaque, unsigned long *key,
704	      size_t index, void *__func)
705{
706	visitorl_t func = __func;
707
708	func(elem, opaque, *key, index);
709}
710EXPORT_SYMBOL_GPL(visitorl);
711
712void visitor32(void *elem, unsigned long opaque, unsigned long *__key,
713	       size_t index, void *__func)
714{
715	visitor32_t func = __func;
716	u32 *key = (void *)__key;
717
718	func(elem, opaque, *key, index);
719}
720EXPORT_SYMBOL_GPL(visitor32);
721
722void visitor64(void *elem, unsigned long opaque, unsigned long *__key,
723	       size_t index, void *__func)
724{
725	visitor64_t func = __func;
726	u64 *key = (void *)__key;
727
728	func(elem, opaque, *key, index);
729}
730EXPORT_SYMBOL_GPL(visitor64);
731
732void visitor128(void *elem, unsigned long opaque, unsigned long *__key,
733		size_t index, void *__func)
734{
735	visitor128_t func = __func;
736	u64 *key = (void *)__key;
737
738	func(elem, opaque, key[0], key[1], index);
739}
740EXPORT_SYMBOL_GPL(visitor128);
741
742size_t btree_visitor(struct btree_head *head, struct btree_geo *geo,
743		     unsigned long opaque,
744		     void (*func)(void *elem, unsigned long opaque,
745		     		  unsigned long *key,
746		     		  size_t index, void *func2),
747		     void *func2)
748{
749	size_t count = 0;
750
751	if (!func2)
752		func = empty;
753	if (head->node)
754		count = __btree_for_each(head, geo, head->node, opaque, func,
755				func2, 0, head->height, 0);
756	return count;
757}
758EXPORT_SYMBOL_GPL(btree_visitor);
759
760size_t btree_grim_visitor(struct btree_head *head, struct btree_geo *geo,
761			  unsigned long opaque,
762			  void (*func)(void *elem, unsigned long opaque,
763				       unsigned long *key,
764				       size_t index, void *func2),
765			  void *func2)
766{
767	size_t count = 0;
768
769	if (!func2)
770		func = empty;
771	if (head->node)
772		count = __btree_for_each(head, geo, head->node, opaque, func,
773				func2, 1, head->height, 0);
774	__btree_init(head);
775	return count;
776}
777EXPORT_SYMBOL_GPL(btree_grim_visitor);
778
779static int __init btree_module_init(void)
780{
781	btree_cachep = kmem_cache_create("btree_node", NODESIZE, 0,
782			SLAB_HWCACHE_ALIGN, NULL);
783	return 0;
784}
785
786static void __exit btree_module_exit(void)
787{
788	kmem_cache_destroy(btree_cachep);
789}
790
791/* If core code starts using btree, initialization should happen even earlier */
792module_init(btree_module_init);
793module_exit(btree_module_exit);
794
795MODULE_AUTHOR("Joern Engel <joern@logfs.org>");
796MODULE_AUTHOR("Johannes Berg <johannes@sipsolutions.net>");
797