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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 <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;
322 longcpy(key, __key, geo->keylen);
323retry:
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 longcpy(key, retry_key, geo->keylen);
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 BUG_ON(!val);
513 return btree_insert_level(head, geo, key, val, 1, gfp);
514}
515EXPORT_SYMBOL_GPL(btree_insert);
516
517static void *btree_remove_level(struct btree_head *head, struct btree_geo *geo,
518 unsigned long *key, int level);
519static void merge(struct btree_head *head, struct btree_geo *geo, int level,
520 unsigned long *left, int lfill,
521 unsigned long *right, int rfill,
522 unsigned long *parent, int lpos)
523{
524 int i;
525
526 for (i = 0; i < rfill; i++) {
527 /* Move all keys to the left */
528 setkey(geo, left, lfill + i, bkey(geo, right, i));
529 setval(geo, left, lfill + i, bval(geo, right, i));
530 }
531 /* Exchange left and right child in parent */
532 setval(geo, parent, lpos, right);
533 setval(geo, parent, lpos + 1, left);
534 /* Remove left (formerly right) child from parent */
535 btree_remove_level(head, geo, bkey(geo, parent, lpos), level + 1);
536 mempool_free(right, head->mempool);
537}
538
539static void rebalance(struct btree_head *head, struct btree_geo *geo,
540 unsigned long *key, int level, unsigned long *child, int fill)
541{
542 unsigned long *parent, *left = NULL, *right = NULL;
543 int i, no_left, no_right;
544
545 if (fill == 0) {
546 /* Because we don't steal entries from a neighbour, this case
547 * can happen. Parent node contains a single child, this
548 * node, so merging with a sibling never happens.
549 */
550 btree_remove_level(head, geo, key, level + 1);
551 mempool_free(child, head->mempool);
552 return;
553 }
554
555 parent = find_level(head, geo, key, level + 1);
556 i = getpos(geo, parent, key);
557 BUG_ON(bval(geo, parent, i) != child);
558
559 if (i > 0) {
560 left = bval(geo, parent, i - 1);
561 no_left = getfill(geo, left, 0);
562 if (fill + no_left <= geo->no_pairs) {
563 merge(head, geo, level,
564 left, no_left,
565 child, fill,
566 parent, i - 1);
567 return;
568 }
569 }
570 if (i + 1 < getfill(geo, parent, i)) {
571 right = bval(geo, parent, i + 1);
572 no_right = getfill(geo, right, 0);
573 if (fill + no_right <= geo->no_pairs) {
574 merge(head, geo, level,
575 child, fill,
576 right, no_right,
577 parent, i);
578 return;
579 }
580 }
581 /*
582 * We could also try to steal one entry from the left or right
583 * neighbor. By not doing so we changed the invariant from
584 * "all nodes are at least half full" to "no two neighboring
585 * nodes can be merged". Which means that the average fill of
586 * all nodes is still half or better.
