// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2010 Kent Overstreet <kent.overstreet@gmail.com>
 * Copyright (C) 2014 Datera Inc.
 */

#include "bcachefs.h"

#include "alloc/accounting.h"
#include "alloc/background.h"
#include "alloc/backpointers.h"
#include "alloc/buckets.h"
#include "alloc/foreground.h"
#include "alloc/replicas.h"

#include "btree/bkey_methods.h"
#include "btree/bkey_buf.h"
#include "btree/check.h"
#include "btree/key_cache.h"
#include "btree/locking.h"
#include "btree/node_scan.h"
#include "btree/interior.h"
#include "btree/journal_overlay.h"
#include "btree/read.h"

#include "data/ec/trigger.h"
#include "data/extents.h"
#include "data/keylist.h"
#include "data/move.h"
#include "data/reflink.h"

#include "init/error.h"
#include "init/progress.h"
#include "init/passes.h"
#include "init/recovery.h"

#include "journal/journal.h"

#include "sb/counters.h"
#include "sb/io.h"

#include "util/enumerated_ref.h"

#include <linux/slab.h>
#include <linux/bitops.h>
#include <linux/freezer.h>
#include <linux/kthread.h>
#include <linux/preempt.h>
#include <linux/rcupdate.h>
#include <linux/sched/task.h>

static const char * const bch2_gc_phase_strs[] = {
#define x(n)	#n,
	GC_PHASES()
#undef x
	NULL
};

__cold void bch2_gc_pos_to_text(struct printbuf *out, struct gc_pos *p)
{
	prt_str(out, bch2_gc_phase_strs[p->phase]);
	prt_char(out, ' ');
	bch2_btree_id_level_to_text(out, p->btree, p->level);
	prt_char(out, ' ');
	bch2_bpos_to_text(out, p->pos);
}

static struct bkey_s unsafe_bkey_s_c_to_s(struct bkey_s_c k)
{
	return (struct bkey_s) {{{
		(struct bkey *) k.k,
		(struct bch_val *) k.v
	}}};
}

static inline void __gc_pos_set(struct bch_fs *c, struct gc_pos new_pos)
{
	guard(preempt)();
	write_seqcount_begin(&c->gc.pos_lock);
	c->gc.pos = new_pos;
	write_seqcount_end(&c->gc.pos_lock);
}

static inline void gc_pos_set(struct bch_fs *c, struct gc_pos new_pos)
{
	BUG_ON(gc_pos_cmp(new_pos, c->gc.pos) < 0);
	__gc_pos_set(c, new_pos);
}

static void btree_ptr_to_v2(struct btree *b, struct bkey_i_btree_ptr_v2 *dst)
{
	switch (b->key.k.type) {
	case KEY_TYPE_btree_ptr: {
		struct bkey_i_btree_ptr *src = bkey_i_to_btree_ptr(&b->key);

		dst->k.p		= src->k.p;
		dst->v.mem_ptr		= 0;
		dst->v.seq		= b->data->keys.seq;
		dst->v.sectors_written	= 0;
		dst->v.flags		= 0;
		dst->v.min_key		= b->data->min_key;
		set_bkey_val_bytes(&dst->k, sizeof(dst->v) + bkey_val_bytes(&src->k));
		memcpy(dst->v.start, src->v.start, bkey_val_bytes(&src->k));
		break;
	}
	case KEY_TYPE_btree_ptr_v2:
		bkey_copy(&dst->k_i, &b->key);
		break;
	default:
		BUG();
	}
}

static int set_node_min(struct bch_fs *c, struct btree *b, struct bpos new_min)
{
	struct bkey_i_btree_ptr_v2 *new;
	int ret;

	if (c->opts.verbose) {
		CLASS(printbuf, buf)();

		bch2_bkey_val_to_text(&buf, c, bkey_i_to_s_c(&b->key));
		prt_str(&buf, " -> ");
		bch2_bpos_to_text(&buf, new_min);

		bch_info(c, "%s(): %s", __func__, buf.buf);
	}

	new = kmalloc_array(BKEY_BTREE_PTR_U64s_MAX, sizeof(u64), GFP_KERNEL);
	if (!new)
		return bch_err_throw(c, ENOMEM_gc_repair_key);

	btree_ptr_to_v2(b, new);
	b->data->min_key	= new_min;
	new->v.min_key		= new_min;
	SET_BTREE_PTR_RANGE_UPDATED(&new->v, true);

	ret = bch2_journal_key_insert_take(c, b->c.btree_id, b->c.level + 1, &new->k_i);
	if (ret) {
		kfree(new);
		return ret;
	}

	bch2_btree_node_drop_keys_outside_node(b);
	bkey_copy(&b->key, &new->k_i);
	return 0;
}

static int set_node_max(struct bch_fs *c, struct btree *b, struct bpos new_max)
{
	struct bkey_i_btree_ptr_v2 *new;

	if (c->opts.verbose) {
		CLASS(printbuf, buf)();

		bch2_bkey_val_to_text(&buf, c, bkey_i_to_s_c(&b->key));
		prt_str(&buf, " -> ");
		bch2_bpos_to_text(&buf, new_max);

		bch_info(c, "%s(): %s", __func__, buf.buf);
	}

	try(bch2_journal_key_delete(c, b->c.btree_id, b->c.level + 1, b->key.k.p));

	new = kmalloc_array(BKEY_BTREE_PTR_U64s_MAX, sizeof(u64), GFP_KERNEL);
	if (!new)
		return bch_err_throw(c, ENOMEM_gc_repair_key);

	btree_ptr_to_v2(b, new);
	b->data->max_key	= new_max;
	new->k.p		= new_max;
	SET_BTREE_PTR_RANGE_UPDATED(&new->v, true);

	int ret = bch2_journal_key_insert_take(c, b->c.btree_id, b->c.level + 1, &new->k_i);
	if (ret) {
		kfree(new);
		return ret;
	}

	bch2_btree_node_drop_keys_outside_node(b);

	struct bch_fs_btree_cache *bc = &c->btree.cache;

	/* unhash, rehash */
	BUG_ON(bch2_btree_node_transition_state(bc, b, BTREE_NODE_CACHE_FREEABLE));
	bkey_copy(&b->key, &new->k_i);
	BUG_ON(bch2_btree_node_transition_state(bc, b, btree_node_live_state(b)));
	return 0;
}

