1 // SPDX-License-Identifier: GPL-2.0
4 #include "alloc_background.h"
5 #include "backpointers.h"
6 #include "btree_cache.h"
7 #include "btree_update.h"
8 #include "btree_write_buffer.h"
13 static bool extent_matches_bp(struct bch_fs *c,
14 enum btree_id btree_id, unsigned level,
17 struct bch_backpointer bp)
19 struct bkey_ptrs_c ptrs = bch2_bkey_ptrs_c(k);
20 const union bch_extent_entry *entry;
21 struct extent_ptr_decoded p;
23 bkey_for_each_ptr_decode(k.k, ptrs, p, entry) {
25 struct bch_backpointer bp2;
30 bch2_extent_ptr_to_bp(c, btree_id, level, k, p,
32 if (bpos_eq(bucket, bucket2) &&
33 !memcmp(&bp, &bp2, sizeof(bp)))
40 int bch2_backpointer_invalid(const struct bch_fs *c, struct bkey_s_c k,
41 unsigned flags, struct printbuf *err)
43 struct bkey_s_c_backpointer bp = bkey_s_c_to_backpointer(k);
44 struct bpos bucket = bp_pos_to_bucket(c, bp.k->p);
46 if (!bpos_eq(bp.k->p, bucket_pos_to_bp(c, bucket, bp.v->bucket_offset))) {
47 prt_str(err, "backpointer at wrong pos");
48 return -BCH_ERR_invalid_bkey;
54 void bch2_backpointer_to_text(struct printbuf *out, const struct bch_backpointer *bp)
56 prt_printf(out, "btree=%s l=%u offset=%llu:%u len=%u pos=",
57 bch2_btree_ids[bp->btree_id],
59 (u64) (bp->bucket_offset >> MAX_EXTENT_COMPRESS_RATIO_SHIFT),
60 (u32) bp->bucket_offset & ~(~0U << MAX_EXTENT_COMPRESS_RATIO_SHIFT),
62 bch2_bpos_to_text(out, bp->pos);
65 void bch2_backpointer_k_to_text(struct printbuf *out, struct bch_fs *c, struct bkey_s_c k)
67 prt_str(out, "bucket=");
68 bch2_bpos_to_text(out, bp_pos_to_bucket(c, k.k->p));
71 bch2_backpointer_to_text(out, bkey_s_c_to_backpointer(k).v);
74 void bch2_backpointer_swab(struct bkey_s k)
76 struct bkey_s_backpointer bp = bkey_s_to_backpointer(k);
78 bp.v->bucket_offset = swab32(bp.v->bucket_offset);
79 bp.v->bucket_len = swab32(bp.v->bucket_len);
80 bch2_bpos_swab(&bp.v->pos);
83 static noinline int backpointer_mod_err(struct btree_trans *trans,
84 struct bch_backpointer bp,
86 struct bkey_s_c orig_k,
89 struct bch_fs *c = trans->c;
90 struct printbuf buf = PRINTBUF;
93 prt_printf(&buf, "existing backpointer found when inserting ");
94 bch2_backpointer_to_text(&buf, &bp);
96 printbuf_indent_add(&buf, 2);
98 prt_printf(&buf, "found ");
99 bch2_bkey_val_to_text(&buf, c, bp_k);
102 prt_printf(&buf, "for ");
103 bch2_bkey_val_to_text(&buf, c, orig_k);
105 bch_err(c, "%s", buf.buf);
106 } else if (test_bit(BCH_FS_CHECK_BACKPOINTERS_DONE, &c->flags)) {
107 prt_printf(&buf, "backpointer not found when deleting");
109 printbuf_indent_add(&buf, 2);
111 prt_printf(&buf, "searching for ");
112 bch2_backpointer_to_text(&buf, &bp);
115 prt_printf(&buf, "got ");
116 bch2_bkey_val_to_text(&buf, c, bp_k);
119 prt_printf(&buf, "for ");
120 bch2_bkey_val_to_text(&buf, c, orig_k);
122 bch_err(c, "%s", buf.buf);
127 if (test_bit(BCH_FS_CHECK_BACKPOINTERS_DONE, &c->flags)) {
128 bch2_inconsistent_error(c);
135 int bch2_bucket_backpointer_mod_nowritebuffer(struct btree_trans *trans,
137 struct bch_backpointer bp,
138 struct bkey_s_c orig_k,
141 struct bch_fs *c = trans->c;
