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1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Copyright (C) 2011 Red Hat, Inc.
4 *
5 * This file is released under the GPL.
6 */
7
8#include "dm-btree.h"
9#include "dm-btree-internal.h"
10#include "dm-transaction-manager.h"
11
12#include <linux/export.h>
13#include <linux/device-mapper.h>
14
15#define DM_MSG_PREFIX "btree"
16
17/*
18 * Removing an entry from a btree
19 * ==============================
20 *
21 * A very important constraint for our btree is that no node, except the
22 * root, may have fewer than a certain number of entries.
23 * (MIN_ENTRIES <= nr_entries <= MAX_ENTRIES).
24 *
25 * Ensuring this is complicated by the way we want to only ever hold the
26 * locks on 2 nodes concurrently, and only change nodes in a top to bottom
27 * fashion.
28 *
29 * Each node may have a left or right sibling. When decending the spine,
30 * if a node contains only MIN_ENTRIES then we try and increase this to at
31 * least MIN_ENTRIES + 1. We do this in the following ways:
32 *
33 * [A] No siblings => this can only happen if the node is the root, in which
34 * case we copy the childs contents over the root.
35 *
36 * [B] No left sibling
37 * ==> rebalance(node, right sibling)
38 *
39 * [C] No right sibling
40 * ==> rebalance(left sibling, node)
41 *
42 * [D] Both siblings, total_entries(left, node, right) <= DEL_THRESHOLD
43 * ==> delete node adding it's contents to left and right
44 *
45 * [E] Both siblings, total_entries(left, node, right) > DEL_THRESHOLD
46 * ==> rebalance(left, node, right)
47 *
48 * After these operations it's possible that the our original node no
49 * longer contains the desired sub tree. For this reason this rebalancing
50 * is performed on the children of the current node. This also avoids
51 * having a special case for the root.
52 *
53 * Once this rebalancing has occurred we can then step into the child node
54 * for internal nodes. Or delete the entry for leaf nodes.
55 */
56
57/*
58 * Some little utilities for moving node data around.
59 */
60static void node_shift(struct btree_node *n, int shift)
61{
62 uint32_t nr_entries = le32_to_cpu(n->header.nr_entries);
63 uint32_t value_size = le32_to_cpu(n->header.value_size);
64
65 if (shift < 0) {
66 shift = -shift;
67 BUG_ON(shift > nr_entries);
68 BUG_ON((void *) key_ptr(n, shift) >= value_ptr(n, shift));
69 memmove(key_ptr(n, 0),
70 key_ptr(n, shift),
71 (nr_entries - shift) * sizeof(__le64));
72 memmove(value_ptr(n, 0),
73 value_ptr(n, shift),
74 (nr_entries - shift) * value_size);
75 } else {
76 BUG_ON(nr_entries + shift > le32_to_cpu(n->header.max_entries));
77 memmove(key_ptr(n, shift),
78 key_ptr(n, 0),
79 nr_entries * sizeof(__le64));
80 memmove(value_ptr(n, shift),
81 value_ptr(n, 0),
82 nr_entries * value_size);
83 }
84}
85
86static int node_copy(struct btree_node *left, struct btree_node *right, int shift)
87{
88 uint32_t nr_left = le32_to_cpu(left->header.nr_entries);
89 uint32_t value_size = le32_to_cpu(left->header.value_size);
90
91 if (value_size != le32_to_cpu(right->header.value_size)) {
92 DMERR("mismatched value size");
93 return -EILSEQ;
94 }
95
96 if (shift < 0) {
97 shift = -shift;
98
99 if (nr_left + shift > le32_to_cpu(left->header.max_entries)) {
100 DMERR("bad shift");
101 return -EINVAL;
102 }
103
104 memcpy(key_ptr(left, nr_left),
105 key_ptr(right, 0),
106 shift * sizeof(__le64));
107 memcpy(value_ptr(left, nr_left),
108 value_ptr(right, 0),
109 shift * value_size);
110 } else {
111 if (shift > le32_to_cpu(right->header.max_entries)) {
112 DMERR("bad shift");
113 return -EINVAL;
114 }
115
116 memcpy(key_ptr(right, 0),
117 key_ptr(left, nr_left - shift),
118 shift * sizeof(__le64));
119 memcpy(value_ptr(right, 0),
120 value_ptr(left, nr_left - shift),
121 shift * value_size);
122 }
123 return 0;
124}
125
126/*
127 * Delete a specific entry from a leaf node.