/*
 * Commit the fsck "repaired" log entry queued by mustfix_fsck_err().
 *
 * Topology repair runs before we go rw and applies its fixes through journal
 * keys (not transactional updates), so nothing else here commits - but the log
 * is a transaction update, and the next bch2_trans_begin() would silently drop
 * it. Commit it here, at the check, *before* the mutation: a commit can return
 * a transaction restart (fault injection, journal, ...), and doing it first
 * means the restart re-runs only the check - which re-queues the log - never
 * the non-transactional mutation, which must run exactly once.
 */
static int commit_topology_repair_log(struct btree_trans *trans)
{
	return bch2_trans_has_updates(trans)
		? bch2_trans_commit(trans, NULL, NULL, BCH_TRANS_COMMIT_no_enospc)
		: 0;
}

static int btree_check_node_boundaries(struct btree_trans *trans, struct btree *b,
				       struct btree *prev, struct btree *cur)
{
	struct bch_fs *c = trans->c;
	struct bpos expected_start = !prev
		? b->data->min_key
		: bpos_successor(prev->key.k.p);
	CLASS(printbuf, buf)();
	int ret = 0;

	BUG_ON(b->key.k.type == KEY_TYPE_btree_ptr_v2 &&
	       !bpos_eq(bkey_i_to_btree_ptr_v2(&b->key)->v.min_key,
			b->data->min_key));

	if (bpos_eq(expected_start, cur->data->min_key))
		return 0;

	prt_printf(&buf, " at ");
	bch2_btree_id_level_to_text(&buf, b->c.btree_id, b->c.level);
	prt_printf(&buf, ":\nparent: ");
	bch2_bkey_val_to_text(&buf, c, bkey_i_to_s_c(&b->key));

	if (prev) {
		prt_printf(&buf, "\nprev: ");
		bch2_bkey_val_to_text(&buf, c, bkey_i_to_s_c(&prev->key));
	}

	prt_str(&buf, "\nnext: ");
	bch2_bkey_val_to_text(&buf, c, bkey_i_to_s_c(&cur->key));
	prt_newline(&buf);

	if (bpos_lt(expected_start, cur->data->min_key)) {				/* gap */
		size_t nodes_found = 0;

		if (b->c.level == 1 &&
		    btree_id_recovers_from_scan(b->c.btree_id)) {
			try(bch2_get_scanned_nodes(c, b->c.btree_id, 0,
						   expected_start,
						   bpos_predecessor(cur->data->min_key),
						   &buf, &nodes_found));
			if (!nodes_found)
				prt_printf(&buf, "btree node scan found no nodes this range\n");
		}

		if (mustfix_fsck_err(trans, btree_node_topology_gap_between_nodes,
				     "gap between btree nodes%s", buf.buf)) {
			try(commit_topology_repair_log(trans));
			if (nodes_found)
				return bch_err_throw(c, topology_repair_did_fill_from_scan);
			else
				return set_node_min(c, cur, expected_start);
		}
	} else {									/* overlap */
		if (prev && BTREE_NODE_SEQ(cur->data) > BTREE_NODE_SEQ(prev->data)) {	/* cur overwrites prev */
			if (bpos_ge(prev->data->min_key, cur->data->min_key)) {		/* fully? */
				if (mustfix_fsck_err(trans, btree_node_topology_overwritten_by_next_node,
						     "btree node overwritten by next node%s", buf.buf)) {
					try(commit_topology_repair_log(trans));
					return bch_err_throw(c, topology_repair_drop_prev_node);
				}
			} else {
				if (mustfix_fsck_err(trans, btree_node_topology_bad_max_key,
						     "btree node with incorrect max_key%s", buf.buf)) {
					try(commit_topology_repair_log(trans));
					return set_node_max(c, prev, bpos_predecessor(cur->data->min_key));
				}
			}
		} else {
			if (bpos_ge(expected_start, cur->data->max_key)) {		/* fully? */
				if (mustfix_fsck_err(trans, btree_node_topology_overwritten_by_prev_node,
						     "btree node overwritten by prev node%s", buf.buf)) {
					try(commit_topology_repair_log(trans));
					return bch_err_throw(c, topology_repair_drop_this_node);
				}
			} else {
				if (mustfix_fsck_err(trans, btree_node_topology_bad_min_key,
						     "btree node with incorrect min_key%s", buf.buf)) {
					try(commit_topology_repair_log(trans));
					return set_node_min(c, cur, expected_start);
				}
			}
		}
	}
fsck_err:
	return ret;
}

static int btree_check_root_boundaries(struct btree_trans *trans, struct btree *b)
{
	struct bch_fs *c = trans->c;
	int ret = 0;

	BUG_ON(b->key.k.type == KEY_TYPE_btree_ptr_v2 &&
	       !bpos_eq(bkey_i_to_btree_ptr_v2(&b->key)->v.min_key,
			b->data->min_key));

	CLASS(printbuf, buf)();
	prt_str(&buf, "  at ");
	bch2_btree_pos_to_text(&buf, c, b);

	if (mustfix_fsck_err_on(!bpos_eq(b->data->min_key, POS_MIN),
				trans, btree_node_topology_bad_root_min_key,
			     "btree root with incorrect min_key%s", buf.buf))
		try(set_node_min(c, b, POS_MIN));

	if (mustfix_fsck_err_on(!bpos_eq(b->data->max_key, SPOS_MAX),
				trans, btree_node_topology_bad_root_max_key,
			     "btree root with incorrect min_key%s", buf.buf))
		try(set_node_max(c, b, SPOS_MAX));
fsck_err:
	return ret;
}

static int btree_repair_node_end(struct btree_trans *trans, struct btree *b, struct btree *child)
{
	struct bch_fs *c = trans->c;
	int ret = 0;

	if (bpos_eq(child->key.k.p, b->key.k.p))
		return 0;

	CLASS(printbuf, buf)();
	prt_printf(&buf, "\nat: ");
	bch2_btree_id_level_to_text(&buf, b->c.btree_id, b->c.level);
	prt_printf(&buf, "\nparent: ");
	bch2_bkey_val_to_text(&buf, c, bkey_i_to_s_c(&b->key));

	prt_str(&buf, "\nchild: ");
	bch2_bkey_val_to_text(&buf, c, bkey_i_to_s_c(&child->key));

	size_t nodes_found = 0;
	if (b->c.level == 1)
		try(bch2_get_scanned_nodes(c, b->c.btree_id, 0,
					   bpos_successor(child->key.k.p), b->key.k.p,
					   &buf, &nodes_found));

	if (mustfix_fsck_err(trans, btree_node_topology_bad_max_key,
			     "btree node with incorrect max_key%s", buf.buf)) {
		try(commit_topology_repair_log(trans));

		if (nodes_found)
			return bch_err_throw(c, topology_repair_did_fill_from_scan);
		else
			return set_node_max(c, child, b->key.k.p);
	}
fsck_err:
	return ret;
}

static int bch2_btree_repair_topology_recurse(struct btree_trans *trans, struct btree *b)
{
	struct bch_fs *c = trans->c;
	struct btree_and_journal_iter iter;
	struct bkey_s_c k;
	struct btree *prev = NULL, *cur = NULL;
	bool have_child, new_pass = false;
	CLASS(printbuf, buf)();
	int ret = 0;

