Adding upstream version 6.7.7.upstream/6.7.7

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 3261 insertions, 0 deletions

diff --git a/fs/bcachefs/btree_iter.c b/fs/bcachefs/btree_iter.c
new file mode 100644
index 0000000000..da594e0067
--- /dev/null
+++ b/fs/bcachefs/btree_iter.c
@@ -0,0 +1,3261 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include "bcachefs.h"
+#include "bkey_methods.h"
+#include "bkey_buf.h"
+#include "btree_cache.h"
+#include "btree_iter.h"
+#include "btree_journal_iter.h"
+#include "btree_key_cache.h"
+#include "btree_locking.h"
+#include "btree_update.h"
+#include "debug.h"
+#include "error.h"
+#include "extents.h"
+#include "journal.h"
+#include "replicas.h"
+#include "snapshot.h"
+#include "trace.h"
+
+#include <linux/random.h>
+#include <linux/prefetch.h>
+
+static inline void btree_path_list_remove(struct btree_trans *, struct btree_path *);
+static inline void btree_path_list_add(struct btree_trans *, struct btree_path *,
+				       struct btree_path *);
+
+static inline unsigned long btree_iter_ip_allocated(struct btree_iter *iter)
+{
+#ifdef TRACK_PATH_ALLOCATED
+	return iter->ip_allocated;
+#else
+	return 0;
+#endif
+}
+
+static struct btree_path *btree_path_alloc(struct btree_trans *, struct btree_path *);
+
+static inline int __btree_path_cmp(const struct btree_path *l,
+				   enum btree_id	r_btree_id,
+				   bool			r_cached,
+				   struct bpos		r_pos,
+				   unsigned		r_level)
+{
+	/*
+	 * Must match lock ordering as defined by __bch2_btree_node_lock:
+	 */
+	return   cmp_int(l->btree_id,	r_btree_id) ?:
+		 cmp_int((int) l->cached,	(int) r_cached) ?:
+		 bpos_cmp(l->pos,	r_pos) ?:
+		-cmp_int(l->level,	r_level);
+}
+
+static inline int btree_path_cmp(const struct btree_path *l,
+				 const struct btree_path *r)
+{
+	return __btree_path_cmp(l, r->btree_id, r->cached, r->pos, r->level);
+}
+
+static inline struct bpos bkey_successor(struct btree_iter *iter, struct bpos p)
+{
+	/* Are we iterating over keys in all snapshots? */
+	if (iter->flags & BTREE_ITER_ALL_SNAPSHOTS) {
+		p = bpos_successor(p);
+	} else {
+		p = bpos_nosnap_successor(p);
+		p.snapshot = iter->snapshot;
+	}
+
+	return p;
+}
+
+static inline struct bpos bkey_predecessor(struct btree_iter *iter, struct bpos p)
+{
+	/* Are we iterating over keys in all snapshots? */
+	if (iter->flags & BTREE_ITER_ALL_SNAPSHOTS) {
+		p = bpos_predecessor(p);
+	} else {
+		p = bpos_nosnap_predecessor(p);
+		p.snapshot = iter->snapshot;
+	}
+
+	return p;
+}
+
+static inline struct bpos btree_iter_search_key(struct btree_iter *iter)
+{
+	struct bpos pos = iter->pos;
+
+	if ((iter->flags & BTREE_ITER_IS_EXTENTS) &&
+	    !bkey_eq(pos, POS_MAX))
+		pos = bkey_successor(iter, pos);
+	return pos;
+}
+
+static inline bool btree_path_pos_before_node(struct btree_path *path,
+					      struct btree *b)
+{
+	return bpos_lt(path->pos, b->data->min_key);
+}
+
+static inline bool btree_path_pos_after_node(struct btree_path *path,
+					     struct btree *b)
+{
+	return bpos_gt(path->pos, b->key.k.p);
+}
+
+static inline bool btree_path_pos_in_node(struct btree_path *path,
+					  struct btree *b)
+{
+	return path->btree_id == b->c.btree_id &&
+		!btree_path_pos_before_node(path, b) &&
+		!btree_path_pos_after_node(path, b);
+}
+
+/* Btree iterator: */
+
+#ifdef CONFIG_BCACHEFS_DEBUG
+
+static void bch2_btree_path_verify_cached(struct btree_trans *trans,
+					  struct btree_path *path)
+{
+	struct bkey_cached *ck;
+	bool locked = btree_node_locked(path, 0);
+
+	if (!bch2_btree_node_relock(trans, path, 0))
+		return;
+
+	ck = (void *) path->l[0].b;
+	BUG_ON(ck->key.btree_id != path->btree_id ||
+	       !bkey_eq(ck->key.pos, path->pos));
+
+	if (!locked)
+		btree_node_unlock(trans, path, 0);
+}
+
+static void bch2_btree_path_verify_level(struct btree_trans *trans,
+				struct btree_path *path, unsigned level)
+{
+	struct btree_path_level *l;
+	struct btree_node_iter tmp;
+	bool locked;
+	struct bkey_packed *p, *k;
+	struct printbuf buf1 = PRINTBUF;
+	struct printbuf buf2 = PRINTBUF;
+	struct printbuf buf3 = PRINTBUF;
+	const char *msg;
+
+	if (!bch2_debug_check_iterators)
+		return;
+
+	l	= &path->l[level];
+	tmp	= l->iter;
+	locked	= btree_node_locked(path, level);
+
+	if (path->cached) {
+		if (!level)
+			bch2_btree_path_verify_cached(trans, path);
+		return;
+	}
+
+	if (!btree_path_node(path, level))
+		return;
+
+	if (!bch2_btree_node_relock_notrace(trans, path, level))
+		return;
+
+	BUG_ON(!btree_path_pos_in_node(path, l->b));
+
