fs/bcachefs/backpointers.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 #include "bcachefs.h"
 #include "bbpos.h"
 #include "alloc_background.h"
 #include "backpointers.h"
 #include "btree_cache.h"
 #include "btree_update.h"
 #include "btree_write_buffer.h"
 #include "error.h"

 #include <linux/mm.h>

 static bool extent_matches_bp(struct bch_fs *c,
 			      enum btree_id btree_id, unsigned level,
 			      struct bkey_s_c k,
 			      struct bpos bucket,
 			      struct bch_backpointer bp)
 {
 	struct bkey_ptrs_c ptrs = bch2_bkey_ptrs_c(k);
 	const union bch_extent_entry *entry;
 	struct extent_ptr_decoded p;

 	bkey_for_each_ptr_decode(k.k, ptrs, p, entry) {
 		struct bpos bucket2;
 		struct bch_backpointer bp2;

 		if (p.ptr.cached)
 			continue;

 		bch2_extent_ptr_to_bp(c, btree_id, level, k, p,
 				      &bucket2, &bp2);
 		if (bpos_eq(bucket, bucket2) &&
 		    !memcmp(&bp, &bp2, sizeof(bp)))
 			return true;
 	}

 	return false;
 }

 int bch2_backpointer_invalid(const struct bch_fs *c, struct bkey_s_c k,
 			     enum bkey_invalid_flags flags,
 			     struct printbuf *err)
 {
 	struct bkey_s_c_backpointer bp = bkey_s_c_to_backpointer(k);
 	struct bpos bucket = bp_pos_to_bucket(c, bp.k->p);

 	if (!bpos_eq(bp.k->p, bucket_pos_to_bp(c, bucket, bp.v->bucket_offset))) {
 		prt_str(err, "backpointer at wrong pos");
 		return -BCH_ERR_invalid_bkey;
 	}

 	return 0;
 }

 void bch2_backpointer_to_text(struct printbuf *out, const struct bch_backpointer *bp)
 {
 	prt_printf(out, "btree=%s l=%u offset=%llu:%u len=%u pos=",
 	       bch2_btree_ids[bp->btree_id],
 	       bp->level,
 	       (u64) (bp->bucket_offset >> MAX_EXTENT_COMPRESS_RATIO_SHIFT),
 	       (u32) bp->bucket_offset & ~(~0U << MAX_EXTENT_COMPRESS_RATIO_SHIFT),
 	       bp->bucket_len);
 	bch2_bpos_to_text(out, bp->pos);
 }

 void bch2_backpointer_k_to_text(struct printbuf *out, struct bch_fs *c, struct bkey_s_c k)
 {
 	prt_str(out, "bucket=");
 	bch2_bpos_to_text(out, bp_pos_to_bucket(c, k.k->p));
 	prt_str(out, " ");

 	bch2_backpointer_to_text(out, bkey_s_c_to_backpointer(k).v);
 }

 void bch2_backpointer_swab(struct bkey_s k)
 {
 	struct bkey_s_backpointer bp = bkey_s_to_backpointer(k);

 	bp.v->bucket_offset	= swab32(bp.v->bucket_offset);
 	bp.v->bucket_len	= swab32(bp.v->bucket_len);
 	bch2_bpos_swab(&bp.v->pos);
 }

 static noinline int backpointer_mod_err(struct btree_trans *trans,
 					struct bch_backpointer bp,
 					struct bkey_s_c bp_k,
 					struct bkey_s_c orig_k,
 					bool insert)
 {
 	struct bch_fs *c = trans->c;
 	struct printbuf buf = PRINTBUF;

 	if (insert) {
 		prt_printf(&buf, "existing backpointer found when inserting ");
 		bch2_backpointer_to_text(&buf, &bp);
 		prt_newline(&buf);
 		printbuf_indent_add(&buf, 2);

 		prt_printf(&buf, "found ");
 		bch2_bkey_val_to_text(&buf, c, bp_k);
 		prt_newline(&buf);

 		prt_printf(&buf, "for ");
 		bch2_bkey_val_to_text(&buf, c, orig_k);

 		bch_err(c, "%s", buf.buf);
 	} else if (c->curr_recovery_pass > BCH_RECOVERY_PASS_check_extents_to_backpointers) {
 		prt_printf(&buf, "backpointer not found when deleting");
 		prt_newline(&buf);
 		printbuf_indent_add(&buf, 2);

 		prt_printf(&buf, "searching for ");
 		bch2_backpointer_to_text(&buf, &bp);
 		prt_newline(&buf);

 		prt_printf(&buf, "got ");
 		bch2_bkey_val_to_text(&buf, c, bp_k);
 		prt_newline(&buf);

 		prt_printf(&buf, "for ");
 		bch2_bkey_val_to_text(&buf, c, orig_k);

 		bch_err(c, "%s", buf.buf);
 	}

 	printbuf_exit(&buf);

 	if (c->curr_recovery_pass > BCH_RECOVERY_PASS_check_extents_to_backpointers) {
 		bch2_inconsistent_error(c);
 		return -EIO;
 	} else {
 		return 0;
 	}
 }

 int bch2_bucket_backpointer_mod_nowritebuffer(struct btree_trans *trans,
 				struct bkey_i_backpointer *bp_k,
 				struct bch_backpointer bp,
 				struct bkey_s_c orig_k,
 				bool insert)
 {
 	struct btree_iter bp_iter;
 	struct bkey_s_c k;
 	int ret;

 	k = bch2_bkey_get_iter(trans, &bp_iter, BTREE_ID_backpointers,
 			       bp_k->k.p,
 			       BTREE_ITER_INTENT|
 			       BTREE_ITER_SLOTS|
 			       BTREE_ITER_WITH_UPDATES);
 	ret = bkey_err(k);
 	if (ret)
 		goto err;

 	if (insert
 	    ? k.k->type
 	    : (k.k->type != KEY_TYPE_backpointer ||
 	       memcmp(bkey_s_c_to_backpointer(k).v, &bp, sizeof(bp)))) {
 		ret = backpointer_mod_err(trans, bp, k, orig_k, insert);
 		if (ret)
 			goto err;
 	}

 	ret = bch2_trans_update(trans, &bp_iter, &bp_k->k_i, 0);
 err:
 	bch2_trans_iter_exit(trans, &bp_iter);
 	return ret;
 }

 /*
  * Find the next backpointer >= *bp_offset:
  */
 int bch2_get_next_backpointer(struct btree_trans *trans,
 			      struct bpos bucket, int gen,
 			      struct bpos *bp_pos,
 			      struct bch_backpointer *bp,
 			      unsigned iter_flags)
 {
 	struct bch_fs *c = trans->c;
 	struct bpos bp_end_pos = bucket_pos_to_bp(c, bpos_nosnap_successor(bucket), 0);
 	struct btree_iter alloc_iter = { NULL }, bp_iter = { NULL };
 	struct bkey_s_c k;
 	int ret = 0;

 	if (bpos_ge(*bp_pos, bp_end_pos))
 		goto done;

 	if (gen >= 0) {
 		k = bch2_bkey_get_iter(trans, &alloc_iter, BTREE_ID_alloc,
 				       bucket, BTREE_ITER_CACHED|iter_flags);
 		ret = bkey_err(k);
 		if (ret)
 			goto out;

 		if (k.k->type != KEY_TYPE_alloc_v4 ||
 		    bkey_s_c_to_alloc_v4(k).v->gen != gen)
 			goto done;
 	}

 	*bp_pos = bpos_max(*bp_pos, bucket_pos_to_bp(c, bucket, 0));

 	for_each_btree_key_norestart(trans, bp_iter, BTREE_ID_backpointers,
 				     *bp_pos, iter_flags, k, ret) {
 		if (bpos_ge(k.k->p, bp_end_pos))
 			break;

