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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 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 node *left, struct 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 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 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 node *n;
140};
141
142static struct dm_btree_value_type le64_type = {
143 .context = NULL,
144 .size = sizeof(__le64),
145 .inc = NULL,
146 .dec = NULL,
147 .equal = NULL
148};
149
150static int init_child(struct dm_btree_info *info, struct node *parent,
151 unsigned index, struct child *result)
152{
153 int r, inc;
154 dm_block_t root;
155
156 result->index = index;
157 root = value64(parent, index);
158
159 r = dm_tm_shadow_block(info->tm, root, &btree_node_validator,
160 &result->block, &inc);
161 if (r)
162 return r;
163
164 result->n = dm_block_data(result->block);
165
166 if (inc)
167 inc_children(info->tm, result->n, &le64_type);
168
169 *((__le64 *) value_ptr(parent, index)) =
170 cpu_to_le64(dm_block_location(result->block));
171
172 return 0;
173}
174
175static int exit_child(struct dm_btree_info *info, struct child *c)
176{
177 return dm_tm_unlock(info->tm, c->block);
178}
179
180static void shift(struct node *left, struct node *right, int count)
181{
182 uint32_t nr_left = le32_to_cpu(left->header.nr_entries);
183 uint32_t nr_right = le32_to_cpu(right->header.nr_entries);
184 uint32_t max_entries = le32_to_cpu(left->header.max_entries);
185 uint32_t r_max_entries = le32_to_cpu(right->header.max_entries);
186
187 BUG_ON(max_entries != r_max_entries);
188 BUG_ON(nr_left - count > max_entries);
189 BUG_ON(nr_right + count > max_entries);
190
191 if (!count)
192 return;
193
194 if (count > 0) {
195 node_shift(right, count);
196 node_copy(left, right, count);
197 } else {
198 node_copy(left, right, count);
199 node_shift(right, count);
200 }
201
202 left->header.nr_entries = cpu_to_le32(nr_left - count);
203 right->header.nr_entries = cpu_to_le32(nr_right + count);
204}
205
206static void __rebalance2(struct dm_btree_info *info, struct node *parent,
207 struct child *l, struct child *r)
208{
209 struct node *left = l->n;
210 struct node *right = r->n;
211 uint32_t nr_left = le32_to_cpu(left->header.nr_entries);
212 uint32_t nr_right = le32_to_cpu(right->header.nr_entries);
213 unsigned threshold = 2 * merge_threshold(left) + 1;
214
215 if (nr_left + nr_right < threshold) {
216 /*
217 * Merge
218 */
219 node_copy(left, right, -nr_right);
220 left->header.nr_entries = cpu_to_le32(nr_left + nr_right);
221 delete_at(parent, r->index);
222
223 /*
224 * We need to decrement the right block, but not it's
225 * children, since they're still referenced by left.
226 */
227 dm_tm_dec(info->tm, dm_block_location(r->block));
228 } else {
229 /*
230 * Rebalance.
231 */
232 unsigned target_left = (nr_left + nr_right) / 2;
233 shift(left, right, nr_left - target_left);
234 *key_ptr(parent, r->index) = right->keys[0];
235 }
236}
237
238static int rebalance2(struct shadow_spine *s, struct dm_btree_info *info,
239 unsigned left_index)
240{
241 int r;
242 struct node *parent;
243 struct child left, right;
244
245 parent = dm_block_data(shadow_current(s));
246
247 r = init_child(info, parent, left_index, &left);
248 if (r)
249 return r;
250
251 r = init_child(info, parent, left_index + 1, &right);
252 if (r) {
253 exit_child(info, &left);
254 return r;
255 }
256
257 __rebalance2(info, parent, &left, &right);
258
259 r = exit_child(info, &left);
260 if (r) {
261 exit_child(info, &right);
262 return r;
263 }
264
265 return exit_child(info, &right);
266}
267
268/*
269 * We dump as many entries from center as possible into left, then the rest
270 * in right, then rebalance2. This wastes some cpu, but I want something
271 * simple atm.
272 */
273static void delete_center_node(struct dm_btree_info *info, struct node *parent,
274 struct child *l, struct child *c, struct child *r,
275 struct node *left, struct node *center, struct node *right,
276 uint32_t nr_left, uint32_t nr_center, uint32_t nr_right)
277{
278 uint32_t max_entries = le32_to_cpu(left->header.max_entries);
279 unsigned shift = min(max_entries - nr_left, nr_center);
280
281 BUG_ON(nr_left + shift > max_entries);
282 node_copy(left, center, -shift);
283 left->header.nr_entries = cpu_to_le32(nr_left + shift);
284
285 if (shift != nr_center) {
286 shift = nr_center - shift;
287 BUG_ON((nr_right + shift) > max_entries);
288 node_shift(right, shift);
289 node_copy(center, right, shift);
290 right->header.nr_entries = cpu_to_le32(nr_right + shift);
291 }
292 *key_ptr(parent, r->index) = right->keys[0];
293
294 delete_at(parent, c->index);
295 r->index--;
296
297 dm_tm_dec(info->tm, dm_block_location(c->block));
298 __rebalance2(info, parent, l, r);
299}
300
301/*
302 * Redistributes entries among 3 sibling nodes.