+	bch2_btree_node_iter_verify(&l->iter, l->b);
+
+	/*
+	 * For interior nodes, the iterator will have skipped past deleted keys:
+	 */
+	p = level
+		? bch2_btree_node_iter_prev(&tmp, l->b)
+		: bch2_btree_node_iter_prev_all(&tmp, l->b);
+	k = bch2_btree_node_iter_peek_all(&l->iter, l->b);
+
+	if (p && bkey_iter_pos_cmp(l->b, p, &path->pos) >= 0) {
+		msg = "before";
+		goto err;
+	}
+
+	if (k && bkey_iter_pos_cmp(l->b, k, &path->pos) < 0) {
+		msg = "after";
+		goto err;
+	}
+
+	if (!locked)
+		btree_node_unlock(trans, path, level);
+	return;
+err:
+	bch2_bpos_to_text(&buf1, path->pos);
+
+	if (p) {
+		struct bkey uk = bkey_unpack_key(l->b, p);
+
+		bch2_bkey_to_text(&buf2, &uk);
+	} else {
+		prt_printf(&buf2, "(none)");
+	}
+
+	if (k) {
+		struct bkey uk = bkey_unpack_key(l->b, k);
+
+		bch2_bkey_to_text(&buf3, &uk);
+	} else {
+		prt_printf(&buf3, "(none)");
+	}
+
+	panic("path should be %s key at level %u:\n"
+	      "path pos %s\n"
+	      "prev key %s\n"
+	      "cur  key %s\n",
+	      msg, level, buf1.buf, buf2.buf, buf3.buf);
+}
+
+static void bch2_btree_path_verify(struct btree_trans *trans,
+				   struct btree_path *path)
+{
+	struct bch_fs *c = trans->c;
+	unsigned i;
+
+	EBUG_ON(path->btree_id >= BTREE_ID_NR);
+
+	for (i = 0; i < (!path->cached ? BTREE_MAX_DEPTH : 1); i++) {
+		if (!path->l[i].b) {
+			BUG_ON(!path->cached &&
+			       bch2_btree_id_root(c, path->btree_id)->b->c.level > i);
+			break;
+		}
+
+		bch2_btree_path_verify_level(trans, path, i);
+	}
+
+	bch2_btree_path_verify_locks(path);
+}
+
+void bch2_trans_verify_paths(struct btree_trans *trans)
+{
+	struct btree_path *path;
+
+	trans_for_each_path(trans, path)
+		bch2_btree_path_verify(trans, path);
+}
+
+static void bch2_btree_iter_verify(struct btree_iter *iter)
+{
+	struct btree_trans *trans = iter->trans;
+
+	BUG_ON(iter->btree_id >= BTREE_ID_NR);
+
+	BUG_ON(!!(iter->flags & BTREE_ITER_CACHED) != iter->path->cached);
+
+	BUG_ON((iter->flags & BTREE_ITER_IS_EXTENTS) &&
+	       (iter->flags & BTREE_ITER_ALL_SNAPSHOTS));
+
+	BUG_ON(!(iter->flags & __BTREE_ITER_ALL_SNAPSHOTS) &&
+	       (iter->flags & BTREE_ITER_ALL_SNAPSHOTS) &&
+	       !btree_type_has_snapshot_field(iter->btree_id));
+
+	if (iter->update_path)
+		bch2_btree_path_verify(trans, iter->update_path);
+	bch2_btree_path_verify(trans, iter->path);
+}
+
+static void bch2_btree_iter_verify_entry_exit(struct btree_iter *iter)
+{
+	BUG_ON((iter->flags & BTREE_ITER_FILTER_SNAPSHOTS) &&
+	       !iter->pos.snapshot);
+
+	BUG_ON(!(iter->flags & BTREE_ITER_ALL_SNAPSHOTS) &&
+	       iter->pos.snapshot != iter->snapshot);
+
+	BUG_ON(bkey_lt(iter->pos, bkey_start_pos(&iter->k)) ||
+	       bkey_gt(iter->pos, iter->k.p));
+}
+
+static int bch2_btree_iter_verify_ret(struct btree_iter *iter, struct bkey_s_c k)
+{
+	struct btree_trans *trans = iter->trans;
+	struct btree_iter copy;
+	struct bkey_s_c prev;
+	int ret = 0;
+
+	if (!bch2_debug_check_iterators)
+		return 0;
+
+	if (!(iter->flags & BTREE_ITER_FILTER_SNAPSHOTS))
+		return 0;
+
+	if (bkey_err(k) || !k.k)
+		return 0;
+
+	BUG_ON(!bch2_snapshot_is_ancestor(trans->c,
+					  iter->snapshot,
+					  k.k->p.snapshot));
+
+	bch2_trans_iter_init(trans, &copy, iter->btree_id, iter->pos,
+			     BTREE_ITER_NOPRESERVE|
+			     BTREE_ITER_ALL_SNAPSHOTS);
+	prev = bch2_btree_iter_prev(&copy);
+	if (!prev.k)
+		goto out;
+
+	ret = bkey_err(prev);
+	if (ret)
+		goto out;
+
+	if (bkey_eq(prev.k->p, k.k->p) &&
+	    bch2_snapshot_is_ancestor(trans->c, iter->snapshot,
+				      prev.k->p.snapshot) > 0) {
+		struct printbuf buf1 = PRINTBUF, buf2 = PRINTBUF;
+
+		bch2_bkey_to_text(&buf1, k.k);
+		bch2_bkey_to_text(&buf2, prev.k);
+
+		panic("iter snap %u\n"
+		      "k    %s\n"
+		      "prev %s\n",
+		      iter->snapshot,
+		      buf1.buf, buf2.buf);
+	}
+out:
+	bch2_trans_iter_exit(trans, &copy);
+	return ret;
+}
+
+void bch2_assert_pos_locked(struct btree_trans *trans, enum btree_id id,
+			    struct bpos pos, bool key_cache)
+{
+	struct btree_path *path;
+	unsigned idx;
+	struct printbuf buf = PRINTBUF;
+
+	btree_trans_sort_paths(trans);
+
+	trans_for_each_path_inorder(trans, path, idx) {
+		int cmp = cmp_int(path->btree_id, id) ?:
+			cmp_int(path->cached, key_cache);
+
+		if (cmp > 0)
+			break;
+		if (cmp < 0)
+			continue;
+
+		if (!btree_node_locked(path, 0) ||
+		    !path->should_be_locked)
+			continue;
+
+		if (!key_cache) {
+			if (bkey_ge(pos, path->l[0].b->data->min_key) &&
+			    bkey_le(pos, path->l[0].b->key.k.p))
+				return;
+		} else {
+			if (bkey_eq(pos, path->pos))