 		*bp_pos = k.k->p;
 		*bp = *bkey_s_c_to_backpointer(k).v;
 		goto out;
 	}
 done:
 	*bp_pos = SPOS_MAX;
 out:
 	bch2_trans_iter_exit(trans, &bp_iter);
 	bch2_trans_iter_exit(trans, &alloc_iter);
 	return ret;
 }

 static void backpointer_not_found(struct btree_trans *trans,
 				  struct bpos bp_pos,
 				  struct bch_backpointer bp,
 				  struct bkey_s_c k,
 				  const char *thing_it_points_to)
 {
 	struct bch_fs *c = trans->c;
 	struct printbuf buf = PRINTBUF;
 	struct bpos bucket = bp_pos_to_bucket(c, bp_pos);

 	if (likely(!bch2_backpointers_no_use_write_buffer))
 		return;

 	prt_printf(&buf, "backpointer doesn't match %s it points to:\n  ",
 		   thing_it_points_to);
 	prt_printf(&buf, "bucket: ");
 	bch2_bpos_to_text(&buf, bucket);
 	prt_printf(&buf, "\n  ");

 	prt_printf(&buf, "backpointer pos: ");
 	bch2_bpos_to_text(&buf, bp_pos);
 	prt_printf(&buf, "\n  ");

 	bch2_backpointer_to_text(&buf, &bp);
 	prt_printf(&buf, "\n  ");
 	bch2_bkey_val_to_text(&buf, c, k);
 	if (c->curr_recovery_pass >= BCH_RECOVERY_PASS_check_extents_to_backpointers)
 		bch_err_ratelimited(c, "%s", buf.buf);
 	else
 		bch2_trans_inconsistent(trans, "%s", buf.buf);

 	printbuf_exit(&buf);
 }

 struct bkey_s_c bch2_backpointer_get_key(struct btree_trans *trans,
 					 struct btree_iter *iter,
 					 struct bpos bp_pos,
 					 struct bch_backpointer bp,
 					 unsigned iter_flags)
 {
 	struct bch_fs *c = trans->c;
 	struct btree_root *r = bch2_btree_id_root(c, bp.btree_id);
 	struct bpos bucket = bp_pos_to_bucket(c, bp_pos);
 	struct bkey_s_c k;

 	bch2_trans_node_iter_init(trans, iter,
 				  bp.btree_id,
 				  bp.pos,
 				  0,
 				  min(bp.level, r->level),
 				  iter_flags);
 	k = bch2_btree_iter_peek_slot(iter);
 	if (bkey_err(k)) {
 		bch2_trans_iter_exit(trans, iter);
 		return k;
 	}

 	if (bp.level == r->level + 1)
 		k = bkey_i_to_s_c(&r->key);

 	if (k.k && extent_matches_bp(c, bp.btree_id, bp.level, k, bucket, bp))
 		return k;

 	bch2_trans_iter_exit(trans, iter);

 	if (unlikely(bch2_backpointers_no_use_write_buffer)) {
 		if (bp.level) {
 			struct btree *b;

 			/*
 			 * If a backpointer for a btree node wasn't found, it may be
 			 * because it was overwritten by a new btree node that hasn't
 			 * been written out yet - backpointer_get_node() checks for
 			 * this:
 			 */
 			b = bch2_backpointer_get_node(trans, iter, bp_pos, bp);
 			if (!IS_ERR_OR_NULL(b))
 				return bkey_i_to_s_c(&b->key);

 			bch2_trans_iter_exit(trans, iter);

 			if (IS_ERR(b))
 				return bkey_s_c_err(PTR_ERR(b));
 			return bkey_s_c_null;
 		}

 		backpointer_not_found(trans, bp_pos, bp, k, "extent");
 	}

 	return bkey_s_c_null;
 }

 struct btree *bch2_backpointer_get_node(struct btree_trans *trans,
 					struct btree_iter *iter,
 					struct bpos bp_pos,
 					struct bch_backpointer bp)
 {
 	struct bch_fs *c = trans->c;
 	struct bpos bucket = bp_pos_to_bucket(c, bp_pos);
 	struct btree *b;

 	BUG_ON(!bp.level);

 	bch2_trans_node_iter_init(trans, iter,
 				  bp.btree_id,
 				  bp.pos,
 				  0,
 				  bp.level - 1,
 				  0);
 	b = bch2_btree_iter_peek_node(iter);
 	if (IS_ERR(b))
 		goto err;

 	if (b && extent_matches_bp(c, bp.btree_id, bp.level,
 				   bkey_i_to_s_c(&b->key),
 				   bucket, bp))
 		return b;

 	if (b && btree_node_will_make_reachable(b)) {
 		b = ERR_PTR(-BCH_ERR_backpointer_to_overwritten_btree_node);
 	} else {
 		backpointer_not_found(trans, bp_pos, bp,
 				      bkey_i_to_s_c(&b->key), "btree node");
 		b = NULL;
 	}
 err:
 	bch2_trans_iter_exit(trans, iter);
 	return b;
 }

 static int bch2_check_btree_backpointer(struct btree_trans *trans, struct btree_iter *bp_iter,
 					struct bkey_s_c k)
 {
 	struct bch_fs *c = trans->c;
 	struct btree_iter alloc_iter = { NULL };
 	struct bch_dev *ca;
 	struct bkey_s_c alloc_k;
 	struct printbuf buf = PRINTBUF;
 	int ret = 0;

 	if (fsck_err_on(!bch2_dev_exists2(c, k.k->p.inode), c,
 			"backpointer for missing device:\n%s",
 			(bch2_bkey_val_to_text(&buf, c, k), buf.buf))) {
 		ret = bch2_btree_delete_at(trans, bp_iter, 0);
 		goto out;
 	}

 	ca = bch_dev_bkey_exists(c, k.k->p.inode);

 	alloc_k = bch2_bkey_get_iter(trans, &alloc_iter, BTREE_ID_alloc,
 				     bp_pos_to_bucket(c, k.k->p), 0);
 	ret = bkey_err(alloc_k);
 	if (ret)
 		goto out;

 	if (fsck_err_on(alloc_k.k->type != KEY_TYPE_alloc_v4, c,
 			"backpointer for nonexistent alloc key: %llu:%llu:0\n%s",
 			alloc_iter.pos.inode, alloc_iter.pos.offset,
 			(bch2_bkey_val_to_text(&buf, c, alloc_k), buf.buf))) {
 		ret = bch2_btree_delete_at(trans, bp_iter, 0);
 		goto out;
 	}
 out:
 fsck_err:
 	bch2_trans_iter_exit(trans, &alloc_iter);
 	printbuf_exit(&buf);
 	return ret;
 }

 /* verify that every backpointer has a corresponding alloc key */
 int bch2_check_btree_backpointers(struct bch_fs *c)
 {
 	struct btree_iter iter;
 	struct bkey_s_c k;
 	int ret;

 	ret = bch2_trans_run(c,
 		for_each_btree_key_commit(&trans, iter,
 			BTREE_ID_backpointers, POS_MIN, 0, k,
 			NULL, NULL, BTREE_INSERT_LAZY_RW|BTREE_INSERT_NOFAIL,
 		  bch2_check_btree_backpointer(&trans, &iter, k)));
 	if (ret)
 		bch_err_fn(c, ret);
 	return ret;
 }

 struct bpos_level {
 	unsigned	level;
 	struct bpos	pos;
 };

 static int check_bp_exists(struct btree_trans *trans,
 			   struct bpos bucket,
 			   struct bch_backpointer bp,
 			   struct bkey_s_c orig_k,
 			   struct bpos bucket_start,
 			   struct bpos bucket_end,
 			   struct bpos_level *last_flushed)
 {
 	struct bch_fs *c = trans->c;
 	struct btree_iter bp_iter = { NULL };
 	struct printbuf buf = PRINTBUF;
 	struct bkey_s_c bp_k;
 	int ret;

