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1/*
2 * Copyright (C) 2011 Red Hat, Inc.
3 *
4 * This file is released under the GPL.
5 */
6
7#include "dm-btree.h"
8#include "dm-btree-internal.h"
9#include "dm-transaction-manager.h"
10
11#include <linux/export.h>
12
13/*
14 * Removing an entry from a btree
15 * ==============================
16 *
17 * A very important constraint for our btree is that no node, except the
18 * root, may have fewer than a certain number of entries.
19 * (MIN_ENTRIES <= nr_entries <= MAX_ENTRIES).
20 *
21 * Ensuring this is complicated by the way we want to only ever hold the
22 * locks on 2 nodes concurrently, and only change nodes in a top to bottom
23 * fashion.
24 *
25 * Each node may have a left or right sibling. When decending the spine,
26 * if a node contains only MIN_ENTRIES then we try and increase this to at
27 * least MIN_ENTRIES + 1. We do this in the following ways:
28 *
29 * [A] No siblings => this can only happen if the node is the root, in which
30 * case we copy the childs contents over the root.
31 *
32 * [B] No left sibling
33 * ==> rebalance(node, right sibling)
34 *
35 * [C] No right sibling
36 * ==> rebalance(left sibling, node)
37 *
38 * [D] Both siblings, total_entries(left, node, right) <= DEL_THRESHOLD
39 * ==> delete node adding it's contents to left and right
40 *
41 * [E] Both siblings, total_entries(left, node, right) > DEL_THRESHOLD
42 * ==> rebalance(left, node, right)
43 *
44 * After these operations it's possible that the our original node no
45 * longer contains the desired sub tree. For this reason this rebalancing
46 * is performed on the children of the current node. This also avoids
47 * having a special case for the root.
48 *
49 * Once this rebalancing has occurred we can then step into the child node
50 * for internal nodes. Or delete the entry for leaf nodes.
51 */
52
53/*
54 * Some little utilities for moving node data around.
55 */
56static void node_shift(struct btree_node *n, int shift)
57{
58 uint32_t nr_entries = le32_to_cpu(n->header.nr_entries);
59 uint32_t value_size = le32_to_cpu(n->header.value_size);
60
61 if (shift < 0) {
62 shift = -shift;
63 BUG_ON(shift > nr_entries);
64 BUG_ON((void *) key_ptr(n, shift) >= value_ptr(n, shift));
65 memmove(key_ptr(n, 0),
66 key_ptr(n, shift),
67 (nr_entries - shift) * sizeof(__le64));
68 memmove(value_ptr(n, 0),
69 value_ptr(n, shift),
70 (nr_entries - shift) * value_size);
71 } else {
72 BUG_ON(nr_entries + shift > le32_to_cpu(n->header.max_entries));
73 memmove(key_ptr(n, shift),
74 key_ptr(n, 0),
75 nr_entries * sizeof(__le64));
76 memmove(value_ptr(n, shift),
77 value_ptr(n, 0),
78 nr_entries * value_size);
79 }
80}
81
82static void node_copy(struct btree_node *left, struct btree_node *right, int shift)
83{
84 uint32_t nr_left = le32_to_cpu(left->header.nr_entries);
85 uint32_t value_size = le32_to_cpu(left->header.value_size);
86 BUG_ON(value_size != le32_to_cpu(right->header.value_size));
87
88 if (shift < 0) {
89 shift = -shift;
90 BUG_ON(nr_left + shift > le32_to_cpu(left->header.max_entries));
91 memcpy(key_ptr(left, nr_left),
92 key_ptr(right, 0),
93 shift * sizeof(__le64));
94 memcpy(value_ptr(left, nr_left),
95 value_ptr(right, 0),
96 shift * value_size);
97 } else {
98 BUG_ON(shift > le32_to_cpu(right->header.max_entries));
99 memcpy(key_ptr(right, 0),
100 key_ptr(left, nr_left - shift),
101 shift * sizeof(__le64));
102 memcpy(value_ptr(right, 0),
103 value_ptr(left, nr_left - shift),
104 shift * value_size);
105 }
106}
107
108/*
109 * Delete a specific entry from a leaf node.