128 */
129static void delete_at(struct btree_node *n, unsigned int index)
130{
131 unsigned int nr_entries = le32_to_cpu(n->header.nr_entries);
132 unsigned int nr_to_copy = nr_entries - (index + 1);
133 uint32_t value_size = le32_to_cpu(n->header.value_size);
134
135 BUG_ON(index >= nr_entries);
136
137 if (nr_to_copy) {
138 memmove(key_ptr(n, index),
139 key_ptr(n, index + 1),
140 nr_to_copy * sizeof(__le64));
141
142 memmove(value_ptr(n, index),
143 value_ptr(n, index + 1),
144 nr_to_copy * value_size);
145 }
146
147 n->header.nr_entries = cpu_to_le32(nr_entries - 1);
148}
149
150static unsigned int merge_threshold(struct btree_node *n)
151{
152 return le32_to_cpu(n->header.max_entries) / 3;
153}
154
155struct child {
156 unsigned int index;
157 struct dm_block *block;
158 struct btree_node *n;
159};
160
161static int init_child(struct dm_btree_info *info, struct dm_btree_value_type *vt,
162 struct btree_node *parent,
163 unsigned int index, struct child *result)
164{
165 int r, inc;
166 dm_block_t root;
167
168 result->index = index;
169 root = value64(parent, index);
170
171 r = dm_tm_shadow_block(info->tm, root, &btree_node_validator,
172 &result->block, &inc);
173 if (r)
174 return r;
175
176 result->n = dm_block_data(result->block);
177
178 if (inc)
179 inc_children(info->tm, result->n, vt);
180
181 *((__le64 *) value_ptr(parent, index)) =
182 cpu_to_le64(dm_block_location(result->block));
183
184 return 0;
185}
186
187static void exit_child(struct dm_btree_info *info, struct child *c)
188{
189 dm_tm_unlock(info->tm, c->block);
190}
191
192static int shift(struct btree_node *left, struct btree_node *right, int count)
193{
194 int r;
195 uint32_t nr_left = le32_to_cpu(left->header.nr_entries);
196 uint32_t nr_right = le32_to_cpu(right->header.nr_entries);
197 uint32_t max_entries = le32_to_cpu(left->header.max_entries);
198 uint32_t r_max_entries = le32_to_cpu(right->header.max_entries);
199
200 if (max_entries != r_max_entries) {
201 DMERR("node max_entries mismatch");
202 return -EILSEQ;
203 }
204
205 if (nr_left - count > max_entries) {
206 DMERR("node shift out of bounds");
207 return -EINVAL;
208 }
209
210 if (nr_right + count > max_entries) {
211 DMERR("node shift out of bounds");
212 return -EINVAL;
213 }
214
215 if (!count)
216 return 0;
217
218 if (count > 0) {
219 node_shift(right, count);
220 r = node_copy(left, right, count);
221 if (r)
222 return r;
223 } else {
224 r = node_copy(left, right, count);
225 if (r)
226 return r;
227 node_shift(right, count);
228 }
229
230 left->header.nr_entries = cpu_to_le32(nr_left - count);
231 right->header.nr_entries = cpu_to_le32(nr_right + count);
232
233 return 0;
234}
235
236static int __rebalance2(struct dm_btree_info *info, struct btree_node *parent,
237 struct child *l, struct child *r)
238{
239 int ret;
240 struct btree_node *left = l->n;
241 struct btree_node *right = r->n;
242 uint32_t nr_left = le32_to_cpu(left->header.nr_entries);
243 uint32_t nr_right = le32_to_cpu(right->header.nr_entries);
244 /*
245 * Ensure the number of entries in each child will be greater
246 * than or equal to (max_entries / 3 + 1), so no matter which
247 * child is used for removal, the number will still be not
248 * less than (max_entries / 3).