+				return;
+		}
+	}
+
+	bch2_dump_trans_paths_updates(trans);
+	bch2_bpos_to_text(&buf, pos);
+
+	panic("not locked: %s %s%s\n",
+	      bch2_btree_id_str(id), buf.buf,
+	      key_cache ? " cached" : "");
+}
+
+#else
+
+static inline void bch2_btree_path_verify_level(struct btree_trans *trans,
+						struct btree_path *path, unsigned l) {}
+static inline void bch2_btree_path_verify(struct btree_trans *trans,
+					  struct btree_path *path) {}
+static inline void bch2_btree_iter_verify(struct btree_iter *iter) {}
+static inline void bch2_btree_iter_verify_entry_exit(struct btree_iter *iter) {}
+static inline int bch2_btree_iter_verify_ret(struct btree_iter *iter, struct bkey_s_c k) { return 0; }
+
+#endif
+
+/* Btree path: fixups after btree updates */
+
+static void btree_node_iter_set_set_pos(struct btree_node_iter *iter,
+					struct btree *b,
+					struct bset_tree *t,
+					struct bkey_packed *k)
+{
+	struct btree_node_iter_set *set;
+
+	btree_node_iter_for_each(iter, set)
+		if (set->end == t->end_offset) {
+			set->k = __btree_node_key_to_offset(b, k);
+			bch2_btree_node_iter_sort(iter, b);
+			return;
+		}
+
+	bch2_btree_node_iter_push(iter, b, k, btree_bkey_last(b, t));
+}
+
+static void __bch2_btree_path_fix_key_modified(struct btree_path *path,
+					       struct btree *b,
+					       struct bkey_packed *where)
+{
+	struct btree_path_level *l = &path->l[b->c.level];
+
+	if (where != bch2_btree_node_iter_peek_all(&l->iter, l->b))
+		return;
+
+	if (bkey_iter_pos_cmp(l->b, where, &path->pos) < 0)
+		bch2_btree_node_iter_advance(&l->iter, l->b);
+}
+
+void bch2_btree_path_fix_key_modified(struct btree_trans *trans,
+				      struct btree *b,
+				      struct bkey_packed *where)
+{
+	struct btree_path *path;
+
+	trans_for_each_path_with_node(trans, b, path) {
+		__bch2_btree_path_fix_key_modified(path, b, where);
+		bch2_btree_path_verify_level(trans, path, b->c.level);
+	}
+}
+
+static void __bch2_btree_node_iter_fix(struct btree_path *path,
+				       struct btree *b,
+				       struct btree_node_iter *node_iter,
+				       struct bset_tree *t,
+				       struct bkey_packed *where,
+				       unsigned clobber_u64s,
+				       unsigned new_u64s)
+{
+	const struct bkey_packed *end = btree_bkey_last(b, t);
+	struct btree_node_iter_set *set;
+	unsigned offset = __btree_node_key_to_offset(b, where);
+	int shift = new_u64s - clobber_u64s;
+	unsigned old_end = t->end_offset - shift;
+	unsigned orig_iter_pos = node_iter->data[0].k;
+	bool iter_current_key_modified =
+		orig_iter_pos >= offset &&
+		orig_iter_pos <= offset + clobber_u64s;
+
+	btree_node_iter_for_each(node_iter, set)
+		if (set->end == old_end)
+			goto found;
+
+	/* didn't find the bset in the iterator - might have to readd it: */
+	if (new_u64s &&
+	    bkey_iter_pos_cmp(b, where, &path->pos) >= 0) {
+		bch2_btree_node_iter_push(node_iter, b, where, end);
+		goto fixup_done;
+	} else {
+		/* Iterator is after key that changed */
+		return;
+	}
+found:
+	set->end = t->end_offset;
+
+	/* Iterator hasn't gotten to the key that changed yet: */
+	if (set->k < offset)
+		return;
+
+	if (new_u64s &&
+	    bkey_iter_pos_cmp(b, where, &path->pos) >= 0) {
+		set->k = offset;
+	} else if (set->k < offset + clobber_u64s) {
+		set->k = offset + new_u64s;
+		if (set->k == set->end)
+			bch2_btree_node_iter_set_drop(node_iter, set);
+	} else {
+		/* Iterator is after key that changed */
+		set->k = (int) set->k + shift;
+		return;
+	}
+
+	bch2_btree_node_iter_sort(node_iter, b);
+fixup_done:
+	if (node_iter->data[0].k != orig_iter_pos)
+		iter_current_key_modified = true;
+
+	/*
+	 * When a new key is added, and the node iterator now points to that
+	 * key, the iterator might have skipped past deleted keys that should
+	 * come after the key the iterator now points to. We have to rewind to
+	 * before those deleted keys - otherwise
+	 * bch2_btree_node_iter_prev_all() breaks:
+	 */
+	if (!bch2_btree_node_iter_end(node_iter) &&
+	    iter_current_key_modified &&
+	    b->c.level) {
+		struct bkey_packed *k, *k2, *p;
+
+		k = bch2_btree_node_iter_peek_all(node_iter, b);
+
+		for_each_bset(b, t) {
+			bool set_pos = false;
+
+			if (node_iter->data[0].end == t->end_offset)
+				continue;
+
+			k2 = bch2_btree_node_iter_bset_pos(node_iter, b, t);
+
+			while ((p = bch2_bkey_prev_all(b, t, k2)) &&
+			       bkey_iter_cmp(b, k, p) < 0) {
+				k2 = p;
+				set_pos = true;
+			}
+
+			if (set_pos)
+				btree_node_iter_set_set_pos(node_iter,
+							    b, t, k2);
+		}