 	if (bpos_lt(bucket, bucket_start) ||
 	    bpos_gt(bucket, bucket_end))
 		return 0;

 	if (!bch2_dev_bucket_exists(c, bucket))
 		goto missing;

 	bp_k = bch2_bkey_get_iter(trans, &bp_iter, BTREE_ID_backpointers,
 				  bucket_pos_to_bp(c, bucket, bp.bucket_offset),
 				  0);
 	ret = bkey_err(bp_k);
 	if (ret)
 		goto err;

 	if (bp_k.k->type != KEY_TYPE_backpointer ||
 	    memcmp(bkey_s_c_to_backpointer(bp_k).v, &bp, sizeof(bp))) {
 		if (last_flushed->level != bp.level ||
 		    !bpos_eq(last_flushed->pos, orig_k.k->p)) {
 			last_flushed->level = bp.level;
 			last_flushed->pos = orig_k.k->p;

 			ret = bch2_btree_write_buffer_flush_sync(trans) ?:
 				-BCH_ERR_transaction_restart_write_buffer_flush;
 			goto out;
 		}
 		goto missing;
 	}
 out:
 err:
 fsck_err:
 	bch2_trans_iter_exit(trans, &bp_iter);
 	printbuf_exit(&buf);
 	return ret;
 missing:
 	prt_printf(&buf, "missing backpointer for btree=%s l=%u ",
 	       bch2_btree_ids[bp.btree_id], bp.level);
 	bch2_bkey_val_to_text(&buf, c, orig_k);
 	prt_printf(&buf, "\nbp pos ");
 	bch2_bpos_to_text(&buf, bp_iter.pos);

 	if (c->sb.version_upgrade_complete < bcachefs_metadata_version_backpointers ||
 	    c->opts.reconstruct_alloc ||
 	    fsck_err(c, "%s", buf.buf))
 		ret = bch2_bucket_backpointer_mod(trans, bucket, bp, orig_k, true);

 	goto out;
 }

 static int check_extent_to_backpointers(struct btree_trans *trans,
 					struct btree_iter *iter,
 					struct bpos bucket_start,
 					struct bpos bucket_end,
 					struct bpos_level *last_flushed)
 {
 	struct bch_fs *c = trans->c;
 	struct bkey_ptrs_c ptrs;
 	const union bch_extent_entry *entry;
 	struct extent_ptr_decoded p;
 	struct bkey_s_c k;
 	int ret;

 	k = bch2_btree_iter_peek_all_levels(iter);
 	ret = bkey_err(k);
 	if (ret)
 		return ret;
 	if (!k.k)
 		return 0;

 	ptrs = bch2_bkey_ptrs_c(k);
 	bkey_for_each_ptr_decode(k.k, ptrs, p, entry) {
 		struct bpos bucket_pos;
 		struct bch_backpointer bp;

 		if (p.ptr.cached)
 			continue;

 		bch2_extent_ptr_to_bp(c, iter->btree_id, iter->path->level,
 				      k, p, &bucket_pos, &bp);

 		ret = check_bp_exists(trans, bucket_pos, bp, k,
 				      bucket_start, bucket_end,
 				      last_flushed);
 		if (ret)
 			return ret;
 	}

 	return 0;
 }

 static int check_btree_root_to_backpointers(struct btree_trans *trans,
 					    enum btree_id btree_id,
 					    struct bpos bucket_start,
 					    struct bpos bucket_end,
 					    struct bpos_level *last_flushed)
 {
 	struct bch_fs *c = trans->c;
 	struct btree_root *r = bch2_btree_id_root(c, btree_id);
 	struct btree_iter iter;
 	struct btree *b;
 	struct bkey_s_c k;
 	struct bkey_ptrs_c ptrs;
 	struct extent_ptr_decoded p;
 	const union bch_extent_entry *entry;
 	int ret;

 	bch2_trans_node_iter_init(trans, &iter, btree_id, POS_MIN, 0, r->level, 0);
 	b = bch2_btree_iter_peek_node(&iter);
 	ret = PTR_ERR_OR_ZERO(b);
 	if (ret)
 		goto err;

 	BUG_ON(b != btree_node_root(c, b));

 	k = bkey_i_to_s_c(&b->key);
 	ptrs = bch2_bkey_ptrs_c(k);
 	bkey_for_each_ptr_decode(k.k, ptrs, p, entry) {
 		struct bpos bucket_pos;
 		struct bch_backpointer bp;

 		if (p.ptr.cached)
 			continue;

 		bch2_extent_ptr_to_bp(c, iter.btree_id, b->c.level + 1,
 				      k, p, &bucket_pos, &bp);

 		ret = check_bp_exists(trans, bucket_pos, bp, k,
 				      bucket_start, bucket_end,
 				      last_flushed);
 		if (ret)
 			goto err;
 	}
 err:
 	bch2_trans_iter_exit(trans, &iter);
 	return ret;
 }

 static inline struct bbpos bp_to_bbpos(struct bch_backpointer bp)
 {
 	return (struct bbpos) {
 		.btree	= bp.btree_id,
 		.pos	= bp.pos,
 	};
 }

 static size_t btree_nodes_fit_in_ram(struct bch_fs *c)
 {
 	struct sysinfo i;
 	u64 mem_bytes;

 	si_meminfo(&i);
 	mem_bytes = i.totalram * i.mem_unit;
 	return div_u64(mem_bytes >> 1, btree_bytes(c));
 }

 static int bch2_get_btree_in_memory_pos(struct btree_trans *trans,
 					unsigned btree_leaf_mask,
 					unsigned btree_interior_mask,
 					struct bbpos start, struct bbpos *end)
 {
 	struct btree_iter iter;
 	struct bkey_s_c k;
 	size_t btree_nodes = btree_nodes_fit_in_ram(trans->c);
 	enum btree_id btree;
 	int ret = 0;

 	for (btree = start.btree; btree < BTREE_ID_NR && !ret; btree++) {
 		unsigned depth = ((1U << btree) & btree_leaf_mask) ? 1 : 2;

 		if (!((1U << btree) & btree_leaf_mask) &&
 		    !((1U << btree) & btree_interior_mask))
 			continue;

 		bch2_trans_node_iter_init(trans, &iter, btree,
 					  btree == start.btree ? start.pos : POS_MIN,
 					  0, depth, 0);
 		/*
 		 * for_each_btree_key_contineu() doesn't check the return value
 		 * from bch2_btree_iter_advance(), which is needed when
 		 * iterating over interior nodes where we'll see keys at
 		 * SPOS_MAX:
 		 */
 		do {
 			k = __bch2_btree_iter_peek_and_restart(trans, &iter, 0);
 			ret = bkey_err(k);
 			if (!k.k || ret)
 				break;

 			--btree_nodes;
 			if (!btree_nodes) {
 				*end = BBPOS(btree, k.k->p);
 				bch2_trans_iter_exit(trans, &iter);
 				return 0;
 			}
 		} while (bch2_btree_iter_advance(&iter));
 		bch2_trans_iter_exit(trans, &iter);
 	}