249 */
250 unsigned int threshold = 2 * (merge_threshold(left) + 1);
251
252 if (nr_left + nr_right < threshold) {
253 /*
254 * Merge
255 */
256 node_copy(left, right, -nr_right);
257 left->header.nr_entries = cpu_to_le32(nr_left + nr_right);
258 delete_at(parent, r->index);
259
260 /*
261 * We need to decrement the right block, but not it's
262 * children, since they're still referenced by left.
263 */
264 dm_tm_dec(info->tm, dm_block_location(r->block));
265 } else {
266 /*
267 * Rebalance.
268 */
269 unsigned int target_left = (nr_left + nr_right) / 2;
270
271 ret = shift(left, right, nr_left - target_left);
272 if (ret)
273 return ret;
274 *key_ptr(parent, r->index) = right->keys[0];
275 }
276 return 0;
277}
278
279static int rebalance2(struct shadow_spine *s, struct dm_btree_info *info,
280 struct dm_btree_value_type *vt, unsigned int left_index)
281{
282 int r;
283 struct btree_node *parent;
284 struct child left, right;
285
286 parent = dm_block_data(shadow_current(s));
287
288 r = init_child(info, vt, parent, left_index, &left);
289 if (r)
290 return r;
291
292 r = init_child(info, vt, parent, left_index + 1, &right);
293 if (r) {
294 exit_child(info, &left);
295 return r;
296 }
297
298 r = __rebalance2(info, parent, &left, &right);
299
300 exit_child(info, &left);
301 exit_child(info, &right);
302
303 return r;
304}
305
306/*
307 * We dump as many entries from center as possible into left, then the rest
308 * in right, then rebalance2. This wastes some cpu, but I want something
309 * simple atm.
310 */
311static int delete_center_node(struct dm_btree_info *info, struct btree_node *parent,
312 struct child *l, struct child *c, struct child *r,
313 struct btree_node *left, struct btree_node *center, struct btree_node *right,
314 uint32_t nr_left, uint32_t nr_center, uint32_t nr_right)
315{
316 uint32_t max_entries = le32_to_cpu(left->header.max_entries);
317 unsigned int shift = min(max_entries - nr_left, nr_center);
318
319 if (nr_left + shift > max_entries) {
320 DMERR("node shift out of bounds");
321 return -EINVAL;
322 }
323
324 node_copy(left, center, -shift);
325 left->header.nr_entries = cpu_to_le32(nr_left + shift);
326
327 if (shift != nr_center) {
328 shift = nr_center - shift;
329
330 if ((nr_right + shift) > max_entries) {
331 DMERR("node shift out of bounds");
332 return -EINVAL;
333 }
334
335 node_shift(right, shift);
336 node_copy(center, right, shift);
337 right->header.nr_entries = cpu_to_le32(nr_right + shift);
338 }
339 *key_ptr(parent, r->index) = right->keys[0];
340
341 delete_at(parent, c->index);
342 r->index--;
343
344 dm_tm_dec(info->tm, dm_block_location(c->block));
345 return __rebalance2(info, parent, l, r);
346}
347
348/*
349 * Redistributes entries among 3 sibling nodes.