+	}
+}
+
+void bch2_btree_node_iter_fix(struct btree_trans *trans,
+			      struct btree_path *path,
+			      struct btree *b,
+			      struct btree_node_iter *node_iter,
+			      struct bkey_packed *where,
+			      unsigned clobber_u64s,
+			      unsigned new_u64s)
+{
+	struct bset_tree *t = bch2_bkey_to_bset_inlined(b, where);
+	struct btree_path *linked;
+
+	if (node_iter != &path->l[b->c.level].iter) {
+		__bch2_btree_node_iter_fix(path, b, node_iter, t,
+					   where, clobber_u64s, new_u64s);
+
+		if (bch2_debug_check_iterators)
+			bch2_btree_node_iter_verify(node_iter, b);
+	}
+
+	trans_for_each_path_with_node(trans, b, linked) {
+		__bch2_btree_node_iter_fix(linked, b,
+					   &linked->l[b->c.level].iter, t,
+					   where, clobber_u64s, new_u64s);
+		bch2_btree_path_verify_level(trans, linked, b->c.level);
+	}
+}
+
+/* Btree path level: pointer to a particular btree node and node iter */
+
+static inline struct bkey_s_c __btree_iter_unpack(struct bch_fs *c,
+						  struct btree_path_level *l,
+						  struct bkey *u,
+						  struct bkey_packed *k)
+{
+	if (unlikely(!k)) {
+		/*
+		 * signal to bch2_btree_iter_peek_slot() that we're currently at
+		 * a hole
+		 */
+		u->type = KEY_TYPE_deleted;
+		return bkey_s_c_null;
+	}
+
+	return bkey_disassemble(l->b, k, u);
+}
+
+static inline struct bkey_s_c btree_path_level_peek_all(struct bch_fs *c,
+							struct btree_path_level *l,
+							struct bkey *u)
+{
+	return __btree_iter_unpack(c, l, u,
+			bch2_btree_node_iter_peek_all(&l->iter, l->b));
+}
+
+static inline struct bkey_s_c btree_path_level_peek(struct btree_trans *trans,
+						    struct btree_path *path,
+						    struct btree_path_level *l,
+						    struct bkey *u)
+{
+	struct bkey_s_c k = __btree_iter_unpack(trans->c, l, u,
+			bch2_btree_node_iter_peek(&l->iter, l->b));
+
+	path->pos = k.k ? k.k->p : l->b->key.k.p;
+	trans->paths_sorted = false;
+	bch2_btree_path_verify_level(trans, path, l - path->l);
+	return k;
+}
+
+static inline struct bkey_s_c btree_path_level_prev(struct btree_trans *trans,
+						    struct btree_path *path,
+						    struct btree_path_level *l,
+						    struct bkey *u)
+{
+	struct bkey_s_c k = __btree_iter_unpack(trans->c, l, u,
+			bch2_btree_node_iter_prev(&l->iter, l->b));
+
+	path->pos = k.k ? k.k->p : l->b->data->min_key;
+	trans->paths_sorted = false;
+	bch2_btree_path_verify_level(trans, path, l - path->l);
+	return k;
+}
+
+static inline bool btree_path_advance_to_pos(struct btree_path *path,
+					     struct btree_path_level *l,
+					     int max_advance)
+{
+	struct bkey_packed *k;
+	int nr_advanced = 0;
+
+	while ((k = bch2_btree_node_iter_peek_all(&l->iter, l->b)) &&
+	       bkey_iter_pos_cmp(l->b, k, &path->pos) < 0) {
+		if (max_advance > 0 && nr_advanced >= max_advance)
+			return false;
+
+		bch2_btree_node_iter_advance(&l->iter, l->b);
+		nr_advanced++;
+	}
+
+	return true;
+}
+
+static inline void __btree_path_level_init(struct btree_path *path,
+					   unsigned level)
+{
+	struct btree_path_level *l = &path->l[level];
+
+	bch2_btree_node_iter_init(&l->iter, l->b, &path->pos);
+
+	/*
+	 * Iterators to interior nodes should always be pointed at the first non
+	 * whiteout:
+	 */
+	if (level)
+		bch2_btree_node_iter_peek(&l->iter, l->b);
+}
+
+void bch2_btree_path_level_init(struct btree_trans *trans,
+				struct btree_path *path,
+				struct btree *b)
+{
+	BUG_ON(path->cached);
+
+	EBUG_ON(!btree_path_pos_in_node(path, b));
+
+	path->l[b->c.level].lock_seq = six_lock_seq(&b->c.lock);
+	path->l[b->c.level].b = b;
+	__btree_path_level_init(path, b->c.level);
+}
+
+/* Btree path: fixups after btree node updates: */
+
+static void bch2_trans_revalidate_updates_in_node(struct btree_trans *trans, struct btree *b)
+{
+	struct bch_fs *c = trans->c;
+	struct btree_insert_entry *i;
+
+	trans_for_each_update(trans, i)
+		if (!i->cached &&
+		    i->level	== b->c.level &&
+		    i->btree_id	== b->c.btree_id &&
+		    bpos_cmp(i->k->k.p, b->data->min_key) >= 0 &&
+		    bpos_cmp(i->k->k.p, b->data->max_key) <= 0) {
+			i->old_v = bch2_btree_path_peek_slot(i->path, &i->old_k).v;
+
+			if (unlikely(trans->journal_replay_not_finished)) {
+				struct bkey_i *j_k =
+					bch2_journal_keys_peek_slot(c, i->btree_id, i->level,
+								    i->k->k.p);
+
+				if (j_k) {
+					i->old_k = j_k->k;
+					i->old_v = &j_k->v;
+				}
+			}
+		}
+}
+
+/*
+ * A btree node is being replaced - update the iterator to point to the new
+ * node:
+ */
+void bch2_trans_node_add(struct btree_trans *trans, struct btree *b)