 	*end = BBPOS_MAX;
 	return ret;
 }

 static int bch2_check_extents_to_backpointers_pass(struct btree_trans *trans,
 						   struct bpos bucket_start,
 						   struct bpos bucket_end)
 {
 	struct bch_fs *c = trans->c;
 	struct btree_iter iter;
 	enum btree_id btree_id;
 	struct bpos_level last_flushed = { UINT_MAX };
 	int ret = 0;

 	for (btree_id = 0; btree_id < btree_id_nr_alive(c); btree_id++) {
 		unsigned depth = btree_type_has_ptrs(btree_id) ? 0 : 1;

 		bch2_trans_node_iter_init(trans, &iter, btree_id, POS_MIN, 0,
 					  depth,
 					  BTREE_ITER_ALL_LEVELS|
 					  BTREE_ITER_PREFETCH);

 		do {
 			ret = commit_do(trans, NULL, NULL,
 					BTREE_INSERT_LAZY_RW|
 					BTREE_INSERT_NOFAIL,
 					check_extent_to_backpointers(trans, &iter,
 								bucket_start, bucket_end,
 								&last_flushed));
 			if (ret)
 				break;
 		} while (!bch2_btree_iter_advance(&iter));

 		bch2_trans_iter_exit(trans, &iter);

 		if (ret)
 			break;

 		ret = commit_do(trans, NULL, NULL,
 				BTREE_INSERT_LAZY_RW|
 				BTREE_INSERT_NOFAIL,
 				check_btree_root_to_backpointers(trans, btree_id,
 							bucket_start, bucket_end,
 							&last_flushed));
 		if (ret)
 			break;
 	}
 	return ret;
 }

 static struct bpos bucket_pos_to_bp_safe(const struct bch_fs *c,
 					 struct bpos bucket)
 {
 	return bch2_dev_exists2(c, bucket.inode)
 		? bucket_pos_to_bp(c, bucket, 0)
 		: bucket;
 }

 static int bch2_get_alloc_in_memory_pos(struct btree_trans *trans,
 					struct bpos start, struct bpos *end)
 {
 	struct btree_iter alloc_iter;
 	struct btree_iter bp_iter;
 	struct bkey_s_c alloc_k, bp_k;
 	size_t btree_nodes = btree_nodes_fit_in_ram(trans->c);
 	bool alloc_end = false, bp_end = false;
 	int ret = 0;

 	bch2_trans_node_iter_init(trans, &alloc_iter, BTREE_ID_alloc,
 				  start, 0, 1, 0);
 	bch2_trans_node_iter_init(trans, &bp_iter, BTREE_ID_backpointers,
 				  bucket_pos_to_bp_safe(trans->c, start), 0, 1, 0);
 	while (1) {
 		alloc_k = !alloc_end
 			? __bch2_btree_iter_peek_and_restart(trans, &alloc_iter, 0)
 			: bkey_s_c_null;
 		bp_k = !bp_end
 			? __bch2_btree_iter_peek_and_restart(trans, &bp_iter, 0)
 			: bkey_s_c_null;

 		ret = bkey_err(alloc_k) ?: bkey_err(bp_k);
 		if ((!alloc_k.k && !bp_k.k) || ret) {
 			*end = SPOS_MAX;
 			break;
 		}

 		--btree_nodes;
 		if (!btree_nodes) {
 			*end = alloc_k.k->p;
 			break;
 		}

 		if (bpos_lt(alloc_iter.pos, SPOS_MAX) &&
 		    bpos_lt(bucket_pos_to_bp_safe(trans->c, alloc_iter.pos), bp_iter.pos)) {
 			if (!bch2_btree_iter_advance(&alloc_iter))
 				alloc_end = true;
 		} else {
 			if (!bch2_btree_iter_advance(&bp_iter))
 				bp_end = true;
 		}
 	}
 	bch2_trans_iter_exit(trans, &bp_iter);
 	bch2_trans_iter_exit(trans, &alloc_iter);
 	return ret;
 }

 int bch2_check_extents_to_backpointers(struct bch_fs *c)
 {
 	struct btree_trans trans;
 	struct bpos start = POS_MIN, end;
 	int ret;

 	bch2_trans_init(&trans, c, 0, 0);
 	while (1) {
 		ret = bch2_get_alloc_in_memory_pos(&trans, start, &end);
 		if (ret)
 			break;

 		if (bpos_eq(start, POS_MIN) && !bpos_eq(end, SPOS_MAX))
 			bch_verbose(c, "%s(): alloc info does not fit in ram, running in multiple passes with %zu nodes per pass",
 				    __func__, btree_nodes_fit_in_ram(c));

 		if (!bpos_eq(start, POS_MIN) || !bpos_eq(end, SPOS_MAX)) {
 			struct printbuf buf = PRINTBUF;

 			prt_str(&buf, "check_extents_to_backpointers(): ");
 			bch2_bpos_to_text(&buf, start);
 			prt_str(&buf, "-");
 			bch2_bpos_to_text(&buf, end);

 			bch_verbose(c, "%s", buf.buf);
 			printbuf_exit(&buf);
 		}

 		ret = bch2_check_extents_to_backpointers_pass(&trans, start, end);
 		if (ret || bpos_eq(end, SPOS_MAX))
 			break;

 		start = bpos_successor(end);
 	}
 	bch2_trans_exit(&trans);

 	if (ret)
 		bch_err_fn(c, ret);
 	return ret;
 }

 static int check_one_backpointer(struct btree_trans *trans,
 				 struct bbpos start,
 				 struct bbpos end,
 				 struct bkey_s_c_backpointer bp,
 				 struct bpos *last_flushed_pos)
 {
 	struct bch_fs *c = trans->c;
 	struct btree_iter iter;
 	struct bbpos pos = bp_to_bbpos(*bp.v);
 	struct bkey_s_c k;
 	struct printbuf buf = PRINTBUF;
 	int ret;

 	if (bbpos_cmp(pos, start) < 0 ||
 	    bbpos_cmp(pos, end) > 0)
 		return 0;

 	k = bch2_backpointer_get_key(trans, &iter, bp.k->p, *bp.v, 0);
 	ret = bkey_err(k);
 	if (ret == -BCH_ERR_backpointer_to_overwritten_btree_node)
 		return 0;
 	if (ret)
 		return ret;

 	if (!k.k && !bpos_eq(*last_flushed_pos, bp.k->p)) {
 		*last_flushed_pos = bp.k->p;
 		ret = bch2_btree_write_buffer_flush_sync(trans) ?:
 			-BCH_ERR_transaction_restart_write_buffer_flush;
 		goto out;
 	}

 	if (fsck_err_on(!k.k, c,
 			"backpointer for missing extent\n  %s",
 			(bch2_bkey_val_to_text(&buf, c, bp.s_c), buf.buf))) {
 		ret = bch2_btree_delete_at_buffered(trans, BTREE_ID_backpointers, bp.k->p);
 		goto out;
 	}
 out:
 fsck_err:
 	bch2_trans_iter_exit(trans, &iter);
 	printbuf_exit(&buf);
 	return ret;
 }

 static int bch2_check_backpointers_to_extents_pass(struct btree_trans *trans,
 						   struct bbpos start,
 						   struct bbpos end)
 {
 	struct btree_iter iter;
 	struct bkey_s_c k;
 	struct bpos last_flushed_pos = SPOS_MAX;

 	return for_each_btree_key_commit(trans, iter, BTREE_ID_backpointers,
 				  POS_MIN, BTREE_ITER_PREFETCH, k,
 				  NULL, NULL, BTREE_INSERT_LAZY_RW|BTREE_INSERT_NOFAIL,
 		check_one_backpointer(trans, start, end,
 				      bkey_s_c_to_backpointer(k),
 				      &last_flushed_pos));
 }

 int bch2_check_backpointers_to_extents(struct bch_fs *c)
 {
 	struct btree_trans trans;
 	struct bbpos start = (struct bbpos) { .btree = 0, .pos = POS_MIN, }, end;
 	int ret;

 	bch2_trans_init(&trans, c, 0, 0);
 	while (1) {
 		ret = bch2_get_btree_in_memory_pos(&trans,
 						   (1U << BTREE_ID_extents)|
 						   (1U << BTREE_ID_reflink),
 						   ~0,
 						   start, &end);
 		if (ret)
 			break;

 		if (!bbpos_cmp(start, BBPOS_MIN) &&
 		    bbpos_cmp(end, BBPOS_MAX))
 			bch_verbose(c, "%s(): extents do not fit in ram, running in multiple passes with %zu nodes per pass",
 				    __func__, btree_nodes_fit_in_ram(c));