110 */
111static void delete_at(struct btree_node *n, unsigned index)
112{
113 unsigned nr_entries = le32_to_cpu(n->header.nr_entries);
114 unsigned nr_to_copy = nr_entries - (index + 1);
115 uint32_t value_size = le32_to_cpu(n->header.value_size);
116 BUG_ON(index >= nr_entries);
117
118 if (nr_to_copy) {
119 memmove(key_ptr(n, index),
120 key_ptr(n, index + 1),
121 nr_to_copy * sizeof(__le64));
122
123 memmove(value_ptr(n, index),
124 value_ptr(n, index + 1),
125 nr_to_copy * value_size);
126 }
127
128 n->header.nr_entries = cpu_to_le32(nr_entries - 1);
129}
130
131static unsigned merge_threshold(struct btree_node *n)
132{
133 return le32_to_cpu(n->header.max_entries) / 3;
134}
135
136struct child {
137 unsigned index;
138 struct dm_block *block;
139 struct btree_node *n;
140};
141
142static int init_child(struct dm_btree_info *info, struct dm_btree_value_type *vt,
143 struct btree_node *parent,
144 unsigned index, struct child *result)
145{
146 int r, inc;
147 dm_block_t root;
148
149 result->index = index;
150 root = value64(parent, index);
151
152 r = dm_tm_shadow_block(info->tm, root, &btree_node_validator,
153 &result->block, &inc);
154 if (r)
155 return r;
156
157 result->n = dm_block_data(result->block);
158
159 if (inc)
160 inc_children(info->tm, result->n, vt);
161
162 *((__le64 *) value_ptr(parent, index)) =
163 cpu_to_le64(dm_block_location(result->block));
164
165 return 0;
166}
167
168static void exit_child(struct dm_btree_info *info, struct child *c)
169{
170 dm_tm_unlock(info->tm, c->block);
171}
172
173static void shift(struct btree_node *left, struct btree_node *right, int count)
174{
175 uint32_t nr_left = le32_to_cpu(left->header.nr_entries);
176 uint32_t nr_right = le32_to_cpu(right->header.nr_entries);
177 uint32_t max_entries = le32_to_cpu(left->header.max_entries);
178 uint32_t r_max_entries = le32_to_cpu(right->header.max_entries);
179
180 BUG_ON(max_entries != r_max_entries);
181 BUG_ON(nr_left - count > max_entries);
182 BUG_ON(nr_right + count > max_entries);
183
184 if (!count)
185 return;
186
187 if (count > 0) {
188 node_shift(right, count);
189 node_copy(left, right, count);
190 } else {
191 node_copy(left, right, count);
192 node_shift(right, count);
193 }
194
195 left->header.nr_entries = cpu_to_le32(nr_left - count);
196 right->header.nr_entries = cpu_to_le32(nr_right + count);
197}
198
199static void __rebalance2(struct dm_btree_info *info, struct btree_node *parent,
200 struct child *l, struct child *r)
201{
202 struct btree_node *left = l->n;
203 struct btree_node *right = r->n;
204 uint32_t nr_left = le32_to_cpu(left->header.nr_entries);
205 uint32_t nr_right = le32_to_cpu(right->header.nr_entries);
206 unsigned threshold = 2 * merge_threshold(left) + 1;
207
208 if (nr_left + nr_right < threshold) {
209 /*
210 * Merge
211 */
212 node_copy(left, right, -nr_right);
213 left->header.nr_entries = cpu_to_le32(nr_left + nr_right);
214 delete_at(parent, r->index);
215
216 /*
217 * We need to decrement the right block, but not it's
218 * children, since they're still referenced by left.
219 */
220 dm_tm_dec(info->tm, dm_block_location(r->block));
221 } else {
222 /*
223 * Rebalance.
224 */
225 unsigned target_left = (nr_left + nr_right) / 2;
226 shift(left, right, nr_left - target_left);
227 *key_ptr(parent, r->index) = right->keys[0];
228 }
229}
230
231static int rebalance2(struct shadow_spine *s, struct dm_btree_info *info,
232 struct dm_btree_value_type *vt, unsigned left_index)
233{
234 int r;
235 struct btree_node *parent;
236 struct child left, right;
237
238 parent = dm_block_data(shadow_current(s));
239
240 r = init_child(info, vt, parent, left_index, &left);
241 if (r)
242 return r;
243
244 r = init_child(info, vt, parent, left_index + 1, &right);
245 if (r) {
246 exit_child(info, &left);
247 return r;
248 }
249
250 __rebalance2(info, parent, &left, &right);
251
252 exit_child(info, &left);
253 exit_child(info, &right);
254
255 return 0;
256}
257
258/*
259 * We dump as many entries from center as possible into left, then the rest
260 * in right, then rebalance2. This wastes some cpu, but I want something
261 * simple atm.