+{
+	struct btree_path *path;
+
+	trans_for_each_path(trans, path)
+		if (path->uptodate == BTREE_ITER_UPTODATE &&
+		    !path->cached &&
+		    btree_path_pos_in_node(path, b)) {
+			enum btree_node_locked_type t =
+				btree_lock_want(path, b->c.level);
+
+			if (t != BTREE_NODE_UNLOCKED) {
+				btree_node_unlock(trans, path, b->c.level);
+				six_lock_increment(&b->c.lock, (enum six_lock_type) t);
+				mark_btree_node_locked(trans, path, b->c.level, t);
+			}
+
+			bch2_btree_path_level_init(trans, path, b);
+		}
+
+	bch2_trans_revalidate_updates_in_node(trans, b);
+}
+
+/*
+ * A btree node has been modified in such a way as to invalidate iterators - fix
+ * them:
+ */
+void bch2_trans_node_reinit_iter(struct btree_trans *trans, struct btree *b)
+{
+	struct btree_path *path;
+
+	trans_for_each_path_with_node(trans, b, path)
+		__btree_path_level_init(path, b->c.level);
+
+	bch2_trans_revalidate_updates_in_node(trans, b);
+}
+
+/* Btree path: traverse, set_pos: */
+
+static inline int btree_path_lock_root(struct btree_trans *trans,
+				       struct btree_path *path,
+				       unsigned depth_want,
+				       unsigned long trace_ip)
+{
+	struct bch_fs *c = trans->c;
+	struct btree *b, **rootp = &bch2_btree_id_root(c, path->btree_id)->b;
+	enum six_lock_type lock_type;
+	unsigned i;
+	int ret;
+
+	EBUG_ON(path->nodes_locked);
+
+	while (1) {
+		b = READ_ONCE(*rootp);
+		path->level = READ_ONCE(b->c.level);
+
+		if (unlikely(path->level < depth_want)) {
+			/*
+			 * the root is at a lower depth than the depth we want:
+			 * got to the end of the btree, or we're walking nodes
+			 * greater than some depth and there are no nodes >=
+			 * that depth
+			 */
+			path->level = depth_want;
+			for (i = path->level; i < BTREE_MAX_DEPTH; i++)
+				path->l[i].b = NULL;
+			return 1;
+		}
+
+		lock_type = __btree_lock_want(path, path->level);
+		ret = btree_node_lock(trans, path, &b->c,
+				      path->level, lock_type, trace_ip);
+		if (unlikely(ret)) {
+			if (bch2_err_matches(ret, BCH_ERR_lock_fail_root_changed))
+				continue;
+			if (bch2_err_matches(ret, BCH_ERR_transaction_restart))
+				return ret;
+			BUG();
+		}
+
+		if (likely(b == READ_ONCE(*rootp) &&
+			   b->c.level == path->level &&
+			   !race_fault())) {
+			for (i = 0; i < path->level; i++)
+				path->l[i].b = ERR_PTR(-BCH_ERR_no_btree_node_lock_root);
+			path->l[path->level].b = b;
+			for (i = path->level + 1; i < BTREE_MAX_DEPTH; i++)
+				path->l[i].b = NULL;
+
+			mark_btree_node_locked(trans, path, path->level,
+					       (enum btree_node_locked_type) lock_type);
+			bch2_btree_path_level_init(trans, path, b);
+			return 0;
+		}
+
+		six_unlock_type(&b->c.lock, lock_type);
+	}
+}
+
+noinline
+static int btree_path_prefetch(struct btree_trans *trans, struct btree_path *path)
+{
+	struct bch_fs *c = trans->c;
+	struct btree_path_level *l = path_l(path);
+	struct btree_node_iter node_iter = l->iter;
+	struct bkey_packed *k;
+	struct bkey_buf tmp;
+	unsigned nr = test_bit(BCH_FS_STARTED, &c->flags)
+		? (path->level > 1 ? 0 :  2)
+		: (path->level > 1 ? 1 : 16);
+	bool was_locked = btree_node_locked(path, path->level);
+	int ret = 0;
+
+	bch2_bkey_buf_init(&tmp);
+
+	while (nr-- && !ret) {
+		if (!bch2_btree_node_relock(trans, path, path->level))
+			break;
+
+		bch2_btree_node_iter_advance(&node_iter, l->b);
+		k = bch2_btree_node_iter_peek(&node_iter, l->b);
+		if (!k)
+			break;
+
+		bch2_bkey_buf_unpack(&tmp, c, l->b, k);
+		ret = bch2_btree_node_prefetch(trans, path, tmp.k, path->btree_id,
+					       path->level - 1);
+	}
+
+	if (!was_locked)
+		btree_node_unlock(trans, path, path->level);
+
+	bch2_bkey_buf_exit(&tmp, c);
+	return ret;
+}
+
+static int btree_path_prefetch_j(struct btree_trans *trans, struct btree_path *path,
+				 struct btree_and_journal_iter *jiter)
+{
+	struct bch_fs *c = trans->c;
+	struct bkey_s_c k;
+	struct bkey_buf tmp;
+	unsigned nr = test_bit(BCH_FS_STARTED, &c->flags)
+		? (path->level > 1 ? 0 :  2)
+		: (path->level > 1 ? 1 : 16);
+	bool was_locked = btree_node_locked(path, path->level);
+	int ret = 0;
+
+	bch2_bkey_buf_init(&tmp);
+
+	while (nr-- && !ret) {
+		if (!bch2_btree_node_relock(trans, path, path->level))
+			break;
+
+		bch2_btree_and_journal_iter_advance(jiter);
+		k = bch2_btree_and_journal_iter_peek(jiter);
+		if (!k.k)
+			break;
+
+		bch2_bkey_buf_reassemble(&tmp, c, k);
+		ret = bch2_btree_node_prefetch(trans, path, tmp.k, path->btree_id,
+					       path->level - 1);
+	}
+
+	if (!was_locked)