 		if (bbpos_cmp(start, BBPOS_MIN) ||
 		    bbpos_cmp(end, BBPOS_MAX)) {
 			struct printbuf buf = PRINTBUF;

 			prt_str(&buf, "check_backpointers_to_extents(): ");
 			bch2_bbpos_to_text(&buf, start);
 			prt_str(&buf, "-");
 			bch2_bbpos_to_text(&buf, end);

 			bch_verbose(c, "%s", buf.buf);
 			printbuf_exit(&buf);
 		}

 		ret = bch2_check_backpointers_to_extents_pass(&trans, start, end);
 		if (ret || !bbpos_cmp(end, BBPOS_MAX))
 			break;

 		start = bbpos_successor(end);
 	}
 	bch2_trans_exit(&trans);

 	if (ret)
 		bch_err_fn(c, ret);
 	return ret;
 }
	// SPDX-License-Identifier: GPL-2.0
	#include "bcachefs.h"
	#include "bbpos.h"
	#include "alloc_background.h"
	#include "backpointers.h"
	#include "btree_cache.h"
	#include "btree_update.h"
	#include "btree_write_buffer.h"
	#include "error.h"

	#include <linux/mm.h>

	static bool extent_matches_bp(struct bch_fs *c,
	enum btree_id btree_id, unsigned level,
	struct bkey_s_c k,
	struct bpos bucket,
	struct bch_backpointer bp)
	{
	struct bkey_ptrs_c ptrs = bch2_bkey_ptrs_c(k);
	const union bch_extent_entry *entry;
	struct extent_ptr_decoded p;

	bkey_for_each_ptr_decode(k.k, ptrs, p, entry) {
	struct bpos bucket2;
	struct bch_backpointer bp2;

	if (p.ptr.cached)
	continue;

	bch2_extent_ptr_to_bp(c, btree_id, level, k, p,
	&bucket2, &bp2);
	if (bpos_eq(bucket, bucket2) &&
	!memcmp(&bp, &bp2, sizeof(bp)))
	return true;
	}

	return false;
	}

	int bch2_backpointer_invalid(const struct bch_fs *c, struct bkey_s_c k,
	enum bkey_invalid_flags flags,
	struct printbuf *err)
	{
	struct bkey_s_c_backpointer bp = bkey_s_c_to_backpointer(k);
	struct bpos bucket = bp_pos_to_bucket(c, bp.k->p);

	if (!bpos_eq(bp.k->p, bucket_pos_to_bp(c, bucket, bp.v->bucket_offset))) {
	prt_str(err, "backpointer at wrong pos");
	return -BCH_ERR_invalid_bkey;
	}

	return 0;
	}

	void bch2_backpointer_to_text(struct printbuf out, const struct bch_backpointer bp)
	{
	prt_printf(out, "btree=%s l=%u offset=%llu:%u len=%u pos=",
	bch2_btree_ids[bp->btree_id],
	bp->level,
	(u64) (bp->bucket_offset >> MAX_EXTENT_COMPRESS_RATIO_SHIFT),
	(u32) bp->bucket_offset & ~(~0U << MAX_EXTENT_COMPRESS_RATIO_SHIFT),
	bp->bucket_len);
	bch2_bpos_to_text(out, bp->pos);
	}

	void bch2_backpointer_k_to_text(struct printbuf out, struct bch_fs c, struct bkey_s_c k)
	{
	prt_str(out, "bucket=");
	bch2_bpos_to_text(out, bp_pos_to_bucket(c, k.k->p));
	prt_str(out, " ");

	bch2_backpointer_to_text(out, bkey_s_c_to_backpointer(k).v);
	}

	void bch2_backpointer_swab(struct bkey_s k)
	{
	struct bkey_s_backpointer bp = bkey_s_to_backpointer(k);

	bp.v->bucket_offset = swab32(bp.v->bucket_offset);
	bp.v->bucket_len = swab32(bp.v->bucket_len);
	bch2_bpos_swab(&bp.v->pos);
	}

	static noinline int backpointer_mod_err(struct btree_trans *trans,
	struct bch_backpointer bp,
	struct bkey_s_c bp_k,
	struct bkey_s_c orig_k,
	bool insert)
	{
	struct bch_fs *c = trans->c;
	struct printbuf buf = PRINTBUF;

	if (insert) {
	prt_printf(&buf, "existing backpointer found when inserting ");
	bch2_backpointer_to_text(&buf, &bp);
	prt_newline(&buf);
	printbuf_indent_add(&buf, 2);

	prt_printf(&buf, "found ");
	bch2_bkey_val_to_text(&buf, c, bp_k);
	prt_newline(&buf);

	prt_printf(&buf, "for ");
	bch2_bkey_val_to_text(&buf, c, orig_k);

	bch_err(c, "%s", buf.buf);
	} else if (c->curr_recovery_pass > BCH_RECOVERY_PASS_check_extents_to_backpointers) {
	prt_printf(&buf, "backpointer not found when deleting");
	prt_newline(&buf);
	printbuf_indent_add(&buf, 2);

	prt_printf(&buf, "searching for ");
	bch2_backpointer_to_text(&buf, &bp);
	prt_newline(&buf);

	prt_printf(&buf, "got ");
	bch2_bkey_val_to_text(&buf, c, bp_k);
	prt_newline(&buf);

	prt_printf(&buf, "for ");
	bch2_bkey_val_to_text(&buf, c, orig_k);

	bch_err(c, "%s", buf.buf);
	}

	printbuf_exit(&buf);

	if (c->curr_recovery_pass > BCH_RECOVERY_PASS_check_extents_to_backpointers) {
	bch2_inconsistent_error(c);
	return -EIO;
	} else {
	return 0;
	}
	}

	int bch2_bucket_backpointer_mod_nowritebuffer(struct btree_trans *trans,
	struct bkey_i_backpointer *bp_k,
	struct bch_backpointer bp,
	struct bkey_s_c orig_k,
	bool insert)
	{
	struct btree_iter bp_iter;
	struct bkey_s_c k;
	int ret;

	k = bch2_bkey_get_iter(trans, &bp_iter, BTREE_ID_backpointers,
	bp_k->k.p,
	BTREE_ITER_INTENT\|
	BTREE_ITER_SLOTS\|
	BTREE_ITER_WITH_UPDATES);
	ret = bkey_err(k);
	if (ret)
	goto err;

	if (insert
	? k.k->type
	: (k.k->type != KEY_TYPE_backpointer \|\|
	memcmp(bkey_s_c_to_backpointer(k).v, &bp, sizeof(bp)))) {
	ret = backpointer_mod_err(trans, bp, k, orig_k, insert);
	if (ret)
	goto err;
	}

	ret = bch2_trans_update(trans, &bp_iter, &bp_k->k_i, 0);
	err:
	bch2_trans_iter_exit(trans, &bp_iter);
	return ret;
	}

	/*
	* Find the next backpointer >= *bp_offset:
	*/
	int bch2_get_next_backpointer(struct btree_trans *trans,
	struct bpos bucket, int gen,
	struct bpos *bp_pos,
	struct bch_backpointer *bp,
	unsigned iter_flags)
	{
	struct bch_fs *c = trans->c;
	struct bpos bp_end_pos = bucket_pos_to_bp(c, bpos_nosnap_successor(bucket), 0);
	struct btree_iter alloc_iter = { NULL }, bp_iter = { NULL };
	struct bkey_s_c k;
	int ret = 0;

	if (bpos_ge(*bp_pos, bp_end_pos))
	goto done;

	if (gen >= 0) {
	k = bch2_bkey_get_iter(trans, &alloc_iter, BTREE_ID_alloc,
	bucket, BTREE_ITER_CACHED\|iter_flags);
	ret = bkey_err(k);
	if (ret)
	goto out;

	if (k.k->type != KEY_TYPE_alloc_v4 \|\|
	bkey_s_c_to_alloc_v4(k).v->gen != gen)
	goto done;
	}

	bp_pos = bpos_max(bp_pos, bucket_pos_to_bp(c, bucket, 0));

	for_each_btree_key_norestart(trans, bp_iter, BTREE_ID_backpointers,
	*bp_pos, iter_flags, k, ret) {
	if (bpos_ge(k.k->p, bp_end_pos))
	break;