587 */
588}
589
590static void *btree_remove_level(struct btree_head *head, struct btree_geo *geo,
591 unsigned long *key, int level)
592{
593 unsigned long *node;
594 int i, pos, fill;
595 void *ret;
596
597 if (level > head->height) {
598 /* we recursed all the way up */
599 head->height = 0;
600 head->node = NULL;
601 return NULL;
602 }
603
604 node = find_level(head, geo, key, level);
605 pos = getpos(geo, node, key);
606 fill = getfill(geo, node, pos);
607 if ((level == 1) && (keycmp(geo, node, pos, key) != 0))
608 return NULL;
609 ret = bval(geo, node, pos);
610
611 /* remove and shift */
612 for (i = pos; i < fill - 1; i++) {
613 setkey(geo, node, i, bkey(geo, node, i + 1));
614 setval(geo, node, i, bval(geo, node, i + 1));
615 }
616 clearpair(geo, node, fill - 1);
617
618 if (fill - 1 < geo->no_pairs / 2) {
619 if (level < head->height)
620 rebalance(head, geo, key, level, node, fill - 1);
621 else if (fill - 1 == 1)
622 btree_shrink(head, geo);
623 }
624
625 return ret;
626}
627
628void *btree_remove(struct btree_head *head, struct btree_geo *geo,
629 unsigned long *key)
630{
631 if (head->height == 0)
632 return NULL;
633
634 return btree_remove_level(head, geo, key, 1);
635}
636EXPORT_SYMBOL_GPL(btree_remove);
637
638int btree_merge(struct btree_head *target, struct btree_head *victim,
639 struct btree_geo *geo, gfp_t gfp)
640{
641 unsigned long key[geo->keylen];
642 unsigned long dup[geo->keylen];
643 void *val;
644 int err;
645
646 BUG_ON(target == victim);
647
648 if (!(target->node)) {
649 /* target is empty, just copy fields over */
650 target->node = victim->node;
651 target->height = victim->height;
652 __btree_init(victim);
653 return 0;
654 }
655
656 /* TODO: This needs some optimizations. Currently we do three tree
657 * walks to remove a single object from the victim.
658 */
659 for (;;) {
660 if (!btree_last(victim, geo, key))
661 break;
662 val = btree_lookup(victim, geo, key);
663 err = btree_insert(target, geo, key, val, gfp);
664 if (err)
665 return err;
666 /* We must make a copy of the key, as the original will get
667 * mangled inside btree_remove. */
668 longcpy(dup, key, geo->keylen);
669 btree_remove(victim, geo, dup);
670 }
671 return 0;
672}
673EXPORT_SYMBOL_GPL(btree_merge);
674
675static size_t __btree_for_each(struct btree_head *head, struct btree_geo *geo,
676 unsigned long *node, unsigned long opaque,
677 void (*func)(void *elem, unsigned long opaque,
678 unsigned long *key, size_t index,
679 void *func2),
680 void *func2, int reap, int height, size_t count)
681{
682 int i;
683 unsigned long *child;
684
685 for (i = 0; i < geo->no_pairs; i++) {
686 child = bval(geo, node, i);
687 if (!child)
688 break;
689 if (height > 1)
690 count = __btree_for_each(head, geo, child, opaque,
691 func, func2, reap, height - 1, count);
692 else
693 func(child, opaque, bkey(geo, node, i), count++,
694 func2);
695 }
696 if (reap)
697 mempool_free(node, head->mempool);
698 return count;
699}
700
701static void empty(void *elem, unsigned long opaque, unsigned long *key,
702 size_t index, void *func2)
703{
704}
705
706void visitorl(void *elem, unsigned long opaque, unsigned long *key,
707 size_t index, void *__func)
708{
709 visitorl_t func = __func;
710
711 func(elem, opaque, *key, index);
712}
713EXPORT_SYMBOL_GPL(visitorl);
714
715void visitor32(void *elem, unsigned long opaque, unsigned long *__key,
716 size_t index, void *__func)
717{
718 visitor32_t func = __func;
719 u32 *key = (void *)__key;
720
721 func(elem, opaque, *key, index);
722}
723EXPORT_SYMBOL_GPL(visitor32);
724
725void visitor64(void *elem, unsigned long opaque, unsigned long *__key,