+		btree_node_unlock(trans, path, path->level);
+
+	bch2_bkey_buf_exit(&tmp, c);
+	return ret;
+}
+
+static noinline void btree_node_mem_ptr_set(struct btree_trans *trans,
+					    struct btree_path *path,
+					    unsigned plevel, struct btree *b)
+{
+	struct btree_path_level *l = &path->l[plevel];
+	bool locked = btree_node_locked(path, plevel);
+	struct bkey_packed *k;
+	struct bch_btree_ptr_v2 *bp;
+
+	if (!bch2_btree_node_relock(trans, path, plevel))
+		return;
+
+	k = bch2_btree_node_iter_peek_all(&l->iter, l->b);
+	BUG_ON(k->type != KEY_TYPE_btree_ptr_v2);
+
+	bp = (void *) bkeyp_val(&l->b->format, k);
+	bp->mem_ptr = (unsigned long)b;
+
+	if (!locked)
+		btree_node_unlock(trans, path, plevel);
+}
+
+static noinline int btree_node_iter_and_journal_peek(struct btree_trans *trans,
+						     struct btree_path *path,
+						     unsigned flags,
+						     struct bkey_buf *out)
+{
+	struct bch_fs *c = trans->c;
+	struct btree_path_level *l = path_l(path);
+	struct btree_and_journal_iter jiter;
+	struct bkey_s_c k;
+	int ret = 0;
+
+	__bch2_btree_and_journal_iter_init_node_iter(&jiter, c, l->b, l->iter, path->pos);
+
+	k = bch2_btree_and_journal_iter_peek(&jiter);
+
+	bch2_bkey_buf_reassemble(out, c, k);
+
+	if (flags & BTREE_ITER_PREFETCH)
+		ret = btree_path_prefetch_j(trans, path, &jiter);
+
+	bch2_btree_and_journal_iter_exit(&jiter);
+	return ret;
+}
+
+static __always_inline int btree_path_down(struct btree_trans *trans,
+					   struct btree_path *path,
+					   unsigned flags,
+					   unsigned long trace_ip)
+{
+	struct bch_fs *c = trans->c;
+	struct btree_path_level *l = path_l(path);
+	struct btree *b;
+	unsigned level = path->level - 1;
+	enum six_lock_type lock_type = __btree_lock_want(path, level);
+	struct bkey_buf tmp;
+	int ret;
+
+	EBUG_ON(!btree_node_locked(path, path->level));
+
+	bch2_bkey_buf_init(&tmp);
+
+	if (unlikely(trans->journal_replay_not_finished)) {
+		ret = btree_node_iter_and_journal_peek(trans, path, flags, &tmp);
+		if (ret)
+			goto err;
+	} else {
+		bch2_bkey_buf_unpack(&tmp, c, l->b,
+				 bch2_btree_node_iter_peek(&l->iter, l->b));
+
+		if (flags & BTREE_ITER_PREFETCH) {
+			ret = btree_path_prefetch(trans, path);
+			if (ret)
+				goto err;
+		}
+	}
+
+	b = bch2_btree_node_get(trans, path, tmp.k, level, lock_type, trace_ip);
+	ret = PTR_ERR_OR_ZERO(b);
+	if (unlikely(ret))
+		goto err;
+
+	if (likely(!trans->journal_replay_not_finished &&
+		   tmp.k->k.type == KEY_TYPE_btree_ptr_v2) &&
+	    unlikely(b != btree_node_mem_ptr(tmp.k)))
+		btree_node_mem_ptr_set(trans, path, level + 1, b);
+
+	if (btree_node_read_locked(path, level + 1))
+		btree_node_unlock(trans, path, level + 1);
+
+	mark_btree_node_locked(trans, path, level,
+			       (enum btree_node_locked_type) lock_type);
+	path->level = level;
+	bch2_btree_path_level_init(trans, path, b);
+
+	bch2_btree_path_verify_locks(path);
+err:
+	bch2_bkey_buf_exit(&tmp, c);
+	return ret;
+}
+
+
+static int bch2_btree_path_traverse_all(struct btree_trans *trans)
+{
+	struct bch_fs *c = trans->c;
+	struct btree_path *path;
+	unsigned long trace_ip = _RET_IP_;
+	int i, ret = 0;
+
+	if (trans->in_traverse_all)
+		return -BCH_ERR_transaction_restart_in_traverse_all;
+
+	trans->in_traverse_all = true;
+retry_all:
+	trans->restarted = 0;
+	trans->last_restarted_ip = 0;
+
+	trans_for_each_path(trans, path)
+		path->should_be_locked = false;
+
+	btree_trans_sort_paths(trans);
+
+	bch2_trans_unlock(trans);
+	cond_resched();
+
+	if (unlikely(trans->memory_allocation_failure)) {
+		struct closure cl;
+
+		closure_init_stack(&cl);
+
+		do {
+			ret = bch2_btree_cache_cannibalize_lock(c, &cl);
+			closure_sync(&cl);
+		} while (ret);
+	}
+
+	/* Now, redo traversals in correct order: */
+	i = 0;
+	while (i < trans->nr_sorted) {
+		path = trans->paths + trans->sorted[i];
+
+		/*
+		 * Traversing a path can cause another path to be added at about
+		 * the same position:
+		 */
+		if (path->uptodate) {
+			__btree_path_get(path, false);
+			ret = bch2_btree_path_traverse_one(trans, path, 0, _THIS_IP_);
+			__btree_path_put(path, false);
+
+			if (bch2_err_matches(ret, BCH_ERR_transaction_restart) ||
+			    bch2_err_matches(ret, ENOMEM))
+				goto retry_all;
+			if (ret)
+				goto err;
+		} else {
+			i++;
+		}
+	}
+
+	/*
+	 * We used to assert that all paths had been traversed here
+	 * (path->uptodate < BTREE_ITER_NEED_TRAVERSE); however, since
+	 * path->should_be_locked is not set yet, we might have unlocked and
+	 * then failed to relock a path - that's fine.