	*bp_pos = k.k->p;
	bp = bkey_s_c_to_backpointer(k).v;
	goto out;
	}
	done:
	*bp_pos = SPOS_MAX;
	out:
	bch2_trans_iter_exit(trans, &bp_iter);
	bch2_trans_iter_exit(trans, &alloc_iter);
	return ret;
	}

	static void backpointer_not_found(struct btree_trans *trans,
	struct bpos bp_pos,
	struct bch_backpointer bp,
	struct bkey_s_c k,
	const char *thing_it_points_to)
	{
	struct bch_fs *c = trans->c;
	struct printbuf buf = PRINTBUF;
	struct bpos bucket = bp_pos_to_bucket(c, bp_pos);

	if (likely(!bch2_backpointers_no_use_write_buffer))
	return;

	prt_printf(&buf, "backpointer doesn't match %s it points to:\n ",
	thing_it_points_to);
	prt_printf(&buf, "bucket: ");
	bch2_bpos_to_text(&buf, bucket);
	prt_printf(&buf, "\n ");

	prt_printf(&buf, "backpointer pos: ");
	bch2_bpos_to_text(&buf, bp_pos);
	prt_printf(&buf, "\n ");

	bch2_backpointer_to_text(&buf, &bp);
	prt_printf(&buf, "\n ");
	bch2_bkey_val_to_text(&buf, c, k);
	if (c->curr_recovery_pass >= BCH_RECOVERY_PASS_check_extents_to_backpointers)
	bch_err_ratelimited(c, "%s", buf.buf);
	else
	bch2_trans_inconsistent(trans, "%s", buf.buf);

	printbuf_exit(&buf);
	}

	struct bkey_s_c bch2_backpointer_get_key(struct btree_trans *trans,
	struct btree_iter *iter,
	struct bpos bp_pos,
	struct bch_backpointer bp,
	unsigned iter_flags)
	{
	struct bch_fs *c = trans->c;
	struct btree_root *r = bch2_btree_id_root(c, bp.btree_id);
	struct bpos bucket = bp_pos_to_bucket(c, bp_pos);
	struct bkey_s_c k;

	bch2_trans_node_iter_init(trans, iter,
	bp.btree_id,
	bp.pos,
	0,
	min(bp.level, r->level),
	iter_flags);
	k = bch2_btree_iter_peek_slot(iter);
	if (bkey_err(k)) {
	bch2_trans_iter_exit(trans, iter);
	return k;
	}

	if (bp.level == r->level + 1)
	k = bkey_i_to_s_c(&r->key);

	if (k.k && extent_matches_bp(c, bp.btree_id, bp.level, k, bucket, bp))
	return k;

	bch2_trans_iter_exit(trans, iter);

	if (unlikely(bch2_backpointers_no_use_write_buffer)) {
	if (bp.level) {
	struct btree *b;

	/*
	* If a backpointer for a btree node wasn't found, it may be
	* because it was overwritten by a new btree node that hasn't
	* been written out yet - backpointer_get_node() checks for
	* this:
	*/
	b = bch2_backpointer_get_node(trans, iter, bp_pos, bp);
	if (!IS_ERR_OR_NULL(b))
	return bkey_i_to_s_c(&b->key);

	bch2_trans_iter_exit(trans, iter);

	if (IS_ERR(b))
	return bkey_s_c_err(PTR_ERR(b));
	return bkey_s_c_null;
	}

	backpointer_not_found(trans, bp_pos, bp, k, "extent");
	}

	return bkey_s_c_null;
	}

	struct btree bch2_backpointer_get_node(struct btree_trans trans,
	struct btree_iter *iter,
	struct bpos bp_pos,
	struct bch_backpointer bp)
	{
	struct bch_fs *c = trans->c;
	struct bpos bucket = bp_pos_to_bucket(c, bp_pos);
	struct btree *b;

	BUG_ON(!bp.level);

	bch2_trans_node_iter_init(trans, iter,
	bp.btree_id,
	bp.pos,
	0,
	bp.level - 1,
	0);
	b = bch2_btree_iter_peek_node(iter);
	if (IS_ERR(b))
	goto err;

	if (b && extent_matches_bp(c, bp.btree_id, bp.level,
	bkey_i_to_s_c(&b->key),
	bucket, bp))
	return b;

	if (b && btree_node_will_make_reachable(b)) {
	b = ERR_PTR(-BCH_ERR_backpointer_to_overwritten_btree_node);
	} else {
	backpointer_not_found(trans, bp_pos, bp,
	bkey_i_to_s_c(&b->key), "btree node");
	b = NULL;
	}
	err:
	bch2_trans_iter_exit(trans, iter);
	return b;
	}

	static int bch2_check_btree_backpointer(struct btree_trans trans, struct btree_iter bp_iter,
	struct bkey_s_c k)
	{
	struct bch_fs *c = trans->c;
	struct btree_iter alloc_iter = { NULL };
	struct bch_dev *ca;
	struct bkey_s_c alloc_k;
	struct printbuf buf = PRINTBUF;
	int ret = 0;

	if (fsck_err_on(!bch2_dev_exists2(c, k.k->p.inode), c,
	"backpointer for missing device:\n%s",
	(bch2_bkey_val_to_text(&buf, c, k), buf.buf))) {
	ret = bch2_btree_delete_at(trans, bp_iter, 0);
	goto out;
	}

	ca = bch_dev_bkey_exists(c, k.k->p.inode);

	alloc_k = bch2_bkey_get_iter(trans, &alloc_iter, BTREE_ID_alloc,
	bp_pos_to_bucket(c, k.k->p), 0);
	ret = bkey_err(alloc_k);
	if (ret)
	goto out;

	if (fsck_err_on(alloc_k.k->type != KEY_TYPE_alloc_v4, c,
	"backpointer for nonexistent alloc key: %llu:%llu:0\n%s",
	alloc_iter.pos.inode, alloc_iter.pos.offset,
	(bch2_bkey_val_to_text(&buf, c, alloc_k), buf.buf))) {
	ret = bch2_btree_delete_at(trans, bp_iter, 0);
	goto out;
	}
	out:
	fsck_err:
	bch2_trans_iter_exit(trans, &alloc_iter);
	printbuf_exit(&buf);
	return ret;
	}