	if (!b->c.level)
		return 0;

	struct bkey_buf prev_k __cleanup(bch2_bkey_buf_exit);
	struct bkey_buf cur_k __cleanup(bch2_bkey_buf_exit);
	bch2_bkey_buf_init(&prev_k);
	bch2_bkey_buf_init(&cur_k);
again:
	cur = prev = NULL;
	have_child = new_pass = false;
	bch2_btree_and_journal_iter_init_node_iter(trans, &iter, b);
	iter.prefetch = true;

	while ((k = bch2_btree_and_journal_iter_peek(c, &iter)).k) {
		BUG_ON(bpos_lt(k.k->p, b->data->min_key));
		BUG_ON(bpos_gt(k.k->p, b->data->max_key));

		bch2_btree_and_journal_iter_advance(&iter);
		bch2_bkey_buf_reassemble(&cur_k, k);

		cur = bch2_btree_node_get_noiter(trans, cur_k.k,
					b->c.btree_id, b->c.level - 1,
					false);
		ret = PTR_ERR_OR_ZERO(cur);

		printbuf_reset(&buf);
		bch2_btree_id_level_to_text(&buf, b->c.btree_id, b->c.level - 1);
		prt_char(&buf, ' ');
		bch2_bkey_val_to_text(&buf, c, bkey_i_to_s_c(cur_k.k));

		if (bch2_err_matches(ret, EIO)) {
			bch2_btree_node_evict(trans, cur_k.k);
			cur = NULL;
			ret = bch2_journal_key_delete(c, b->c.btree_id,
						      b->c.level, cur_k.k->k.p);
			if (ret)
				break;
			continue;
		}

		bch_err_msg(c, ret, "getting btree node");
		if (ret)
			break;

		if (bch2_btree_node_is_stale(c, cur)) {
			bch_info(c, "btree node older than nodes found by scanning\n  %s", buf.buf);
			six_unlock_read(&cur->c.lock);
			bch2_btree_node_evict(trans, cur_k.k);
			ret = bch2_journal_key_delete(c, b->c.btree_id,
						      b->c.level, cur_k.k->k.p);
			cur = NULL;
			if (ret)
				break;
			continue;
		}

		ret = lockrestart_do(trans,
			btree_check_node_boundaries(trans, b, prev, cur));
		if (ret && !bch2_err_matches(ret, BCH_ERR_topology_repair))
			goto err;

		if (bch2_err_matches(ret, BCH_ERR_topology_repair_did_fill_from_scan)) {
			new_pass = true;
			ret = 0;
		}

		if (bch2_err_matches(ret, BCH_ERR_topology_repair_drop_this_node)) {
			six_unlock_read(&cur->c.lock);
			bch2_btree_node_evict(trans, cur_k.k);
			ret = bch2_journal_key_delete(c, b->c.btree_id,
						      b->c.level, cur_k.k->k.p);
			cur = NULL;
			if (ret)
				break;
			continue;
		}

		if (prev)
			six_unlock_read(&prev->c.lock);
		prev = NULL;

		if (bch2_err_matches(ret, BCH_ERR_topology_repair_drop_prev_node)) {
			bch_info(c, "dropped prev node");
			bch2_btree_node_evict(trans, prev_k.k);
			ret = bch2_journal_key_delete(c, b->c.btree_id,
						      b->c.level, prev_k.k->k.p);
			if (ret)
				break;

			/*
			 * cur is still read-locked, and goto again jumps over the
			 * unlock at the end of the loop; drop it here or it leaks
			 * (and later self-deadlocks a write lock on the same node).
			 */
			six_unlock_read(&cur->c.lock);
			cur = NULL;

			bch2_btree_and_journal_iter_exit(&iter);
			goto again;
		} else if (ret)
			break;

		prev = cur;
		cur = NULL;
		bch2_bkey_buf_copy(&prev_k, cur_k.k);
	}

	if (!ret && !IS_ERR_OR_NULL(prev)) {
		BUG_ON(cur);
		ret = lockrestart_do(trans,
			btree_repair_node_end(trans, b, prev));
		if (bch2_err_matches(ret, BCH_ERR_topology_repair_did_fill_from_scan)) {
			new_pass = true;
			ret = 0;
		}
	}

	if (!IS_ERR_OR_NULL(prev))
		six_unlock_read(&prev->c.lock);
	prev = NULL;
	if (!IS_ERR_OR_NULL(cur))
		six_unlock_read(&cur->c.lock);
	cur = NULL;

	if (ret)
		goto err;

	bch2_btree_and_journal_iter_exit(&iter);

	if (new_pass)
		goto again;

	bch2_btree_and_journal_iter_init_node_iter(trans, &iter, b);
	iter.prefetch = true;

	while ((k = bch2_btree_and_journal_iter_peek(c, &iter)).k) {
		bch2_bkey_buf_reassemble(&cur_k, k);
		bch2_btree_and_journal_iter_advance(&iter);

		cur = bch2_btree_node_get_noiter(trans, cur_k.k,
					b->c.btree_id, b->c.level - 1,
					false);
		ret = PTR_ERR_OR_ZERO(cur);

		bch_err_msg(c, ret, "getting btree node");
		if (ret)
			goto err;

		ret = bch2_btree_repair_topology_recurse(trans, cur);
		six_unlock_read(&cur->c.lock);
		cur = NULL;

		if (bch2_err_matches(ret, BCH_ERR_topology_repair_drop_this_node)) {
			bch2_btree_node_evict(trans, cur_k.k);
			ret = bch2_journal_key_delete(c, b->c.btree_id,
						      b->c.level, cur_k.k->k.p);
			new_pass = true;
		}

		if (ret)
			goto err;

		have_child = true;
	}

	printbuf_reset(&buf);
	bch2_btree_id_level_to_text(&buf, b->c.btree_id, b->c.level);
	prt_newline(&buf);
	bch2_bkey_val_to_text(&buf, c, bkey_i_to_s_c(&b->key));

	/*
	 * XXX: we're not passing the trans object here because we're not set up
	 * to handle a transaction restart - this code needs to be rewritten
	 * when we start doing online topology repair
	 */
	bch2_trans_unlock_long(trans);
	if (mustfix_fsck_err_on(!have_child,
			c, btree_node_topology_interior_node_empty,
			"empty interior btree node at %s", buf.buf))
		ret = bch_err_throw(c, topology_repair_drop_this_node);
err:
fsck_err:
	if (!IS_ERR_OR_NULL(prev))
		six_unlock_read(&prev->c.lock);
	if (!IS_ERR_OR_NULL(cur))
		six_unlock_read(&cur->c.lock);

	bch2_btree_and_journal_iter_exit(&iter);

	if (!ret && new_pass)
		goto again;