303 */
304static void redistribute3(struct dm_btree_info *info, struct node *parent,
305 struct child *l, struct child *c, struct child *r,
306 struct node *left, struct node *center, struct node *right,
307 uint32_t nr_left, uint32_t nr_center, uint32_t nr_right)
308{
309 int s;
310 uint32_t max_entries = le32_to_cpu(left->header.max_entries);
311 unsigned target = (nr_left + nr_center + nr_right) / 3;
312 BUG_ON(target > max_entries);
313
314 if (nr_left < nr_right) {
315 s = nr_left - target;
316
317 if (s < 0 && nr_center < -s) {
318 /* not enough in central node */
319 shift(left, center, nr_center);
320 s = nr_center - target;
321 shift(left, right, s);
322 nr_right += s;
323 } else
324 shift(left, center, s);
325
326 shift(center, right, target - nr_right);
327
328 } else {
329 s = target - nr_right;
330 if (s > 0 && nr_center < s) {
331 /* not enough in central node */
332 shift(center, right, nr_center);
333 s = target - nr_center;
334 shift(left, right, s);
335 nr_left -= s;
336 } else
337 shift(center, right, s);
338
339 shift(left, center, nr_left - target);
340 }
341
342 *key_ptr(parent, c->index) = center->keys[0];
343 *key_ptr(parent, r->index) = right->keys[0];
344}
345
346static void __rebalance3(struct dm_btree_info *info, struct node *parent,
347 struct child *l, struct child *c, struct child *r)
348{
349 struct node *left = l->n;
350 struct node *center = c->n;
351 struct node *right = r->n;
352
353 uint32_t nr_left = le32_to_cpu(left->header.nr_entries);
354 uint32_t nr_center = le32_to_cpu(center->header.nr_entries);
355 uint32_t nr_right = le32_to_cpu(right->header.nr_entries);
356
357 unsigned threshold = merge_threshold(left) * 4 + 1;
358
359 BUG_ON(left->header.max_entries != center->header.max_entries);
360 BUG_ON(center->header.max_entries != right->header.max_entries);
361
362 if ((nr_left + nr_center + nr_right) < threshold)
363 delete_center_node(info, parent, l, c, r, left, center, right,
364 nr_left, nr_center, nr_right);
365 else
366 redistribute3(info, parent, l, c, r, left, center, right,
367 nr_left, nr_center, nr_right);
368}
369
370static int rebalance3(struct shadow_spine *s, struct dm_btree_info *info,
371 unsigned left_index)
372{
373 int r;
374 struct node *parent = dm_block_data(shadow_current(s));
375 struct child left, center, right;
376
377 /*
378 * FIXME: fill out an array?