726 size_t index, void *__func)
727{
728 visitor64_t func = __func;
729 u64 *key = (void *)__key;
730
731 func(elem, opaque, *key, index);
732}
733EXPORT_SYMBOL_GPL(visitor64);
734
735void visitor128(void *elem, unsigned long opaque, unsigned long *__key,
736 size_t index, void *__func)
737{
738 visitor128_t func = __func;
739 u64 *key = (void *)__key;
740
741 func(elem, opaque, key[0], key[1], index);
742}
743EXPORT_SYMBOL_GPL(visitor128);
744
745size_t btree_visitor(struct btree_head *head, struct btree_geo *geo,
746 unsigned long opaque,
747 void (*func)(void *elem, unsigned long opaque,
748 unsigned long *key,
749 size_t index, void *func2),
750 void *func2)
751{
752 size_t count = 0;
753
754 if (!func2)
755 func = empty;
756 if (head->node)
757 count = __btree_for_each(head, geo, head->node, opaque, func,
758 func2, 0, head->height, 0);
759 return count;
760}
761EXPORT_SYMBOL_GPL(btree_visitor);
762
763size_t btree_grim_visitor(struct btree_head *head, struct btree_geo *geo,
764 unsigned long opaque,
765 void (*func)(void *elem, unsigned long opaque,
766 unsigned long *key,
767 size_t index, void *func2),
768 void *func2)
769{
770 size_t count = 0;
771
772 if (!func2)
773 func = empty;
774 if (head->node)
775 count = __btree_for_each(head, geo, head->node, opaque, func,
776 func2, 1, head->height, 0);
777 __btree_init(head);
778 return count;
779}
780EXPORT_SYMBOL_GPL(btree_grim_visitor);
781
782static int __init btree_module_init(void)
783{
784 btree_cachep = kmem_cache_create("btree_node", NODESIZE, 0,
785 SLAB_HWCACHE_ALIGN, NULL);
786 return 0;
787}
788
789static void __exit btree_module_exit(void)
790{
791 kmem_cache_destroy(btree_cachep);
792}
793
794/* If core code starts using btree, initialization should happen even earlier */
795module_init(btree_module_init);
796module_exit(btree_module_exit);
797
798MODULE_AUTHOR("Joern Engel <joern@logfs.org>");
799MODULE_AUTHOR("Johannes Berg <johannes@sipsolutions.net>");
800MODULE_LICENSE("GPL");
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}
360
361static int getpos(struct btree_geo *geo, unsigned long *node,
362 unsigned long *key)
363{
364 int i;
365
366 for (i = 0; i < geo->no_pairs; i++) {
367 if (keycmp(geo, node, i, key) <= 0)
368 break;
369 }
370 return i;
371}
372
373static int getfill(struct btree_geo *geo, unsigned long *node, int start)
374{
375 int i;
376
377 for (i = start; i < geo->no_pairs; i++)
378 if (!bval(geo, node, i))
379 break;
380 return i;
381}
382
383/*
384 * locate the correct leaf node in the btree
385 */
386static unsigned long *find_level(struct btree_head *head, struct btree_geo *geo,
387 unsigned long *key, int level)
388{
389 unsigned long *node = head->node;
390 int i, height;
391
392 for (height = head->height; height > level; height--) {
393 for (i = 0; i < geo->no_pairs; i++)
394 if (keycmp(geo, node, i, key) <= 0)
395 break;
396
397 if ((i == geo->no_pairs) || !bval(geo, node, i)) {
398 /* right-most key is too large, update it */
399 /* FIXME: If the right-most key on higher levels is
400 * always zero, this wouldn't be necessary. */
401 i--;
402 setkey(geo, node, i, key);
403 }
404 BUG_ON(i < 0);
405 node = bval(geo, node, i);
406 }
407 BUG_ON(!node);
408 return node;
409}
410
411static int btree_grow(struct btree_head *head, struct btree_geo *geo,
412 gfp_t gfp)
413{
414 unsigned long *node;
415 int fill;
416
417 node = btree_node_alloc(head, gfp);
418 if (!node)
419 return -ENOMEM;
420 if (head->node) {
421 fill = getfill(geo, head->node, 0);
422 setkey(geo, node, 0, bkey(geo, head->node, fill - 1));