	BUG_ON(!ret && bch2_btree_node_check_topology(trans, b));

	if (!bch2_err_matches(ret, BCH_ERR_topology_repair))
		bch_err_fn(c, ret);
	return ret;
}

static int bch2_topology_check_root(struct btree_trans *trans, enum btree_id btree,
				    bool *reconstructed_root)
{
	struct bch_fs *c = trans->c;
	struct btree_root *r = bch2_btree_id_root(c, btree);

	if (!r->error)
		return 0;

	CLASS(bch_log_msg, msg)(c);
	prt_printf(&msg.m, "btree root ");
	bch2_btree_id_to_text(&msg.m, btree);
	prt_printf(&msg.m, " unreadable: %s\n", bch2_err_str(r->error));

	if (!btree_id_recovers_from_scan(btree)) {
		r->alive = false;
		r->error = 0;
		bch2_btree_root_alloc_fake_trans(trans, btree, 0);
		*reconstructed_root = true;

		try(bch2_btree_lost_data(c, &msg.m, btree));
	} else {
		int ret = bch2_btree_has_scanned_nodes(c, btree, &msg.m);
		if (ret < 0)
			return ret;

		if (!ret) {
			msg.m.suppress = true;

			__ret_fsck_err(trans,
				       FSCK_CAN_FIX|(btree_id_can_reconstruct(btree) ? FSCK_AUTOFIX : 0),
				       btree_root_unreadable_and_scan_found_nothing,
				       "%sbtree node scan found no nodes, continue?", msg.m.buf);

			r->alive = false;
			r->error = 0;
			bch2_btree_root_alloc_fake_trans(trans, btree, 0);
			*reconstructed_root = true;
		} else {
			r->alive = false;
			r->error = 0;
			bch2_btree_root_alloc_fake_trans(trans, btree, 1);
			*reconstructed_root = true;

			bch2_shoot_down_journal_keys(c, btree, 1, BTREE_MAX_DEPTH, POS_MIN, SPOS_MAX);

			size_t nodes_found = 0;
			try(bch2_get_scanned_nodes(c, btree, 0, POS_MIN, SPOS_MAX, &msg.m, &nodes_found));
		}
	}

	/*
	 * Commit any fsck_err log entry queued above before returning: this
	 * runs pre-RW (so the commit is queued for journal replay), and the
	 * caller's per-btree loop starts each iteration with a bch2_trans_begin
	 * that would otherwise discard it.
	 */
	return bch2_trans_commit(trans, NULL, NULL, BCH_TRANS_COMMIT_no_enospc);
}

static void ratelimit_reset(struct ratelimit_state *rs)
{
	guard(raw_spinlock)(&rs->lock);
	atomic_set(&rs->rs_n_left, 0);
	atomic_set(&rs->missed, 0);
	rs->flags = 0;
	rs->begin = 0;
}

int bch2_check_topology(struct bch_fs *c)
{
	CLASS(btree_trans, trans)(c);

	bch2_trans_unlock_long(trans);

	for (unsigned i = 0; i < btree_id_nr_alive(c); i++) {
		bool reconstructed_root = false;
recover:
		try(lockrestart_do(trans, bch2_topology_check_root(trans, i, &reconstructed_root)));

		struct btree_root *r = bch2_btree_id_root(c, i);
		struct btree *b = r->b;

		/*
		 * XXX: _nofail() locks need to die in a fire.
		 *
		 * Any nofail lock take is invisible to the cycle detector
		 * (the caller isn't recorded as a holder via any path), and
		 * in multithreaded mode nofail takers piling up on a single
		 * contended lock can blow through the wait_fifo cap and BUG.
		 * The cycle detector can't unwind deadlocks it can't see.
		 *
		 * The correct shape is may-fail: take the lock via a path,
		 * wrap in lockrestart_do, propagate transaction_restart up.
		 * But topology repair is old code that walks the btree with
		 * its own bch2_btree_and_journal_iter_* infrastructure, not
		 * via paths — and shoving a synthetic "I locked the root"
		 * path into that walking code doesn't work (the path's state
		 * isn't maintained by the walk, and verify_locks on mem_alloc
		 * slow paths blows up on the mismatch).
		 *
		 * Keeping nofail here is only OK because topology repair
		 * runs at mount/recovery time, before any worker threads are
		 * started, so there's physically nothing else that could be
		 * contending for these locks — wait_fifo can't fill up, cycle
		 * detection isn't needed.
		 *
		 * Proper fix is either (a) rewrite topology repair on top of
		 * paths, or (b) redo the whole nofail → may-fail plumbing so
		 * nofail callers can still get cycle-detector visibility via
		 * a thin "lock holder record" that isn't a full path. Either
		 * is bigger than this commit wants to be.
		 */
		trans->locking_hash_val = 0;
		trans->locking_root_id	= -1;
		btree_node_lock_nopath(trans, &b->c, SIX_LOCK_read, true, _THIS_IP_, false);
		int ret = btree_check_root_boundaries(trans, b) ?:
			  bch2_btree_repair_topology_recurse(trans, b);
		six_unlock_read(&b->c.lock);

		if (bch2_err_matches(ret, BCH_ERR_topology_repair_drop_this_node)) {
			bch2_btree_node_transition_state(&c->btree.cache, b,
								  BTREE_NODE_CACHE_FREEABLE);

			scoped_guard(mutex, &c->btree.cache.root_lock) {
				r->b = NULL;
				if (likely(i < BTREE_ID_NR))
					WRITE_ONCE(c->btree.cache.roots_b[i], 0);
			}

			if (!reconstructed_root) {
				r->error = -EIO;
				goto recover;
			}

			CLASS(printbuf, buf)();
			bch2_btree_id_to_text(&buf, i);
			bch_err(c, "empty btree root %s", buf.buf);
			bch2_btree_root_alloc_fake_trans(trans, i, 0);
			r->alive = false;
			ret = 0;
		}

		if (ret)
			return ret;
	}

	/*
	 * post topology repair there should be no errored nodes; reset
	 * ratelimiters so we see new unexpected errors
	 */
	ratelimit_reset(&c->btree.read_errors_soft);
	ratelimit_reset(&c->btree.read_errors_hard);

	return 0;
}

/* marking of btree keys/nodes: */

static int bch2_gc_mark_key(struct btree_trans *trans, enum btree_id btree_id,
			    unsigned level, struct btree **prev,
			    struct btree_iter *iter, struct bkey_s_c k,
			    bool initial)
{
	struct bch_fs *c = trans->c;

	if (iter) {
		struct btree_path *path = btree_iter_path(trans, iter);
		struct btree *b = path_l(path)->b;

		if (*prev != b)
			try(bch2_btree_node_check_topology(trans, b));
		*prev = b;
	}

	struct bkey deleted = KEY(0, 0, 0);
	struct bkey_s_c old = (struct bkey_s_c) { &deleted, NULL };
	CLASS(printbuf, buf)();
	int ret = 0;