	/* verify that every backpointer has a corresponding alloc key */
	int bch2_check_btree_backpointers(struct bch_fs *c)
	{
	struct btree_iter iter;
	struct bkey_s_c k;
	int ret;

	ret = bch2_trans_run(c,
	for_each_btree_key_commit(&trans, iter,
	BTREE_ID_backpointers, POS_MIN, 0, k,
	NULL, NULL, BTREE_INSERT_LAZY_RW\|BTREE_INSERT_NOFAIL,
	bch2_check_btree_backpointer(&trans, &iter, k)));
	if (ret)
	bch_err_fn(c, ret);
	return ret;
	}

	struct bpos_level {
	unsigned level;
	struct bpos pos;
	};

	static int check_bp_exists(struct btree_trans *trans,
	struct bpos bucket,
	struct bch_backpointer bp,
	struct bkey_s_c orig_k,
	struct bpos bucket_start,
	struct bpos bucket_end,
	struct bpos_level *last_flushed)
	{
	struct bch_fs *c = trans->c;
	struct btree_iter bp_iter = { NULL };
	struct printbuf buf = PRINTBUF;
	struct bkey_s_c bp_k;
	int ret;

	if (bpos_lt(bucket, bucket_start) \|\|
	bpos_gt(bucket, bucket_end))
	return 0;

	if (!bch2_dev_bucket_exists(c, bucket))
	goto missing;

	bp_k = bch2_bkey_get_iter(trans, &bp_iter, BTREE_ID_backpointers,
	bucket_pos_to_bp(c, bucket, bp.bucket_offset),
	0);
	ret = bkey_err(bp_k);
	if (ret)
	goto err;

	if (bp_k.k->type != KEY_TYPE_backpointer \|\|
	memcmp(bkey_s_c_to_backpointer(bp_k).v, &bp, sizeof(bp))) {
	if (last_flushed->level != bp.level \|\|
	!bpos_eq(last_flushed->pos, orig_k.k->p)) {
	last_flushed->level = bp.level;
	last_flushed->pos = orig_k.k->p;

	ret = bch2_btree_write_buffer_flush_sync(trans) ?:
	-BCH_ERR_transaction_restart_write_buffer_flush;
	goto out;
	}
	goto missing;
	}
	out:
	err:
	fsck_err:
	bch2_trans_iter_exit(trans, &bp_iter);
	printbuf_exit(&buf);
	return ret;
	missing:
	prt_printf(&buf, "missing backpointer for btree=%s l=%u ",
	bch2_btree_ids[bp.btree_id], bp.level);
	bch2_bkey_val_to_text(&buf, c, orig_k);
	prt_printf(&buf, "\nbp pos ");
	bch2_bpos_to_text(&buf, bp_iter.pos);

	if (c->sb.version_upgrade_complete < bcachefs_metadata_version_backpointers \|\|
	c->opts.reconstruct_alloc \|\|
	fsck_err(c, "%s", buf.buf))
	ret = bch2_bucket_backpointer_mod(trans, bucket, bp, orig_k, true);

	goto out;
	}

	static int check_extent_to_backpointers(struct btree_trans *trans,
	struct btree_iter *iter,
	struct bpos bucket_start,
	struct bpos bucket_end,
	struct bpos_level *last_flushed)
	{
	struct bch_fs *c = trans->c;
	struct bkey_ptrs_c ptrs;
	const union bch_extent_entry *entry;
	struct extent_ptr_decoded p;
	struct bkey_s_c k;
	int ret;

	k = bch2_btree_iter_peek_all_levels(iter);
	ret = bkey_err(k);
	if (ret)
	return ret;
	if (!k.k)
	return 0;

	ptrs = bch2_bkey_ptrs_c(k);
	bkey_for_each_ptr_decode(k.k, ptrs, p, entry) {
	struct bpos bucket_pos;
	struct bch_backpointer bp;

	if (p.ptr.cached)
	continue;

	bch2_extent_ptr_to_bp(c, iter->btree_id, iter->path->level,
	k, p, &bucket_pos, &bp);

	ret = check_bp_exists(trans, bucket_pos, bp, k,
	bucket_start, bucket_end,
	last_flushed);
	if (ret)
	return ret;
	}

	return 0;
	}

	static int check_btree_root_to_backpointers(struct btree_trans *trans,
	enum btree_id btree_id,
	struct bpos bucket_start,
	struct bpos bucket_end,
	struct bpos_level *last_flushed)
	{
	struct bch_fs *c = trans->c;
	struct btree_root *r = bch2_btree_id_root(c, btree_id);
	struct btree_iter iter;
	struct btree *b;
	struct bkey_s_c k;
	struct bkey_ptrs_c ptrs;
	struct extent_ptr_decoded p;
	const union bch_extent_entry *entry;
	int ret;

	bch2_trans_node_iter_init(trans, &iter, btree_id, POS_MIN, 0, r->level, 0);
	b = bch2_btree_iter_peek_node(&iter);
	ret = PTR_ERR_OR_ZERO(b);
	if (ret)
	goto err;

	BUG_ON(b != btree_node_root(c, b));

	k = bkey_i_to_s_c(&b->key);
	ptrs = bch2_bkey_ptrs_c(k);
	bkey_for_each_ptr_decode(k.k, ptrs, p, entry) {
	struct bpos bucket_pos;
	struct bch_backpointer bp;

	if (p.ptr.cached)
	continue;

	bch2_extent_ptr_to_bp(c, iter.btree_id, b->c.level + 1,
	k, p, &bucket_pos, &bp);

	ret = check_bp_exists(trans, bucket_pos, bp, k,
	bucket_start, bucket_end,
	last_flushed);
	if (ret)
	goto err;
	}
	err:
	bch2_trans_iter_exit(trans, &iter);
	return ret;
	}

	static inline struct bbpos bp_to_bbpos(struct bch_backpointer bp)
	{
	return (struct bbpos) {
	.btree = bp.btree_id,
	.pos = bp.pos,
	};
	}

	static size_t btree_nodes_fit_in_ram(struct bch_fs *c)
	{
	struct sysinfo i;
	u64 mem_bytes;

	si_meminfo(&i);
	mem_bytes = i.totalram * i.mem_unit;
	return div_u64(mem_bytes >> 1, btree_bytes(c));
	}

	static int bch2_get_btree_in_memory_pos(struct btree_trans *trans,
	unsigned btree_leaf_mask,
	unsigned btree_interior_mask,
	struct bbpos start, struct bbpos *end)
	{
	struct btree_iter iter;
	struct bkey_s_c k;
	size_t btree_nodes = btree_nodes_fit_in_ram(trans->c);
	enum btree_id btree;
	int ret = 0;

	for (btree = start.btree; btree < BTREE_ID_NR && !ret; btree++) {
	unsigned depth = ((1U << btree) & btree_leaf_mask) ? 1 : 2;

	if (!((1U << btree) & btree_leaf_mask) &&
	!((1U << btree) & btree_interior_mask))
	continue;

	bch2_trans_node_iter_init(trans, &iter, btree,
	btree == start.btree ? start.pos : POS_MIN,
	0, depth, 0);
	/*
	* for_each_btree_key_contineu() doesn't check the return value
	* from bch2_btree_iter_advance(), which is needed when
	* iterating over interior nodes where we'll see keys at
	* SPOS_MAX:
	*/
	do {
	k = __bch2_btree_iter_peek_and_restart(trans, &iter, 0);
	ret = bkey_err(k);
	if (!k.k \|\| ret)
	break;

	--btree_nodes;
	if (!btree_nodes) {
	*end = BBPOS(btree, k.k->p);
	bch2_trans_iter_exit(trans, &iter);
	return 0;
	}
	} while (bch2_btree_iter_advance(&iter));
	bch2_trans_iter_exit(trans, &iter);
	}