262 */
263static void delete_center_node(struct dm_btree_info *info, struct btree_node *parent,
264 struct child *l, struct child *c, struct child *r,
265 struct btree_node *left, struct btree_node *center, struct btree_node *right,
266 uint32_t nr_left, uint32_t nr_center, uint32_t nr_right)
267{
268 uint32_t max_entries = le32_to_cpu(left->header.max_entries);
269 unsigned shift = min(max_entries - nr_left, nr_center);
270
271 BUG_ON(nr_left + shift > max_entries);
272 node_copy(left, center, -shift);
273 left->header.nr_entries = cpu_to_le32(nr_left + shift);
274
275 if (shift != nr_center) {
276 shift = nr_center - shift;
277 BUG_ON((nr_right + shift) > max_entries);
278 node_shift(right, shift);
279 node_copy(center, right, shift);
280 right->header.nr_entries = cpu_to_le32(nr_right + shift);
281 }
282 *key_ptr(parent, r->index) = right->keys[0];
283
284 delete_at(parent, c->index);
285 r->index--;
286
287 dm_tm_dec(info->tm, dm_block_location(c->block));
288 __rebalance2(info, parent, l, r);
289}
290
291/*
292 * Redistributes entries among 3 sibling nodes.
293 */
294static void redistribute3(struct dm_btree_info *info, struct btree_node *parent,
295 struct child *l, struct child *c, struct child *r,
296 struct btree_node *left, struct btree_node *center, struct btree_node *right,
297 uint32_t nr_left, uint32_t nr_center, uint32_t nr_right)
298{
299 int s;
300 uint32_t max_entries = le32_to_cpu(left->header.max_entries);
301 unsigned total = nr_left + nr_center + nr_right;
302 unsigned target_right = total / 3;
303 unsigned remainder = (target_right * 3) != total;
304 unsigned target_left = target_right + remainder;
305
306 BUG_ON(target_left > max_entries);
307 BUG_ON(target_right > max_entries);
308
309 if (nr_left < nr_right) {
310 s = nr_left - target_left;
311
312 if (s < 0 && nr_center < -s) {
313 /* not enough in central node */
314 shift(left, center, -nr_center);
315 s += nr_center;
316 shift(left, right, s);
317 nr_right += s;
318 } else
319 shift(left, center, s);
320
321 shift(center, right, target_right - nr_right);
322
323 } else {
324 s = target_right - nr_right;
325 if (s > 0 && nr_center < s) {
326 /* not enough in central node */
327 shift(center, right, nr_center);
328 s -= nr_center;
329 shift(left, right, s);
330 nr_left -= s;
331 } else
332 shift(center, right, s);
333
334 shift(left, center, nr_left - target_left);
335 }
336
337 *key_ptr(parent, c->index) = center->keys[0];
338 *key_ptr(parent, r->index) = right->keys[0];
339}
340
341static void __rebalance3(struct dm_btree_info *info, struct btree_node *parent,
342 struct child *l, struct child *c, struct child *r)
343{
344 struct btree_node *left = l->n;
345 struct btree_node *center = c->n;
346 struct btree_node *right = r->n;
347
348 uint32_t nr_left = le32_to_cpu(left->header.nr_entries);
349 uint32_t nr_center = le32_to_cpu(center->header.nr_entries);
350 uint32_t nr_right = le32_to_cpu(right->header.nr_entries);
351
352 unsigned threshold = merge_threshold(left) * 4 + 1;
353
354 BUG_ON(left->header.max_entries != center->header.max_entries);
355 BUG_ON(center->header.max_entries != right->header.max_entries);
356
357 if ((nr_left + nr_center + nr_right) < threshold)
358 delete_center_node(info, parent, l, c, r, left, center, right,
359 nr_left, nr_center, nr_right);
360 else
361 redistribute3(info, parent, l, c, r, left, center, right,
362 nr_left, nr_center, nr_right);
363}
364
365static int rebalance3(struct shadow_spine *s, struct dm_btree_info *info,
366 struct dm_btree_value_type *vt, unsigned left_index)
367{
368 int r;
369 struct btree_node *parent = dm_block_data(shadow_current(s));
370 struct child left, center, right;
371
372 /*
373 * FIXME: fill out an array?