	deleted.p = k.k->p;

	if (initial) {
		BUG_ON(static_branch_unlikely(&bch2_journal_seq_verify) &&
		       k.k->bversion.lo > atomic64_read(&c->journal.seq));

		if (fsck_err_on(btree_id != BTREE_ID_accounting &&
				k.k->bversion.lo > atomic64_read(&c->key_version),
				trans, bkey_version_in_future,
				"key version number higher than recorded %llu\n%s",
				atomic64_read(&c->key_version),
				(bch2_bkey_val_to_text(&buf, c, k), buf.buf)))
			atomic64_set(&c->key_version, k.k->bversion.lo);
	}

	if (mustfix_fsck_err_on(level && !bch2_dev_btree_bitmap_marked_nogc(c, k),
				trans, btree_bitmap_not_marked,
				"btree ptr not marked in member info btree allocated bitmap\n%s",
				(printbuf_reset(&buf),
				 bch2_bkey_val_to_text(&buf, c, k),
				 buf.buf)))
		bch2_dev_btree_bitmap_mark(c, k);

	try(bch2_bkey_check_repair(trans, iter, btree_id, level, k));

	if (bch2_trans_has_updates(trans)) {
		CLASS(disk_reservation, res)(c);
		return bch2_trans_commit(trans, &res.r, NULL, BCH_TRANS_COMMIT_no_enospc) ?:
			btree_trans_restart(trans, BCH_ERR_transaction_restart_commit);
	}

	struct btree_trigger_op op = {
		.btree		= btree_id,
		.level		= level,
		.old		= old,
		.new		= unsafe_bkey_s_c_to_s(k),
		.new_buf_u64s	= k.k->u64s,
		.flags		= BTREE_TRIGGER_gc|BTREE_TRIGGER_insert,
	};
	try(bch2_key_trigger(trans, op));
fsck_err:
	return ret;
}

static int bch2_gc_btree_root(struct btree_trans *trans, enum btree_id btree, bool initial)
{
	struct bch_fs *c = trans->c;
	CLASS(btree_node_iter, iter)(trans, btree, POS_MIN, 0,
				     bch2_btree_id_root(c, btree)->b->c.level, 0);
	struct btree *b = errptr_try(bch2_btree_iter_peek_node(&iter));

	if (b != btree_node_root(c, b))
		return btree_trans_restart(trans, BCH_ERR_transaction_restart_lock_root_race);

	gc_pos_set(c, gc_pos_btree(btree, b->c.level + 1, SPOS_MAX));
	struct bkey_s_c k = bkey_i_to_s_c(&b->key);
	return bch2_gc_mark_key(trans, btree, b->c.level + 1, NULL, NULL, k, initial);
}

static int bch2_gc_btree(struct btree_trans *trans,
			 struct progress_indicator *progress,
			 enum btree_id btree, unsigned target_depth,
			 bool initial)
{
	for (unsigned level = target_depth; level < BTREE_MAX_DEPTH; level++) {
		struct btree *prev = NULL;
		CLASS(btree_node_iter, iter)(trans, btree, POS_MIN, 0, level, BTREE_ITER_prefetch);

		try(for_each_btree_key_continue(trans, iter, 0, k, ({
			gc_pos_set(trans->c, gc_pos_btree(btree, level, k.k->p));
			bch2_progress_update_iter(trans, progress, &iter) ?:
			bch2_gc_mark_key(trans, btree, level, &prev, &iter, k, initial);
		})));
	}

	return lockrestart_do(trans, bch2_gc_btree_root(trans, btree, initial));
}

static inline int btree_id_gc_phase_cmp(enum btree_id l, enum btree_id r)
{
	return cmp_int(gc_btree_order(l), gc_btree_order(r));
}

static int bch2_gc_btrees(struct bch_fs *c)
{
	CLASS(btree_trans, trans)(c);
	CLASS(printbuf, buf)();
	int ret = 0;

	bch2_progress_init(&c->recovery.progress, "check_allocations", c, ~0ULL, ~0ULL);

	enum btree_id ids[BTREE_ID_NR];
	for (unsigned i = 0; i < BTREE_ID_NR; i++)
		ids[i] = i;
	bubble_sort(ids, BTREE_ID_NR, btree_id_gc_phase_cmp);

	for (unsigned i = 0; i < btree_id_nr_alive(c) && !ret; i++) {
		unsigned btree = i < BTREE_ID_NR ? ids[i] : i;

		if (IS_ERR_OR_NULL(bch2_btree_id_root(c, btree)->b))
			continue;


		unsigned target_depth = BIT_ULL(btree) & btree_leaf_has_triggers_mask ? 0 : 1;

		/*
		 * In fsck, we need to make sure every leaf node is readable
		 * before going RW, otherwise we can no longer rewind inside
		 * btree_lost_data to repair during the current fsck run.
		 *
		 * Otherwise, we can delay the repair to the next
		 * mount or offline fsck.
		 */
		if (test_bit(BCH_FS_in_fsck, &c->flags))
			target_depth = 0;

		ret = bch2_gc_btree(trans, &c->recovery.progress, btree, target_depth, true);
	}

	bch_err_fn(c, ret);
	return ret;
}

static int bch2_mark_superblocks(struct bch_fs *c)
{
	gc_pos_set(c, gc_phase(GC_PHASE_sb));

	return bch2_trans_mark_dev_sbs_flags(c, BTREE_TRIGGER_gc);
}

static void bch2_gc_free(struct bch_fs *c)
{
	bch2_accounting_gc_free(c);

	genradix_free(&c->reflink_gc_table);
	genradix_free(&c->ec.gc_stripes);

	for_each_member_device(c, ca)
		genradix_free(&ca->buckets_gc);
}

static int bch2_gc_start(struct bch_fs *c)
{
	for_each_member_device(c, ca)
		try(bch2_dev_usage_init(ca, true));

	return 0;
}

/* returns true if not equal */
static inline bool bch2_alloc_v4_cmp(struct bch_alloc_v4 l,
				     struct bch_alloc_v4 r)
{
	return  l.generation != r.generation				||
		l.oldest_gen != r.oldest_gen		||
		l.data_type != r.data_type		||
		l.dirty_sectors	!= r.dirty_sectors	||
		l.stripe_sectors != r.stripe_sectors	||
		l.cached_sectors != r.cached_sectors	 ||
		l.stripe_refcount != r.stripe_refcount;
}

static int bch2_alloc_write_key(struct btree_trans *trans,
				struct btree_iter *iter,
				struct bch_dev *ca,
				struct bkey_s_c k)
{
	struct bch_fs *c = trans->c;
	struct bkey_i_alloc_v4 *a;
	struct bch_alloc_v4 old_gc, gc, old_convert, new;
	const struct bch_alloc_v4 *old;

	if (!bucket_valid(ca, k.k->p.offset))
		return 0;

	old = bch2_alloc_to_v4(k, &old_convert);
	gc = new = *old;