142 struct bkey_i_backpointer *bp_k;
143 struct btree_iter bp_iter;
147 bp_k = bch2_trans_kmalloc_nomemzero(trans, sizeof(struct bkey_i_backpointer));
148 ret = PTR_ERR_OR_ZERO(bp_k);
152 bkey_backpointer_init(&bp_k->k_i);
153 bp_k->k.p = bucket_pos_to_bp(c, bucket, bp.bucket_offset);
157 bp_k->k.type = KEY_TYPE_deleted;
158 set_bkey_val_u64s(&bp_k->k, 0);
161 k = bch2_bkey_get_iter(trans, &bp_iter, BTREE_ID_backpointers,
165 BTREE_ITER_WITH_UPDATES);
172 : (k.k->type != KEY_TYPE_backpointer ||
173 memcmp(bkey_s_c_to_backpointer(k).v, &bp, sizeof(bp)))) {
174 ret = backpointer_mod_err(trans, bp, k, orig_k, insert);
179 ret = bch2_trans_update(trans, &bp_iter, &bp_k->k_i, 0);
181 bch2_trans_iter_exit(trans, &bp_iter);
186 * Find the next backpointer >= *bp_offset:
188 int bch2_get_next_backpointer(struct btree_trans *trans,
189 struct bpos bucket, int gen,
191 struct bch_backpointer *bp,
194 struct bch_fs *c = trans->c;
195 struct bpos bp_end_pos = bucket_pos_to_bp(c, bpos_nosnap_successor(bucket), 0);
196 struct btree_iter alloc_iter = { NULL }, bp_iter = { NULL };
200 if (bpos_ge(*bp_pos, bp_end_pos))
204 k = bch2_bkey_get_iter(trans, &alloc_iter, BTREE_ID_alloc,
205 bucket, BTREE_ITER_CACHED|iter_flags);
210 if (k.k->type != KEY_TYPE_alloc_v4 ||
211 bkey_s_c_to_alloc_v4(k).v->gen != gen)
215 *bp_pos = bpos_max(*bp_pos, bucket_pos_to_bp(c, bucket, 0));
217 for_each_btree_key_norestart(trans, bp_iter, BTREE_ID_backpointers,
218 *bp_pos, iter_flags, k, ret) {
219 if (bpos_ge(k.k->p, bp_end_pos))
223 *bp = *bkey_s_c_to_backpointer(k).v;
229 bch2_trans_iter_exit(trans, &bp_iter);
230 bch2_trans_iter_exit(trans, &alloc_iter);
234 static void backpointer_not_found(struct btree_trans *trans,
236 struct bch_backpointer bp,
238 const char *thing_it_points_to)
240 struct bch_fs *c = trans->c;
241 struct printbuf buf = PRINTBUF;
242 struct bpos bucket = bp_pos_to_bucket(c, bp_pos);
244 if (likely(!bch2_backpointers_no_use_write_buffer))
247 prt_printf(&buf, "backpointer doesn't match %s it points to:\n ",
249 prt_printf(&buf, "bucket: ");
250 bch2_bpos_to_text(&buf, bucket);
251 prt_printf(&buf, "\n ");
253 prt_printf(&buf, "backpointer pos: ");
254 bch2_bpos_to_text(&buf, bp_pos);
255 prt_printf(&buf, "\n ");
257 bch2_backpointer_to_text(&buf, &bp);
258 prt_printf(&buf, "\n ");
259 bch2_bkey_val_to_text(&buf, c, k);
260 if (!test_bit(BCH_FS_CHECK_BACKPOINTERS_DONE, &c->flags))
261 bch_err_ratelimited(c, "%s", buf.buf);
263 bch2_trans_inconsistent(trans, "%s", buf.buf);
268 struct bkey_s_c bch2_backpointer_get_key(struct btree_trans *trans,
269 struct btree_iter *iter,
271 struct bch_backpointer bp,
274 struct bch_fs *c = trans->c;
275 struct bpos bucket = bp_pos_to_bucket(c, bp_pos);
278 bch2_trans_node_iter_init(trans, iter,
282 min(bp.level, c->btree_roots[bp.btree_id].level),
284 k = bch2_btree_iter_peek_slot(iter);
286 bch2_trans_iter_exit(trans, iter);
290 if (bp.level == c->btree_roots[bp.btree_id].level + 1)
291 k = bkey_i_to_s_c(&c->btree_roots[bp.btree_id].key);