	*end = BBPOS_MAX;
	return ret;
	}

	static int bch2_check_extents_to_backpointers_pass(struct btree_trans *trans,
	struct bpos bucket_start,
	struct bpos bucket_end)
	{
	struct bch_fs *c = trans->c;
	struct btree_iter iter;
	enum btree_id btree_id;
	struct bpos_level last_flushed = { UINT_MAX };
	int ret = 0;

	for (btree_id = 0; btree_id < btree_id_nr_alive(c); btree_id++) {
	unsigned depth = btree_type_has_ptrs(btree_id) ? 0 : 1;

	bch2_trans_node_iter_init(trans, &iter, btree_id, POS_MIN, 0,
	depth,
	BTREE_ITER_ALL_LEVELS\|
	BTREE_ITER_PREFETCH);

	do {
	ret = commit_do(trans, NULL, NULL,
	BTREE_INSERT_LAZY_RW\|
	BTREE_INSERT_NOFAIL,
	check_extent_to_backpointers(trans, &iter,
	bucket_start, bucket_end,
	&last_flushed));
	if (ret)
	break;
	} while (!bch2_btree_iter_advance(&iter));

	bch2_trans_iter_exit(trans, &iter);

	if (ret)
	break;

	ret = commit_do(trans, NULL, NULL,
	BTREE_INSERT_LAZY_RW\|
	BTREE_INSERT_NOFAIL,
	check_btree_root_to_backpointers(trans, btree_id,
	bucket_start, bucket_end,
	&last_flushed));
	if (ret)
	break;
	}
	return ret;
	}

	static struct bpos bucket_pos_to_bp_safe(const struct bch_fs *c,
	struct bpos bucket)
	{
	return bch2_dev_exists2(c, bucket.inode)
	? bucket_pos_to_bp(c, bucket, 0)
	: bucket;
	}

	static int bch2_get_alloc_in_memory_pos(struct btree_trans *trans,
	struct bpos start, struct bpos *end)
	{
	struct btree_iter alloc_iter;
	struct btree_iter bp_iter;
	struct bkey_s_c alloc_k, bp_k;
	size_t btree_nodes = btree_nodes_fit_in_ram(trans->c);
	bool alloc_end = false, bp_end = false;
	int ret = 0;

	bch2_trans_node_iter_init(trans, &alloc_iter, BTREE_ID_alloc,
	start, 0, 1, 0);
	bch2_trans_node_iter_init(trans, &bp_iter, BTREE_ID_backpointers,
	bucket_pos_to_bp_safe(trans->c, start), 0, 1, 0);
	while (1) {
	alloc_k = !alloc_end
	? __bch2_btree_iter_peek_and_restart(trans, &alloc_iter, 0)
	: bkey_s_c_null;
	bp_k = !bp_end
	? __bch2_btree_iter_peek_and_restart(trans, &bp_iter, 0)
	: bkey_s_c_null;

	ret = bkey_err(alloc_k) ?: bkey_err(bp_k);
	if ((!alloc_k.k && !bp_k.k) \|\| ret) {
	*end = SPOS_MAX;
	break;
	}

	--btree_nodes;
	if (!btree_nodes) {
	*end = alloc_k.k->p;
	break;
	}

	if (bpos_lt(alloc_iter.pos, SPOS_MAX) &&
	bpos_lt(bucket_pos_to_bp_safe(trans->c, alloc_iter.pos), bp_iter.pos)) {
	if (!bch2_btree_iter_advance(&alloc_iter))
	alloc_end = true;
	} else {
	if (!bch2_btree_iter_advance(&bp_iter))
	bp_end = true;
	}
	}
	bch2_trans_iter_exit(trans, &bp_iter);
	bch2_trans_iter_exit(trans, &alloc_iter);
	return ret;
	}

	int bch2_check_extents_to_backpointers(struct bch_fs *c)
	{
	struct btree_trans trans;
	struct bpos start = POS_MIN, end;
	int ret;

	bch2_trans_init(&trans, c, 0, 0);
	while (1) {
	ret = bch2_get_alloc_in_memory_pos(&trans, start, &end);
	if (ret)
	break;

	if (bpos_eq(start, POS_MIN) && !bpos_eq(end, SPOS_MAX))
	bch_verbose(c, "%s(): alloc info does not fit in ram, running in multiple passes with %zu nodes per pass",
	__func__, btree_nodes_fit_in_ram(c));

	if (!bpos_eq(start, POS_MIN) \|\| !bpos_eq(end, SPOS_MAX)) {
	struct printbuf buf = PRINTBUF;

	prt_str(&buf, "check_extents_to_backpointers(): ");
	bch2_bpos_to_text(&buf, start);
	prt_str(&buf, "-");
	bch2_bpos_to_text(&buf, end);

	bch_verbose(c, "%s", buf.buf);
	printbuf_exit(&buf);
	}

	ret = bch2_check_extents_to_backpointers_pass(&trans, start, end);
	if (ret \|\| bpos_eq(end, SPOS_MAX))
	break;

	start = bpos_successor(end);
	}
	bch2_trans_exit(&trans);

	if (ret)
	bch_err_fn(c, ret);
	return ret;
	}

	static int check_one_backpointer(struct btree_trans *trans,
	struct bbpos start,
	struct bbpos end,
	struct bkey_s_c_backpointer bp,
	struct bpos *last_flushed_pos)
	{
	struct bch_fs *c = trans->c;
	struct btree_iter iter;
	struct bbpos pos = bp_to_bbpos(*bp.v);
	struct bkey_s_c k;
	struct printbuf buf = PRINTBUF;
	int ret;

	if (bbpos_cmp(pos, start) < 0 \|\|
	bbpos_cmp(pos, end) > 0)
	return 0;

	k = bch2_backpointer_get_key(trans, &iter, bp.k->p, *bp.v, 0);
	ret = bkey_err(k);
	if (ret == -BCH_ERR_backpointer_to_overwritten_btree_node)
	return 0;
	if (ret)
	return ret;

	if (!k.k && !bpos_eq(*last_flushed_pos, bp.k->p)) {
	*last_flushed_pos = bp.k->p;
	ret = bch2_btree_write_buffer_flush_sync(trans) ?:
	-BCH_ERR_transaction_restart_write_buffer_flush;
	goto out;
	}

	if (fsck_err_on(!k.k, c,
	"backpointer for missing extent\n %s",
	(bch2_bkey_val_to_text(&buf, c, bp.s_c), buf.buf))) {
	ret = bch2_btree_delete_at_buffered(trans, BTREE_ID_backpointers, bp.k->p);
	goto out;
	}
	out:
	fsck_err:
	bch2_trans_iter_exit(trans, &iter);
	printbuf_exit(&buf);
	return ret;
	}

	static int bch2_check_backpointers_to_extents_pass(struct btree_trans *trans,
	struct bbpos start,
	struct bbpos end)
	{
	struct btree_iter iter;
	struct bkey_s_c k;
	struct bpos last_flushed_pos = SPOS_MAX;

	return for_each_btree_key_commit(trans, iter, BTREE_ID_backpointers,
	POS_MIN, BTREE_ITER_PREFETCH, k,
	NULL, NULL, BTREE_INSERT_LAZY_RW\|BTREE_INSERT_NOFAIL,
	check_one_backpointer(trans, start, end,
	bkey_s_c_to_backpointer(k),
	&last_flushed_pos));
	}

	int bch2_check_backpointers_to_extents(struct bch_fs *c)
	{
	struct btree_trans trans;
	struct bbpos start = (struct bbpos) { .btree = 0, .pos = POS_MIN, }, end;
	int ret;

	bch2_trans_init(&trans, c, 0, 0);
	while (1) {
	ret = bch2_get_btree_in_memory_pos(&trans,
	(1U << BTREE_ID_extents)\|
	(1U << BTREE_ID_reflink),
	~0,
	start, &end);
	if (ret)
	break;

	if (!bbpos_cmp(start, BBPOS_MIN) &&
	bbpos_cmp(end, BBPOS_MAX))
	bch_verbose(c, "%s(): extents do not fit in ram, running in multiple passes with %zu nodes per pass",
	__func__, btree_nodes_fit_in_ram(c));

	if (bbpos_cmp(start, BBPOS_MIN) \|\|
	bbpos_cmp(end, BBPOS_MAX)) {
	struct printbuf buf = PRINTBUF;

	prt_str(&buf, "check_backpointers_to_extents(): ");
	bch2_bbpos_to_text(&buf, start);
	prt_str(&buf, "-");
	bch2_bbpos_to_text(&buf, end);

	bch_verbose(c, "%s", buf.buf);
	printbuf_exit(&buf);
	}

	ret = bch2_check_backpointers_to_extents_pass(&trans, start, end);
	if (ret \|\| !bbpos_cmp(end, BBPOS_MAX))
	break;

	start = bbpos_successor(end);
	}
	bch2_trans_exit(&trans);

	if (ret)
	bch_err_fn(c, ret);
	return ret;
	}