	__bucket_m_to_alloc(&gc, *gc_bucket(ca, iter->pos.offset));

	old_gc = gc;

	if ((old->data_type == BCH_DATA_sb ||
	     old->data_type == BCH_DATA_journal) &&
	    !bch2_dev_is_online(ca)) {
		gc.data_type = old->data_type;
		gc.dirty_sectors = old->dirty_sectors;
	}

	/*
	 * gc tracks sector counts via extent triggers but does not follow
	 * empty-state transitions (need_discard, need_gc_gens) - those are
	 * decided by bch2_trigger_alloc() using old vs new state and stick
	 * in data_type until the discard / gc_gens path clears them.
	 *
	 * For nonempty buckets gc.data_type is authoritative from the
	 * extent walk. For empty buckets gc.data_type is BCH_DATA_free
	 * (gc never sets need_*); use the on-disk hint instead so a bucket
	 * correctly in need_discard or need_gc_gens compares equal.
	 *
	 * Using new.data_type unconditionally would break reconstruct_alloc:
	 * post-kill_btree the on-disk key is zeros, hint=free, and
	 * alloc_data_type() falls into bucket_data_type(free) → free even
	 * with dirty_sectors > 0, contradicting the rebuilt counters.
	 */
	alloc_data_type_set(&gc,
		!data_type_is_empty(gc.data_type) ? gc.data_type : new.data_type);
	if (gc.data_type != old_gc.data_type ||
	    gc.dirty_sectors != old_gc.dirty_sectors) {
		try(bch2_alloc_key_to_dev_counters(trans, ca, &old_gc, &gc, BTREE_TRIGGER_gc));

		/*
		 * Ugly: alloc_key_to_dev_counters(..., BTREE_TRIGGER_gc) is not
		 * safe w.r.t. transaction restarts, so fixup the gc_bucket so
		 * we don't run it twice:
		 */
		struct bucket *gc_m = gc_bucket(ca, iter->pos.offset);
		gc_m->data_type = gc.data_type;
		gc_m->dirty_sectors = gc.dirty_sectors;
	}

	if (ret_fsck_err_on(new.data_type != gc.data_type,
			trans, alloc_key_data_type_wrong,
			"bucket %llu:%llu gen %u has wrong data_type"
			": got %s, should be %s",
			iter->pos.inode, iter->pos.offset,
			gc.generation,
			bch2_data_type_str(new.data_type),
			bch2_data_type_str(gc.data_type))) {
		new.data_type = gc.data_type;

		/*
		 * Reconstruct runs under BTREE_TRIGGER_gc which skips the
		 * transactional path that maintains NEED_DISCARD. Set it
		 * here on non-empty buckets for downgrade compat (older
		 * kernels read the bit to decide need_discard state).
		 */
		if (!data_type_is_empty(new.data_type) &&
		    new.data_type != BCH_DATA_sb &&
		    new.data_type != BCH_DATA_journal)
			SET_BCH_ALLOC_V4_NEED_DISCARD(&new, true);
	}

#define copy_bucket_field(_errtype, _f)					\
	if (ret_fsck_err_on(new._f != gc._f,				\
			trans, _errtype,				\
			"bucket %llu:%llu gen %u data type %s has wrong " #_f	\
			": got %llu, should be %llu",			\
			iter->pos.inode, iter->pos.offset,		\
			gc.generation,						\
			bch2_data_type_str(gc.data_type),		\
			(u64) new._f, (u64) gc._f))				\
		new._f = gc._f;						\

	copy_bucket_field(alloc_key_gen_wrong,			generation);
	copy_bucket_field(alloc_key_dirty_sectors_wrong,	dirty_sectors);
	copy_bucket_field(alloc_key_stripe_sectors_wrong,	stripe_sectors);
	copy_bucket_field(alloc_key_cached_sectors_wrong,	cached_sectors);
	copy_bucket_field(alloc_key_stripe_wrong,		stripe_refcount);
#undef copy_bucket_field

	if (!bch2_alloc_v4_cmp(*old, new))
		return 0;

	a = errptr_try(bch2_alloc_to_v4_mut(trans, k));

	a->v = new;

	/*
	 * The trigger normally makes sure these are set, but we're not running
	 * triggers:
	 */
	if (a->v.data_type == BCH_DATA_cached && !a->v.io_time[READ])
		a->v.io_time[READ] = max_t(u64, 1, atomic64_read(&c->io_clock[READ].now));

	try(bch2_trans_update(trans, iter, &a->k_i, BTREE_TRIGGER_norun));
	return 0;
}

static int bch2_gc_alloc_done(struct bch_fs *c)
{
	CLASS(btree_trans, trans)(c);

	for_each_member_device(c, ca)
		try(for_each_btree_key_max_commit(trans, iter, BTREE_ID_alloc,
					POS(ca->dev_idx, ca->mi.first_bucket),
					POS(ca->dev_idx, ca->mi.nbuckets - 1),
					BTREE_ITER_slots|BTREE_ITER_prefetch, k,
					NULL, NULL, BCH_TRANS_COMMIT_no_enospc,
				bch2_alloc_write_key(trans, &iter, ca, k)));

	return 0;
}

static int bch2_gc_alloc_start(struct bch_fs *c)
{
	for_each_member_device(c, ca) {
		int ret = genradix_prealloc(&ca->buckets_gc, ca->mi.nbuckets, GFP_KERNEL);
		if (ret)
			return bch_err_throw(c, ENOMEM_gc_alloc_start);
	}

	return 0;
}

static int bch2_gc_write_stripes_key(struct btree_trans *trans,
				     struct btree_iter *iter,
				     struct bkey_s_c k)
{
	if (k.k->type != KEY_TYPE_stripe)
		return 0;

	struct bch_fs *c = trans->c;
	CLASS(printbuf, buf)();
	const struct bch_stripe *s = bkey_s_c_to_stripe(k).v;
	struct gc_stripe *m = genradix_ptr(&c->ec.gc_stripes, k.k->p.offset);

	unsigned nr_data = s->nr_blocks - s->nr_redundant;

	bool bad = false;
	bool parity_bad = false;
	for (unsigned i = 0; i < s->nr_blocks; i++) {
		u32 old = stripe_blockcount_get(s, i);
		u32 new = (m ? m->block_sectors[i] : 0);

		if (old != new) {
			prt_printf(&buf, "stripe block %u has wrong sector count: got %u, should be %u\n",
				   i, old, new);
			bad = true;
		}

		parity_bad |= i >= nr_data && old;
	}

	if (bad || parity_bad)
		bch2_bkey_val_to_text(&buf, c, k);