293 if (k.k && extent_matches_bp(c, bp.btree_id, bp.level, k, bucket, bp))
296 bch2_trans_iter_exit(trans, iter);
298 if (unlikely(bch2_backpointers_no_use_write_buffer)) {
303 * If a backpointer for a btree node wasn't found, it may be
304 * because it was overwritten by a new btree node that hasn't
305 * been written out yet - backpointer_get_node() checks for
308 b = bch2_backpointer_get_node(trans, iter, bp_pos, bp);
309 if (!IS_ERR_OR_NULL(b))
310 return bkey_i_to_s_c(&b->key);
312 bch2_trans_iter_exit(trans, iter);
315 return bkey_s_c_err(PTR_ERR(b));
316 return bkey_s_c_null;
319 backpointer_not_found(trans, bp_pos, bp, k, "extent");
322 return bkey_s_c_null;
325 struct btree *bch2_backpointer_get_node(struct btree_trans *trans,
326 struct btree_iter *iter,
328 struct bch_backpointer bp)
330 struct bch_fs *c = trans->c;
331 struct bpos bucket = bp_pos_to_bucket(c, bp_pos);
336 bch2_trans_node_iter_init(trans, iter,
342 b = bch2_btree_iter_peek_node(iter);
346 if (b && extent_matches_bp(c, bp.btree_id, bp.level,
347 bkey_i_to_s_c(&b->key),
351 if (b && btree_node_will_make_reachable(b)) {
352 b = ERR_PTR(-BCH_ERR_backpointer_to_overwritten_btree_node);
354 backpointer_not_found(trans, bp_pos, bp,
355 bkey_i_to_s_c(&b->key), "btree node");
359 bch2_trans_iter_exit(trans, iter);
363 static int bch2_check_btree_backpointer(struct btree_trans *trans, struct btree_iter *bp_iter,
366 struct bch_fs *c = trans->c;
367 struct btree_iter alloc_iter = { NULL };
369 struct bkey_s_c alloc_k;
370 struct printbuf buf = PRINTBUF;
373 if (fsck_err_on(!bch2_dev_exists2(c, k.k->p.inode), c,
374 "backpointer for mising device:\n%s",
375 (bch2_bkey_val_to_text(&buf, c, k), buf.buf))) {
376 ret = bch2_btree_delete_at(trans, bp_iter, 0);
380 ca = bch_dev_bkey_exists(c, k.k->p.inode);
382 alloc_k = bch2_bkey_get_iter(trans, &alloc_iter, BTREE_ID_alloc,
383 bp_pos_to_bucket(c, k.k->p), 0);
384 ret = bkey_err(alloc_k);
388 if (fsck_err_on(alloc_k.k->type != KEY_TYPE_alloc_v4, c,
389 "backpointer for nonexistent alloc key: %llu:%llu:0\n%s",
390 alloc_iter.pos.inode, alloc_iter.pos.offset,
391 (bch2_bkey_val_to_text(&buf, c, alloc_k), buf.buf))) {
392 ret = bch2_btree_delete_at(trans, bp_iter, 0);
397 bch2_trans_iter_exit(trans, &alloc_iter);
402 /* verify that every backpointer has a corresponding alloc key */
403 int bch2_check_btree_backpointers(struct bch_fs *c)
405 struct btree_iter iter;
409 ret = bch2_trans_run(c,
410 for_each_btree_key_commit(&trans, iter,
411 BTREE_ID_backpointers, POS_MIN, 0, k,
412 NULL, NULL, BTREE_INSERT_LAZY_RW|BTREE_INSERT_NOFAIL,
413 bch2_check_btree_backpointer(&trans, &iter, k)));
424 static int check_bp_exists(struct btree_trans *trans,
426 struct bch_backpointer bp,
427 struct bkey_s_c orig_k,
428 struct bpos bucket_start,
429 struct bpos bucket_end,
430 struct bpos_level *last_flushed)
432 struct bch_fs *c = trans->c;
433 struct btree_iter bp_iter = { NULL };
434 struct printbuf buf = PRINTBUF;
435 struct bkey_s_c bp_k;
438 if (bpos_lt(bucket, bucket_start) ||
439 bpos_gt(bucket, bucket_end))