423 setval(geo, node, 0, head->node);
424 }
425 head->node = node;
426 head->height++;
427 return 0;
428}
429
430static void btree_shrink(struct btree_head *head, struct btree_geo *geo)
431{
432 unsigned long *node;
433 int fill;
434
435 if (head->height <= 1)
436 return;
437
438 node = head->node;
439 fill = getfill(geo, node, 0);
440 BUG_ON(fill > 1);
441 head->node = bval(geo, node, 0);
442 head->height--;
443 mempool_free(node, head->mempool);
444}
445
446static int btree_insert_level(struct btree_head *head, struct btree_geo *geo,
447 unsigned long *key, void *val, int level,
448 gfp_t gfp)
449{
450 unsigned long *node;
451 int i, pos, fill, err;
452
453 BUG_ON(!val);
454 if (head->height < level) {
455 err = btree_grow(head, geo, gfp);
456 if (err)
457 return err;
458 }
459
460retry:
461 node = find_level(head, geo, key, level);
462 pos = getpos(geo, node, key);
463 fill = getfill(geo, node, pos);
464 /* two identical keys are not allowed */
465 BUG_ON(pos < fill && keycmp(geo, node, pos, key) == 0);
466
467 if (fill == geo->no_pairs) {
468 /* need to split node */
469 unsigned long *new;
470
471 new = btree_node_alloc(head, gfp);
472 if (!new)
473 return -ENOMEM;
474 err = btree_insert_level(head, geo,
475 bkey(geo, node, fill / 2 - 1),
476 new, level + 1, gfp);
477 if (err) {
478 mempool_free(new, head->mempool);
479 return err;
480 }
481 for (i = 0; i < fill / 2; i++) {
482 setkey(geo, new, i, bkey(geo, node, i));
483 setval(geo, new, i, bval(geo, node, i));
484 setkey(geo, node, i, bkey(geo, node, i + fill / 2));
485 setval(geo, node, i, bval(geo, node, i + fill / 2));
486 clearpair(geo, node, i + fill / 2);
487 }
488 if (fill & 1) {
489 setkey(geo, node, i, bkey(geo, node, fill - 1));
490 setval(geo, node, i, bval(geo, node, fill - 1));
491 clearpair(geo, node, fill - 1);
492 }
493 goto retry;
494 }
495 BUG_ON(fill >= geo->no_pairs);
496
497 /* shift and insert */
498 for (i = fill; i > pos; i--) {
499 setkey(geo, node, i, bkey(geo, node, i - 1));
500 setval(geo, node, i, bval(geo, node, i - 1));
501 }
502 setkey(geo, node, pos, key);
503 setval(geo, node, pos, val);
504
505 return 0;
506}
507
508int btree_insert(struct btree_head *head, struct btree_geo *geo,
509 unsigned long *key, void *val, gfp_t gfp)
510{
511 return btree_insert_level(head, geo, key, val, 1, gfp);
512}
513EXPORT_SYMBOL_GPL(btree_insert);
514
515static void *btree_remove_level(struct btree_head *head, struct btree_geo *geo,
516 unsigned long *key, int level);
517static void merge(struct btree_head *head, struct btree_geo *geo, int level,
518 unsigned long *left, int lfill,
519 unsigned long *right, int rfill,
520 unsigned long *parent, int lpos)
521{
522 int i;
523
524 for (i = 0; i < rfill; i++) {
525 /* Move all keys to the left */
526 setkey(geo, left, lfill + i, bkey(geo, right, i));
527 setval(geo, left, lfill + i, bval(geo, right, i));
528 }
529 /* Exchange left and right child in parent */
530 setval(geo, parent, lpos, right);
531 setval(geo, parent, lpos + 1, left);
532 /* Remove left (formerly right) child from parent */
533 btree_remove_level(head, geo, bkey(geo, parent, lpos), level + 1);
534 mempool_free(right, head->mempool);
535}
536
537static void rebalance(struct btree_head *head, struct btree_geo *geo,
538 unsigned long *key, int level, unsigned long *child, int fill)
539{
540 unsigned long *parent, *left = NULL, *right = NULL;
541 int i, no_left, no_right;
542
543 if (fill == 0) {
544 /* Because we don't steal entries from a neighbour, this case
545 * can happen. Parent node contains a single child, this
546 * node, so merging with a sibling never happens.