350 */
351static int redistribute3(struct dm_btree_info *info, struct btree_node *parent,
352 struct child *l, struct child *c, struct child *r,
353 struct btree_node *left, struct btree_node *center, struct btree_node *right,
354 uint32_t nr_left, uint32_t nr_center, uint32_t nr_right)
355{
356 int s, ret;
357 uint32_t max_entries = le32_to_cpu(left->header.max_entries);
358 unsigned int total = nr_left + nr_center + nr_right;
359 unsigned int target_right = total / 3;
360 unsigned int remainder = (target_right * 3) != total;
361 unsigned int target_left = target_right + remainder;
362
363 BUG_ON(target_left > max_entries);
364 BUG_ON(target_right > max_entries);
365
366 if (nr_left < nr_right) {
367 s = nr_left - target_left;
368
369 if (s < 0 && nr_center < -s) {
370 /* not enough in central node */
371 ret = shift(left, center, -nr_center);
372 if (ret)
373 return ret;
374
375 s += nr_center;
376 ret = shift(left, right, s);
377 if (ret)
378 return ret;
379
380 nr_right += s;
381 } else {
382 ret = shift(left, center, s);
383 if (ret)
384 return ret;
385 }
386
387 ret = shift(center, right, target_right - nr_right);
388 if (ret)
389 return ret;
390 } else {
391 s = target_right - nr_right;
392 if (s > 0 && nr_center < s) {
393 /* not enough in central node */
394 ret = shift(center, right, nr_center);
395 if (ret)
396 return ret;
397 s -= nr_center;
398 ret = shift(left, right, s);
399 if (ret)
400 return ret;
401 nr_left -= s;
402 } else {
403 ret = shift(center, right, s);
404 if (ret)
405 return ret;
406 }
407
408 ret = shift(left, center, nr_left - target_left);
409 if (ret)
410 return ret;
411 }
412
413 *key_ptr(parent, c->index) = center->keys[0];
414 *key_ptr(parent, r->index) = right->keys[0];
415 return 0;
416}
417
418static int __rebalance3(struct dm_btree_info *info, struct btree_node *parent,
419 struct child *l, struct child *c, struct child *r)
420{
421 struct btree_node *left = l->n;
422 struct btree_node *center = c->n;
423 struct btree_node *right = r->n;
424
425 uint32_t nr_left = le32_to_cpu(left->header.nr_entries);
426 uint32_t nr_center = le32_to_cpu(center->header.nr_entries);
427 uint32_t nr_right = le32_to_cpu(right->header.nr_entries);
428
429 unsigned int threshold = merge_threshold(left) * 4 + 1;
430
431 if ((left->header.max_entries != center->header.max_entries) ||
432 (center->header.max_entries != right->header.max_entries)) {
433 DMERR("bad btree metadata, max_entries differ");
434 return -EILSEQ;
435 }
436
437 if ((nr_left + nr_center + nr_right) < threshold) {
438 return delete_center_node(info, parent, l, c, r, left, center, right,
439 nr_left, nr_center, nr_right);
440 }
441
442 return redistribute3(info, parent, l, c, r, left, center, right,
443 nr_left, nr_center, nr_right);
444}
445
446static int rebalance3(struct shadow_spine *s, struct dm_btree_info *info,
447 struct dm_btree_value_type *vt, unsigned int left_index)
448{
449 int r;
450 struct btree_node *parent = dm_block_data(shadow_current(s));
451 struct child left, center, right;
452
453 /*
454 * FIXME: fill out an array?
455 */
456 r = init_child(info, vt, parent, left_index, &left);
457 if (r)
458 return r;
459
460 r = init_child(info, vt, parent, left_index + 1, &center);
461 if (r) {
462 exit_child(info, &left);
463 return r;
464 }
465
466 r = init_child(info, vt, parent, left_index + 2, &right);
467 if (r) {
468 exit_child(info, &left);
469 exit_child(info, &center);
470 return r;
471 }
472
473 r = __rebalance3(info, parent, &left, &center, &right);