442 if (!bch2_dev_bucket_exists(c, bucket))
445 bp_k = bch2_bkey_get_iter(trans, &bp_iter, BTREE_ID_backpointers,
446 bucket_pos_to_bp(c, bucket, bp.bucket_offset),
448 ret = bkey_err(bp_k);
452 if (bp_k.k->type != KEY_TYPE_backpointer ||
453 memcmp(bkey_s_c_to_backpointer(bp_k).v, &bp, sizeof(bp))) {
454 if (last_flushed->level != bp.level ||
455 !bpos_eq(last_flushed->pos, orig_k.k->p)) {
456 last_flushed->level = bp.level;
457 last_flushed->pos = orig_k.k->p;
459 ret = bch2_btree_write_buffer_flush_sync(trans) ?:
460 -BCH_ERR_transaction_restart_write_buffer_flush;
468 bch2_trans_iter_exit(trans, &bp_iter);
472 prt_printf(&buf, "missing backpointer for btree=%s l=%u ",
473 bch2_btree_ids[bp.btree_id], bp.level);
474 bch2_bkey_val_to_text(&buf, c, orig_k);
475 prt_printf(&buf, "\nbp pos ");
476 bch2_bpos_to_text(&buf, bp_iter.pos);
478 if (c->sb.version < bcachefs_metadata_version_backpointers ||
479 c->opts.reconstruct_alloc ||
480 fsck_err(c, "%s", buf.buf))
481 ret = bch2_bucket_backpointer_mod(trans, bucket, bp, orig_k, true);
486 static int check_extent_to_backpointers(struct btree_trans *trans,
487 struct btree_iter *iter,
488 struct bpos bucket_start,
489 struct bpos bucket_end,
490 struct bpos_level *last_flushed)
492 struct bch_fs *c = trans->c;
493 struct bkey_ptrs_c ptrs;
494 const union bch_extent_entry *entry;
495 struct extent_ptr_decoded p;
499 k = bch2_btree_iter_peek_all_levels(iter);
506 ptrs = bch2_bkey_ptrs_c(k);
507 bkey_for_each_ptr_decode(k.k, ptrs, p, entry) {
508 struct bpos bucket_pos;
509 struct bch_backpointer bp;
514 bch2_extent_ptr_to_bp(c, iter->btree_id, iter->path->level,
515 k, p, &bucket_pos, &bp);
517 ret = check_bp_exists(trans, bucket_pos, bp, k,
518 bucket_start, bucket_end,
527 static int check_btree_root_to_backpointers(struct btree_trans *trans,
528 enum btree_id btree_id,
529 struct bpos bucket_start,
530 struct bpos bucket_end,
531 struct bpos_level *last_flushed)
533 struct bch_fs *c = trans->c;
534 struct btree_iter iter;
537 struct bkey_ptrs_c ptrs;
538 struct extent_ptr_decoded p;
539 const union bch_extent_entry *entry;
542 bch2_trans_node_iter_init(trans, &iter, btree_id, POS_MIN, 0,
543 c->btree_roots[btree_id].level, 0);
544 b = bch2_btree_iter_peek_node(&iter);
545 ret = PTR_ERR_OR_ZERO(b);
549 BUG_ON(b != btree_node_root(c, b));
551 k = bkey_i_to_s_c(&b->key);
552 ptrs = bch2_bkey_ptrs_c(k);
553 bkey_for_each_ptr_decode(k.k, ptrs, p, entry) {
554 struct bpos bucket_pos;
555 struct bch_backpointer bp;
560 bch2_extent_ptr_to_bp(c, iter.btree_id, b->c.level + 1,
561 k, p, &bucket_pos, &bp);
563 ret = check_bp_exists(trans, bucket_pos, bp, k,
564 bucket_start, bucket_end,
570 bch2_trans_iter_exit(trans, &iter);
574 static inline struct bbpos bp_to_bbpos(struct bch_backpointer bp)
576 return (struct bbpos) {
577 .btree = bp.btree_id,
582 static size_t btree_nodes_fit_in_ram(struct bch_fs *c)
588 mem_bytes = i.totalram * i.mem_unit;
589 return div_u64(mem_bytes >> 1, btree_bytes(c));
592 int bch2_get_btree_in_memory_pos(struct btree_trans *trans,
593 unsigned btree_leaf_mask,