547 */
548 btree_remove_level(head, geo, key, level + 1);
549 mempool_free(child, head->mempool);
550 return;
551 }
552
553 parent = find_level(head, geo, key, level + 1);
554 i = getpos(geo, parent, key);
555 BUG_ON(bval(geo, parent, i) != child);
556
557 if (i > 0) {
558 left = bval(geo, parent, i - 1);
559 no_left = getfill(geo, left, 0);
560 if (fill + no_left <= geo->no_pairs) {
561 merge(head, geo, level,
562 left, no_left,
563 child, fill,
564 parent, i - 1);
565 return;
566 }
567 }
568 if (i + 1 < getfill(geo, parent, i)) {
569 right = bval(geo, parent, i + 1);
570 no_right = getfill(geo, right, 0);
571 if (fill + no_right <= geo->no_pairs) {
572 merge(head, geo, level,
573 child, fill,
574 right, no_right,
575 parent, i);
576 return;
577 }
578 }
579 /*
580 * We could also try to steal one entry from the left or right
581 * neighbor. By not doing so we changed the invariant from
582 * "all nodes are at least half full" to "no two neighboring
583 * nodes can be merged". Which means that the average fill of
584 * all nodes is still half or better.
585 */
586}
587
588static void *btree_remove_level(struct btree_head *head, struct btree_geo *geo,
589 unsigned long *key, int level)
590{
591 unsigned long *node;
592 int i, pos, fill;
593 void *ret;
594
595 if (level > head->height) {
596 /* we recursed all the way up */
597 head->height = 0;
598 head->node = NULL;
599 return NULL;
600 }
601
602 node = find_level(head, geo, key, level);
603 pos = getpos(geo, node, key);
604 fill = getfill(geo, node, pos);
605 if ((level == 1) && (keycmp(geo, node, pos, key) != 0))
606 return NULL;
607 ret = bval(geo, node, pos);
608
609 /* remove and shift */
610 for (i = pos; i < fill - 1; i++) {
611 setkey(geo, node, i, bkey(geo, node, i + 1));
612 setval(geo, node, i, bval(geo, node, i + 1));
613 }
614 clearpair(geo, node, fill - 1);
615
616 if (fill - 1 < geo->no_pairs / 2) {
617 if (level < head->height)
618 rebalance(head, geo, key, level, node, fill - 1);
619 else if (fill - 1 == 1)
620 btree_shrink(head, geo);
621 }
622
623 return ret;
624}
625
626void *btree_remove(struct btree_head *head, struct btree_geo *geo,
627 unsigned long *key)
628{
629 if (head->height == 0)
630 return NULL;
631
632 return btree_remove_level(head, geo, key, 1);
633}
634EXPORT_SYMBOL_GPL(btree_remove);
635
636int btree_merge(struct btree_head *target, struct btree_head *victim,
637 struct btree_geo *geo, gfp_t gfp)
638{
639 unsigned long key[geo->keylen];
640 unsigned long dup[geo->keylen];
641 void *val;
642 int err;
643
644 BUG_ON(target == victim);
645
646 if (!(target->node)) {
647 /* target is empty, just copy fields over */
648 target->node = victim->node;
649 target->height = victim->height;
650 __btree_init(victim);
651 return 0;
652 }
653
654 /* TODO: This needs some optimizations. Currently we do three tree
655 * walks to remove a single object from the victim.