374 */
375 r = init_child(info, vt, parent, left_index, &left);
376 if (r)
377 return r;
378
379 r = init_child(info, vt, parent, left_index + 1, ¢er);
380 if (r) {
381 exit_child(info, &left);
382 return r;
383 }
384
385 r = init_child(info, vt, parent, left_index + 2, &right);
386 if (r) {
387 exit_child(info, &left);
388 exit_child(info, ¢er);
389 return r;
390 }
391
392 __rebalance3(info, parent, &left, ¢er, &right);
393
394 exit_child(info, &left);
395 exit_child(info, ¢er);
396 exit_child(info, &right);
397
398 return 0;
399}
400
401static int rebalance_children(struct shadow_spine *s,
402 struct dm_btree_info *info,
403 struct dm_btree_value_type *vt, uint64_t key)
404{
405 int i, r, has_left_sibling, has_right_sibling;
406 struct btree_node *n;
407
408 n = dm_block_data(shadow_current(s));
409
410 if (le32_to_cpu(n->header.nr_entries) == 1) {
411 struct dm_block *child;
412 dm_block_t b = value64(n, 0);
413
414 r = dm_tm_read_lock(info->tm, b, &btree_node_validator, &child);
415 if (r)
416 return r;
417
418 memcpy(n, dm_block_data(child),
419 dm_bm_block_size(dm_tm_get_bm(info->tm)));
420 dm_tm_unlock(info->tm, child);
421
422 dm_tm_dec(info->tm, dm_block_location(child));
423 return 0;
424 }
425
426 i = lower_bound(n, key);
427 if (i < 0)
428 return -ENODATA;
429
430 has_left_sibling = i > 0;
431 has_right_sibling = i < (le32_to_cpu(n->header.nr_entries) - 1);
432
433 if (!has_left_sibling)
434 r = rebalance2(s, info, vt, i);
435
436 else if (!has_right_sibling)
437 r = rebalance2(s, info, vt, i - 1);
438
439 else
440 r = rebalance3(s, info, vt, i - 1);
441
442 return r;
443}
444
445static int do_leaf(struct btree_node *n, uint64_t key, unsigned *index)
446{
447 int i = lower_bound(n, key);
448
449 if ((i < 0) ||
450 (i >= le32_to_cpu(n->header.nr_entries)) ||
451 (le64_to_cpu(n->keys[i]) != key))
452 return -ENODATA;
453
454 *index = i;
455
456 return 0;
457}
458
459/*
460 * Prepares for removal from one level of the hierarchy. The caller must
461 * call delete_at() to remove the entry at index.
462 */
463static int remove_raw(struct shadow_spine *s, struct dm_btree_info *info,
464 struct dm_btree_value_type *vt, dm_block_t root,
465 uint64_t key, unsigned *index)
466{
467 int i = *index, r;
468 struct btree_node *n;
469
470 for (;;) {
471 r = shadow_step(s, root, vt);
472 if (r < 0)
473 break;
474
475 /*
476 * We have to patch up the parent node, ugly, but I don't
477 * see a way to do this automatically as part of the spine
478 * op.
479 */
480 if (shadow_has_parent(s)) {
481 __le64 location = cpu_to_le64(dm_block_location(shadow_current(s)));
482 memcpy(value_ptr(dm_block_data(shadow_parent(s)), i),
483 &location, sizeof(__le64));
484 }
485
486 n = dm_block_data(shadow_current(s));
487
488 if (le32_to_cpu(n->header.flags) & LEAF_NODE)
489 return do_leaf(n, key, index);
490
491 r = rebalance_children(s, info, vt, key);
492 if (r)
493 break;
494
495 n = dm_block_data(shadow_current(s));
496 if (le32_to_cpu(n->header.flags) & LEAF_NODE)
497 return do_leaf(n, key, index);
498
499 i = lower_bound(n, key);
500
501 /*
502 * We know the key is present, or else
503 * rebalance_children would have returned
504 * -ENODATA
505 */
506 root = value64(n, i);
507 }
508
509 return r;
510}
511
512int dm_btree_remove(struct dm_btree_info *info, dm_block_t root,
513 uint64_t *keys, dm_block_t *new_root)
514{
515 unsigned level, last_level = info->levels - 1;
516 int index = 0, r = 0;
517 struct shadow_spine spine;
518 struct btree_node *n;
519 struct dm_btree_value_type le64_vt;
520
521 init_le64_type(info->tm, &le64_vt);
522 init_shadow_spine(&spine, info);
523 for (level = 0; level < info->levels; level++) {
524 r = remove_raw(&spine, info,
525 (level == last_level ?