379 */
380 r = init_child(info, parent, left_index, &left);
381 if (r)
382 return r;
383
384 r = init_child(info, parent, left_index + 1, ¢er);
385 if (r) {
386 exit_child(info, &left);
387 return r;
388 }
389
390 r = init_child(info, parent, left_index + 2, &right);
391 if (r) {
392 exit_child(info, &left);
393 exit_child(info, ¢er);
394 return r;
395 }
396
397 __rebalance3(info, parent, &left, ¢er, &right);
398
399 r = exit_child(info, &left);
400 if (r) {
401 exit_child(info, ¢er);
402 exit_child(info, &right);
403 return r;
404 }
405
406 r = exit_child(info, ¢er);
407 if (r) {
408 exit_child(info, &right);
409 return r;
410 }
411
412 r = exit_child(info, &right);
413 if (r)
414 return r;
415
416 return 0;
417}
418
419static int get_nr_entries(struct dm_transaction_manager *tm,
420 dm_block_t b, uint32_t *result)
421{
422 int r;
423 struct dm_block *block;
424 struct node *n;
425
426 r = dm_tm_read_lock(tm, b, &btree_node_validator, &block);
427 if (r)
428 return r;
429
430 n = dm_block_data(block);
431 *result = le32_to_cpu(n->header.nr_entries);
432
433 return dm_tm_unlock(tm, block);
434}
435
436static int rebalance_children(struct shadow_spine *s,
437 struct dm_btree_info *info, uint64_t key)
438{
439 int i, r, has_left_sibling, has_right_sibling;
440 uint32_t child_entries;
441 struct node *n;
442
443 n = dm_block_data(shadow_current(s));
444
445 if (le32_to_cpu(n->header.nr_entries) == 1) {
446 struct dm_block *child;
447 dm_block_t b = value64(n, 0);
448
449 r = dm_tm_read_lock(info->tm, b, &btree_node_validator, &child);
450 if (r)
451 return r;
452
453 memcpy(n, dm_block_data(child),
454 dm_bm_block_size(dm_tm_get_bm(info->tm)));
455 r = dm_tm_unlock(info->tm, child);
456 if (r)
457 return r;
458
459 dm_tm_dec(info->tm, dm_block_location(child));
460 return 0;
461 }
462
463 i = lower_bound(n, key);
464 if (i < 0)
465 return -ENODATA;
466
467 r = get_nr_entries(info->tm, value64(n, i), &child_entries);
468 if (r)
469 return r;
470
471 has_left_sibling = i > 0;
472 has_right_sibling = i < (le32_to_cpu(n->header.nr_entries) - 1);
473
474 if (!has_left_sibling)
475 r = rebalance2(s, info, i);
476
477 else if (!has_right_sibling)
478 r = rebalance2(s, info, i - 1);
479
480 else
481 r = rebalance3(s, info, i - 1);
482
483 return r;
484}
485
486static int do_leaf(struct node *n, uint64_t key, unsigned *index)
487{
488 int i = lower_bound(n, key);
489
490 if ((i < 0) ||
491 (i >= le32_to_cpu(n->header.nr_entries)) ||
492 (le64_to_cpu(n->keys[i]) != key))
493 return -ENODATA;
494
495 *index = i;
496
497 return 0;
498}
499
500/*
501 * Prepares for removal from one level of the hierarchy. The caller must
502 * call delete_at() to remove the entry at index.
503 */
504static int remove_raw(struct shadow_spine *s, struct dm_btree_info *info,
505 struct dm_btree_value_type *vt, dm_block_t root,
506 uint64_t key, unsigned *index)
507{
508 int i = *index, r;
509 struct node *n;
510
511 for (;;) {
512 r = shadow_step(s, root, vt);
513 if (r < 0)
514 break;
515
516 /*
517 * We have to patch up the parent node, ugly, but I don't
518 * see a way to do this automatically as part of the spine
519 * op.
520 */
521 if (shadow_has_parent(s)) {
522 __le64 location = cpu_to_le64(dm_block_location(shadow_current(s)));
523 memcpy(value_ptr(dm_block_data(shadow_parent(s)), i),
524 &location, sizeof(__le64));
525 }
526
527 n = dm_block_data(shadow_current(s));
528
529 if (le32_to_cpu(n->header.flags) & LEAF_NODE)
530 return do_leaf(n, key, index);
531
532 r = rebalance_children(s, info, key);
533 if (r)
534 break;
535
536 n = dm_block_data(shadow_current(s));
537 if (le32_to_cpu(n->header.flags) & LEAF_NODE)
538 return do_leaf(n, key, index);
539
540 i = lower_bound(n, key);
541
542 /*
543 * We know the key is present, or else
544 * rebalance_children would have returned
545 * -ENODATA
546 */
547 root = value64(n, i);
548 }
549
550 return r;
551}
552
553int dm_btree_remove(struct dm_btree_info *info, dm_block_t root,
554 uint64_t *keys, dm_block_t *new_root)
555{
556 unsigned level, last_level = info->levels - 1;
557 int index = 0, r = 0;
558 struct shadow_spine spine;
559 struct node *n;
560
561 init_shadow_spine(&spine, info);
562 for (level = 0; level < info->levels; level++) {
563 r = remove_raw(&spine, info,
564 (level == last_level ?
565 &info->value_type : &le64_type),
566 root, keys[level], (unsigned *)&index);
567 if (r < 0)
568 break;
569
570 n = dm_block_data(shadow_current(&spine));
571 if (level != last_level) {
572 root = value64(n, index);
573 continue;
574 }
575
576 BUG_ON(index < 0 || index >= le32_to_cpu(n->header.nr_entries));
577
578 if (info->value_type.dec)
579 info->value_type.dec(info->value_type.context,
580 value_ptr(n, index));
581
582 delete_at(n, index);
583 }
584
585 *new_root = shadow_root(&spine);
586 exit_shadow_spine(&spine);
587
588 return r;
589}
590EXPORT_SYMBOL_GPL(dm_btree_remove);