656 */
657 for (;;) {
658 if (!btree_last(victim, geo, key))
659 break;
660 val = btree_lookup(victim, geo, key);
661 err = btree_insert(target, geo, key, val, gfp);
662 if (err)
663 return err;
664 /* We must make a copy of the key, as the original will get
665 * mangled inside btree_remove. */
666 longcpy(dup, key, geo->keylen);
667 btree_remove(victim, geo, dup);
668 }
669 return 0;
670}
671EXPORT_SYMBOL_GPL(btree_merge);
672
673static size_t __btree_for_each(struct btree_head *head, struct btree_geo *geo,
674 unsigned long *node, unsigned long opaque,
675 void (*func)(void *elem, unsigned long opaque,
676 unsigned long *key, size_t index,
677 void *func2),
678 void *func2, int reap, int height, size_t count)
679{
680 int i;
681 unsigned long *child;
682
683 for (i = 0; i < geo->no_pairs; i++) {
684 child = bval(geo, node, i);
685 if (!child)
686 break;
687 if (height > 1)
688 count = __btree_for_each(head, geo, child, opaque,
689 func, func2, reap, height - 1, count);
690 else
691 func(child, opaque, bkey(geo, node, i), count++,
692 func2);
693 }
694 if (reap)
695 mempool_free(node, head->mempool);
696 return count;
697}
698
699static void empty(void *elem, unsigned long opaque, unsigned long *key,
700 size_t index, void *func2)
701{
702}
703
704void visitorl(void *elem, unsigned long opaque, unsigned long *key,
705 size_t index, void *__func)
706{
707 visitorl_t func = __func;
708
709 func(elem, opaque, *key, index);
710}
711EXPORT_SYMBOL_GPL(visitorl);
712
713void visitor32(void *elem, unsigned long opaque, unsigned long *__key,
714 size_t index, void *__func)
715{
716 visitor32_t func = __func;
717 u32 *key = (void *)__key;
718
719 func(elem, opaque, *key, index);
720}
721EXPORT_SYMBOL_GPL(visitor32);
722
723void visitor64(void *elem, unsigned long opaque, unsigned long *__key,
724 size_t index, void *__func)
725{
726 visitor64_t func = __func;
727 u64 *key = (void *)__key;
728
729 func(elem, opaque, *key, index);
730}
731EXPORT_SYMBOL_GPL(visitor64);
732
733void visitor128(void *elem, unsigned long opaque, unsigned long *__key,
734 size_t index, void *__func)
735{
736 visitor128_t func = __func;
737 u64 *key = (void *)__key;
738
739 func(elem, opaque, key[0], key[1], index);
740}
741EXPORT_SYMBOL_GPL(visitor128);
742
743size_t btree_visitor(struct btree_head *head, struct btree_geo *geo,
744 unsigned long opaque,
745 void (*func)(void *elem, unsigned long opaque,
746 unsigned long *key,
747 size_t index, void *func2),
748 void *func2)
749{
750 size_t count = 0;
751
752 if (!func2)
753 func = empty;
754 if (head->node)
755 count = __btree_for_each(head, geo, head->node, opaque, func,
756 func2, 0, head->height, 0);
757 return count;
758}
759EXPORT_SYMBOL_GPL(btree_visitor);
760
761size_t btree_grim_visitor(struct btree_head *head, struct btree_geo *geo,
762 unsigned long opaque,
763 void (*func)(void *elem, unsigned long opaque,
764 unsigned long *key,
765 size_t index, void *func2),
766 void *func2)
767{
768 size_t count = 0;
769
770 if (!func2)
771 func = empty;
772 if (head->node)
773 count = __btree_for_each(head, geo, head->node, opaque, func,
774 func2, 1, head->height, 0);
775 __btree_init(head);
776 return count;
777}
778EXPORT_SYMBOL_GPL(btree_grim_visitor);
779
780static int __init btree_module_init(void)
781{
782 btree_cachep = kmem_cache_create("btree_node", NODESIZE, 0,
783 SLAB_HWCACHE_ALIGN, NULL);
784 return 0;
785}
786
787static void __exit btree_module_exit(void)
788{
789 kmem_cache_destroy(btree_cachep);
790}
791
792/* If core code starts using btree, initialization should happen even earlier */
793module_init(btree_module_init);
794module_exit(btree_module_exit);
795
796MODULE_AUTHOR("Joern Engel <joern@logfs.org>");
797MODULE_AUTHOR("Johannes Berg <johannes@sipsolutions.net>");
798MODULE_LICENSE("GPL");