526 &info->value_type : &le64_vt),
527 root, keys[level], (unsigned *)&index);
528 if (r < 0)
529 break;
530
531 n = dm_block_data(shadow_current(&spine));
532 if (level != last_level) {
533 root = value64(n, index);
534 continue;
535 }
536
537 BUG_ON(index < 0 || index >= le32_to_cpu(n->header.nr_entries));
538
539 if (info->value_type.dec)
540 info->value_type.dec(info->value_type.context,
541 value_ptr(n, index));
542
543 delete_at(n, index);
544 }
545
546 *new_root = shadow_root(&spine);
547 exit_shadow_spine(&spine);
548
549 return r;
550}
551EXPORT_SYMBOL_GPL(dm_btree_remove);
552
553/*----------------------------------------------------------------*/
554
555static int remove_nearest(struct shadow_spine *s, struct dm_btree_info *info,
556 struct dm_btree_value_type *vt, dm_block_t root,
557 uint64_t key, int *index)
558{
559 int i = *index, r;
560 struct btree_node *n;
561
562 for (;;) {
563 r = shadow_step(s, root, vt);
564 if (r < 0)
565 break;
566
567 /*
568 * We have to patch up the parent node, ugly, but I don't
569 * see a way to do this automatically as part of the spine
570 * op.
571 */
572 if (shadow_has_parent(s)) {
573 __le64 location = cpu_to_le64(dm_block_location(shadow_current(s)));
574 memcpy(value_ptr(dm_block_data(shadow_parent(s)), i),
575 &location, sizeof(__le64));
576 }
577
578 n = dm_block_data(shadow_current(s));
579
580 if (le32_to_cpu(n->header.flags) & LEAF_NODE) {
581 *index = lower_bound(n, key);
582 return 0;
583 }
584
585 r = rebalance_children(s, info, vt, key);
586 if (r)
587 break;
588
589 n = dm_block_data(shadow_current(s));
590 if (le32_to_cpu(n->header.flags) & LEAF_NODE) {
591 *index = lower_bound(n, key);
592 return 0;
593 }
594
595 i = lower_bound(n, key);
596
597 /*
598 * We know the key is present, or else
599 * rebalance_children would have returned
600 * -ENODATA
601 */
602 root = value64(n, i);
603 }
604
605 return r;
606}
607
608static int remove_one(struct dm_btree_info *info, dm_block_t root,
609 uint64_t *keys, uint64_t end_key,
610 dm_block_t *new_root, unsigned *nr_removed)
611{
612 unsigned level, last_level = info->levels - 1;
613 int index = 0, r = 0;
614 struct shadow_spine spine;
615 struct btree_node *n;
616 struct dm_btree_value_type le64_vt;
617 uint64_t k;
618
619 init_le64_type(info->tm, &le64_vt);
620 init_shadow_spine(&spine, info);
621 for (level = 0; level < last_level; level++) {
622 r = remove_raw(&spine, info, &le64_vt,
623 root, keys[level], (unsigned *) &index);
624 if (r < 0)
625 goto out;
626
627 n = dm_block_data(shadow_current(&spine));
628 root = value64(n, index);
629 }
630
631 r = remove_nearest(&spine, info, &info->value_type,
632 root, keys[last_level], &index);
633 if (r < 0)
634 goto out;
635
636 n = dm_block_data(shadow_current(&spine));
637
638 if (index < 0)
639 index = 0;
640
641 if (index >= le32_to_cpu(n->header.nr_entries)) {
642 r = -ENODATA;
643 goto out;
644 }
645
646 k = le64_to_cpu(n->keys[index]);
647 if (k >= keys[last_level] && k < end_key) {
648 if (info->value_type.dec)
649 info->value_type.dec(info->value_type.context,
650 value_ptr(n, index));
651
652 delete_at(n, index);
653 keys[last_level] = k + 1ull;
654
655 } else
656 r = -ENODATA;
657
658out:
659 *new_root = shadow_root(&spine);
660 exit_shadow_spine(&spine);
661
662 return r;
663}
664
665int dm_btree_remove_leaves(struct dm_btree_info *info, dm_block_t root,
666 uint64_t *first_key, uint64_t end_key,
667 dm_block_t *new_root, unsigned *nr_removed)
668{
669 int r;
670
671 *nr_removed = 0;
672 do {
673 r = remove_one(info, root, first_key, end_key, &root, nr_removed);
674 if (!r)
675 (*nr_removed)++;
676 } while (!r);
677
678 *new_root = root;
679 return r == -ENODATA ? 0 : r;
680}
681EXPORT_SYMBOL_GPL(dm_btree_remove_leaves);