	if (ret_fsck_err_on(parity_bad,
			trans, stripe_parity_block_sector_count_wrong,
			"stripe parity block with nonzero sector count\n%s",
			buf.buf) ||
	    ret_fsck_err_on(bad,
			trans, stripe_sector_count_wrong,
			"%s", buf.buf)) {
		struct bkey_i_stripe *new =
			errptr_try(bch2_trans_kmalloc(trans, bkey_bytes(k.k)));

		bkey_reassemble(&new->k_i, k);

		for (unsigned i = 0; i < new->v.nr_blocks; i++)
			stripe_blockcount_set(&new->v, i,
				i < nr_data ? (m ? m->block_sectors[i] : 0) : 0);

		try(bch2_trans_update(trans, iter, &new->k_i, 0));
	}

	return 0;
}

static int bch2_gc_stripes_done(struct bch_fs *c)
{
	CLASS(btree_trans, trans)(c);
	return for_each_btree_key_commit(trans, iter,
				BTREE_ID_stripes, POS_MIN,
				BTREE_ITER_prefetch, k,
				NULL, NULL, BCH_TRANS_COMMIT_no_enospc,
			bch2_gc_write_stripes_key(trans, &iter, k));
}

/**
 * bch2_check_allocations - walk all references to buckets, and recompute them:
 *
 * @c:			filesystem object
 *
 * Returns: 0 on success, or standard errcode on failure
 *
 * Order matters here:
 *  - Concurrent GC relies on the fact that we have a total ordering for
 *    everything that GC walks - see  gc_will_visit_node(),
 *    gc_will_visit_root()
 *
 *  - also, references move around in the course of index updates and
 *    various other crap: everything needs to agree on the ordering
 *    references are allowed to move around in - e.g., we're allowed to
 *    start with a reference owned by an open_bucket (the allocator) and
 *    move it to the btree, but not the reverse.
 *
 *    This is necessary to ensure that gc doesn't miss references that
 *    move around - if references move backwards in the ordering GC
 *    uses, GC could skip past them
 */
int bch2_check_allocations(struct bch_fs *c)
{
	int ret;

	guard(rwsem_read)(&c->state_lock);
	guard(rwsem_write)(&c->gc.lock);

	bch2_btree_interior_updates_flush(c);

	ret   = bch2_gc_accounting_start(c) ?:
		bch2_gc_start(c) ?:
		bch2_gc_alloc_start(c) ?:
		bch2_gc_reflink_start(c);
	if (ret)
		goto out;

	gc_pos_set(c, gc_phase(GC_PHASE_start));

	ret = bch2_mark_superblocks(c);
	bch_err_msg(c, ret, "marking superblocks");
	if (ret)
		goto out;

	ret = bch2_gc_btrees(c);
	if (ret)
		goto out;

	ret   = bch2_gc_alloc_done(c) ?:
		bch2_gc_accounting_done(c) ?:
		bch2_gc_stripes_done(c) ?:
		bch2_gc_reflink_done(c);
out:
	scoped_guard(percpu_write_noio, &c->capacity.mark_lock) {
		/* Indicates that gc is no longer in progress: */
		__gc_pos_set(c, gc_phase(GC_PHASE_not_running));
		bch2_gc_free(c);
	}

	/*
	 * At startup, allocations can happen directly instead of via the
	 * allocator thread - issue wakeup in case they blocked on gc_lock:
	 */
	bch2_alloc_wake_all(c);

	if (!ret && !test_bit(BCH_FS_errors_not_fixed, &c->flags))
		bch2_sb_members_clean_deleted(c);

	return ret;
}

static int gc_btree_gens_key(struct btree_trans *trans,
			     struct btree_iter *iter,
			     struct bkey_s_c k)
{
	struct bch_fs *c = trans->c;

	if (unlikely(test_bit(BCH_FS_going_ro, &c->flags)))
		return -EROFS;

	return bch2_bkey_drop_stale_ptrs(trans, iter, k);
}

static int bch2_alloc_write_oldest_gen(struct btree_trans *trans, struct bch_dev *ca,
				       struct btree_iter *iter, struct bkey_s_c k)
{
	struct bch_alloc_v4 a_convert;
	const struct bch_alloc_v4 *a = bch2_alloc_to_v4(k, &a_convert);

	if (a->oldest_gen == ca->oldest_gen[iter->pos.offset])
		return 0;

	struct bkey_i_alloc_v4 *a_mut = errptr_try(bch2_alloc_to_v4_mut(trans, k));

	a_mut->v.oldest_gen = ca->oldest_gen[iter->pos.offset];

	return bch2_trans_update(trans, iter, &a_mut->k_i, 0);
}

int bch2_gc_gens(struct bch_fs *c)
{
	u64 b, start_time = local_clock();
	int ret;

	if (!mutex_trylock(&c->gc_gens.lock))
		return 0;

	event_inc_trace(c, gc_gens_start, buf);

	/*
	 * We have to use trylock here. Otherwise, we would
	 * introduce a deadlock in the RO path - we take the
	 * state lock at the start of going RO.
	 */
	if (!down_read_trylock(&c->state_lock)) {
		mutex_unlock(&c->gc_gens.lock);
		return 0;
	}

	for_each_member_device(c, ca) {
		struct bucket_gens *gens = bucket_gens(ca);

		BUG_ON(ca->oldest_gen);

		ca->oldest_gen = kvmalloc(gens->nbuckets, GFP_KERNEL);
		if (!ca->oldest_gen) {
			ret = bch_err_throw(c, ENOMEM_gc_gens);
			goto err;
		}

		for (b = gens->first_bucket;
		     b < gens->nbuckets; b++)
			ca->oldest_gen[b] = gens->b[b];
	}

	for (unsigned i = 0; i < BTREE_ID_NR; i++)
		if (btree_type_has_data_ptrs(i)) {
			c->gc_gens.pos = BBPOS(i, POS_MIN);

			ret = bch2_trans_run(c,
				for_each_btree_key_commit(trans, iter, i,
						POS_MIN,
						BTREE_ITER_prefetch|BTREE_ITER_all_snapshots,
						k,
						NULL, NULL,
						BCH_TRANS_COMMIT_no_enospc,
					gc_btree_gens_key(trans, &iter, k)));
			if (ret)
				goto err;
		}

	struct bch_dev *ca = NULL;
	ret = bch2_trans_run(c,
		for_each_btree_key_commit(trans, iter, BTREE_ID_alloc,
				POS_MIN,
				BTREE_ITER_prefetch,
				k,
				NULL, NULL,
				BCH_TRANS_COMMIT_no_enospc, ({
			ca = bch2_dev_iterate(c, ca, k.k->p.inode);
			if (!ca) {
				bch2_btree_iter_set_pos(&iter, POS(k.k->p.inode + 1, 0));
				continue;
			}
			bch2_alloc_write_oldest_gen(trans, ca, &iter, k);
		})));
	bch2_dev_put(ca);