594 unsigned btree_interior_mask,
595 struct bbpos start, struct bbpos *end)
597 struct btree_iter iter;
599 size_t btree_nodes = btree_nodes_fit_in_ram(trans->c);
603 for (btree = start.btree; btree < BTREE_ID_NR && !ret; btree++) {
604 unsigned depth = ((1U << btree) & btree_leaf_mask) ? 1 : 2;
606 if (!((1U << btree) & btree_leaf_mask) &&
607 !((1U << btree) & btree_interior_mask))
610 bch2_trans_node_iter_init(trans, &iter, btree,
611 btree == start.btree ? start.pos : POS_MIN,
614 * for_each_btree_key_contineu() doesn't check the return value
615 * from bch2_btree_iter_advance(), which is needed when
616 * iterating over interior nodes where we'll see keys at
620 k = __bch2_btree_iter_peek_and_restart(trans, &iter, 0);
627 *end = BBPOS(btree, k.k->p);
628 bch2_trans_iter_exit(trans, &iter);
631 } while (bch2_btree_iter_advance(&iter));
632 bch2_trans_iter_exit(trans, &iter);
639 static int bch2_check_extents_to_backpointers_pass(struct btree_trans *trans,
640 struct bpos bucket_start,
641 struct bpos bucket_end)
643 struct btree_iter iter;
644 enum btree_id btree_id;
645 struct bpos_level last_flushed = { UINT_MAX };
648 for (btree_id = 0; btree_id < BTREE_ID_NR; btree_id++) {
649 unsigned depth = btree_type_has_ptrs(btree_id) ? 0 : 1;
651 bch2_trans_node_iter_init(trans, &iter, btree_id, POS_MIN, 0,
653 BTREE_ITER_ALL_LEVELS|
654 BTREE_ITER_PREFETCH);
657 ret = commit_do(trans, NULL, NULL,
658 BTREE_INSERT_LAZY_RW|
660 check_extent_to_backpointers(trans, &iter,
661 bucket_start, bucket_end,
665 } while (!bch2_btree_iter_advance(&iter));
667 bch2_trans_iter_exit(trans, &iter);
672 ret = commit_do(trans, NULL, NULL,
673 BTREE_INSERT_LAZY_RW|
675 check_btree_root_to_backpointers(trans, btree_id,
676 bucket_start, bucket_end,
684 static struct bpos bucket_pos_to_bp_safe(const struct bch_fs *c,
687 return bch2_dev_exists2(c, bucket.inode)
688 ? bucket_pos_to_bp(c, bucket, 0)
692 int bch2_get_alloc_in_memory_pos(struct btree_trans *trans,
693 struct bpos start, struct bpos *end)
695 struct btree_iter alloc_iter;
696 struct btree_iter bp_iter;
697 struct bkey_s_c alloc_k, bp_k;
698 size_t btree_nodes = btree_nodes_fit_in_ram(trans->c);
699 bool alloc_end = false, bp_end = false;
702 bch2_trans_node_iter_init(trans, &alloc_iter, BTREE_ID_alloc,
704 bch2_trans_node_iter_init(trans, &bp_iter, BTREE_ID_backpointers,
705 bucket_pos_to_bp_safe(trans->c, start), 0, 1, 0);
708 ? __bch2_btree_iter_peek_and_restart(trans, &alloc_iter, 0)
711 ? __bch2_btree_iter_peek_and_restart(trans, &bp_iter, 0)
714 ret = bkey_err(alloc_k) ?: bkey_err(bp_k);
715 if ((!alloc_k.k && !bp_k.k) || ret) {
726 if (bpos_lt(alloc_iter.pos, SPOS_MAX) &&
727 bpos_lt(bucket_pos_to_bp_safe(trans->c, alloc_iter.pos), bp_iter.pos)) {
728 if (!bch2_btree_iter_advance(&alloc_iter))
731 if (!bch2_btree_iter_advance(&bp_iter))
735 bch2_trans_iter_exit(trans, &bp_iter);
736 bch2_trans_iter_exit(trans, &alloc_iter);
740 int bch2_check_extents_to_backpointers(struct bch_fs *c)
742 struct btree_trans trans;
743 struct bpos start = POS_MIN, end;