474
475 exit_child(info, &left);
476 exit_child(info, &center);
477 exit_child(info, &right);
478
479 return r;
480}
481
482static int rebalance_children(struct shadow_spine *s,
483 struct dm_btree_info *info,
484 struct dm_btree_value_type *vt, uint64_t key)
485{
486 int i, r, has_left_sibling, has_right_sibling;
487 struct btree_node *n;
488
489 n = dm_block_data(shadow_current(s));
490
491 if (le32_to_cpu(n->header.nr_entries) == 1) {
492 struct dm_block *child;
493 int is_shared;
494 dm_block_t b = value64(n, 0);
495
496 r = dm_tm_block_is_shared(info->tm, b, &is_shared);
497 if (r)
498 return r;
499
500 r = dm_tm_read_lock(info->tm, b, &btree_node_validator, &child);
501 if (r)
502 return r;
503
504 if (is_shared)
505 inc_children(info->tm, dm_block_data(child), vt);
506
507 memcpy(n, dm_block_data(child),
508 dm_bm_block_size(dm_tm_get_bm(info->tm)));
509
510 dm_tm_dec(info->tm, dm_block_location(child));
511 dm_tm_unlock(info->tm, child);
512 return 0;
513 }
514
515 i = lower_bound(n, key);
516 if (i < 0)
517 return -ENODATA;
518
519 has_left_sibling = i > 0;
520 has_right_sibling = i < (le32_to_cpu(n->header.nr_entries) - 1);
521
522 if (!has_left_sibling)
523 r = rebalance2(s, info, vt, i);
524
525 else if (!has_right_sibling)
526 r = rebalance2(s, info, vt, i - 1);
527
528 else
529 r = rebalance3(s, info, vt, i - 1);
530
531 return r;
532}
533
534static int do_leaf(struct btree_node *n, uint64_t key, unsigned int *index)
535{
536 int i = lower_bound(n, key);
537
538 if ((i < 0) ||
539 (i >= le32_to_cpu(n->header.nr_entries)) ||
540 (le64_to_cpu(n->keys[i]) != key))
541 return -ENODATA;
542
543 *index = i;
544
545 return 0;
546}
547
548/*
549 * Prepares for removal from one level of the hierarchy. The caller must
550 * call delete_at() to remove the entry at index.
551 */
552static int remove_raw(struct shadow_spine *s, struct dm_btree_info *info,
553 struct dm_btree_value_type *vt, dm_block_t root,
554 uint64_t key, unsigned int *index)
555{
556 int i = *index, r;
557 struct btree_node *n;
558
559 for (;;) {
560 r = shadow_step(s, root, vt);
561 if (r < 0)
562 break;
563
564 /*
565 * We have to patch up the parent node, ugly, but I don't
566 * see a way to do this automatically as part of the spine
567 * op.
568 */
569 if (shadow_has_parent(s)) {
570 __le64 location = cpu_to_le64(dm_block_location(shadow_current(s)));
571
572 memcpy(value_ptr(dm_block_data(shadow_parent(s)), i),
573 &location, sizeof(__le64));
574 }
575
576 n = dm_block_data(shadow_current(s));
577
578 if (le32_to_cpu(n->header.flags) & LEAF_NODE)
579 return do_leaf(n, key, index);
580
581 r = rebalance_children(s, info, vt, key);
582 if (r)
583 break;
584
585 n = dm_block_data(shadow_current(s));
586 if (le32_to_cpu(n->header.flags) & LEAF_NODE)
587 return do_leaf(n, key, index);
588
589 i = lower_bound(n, key);
590
591 /*
592 * We know the key is present, or else
593 * rebalance_children would have returned
594 * -ENODATA
595 */
596 root = value64(n, i);
597 }
598
599 return r;
600}
601
602int dm_btree_remove(struct dm_btree_info *info, dm_block_t root,
603 uint64_t *keys, dm_block_t *new_root)
604{
605 unsigned int level, last_level = info->levels - 1;
606 int index = 0, r = 0;
607 struct shadow_spine spine;
608 struct btree_node *n;
609 struct dm_btree_value_type le64_vt;
610
611 init_le64_type(info->tm, &le64_vt);
612 init_shadow_spine(&spine, info);
613 for (level = 0; level < info->levels; level++) {
614 r = remove_raw(&spine, info,
615 (level == last_level ?