+	 */
+err:
+	bch2_btree_cache_cannibalize_unlock(c);
+
+	trans->in_traverse_all = false;
+
+	trace_and_count(c, trans_traverse_all, trans, trace_ip);
+	return ret;
+}
+
+static inline bool btree_path_check_pos_in_node(struct btree_path *path,
+						unsigned l, int check_pos)
+{
+	if (check_pos < 0 && btree_path_pos_before_node(path, path->l[l].b))
+		return false;
+	if (check_pos > 0 && btree_path_pos_after_node(path, path->l[l].b))
+		return false;
+	return true;
+}
+
+static inline bool btree_path_good_node(struct btree_trans *trans,
+					struct btree_path *path,
+					unsigned l, int check_pos)
+{
+	return is_btree_node(path, l) &&
+		bch2_btree_node_relock(trans, path, l) &&
+		btree_path_check_pos_in_node(path, l, check_pos);
+}
+
+static void btree_path_set_level_down(struct btree_trans *trans,
+				      struct btree_path *path,
+				      unsigned new_level)
+{
+	unsigned l;
+
+	path->level = new_level;
+
+	for (l = path->level + 1; l < BTREE_MAX_DEPTH; l++)
+		if (btree_lock_want(path, l) == BTREE_NODE_UNLOCKED)
+			btree_node_unlock(trans, path, l);
+
+	btree_path_set_dirty(path, BTREE_ITER_NEED_TRAVERSE);
+	bch2_btree_path_verify(trans, path);
+}
+
+static noinline unsigned __btree_path_up_until_good_node(struct btree_trans *trans,
+							 struct btree_path *path,
+							 int check_pos)
+{
+	unsigned i, l = path->level;
+again:
+	while (btree_path_node(path, l) &&
+	       !btree_path_good_node(trans, path, l, check_pos))
+		__btree_path_set_level_up(trans, path, l++);
+
+	/* If we need intent locks, take them too: */
+	for (i = l + 1;
+	     i < path->locks_want && btree_path_node(path, i);
+	     i++)
+		if (!bch2_btree_node_relock(trans, path, i)) {
+			while (l <= i)
+				__btree_path_set_level_up(trans, path, l++);
+			goto again;
+		}
+
+	return l;
+}
+
+static inline unsigned btree_path_up_until_good_node(struct btree_trans *trans,
+						     struct btree_path *path,
+						     int check_pos)
+{
+	return likely(btree_node_locked(path, path->level) &&
+		      btree_path_check_pos_in_node(path, path->level, check_pos))
+		? path->level
+		: __btree_path_up_until_good_node(trans, path, check_pos);
+}
+
+/*
+ * This is the main state machine for walking down the btree - walks down to a
+ * specified depth
+ *
+ * Returns 0 on success, -EIO on error (error reading in a btree node).
+ *
+ * On error, caller (peek_node()/peek_key()) must return NULL; the error is
+ * stashed in the iterator and returned from bch2_trans_exit().
+ */
+int bch2_btree_path_traverse_one(struct btree_trans *trans,
+				 struct btree_path *path,
+				 unsigned flags,
+				 unsigned long trace_ip)
+{
+	unsigned depth_want = path->level;
+	int ret = -((int) trans->restarted);
+
+	if (unlikely(ret))
+		goto out;
+
+	if (unlikely(!trans->srcu_held))
+		bch2_trans_srcu_lock(trans);
+
+	/*
+	 * Ensure we obey path->should_be_locked: if it's set, we can't unlock
+	 * and re-traverse the path without a transaction restart:
+	 */
+	if (path->should_be_locked) {
+		ret = bch2_btree_path_relock(trans, path, trace_ip);
+		goto out;
+	}
+
+	if (path->cached) {
+		ret = bch2_btree_path_traverse_cached(trans, path, flags);
+		goto out;
+	}
+
+	if (unlikely(path->level >= BTREE_MAX_DEPTH))
+		goto out;
+
+	path->level = btree_path_up_until_good_node(trans, path, 0);
+
+	EBUG_ON(btree_path_node(path, path->level) &&
+		!btree_node_locked(path, path->level));
+
+	/*
+	 * Note: path->nodes[path->level] may be temporarily NULL here - that
+	 * would indicate to other code that we got to the end of the btree,
+	 * here it indicates that relocking the root failed - it's critical that
+	 * btree_path_lock_root() comes next and that it can't fail
+	 */
+	while (path->level > depth_want) {
+		ret = btree_path_node(path, path->level)
+			? btree_path_down(trans, path, flags, trace_ip)
+			: btree_path_lock_root(trans, path, depth_want, trace_ip);
+		if (unlikely(ret)) {
+			if (ret == 1) {
+				/*
+				 * No nodes at this level - got to the end of
+				 * the btree:
+				 */
+				ret = 0;
+				goto out;
+			}
+
+			__bch2_btree_path_unlock(trans, path);
+			path->level = depth_want;
+			path->l[path->level].b = ERR_PTR(ret);
+			goto out;
+		}
+	}
+
+	path->uptodate = BTREE_ITER_UPTODATE;
+out:
+	if (bch2_err_matches(ret, BCH_ERR_transaction_restart) != !!trans->restarted)
+		panic("ret %s (%i) trans->restarted %s (%i)\n",
+		      bch2_err_str(ret), ret,
+		      bch2_err_str(trans->restarted), trans->restarted);
+	bch2_btree_path_verify(trans, path);
+	return ret;
+}
+
+static inline void btree_path_copy(struct btree_trans *trans, struct btree_path *dst,
+			    struct btree_path *src)
+{
+	unsigned i, offset = offsetof(struct btree_path, pos);
+
+	memcpy((void *) dst + offset,
+	       (void *) src + offset,
+	       sizeof(struct btree_path) - offset);
+
+	for (i = 0; i < BTREE_MAX_DEPTH; i++) {
+		unsigned t = btree_node_locked_type(dst, i);