	if (ret)
		goto err;

	c->gc_gens.pos = BBPOS_MIN;

	bch2_time_stats_update(&c->times[BCH_TIME_btree_gc], start_time);
	event_inc_trace(c, gc_gens_end, buf);

	if (!(c->sb.compat & BIT_ULL(BCH_COMPAT_no_stale_ptrs))) {
		guard(mutex_noio)(&c->sb_lock);
		c->disk_sb.sb->compat[0] |= cpu_to_le64(BIT_ULL(BCH_COMPAT_no_stale_ptrs));
		bch2_write_super(c);
	}
err:
	for_each_member_device(c, ca) {
		kvfree(ca->oldest_gen);
		ca->oldest_gen = NULL;
	}

	up_read(&c->state_lock);
	mutex_unlock(&c->gc_gens.lock);
	if (!bch2_err_matches(ret, EROFS))
		bch_err_fn(c, ret);
	return ret;
}

static void bch2_gc_gens_work(struct work_struct *work)
{
	struct bch_fs *c = container_of(work, struct bch_fs, gc_gens.work);
	bch2_gc_gens(c);
	enumerated_ref_put(&c->writes, BCH_WRITE_REF_gc_gens);
}

void bch2_gc_gens_async(struct bch_fs *c)
{
	if (enumerated_ref_tryget(&c->writes, BCH_WRITE_REF_gc_gens) &&
	    !queue_work(c->write_ref_wq, &c->gc_gens.work))
		enumerated_ref_put(&c->writes, BCH_WRITE_REF_gc_gens);
}

static int merge_btree_node_one(struct btree_trans *trans,
				struct progress_indicator *progress,
				struct btree_iter *iter,
				u64 *merge_count)
{
	try(bch2_btree_iter_traverse(iter));

	struct btree_path *path = btree_iter_path(trans, iter);
	struct btree *b = path->l[path->level].b;

	if (!b)
		return 1;

	try(bch2_progress_update_iter(trans, progress, iter));

	if (!btree_node_needs_merge(trans->c, b, 0)) {
		if (bpos_eq(b->key.k.p, SPOS_MAX))
			return 1;

		bch2_btree_iter_set_pos(iter, bpos_successor(b->key.k.p));
		return 0;
	}

	try(bch2_btree_path_upgrade(trans, path, path->level + 1));
	try(bch2_foreground_maybe_merge(trans, iter->path, path->level, 0, 0, merge_count));

	return 0;
}

int bch2_merge_btree_nodes(struct bch_fs *c)
{
	bch2_progress_init(&c->recovery.progress, __func__, c, ~0ULL, ~0ULL);

	CLASS(btree_trans, trans)(c);

	for (unsigned i = 0; i < btree_id_nr_alive(c); i++) {
		u64 merge_count = 0;

		for (unsigned level = 0; level < BTREE_MAX_DEPTH; level++) {
			CLASS(btree_node_iter, iter)(trans, i, POS_MIN, 0, level, BTREE_ITER_prefetch);
			while (true) {
				int ret = lockrestart_do(trans, merge_btree_node_one(trans, &c->recovery.progress,
										     &iter, &merge_count));
				if (ret < 0)
					return ret;
				if (ret)
					break;
			}
		}

		if (merge_count) {
			CLASS(printbuf, buf)();
			prt_printf(&buf, "merge_btree_nodes: %llu merges in ", merge_count);
			bch2_btree_id_to_text(&buf, i);
			prt_str(&buf, " btree");
			bch_info(c, "%s", buf.buf);
		}
	}

	return 0;
}

/*
 * For each shard boundary in each shard-aware btree, look up the leaf
 * containing it; if the leaf spans the boundary, rewrite it (which forces
 * a split at the boundary, since bch2_btree_node_alloc_replacement honors
 * the "leaves don't cross shard boundaries" constraint).
 */
static int presplit_shard_boundary_one(struct btree_trans *trans,
				       enum btree_id btree, struct bpos pos,
				       u64 *split_count)
{
	struct bch_fs *c = trans->c;
	CLASS(btree_node_iter, iter)(trans, btree, pos, 0, 0, 0);
	try(bch2_btree_iter_traverse(&iter));

	struct btree *b = path_l(btree_iter_path(trans, &iter))->b;

	struct bpos pivot = bch2_btree_node_shard_pivot(c, b);
	if (bpos_eq(pivot, POS_MIN) || bpos_eq(pivot, b->key.k.p))
		return 1;

	int ret = bch2_btree_split_leaf(trans, iter.path, 0, 0);
	(*split_count) += !ret;
	return ret;
}

int bch2_presplit_shard_boundaries(struct bch_fs *c)
{
	if (!c->opts.shard_inode_numbers_bits)
		return 0;

	if (!enumerated_ref_tryget(&c->writes, BCH_WRITE_REF_presplit_shard_boundaries))
		return 0;

	static const enum btree_id sharded_btrees[] = {
		BTREE_ID_inodes,
		BTREE_ID_extents,
		BTREE_ID_dirents,
		BTREE_ID_xattrs,
	};

	unsigned shard_bits = c->opts.shard_inode_numbers_bits;
	unsigned bits = 63 - shard_bits;
	unsigned n_shards = 1U << shard_bits;
	int ret = 0;

	CLASS(btree_trans, trans)(c);

	for (unsigned i = 0; i < ARRAY_SIZE(sharded_btrees); i++) {
		u64 split_count = 0;
		enum btree_id btree = sharded_btrees[i];

		for (unsigned shard = 1; shard < n_shards; shard++) {
			u64 boundary = (u64) shard << bits;
			struct bpos pos = btree == BTREE_ID_inodes
				? SPOS(0, boundary, 0)
				: SPOS(boundary, 0, 0);
			do {
				ret = lockrestart_do(trans,
					presplit_shard_boundary_one(trans, btree, pos, &split_count));
			} while (!ret);

			if (ret < 0) {
				if (bch2_err_matches(ret, ENOSPC))
					ret = 0;
				break;
			}
			ret = 0;
		}

		if (split_count) {
			CLASS(bch_log_msg_level, msg)(c, LOGLEVEL_info);
			prt_printf(&msg.m, "presplit_shard_boundaries: %llu splits in btree ", split_count);
			bch2_btree_id_to_text(&msg.m, btree);
		}
	}

	enumerated_ref_put(&c->writes, BCH_WRITE_REF_presplit_shard_boundaries);
	return ret;
}

void bch2_fs_btree_gc_init_early(struct bch_fs *c)
{
	seqcount_init(&c->gc.pos_lock);
	INIT_WORK(&c->gc_gens.work, bch2_gc_gens_work);

	init_rwsem(&c->gc.lock);
	mutex_init(&c->gc_gens.lock);
}