746 bch2_trans_init(&trans, c, 0, 0);
748 ret = bch2_get_alloc_in_memory_pos(&trans, start, &end);
752 if (bpos_eq(start, POS_MIN) && !bpos_eq(end, SPOS_MAX))
753 bch_verbose(c, "%s(): alloc info does not fit in ram, running in multiple passes with %zu nodes per pass",
754 __func__, btree_nodes_fit_in_ram(c));
756 if (!bpos_eq(start, POS_MIN) || !bpos_eq(end, SPOS_MAX)) {
757 struct printbuf buf = PRINTBUF;
759 prt_str(&buf, "check_extents_to_backpointers(): ");
760 bch2_bpos_to_text(&buf, start);
762 bch2_bpos_to_text(&buf, end);
764 bch_verbose(c, "%s", buf.buf);
768 ret = bch2_check_extents_to_backpointers_pass(&trans, start, end);
769 if (ret || bpos_eq(end, SPOS_MAX))
772 start = bpos_successor(end);
774 bch2_trans_exit(&trans);
781 static int check_one_backpointer(struct btree_trans *trans,
784 struct bkey_s_c_backpointer bp,
785 struct bpos *last_flushed_pos)
787 struct bch_fs *c = trans->c;
788 struct btree_iter iter;
789 struct bbpos pos = bp_to_bbpos(*bp.v);
791 struct printbuf buf = PRINTBUF;
794 if (bbpos_cmp(pos, start) < 0 ||
795 bbpos_cmp(pos, end) > 0)
798 k = bch2_backpointer_get_key(trans, &iter, bp.k->p, *bp.v, 0);
800 if (ret == -BCH_ERR_backpointer_to_overwritten_btree_node)
805 if (!k.k && !bpos_eq(*last_flushed_pos, bp.k->p)) {
806 *last_flushed_pos = bp.k->p;
807 ret = bch2_btree_write_buffer_flush_sync(trans) ?:
808 -BCH_ERR_transaction_restart_write_buffer_flush;
812 if (fsck_err_on(!k.k, c,
813 "backpointer for missing extent\n %s",
814 (bch2_bkey_val_to_text(&buf, c, bp.s_c), buf.buf))) {
815 ret = bch2_btree_delete_at_buffered(trans, BTREE_ID_backpointers, bp.k->p);
820 bch2_trans_iter_exit(trans, &iter);
825 static int bch2_check_backpointers_to_extents_pass(struct btree_trans *trans,
829 struct btree_iter iter;
831 struct bpos last_flushed_pos = SPOS_MAX;
833 return for_each_btree_key_commit(trans, iter, BTREE_ID_backpointers,
834 POS_MIN, BTREE_ITER_PREFETCH, k,
835 NULL, NULL, BTREE_INSERT_LAZY_RW|BTREE_INSERT_NOFAIL,
836 check_one_backpointer(trans, start, end,
837 bkey_s_c_to_backpointer(k),
841 int bch2_check_backpointers_to_extents(struct bch_fs *c)
843 struct btree_trans trans;
844 struct bbpos start = (struct bbpos) { .btree = 0, .pos = POS_MIN, }, end;
847 bch2_trans_init(&trans, c, 0, 0);
849 ret = bch2_get_btree_in_memory_pos(&trans,
850 (1U << BTREE_ID_extents)|
851 (1U << BTREE_ID_reflink),
857 if (!bbpos_cmp(start, BBPOS_MIN) &&
858 bbpos_cmp(end, BBPOS_MAX))
859 bch_verbose(c, "%s(): extents do not fit in ram, running in multiple passes with %zu nodes per pass",
860 __func__, btree_nodes_fit_in_ram(c));
862 if (bbpos_cmp(start, BBPOS_MIN) ||
863 bbpos_cmp(end, BBPOS_MAX)) {
864 struct printbuf buf = PRINTBUF;
866 prt_str(&buf, "check_backpointers_to_extents(): ");
867 bch2_bbpos_to_text(&buf, start);
869 bch2_bbpos_to_text(&buf, end);
871 bch_verbose(c, "%s", buf.buf);
875 ret = bch2_check_backpointers_to_extents_pass(&trans, start, end);
876 if (ret || !bbpos_cmp(end, BBPOS_MAX))
879 start = bbpos_successor(end);
881 bch2_trans_exit(&trans);