616 &info->value_type : &le64_vt),
617 root, keys[level], (unsigned int *)&index);
618 if (r < 0)
619 break;
620
621 n = dm_block_data(shadow_current(&spine));
622 if (level != last_level) {
623 root = value64(n, index);
624 continue;
625 }
626
627 BUG_ON(index < 0 || index >= le32_to_cpu(n->header.nr_entries));
628
629 if (info->value_type.dec)
630 info->value_type.dec(info->value_type.context,
631 value_ptr(n, index), 1);
632
633 delete_at(n, index);
634 }
635
636 if (!r)
637 *new_root = shadow_root(&spine);
638 exit_shadow_spine(&spine);
639
640 return r;
641}
642EXPORT_SYMBOL_GPL(dm_btree_remove);
643
644/*----------------------------------------------------------------*/
645
646static int remove_nearest(struct shadow_spine *s, struct dm_btree_info *info,
647 struct dm_btree_value_type *vt, dm_block_t root,
648 uint64_t key, int *index)
649{
650 int i = *index, r;
651 struct btree_node *n;
652
653 for (;;) {
654 r = shadow_step(s, root, vt);
655 if (r < 0)
656 break;
657
658 /*
659 * We have to patch up the parent node, ugly, but I don't
660 * see a way to do this automatically as part of the spine
661 * op.
662 */
663 if (shadow_has_parent(s)) {
664 __le64 location = cpu_to_le64(dm_block_location(shadow_current(s)));
665
666 memcpy(value_ptr(dm_block_data(shadow_parent(s)), i),
667 &location, sizeof(__le64));
668 }
669
670 n = dm_block_data(shadow_current(s));
671
672 if (le32_to_cpu(n->header.flags) & LEAF_NODE) {
673 *index = lower_bound(n, key);
674 return 0;
675 }
676
677 r = rebalance_children(s, info, vt, key);
678 if (r)
679 break;
680
681 n = dm_block_data(shadow_current(s));
682 if (le32_to_cpu(n->header.flags) & LEAF_NODE) {
683 *index = lower_bound(n, key);
684 return 0;
685 }
686
687 i = lower_bound(n, key);
688
689 /*
690 * We know the key is present, or else
691 * rebalance_children would have returned
692 * -ENODATA
693 */
694 root = value64(n, i);
695 }
696
697 return r;
698}
699
700static int remove_one(struct dm_btree_info *info, dm_block_t root,
701 uint64_t *keys, uint64_t end_key,
702 dm_block_t *new_root, unsigned int *nr_removed)
703{
704 unsigned int level, last_level = info->levels - 1;
705 int index = 0, r = 0;
706 struct shadow_spine spine;
707 struct btree_node *n;
708 struct dm_btree_value_type le64_vt;
709 uint64_t k;
710
711 init_le64_type(info->tm, &le64_vt);
712 init_shadow_spine(&spine, info);
713 for (level = 0; level < last_level; level++) {
714 r = remove_raw(&spine, info, &le64_vt,
715 root, keys[level], (unsigned int *) &index);
716 if (r < 0)
717 goto out;
718
719 n = dm_block_data(shadow_current(&spine));
720 root = value64(n, index);
721 }
722
723 r = remove_nearest(&spine, info, &info->value_type,
724 root, keys[last_level], &index);
725 if (r < 0)
726 goto out;
727
728 n = dm_block_data(shadow_current(&spine));
729
730 if (index < 0)
731 index = 0;
732
733 if (index >= le32_to_cpu(n->header.nr_entries)) {
734 r = -ENODATA;
735 goto out;
736 }
737
738 k = le64_to_cpu(n->keys[index]);
739 if (k >= keys[last_level] && k < end_key) {
740 if (info->value_type.dec)
741 info->value_type.dec(info->value_type.context,
742 value_ptr(n, index), 1);
743
744 delete_at(n, index);
745 keys[last_level] = k + 1ull;
746
747 } else
748 r = -ENODATA;
749
750out:
751 *new_root = shadow_root(&spine);
752 exit_shadow_spine(&spine);
753
754 return r;
755}
756
757int dm_btree_remove_leaves(struct dm_btree_info *info, dm_block_t root,
758 uint64_t *first_key, uint64_t end_key,
759 dm_block_t *new_root, unsigned int *nr_removed)
760{
761 int r;
762
763 *nr_removed = 0;
764 do {
765 r = remove_one(info, root, first_key, end_key, &root, nr_removed);
766 if (!r)
767 (*nr_removed)++;
768 } while (!r);
769
770 *new_root = root;
771 return r == -ENODATA ? 0 : r;
772}
773EXPORT_SYMBOL_GPL(dm_btree_remove_leaves);