+
+		if (t != BTREE_NODE_UNLOCKED)
+			six_lock_increment(&dst->l[i].b->c.lock, t);
+	}
+}
+
+static struct btree_path *btree_path_clone(struct btree_trans *trans, struct btree_path *src,
+					   bool intent)
+{
+	struct btree_path *new = btree_path_alloc(trans, src);
+
+	btree_path_copy(trans, new, src);
+	__btree_path_get(new, intent);
+	return new;
+}
+
+__flatten
+struct btree_path *__bch2_btree_path_make_mut(struct btree_trans *trans,
+			 struct btree_path *path, bool intent,
+			 unsigned long ip)
+{
+	__btree_path_put(path, intent);
+	path = btree_path_clone(trans, path, intent);
+	path->preserve = false;
+	return path;
+}
+
+struct btree_path * __must_check
+__bch2_btree_path_set_pos(struct btree_trans *trans,
+		   struct btree_path *path, struct bpos new_pos,
+		   bool intent, unsigned long ip, int cmp)
+{
+	unsigned level = path->level;
+
+	bch2_trans_verify_not_in_restart(trans);
+	EBUG_ON(!path->ref);
+
+	path = bch2_btree_path_make_mut(trans, path, intent, ip);
+
+	path->pos		= new_pos;
+	trans->paths_sorted	= false;
+
+	if (unlikely(path->cached)) {
+		btree_node_unlock(trans, path, 0);
+		path->l[0].b = ERR_PTR(-BCH_ERR_no_btree_node_up);
+		btree_path_set_dirty(path, BTREE_ITER_NEED_TRAVERSE);
+		goto out;
+	}
+
+	level = btree_path_up_until_good_node(trans, path, cmp);
+
+	if (btree_path_node(path, level)) {
+		struct btree_path_level *l = &path->l[level];
+
+		BUG_ON(!btree_node_locked(path, level));
+		/*
+		 * We might have to skip over many keys, or just a few: try
+		 * advancing the node iterator, and if we have to skip over too
+		 * many keys just reinit it (or if we're rewinding, since that
+		 * is expensive).
+		 */
+		if (cmp < 0 ||
+		    !btree_path_advance_to_pos(path, l, 8))
+			bch2_btree_node_iter_init(&l->iter, l->b, &path->pos);
+
+		/*
+		 * Iterators to interior nodes should always be pointed at the first non
+		 * whiteout:
+		 */
+		if (unlikely(level))
+			bch2_btree_node_iter_peek(&l->iter, l->b);
+	}
+
+	if (unlikely(level != path->level)) {
+		btree_path_set_dirty(path, BTREE_ITER_NEED_TRAVERSE);
+		__bch2_btree_path_unlock(trans, path);
+	}
+out:
+	bch2_btree_path_verify(trans, path);
+	return path;
+}
+
+/* Btree path: main interface: */
+
+static struct btree_path *have_path_at_pos(struct btree_trans *trans, struct btree_path *path)
+{
+	struct btree_path *sib;
+
+	sib = prev_btree_path(trans, path);
+	if (sib && !btree_path_cmp(sib, path))
+		return sib;
+
+	sib = next_btree_path(trans, path);
+	if (sib && !btree_path_cmp(sib, path))
+		return sib;
+
+	return NULL;
+}
+
+static struct btree_path *have_node_at_pos(struct btree_trans *trans, struct btree_path *path)
+{
+	struct btree_path *sib;
+
+	sib = prev_btree_path(trans, path);
+	if (sib && sib->level == path->level && path_l(sib)->b == path_l(path)->b)
+		return sib;
+
+	sib = next_btree_path(trans, path);
+	if (sib && sib->level == path->level && path_l(sib)->b == path_l(path)->b)
+		return sib;
+
+	return NULL;
+}
+
+static inline void __bch2_path_free(struct btree_trans *trans, struct btree_path *path)
+{
+	__bch2_btree_path_unlock(trans, path);
+	btree_path_list_remove(trans, path);
+	trans->paths_allocated &= ~(1ULL << path->idx);
+}
+
+void bch2_path_put(struct btree_trans *trans, struct btree_path *path, bool intent)
+{
+	struct btree_path *dup;
+
+	EBUG_ON(trans->paths + path->idx != path);
+	EBUG_ON(!path->ref);
+
+	if (!__btree_path_put(path, intent))
+		return;
+
+	dup = path->preserve
+		? have_path_at_pos(trans, path)
+		: have_node_at_pos(trans, path);
+
+	if (!dup && !(!path->preserve && !is_btree_node(path, path->level)))
+		return;
+
+	if (path->should_be_locked &&
+	    !trans->restarted &&
+	    (!dup || !bch2_btree_path_relock_norestart(trans, dup, _THIS_IP_)))
+		return;
+
+	if (dup) {
+		dup->preserve		|= path->preserve;
+		dup->should_be_locked	|= path->should_be_locked;
+	}
+
+	__bch2_path_free(trans, path);
+}
+
+static void bch2_path_put_nokeep(struct btree_trans *trans, struct btree_path *path,
+				 bool intent)
+{
+	EBUG_ON(trans->paths + path->idx != path);
+	EBUG_ON(!path->ref);
+
+	if (!__btree_path_put(path, intent))
+		return;
+
+	__bch2_path_free(trans, path);
+}
+
+void __noreturn bch2_trans_restart_error(struct btree_trans *trans, u32 restart_count)
+{
+	panic("trans->restart_count %u, should be %u, last restarted by %pS\n",
+	      trans->restart_count, restart_count,
+	      (void *) trans->last_begin_ip);
+}
+
+void __noreturn bch2_trans_in_restart_error(struct btree_trans *trans)
+{
+	panic("in transaction restart: %s, last restarted by %pS\n",
+	      bch2_err_str(trans->restarted),
+	      (void *) trans->last_restarted_ip);
+}
+
+noinline __cold
+void bch2_trans_updates_to_text(struct printbuf *buf, struct btree_trans *trans)
+{
+	struct btree_insert_entry *i;
+	struct btree_write_buffered_key *wb;
+
+	prt_printf(buf, "transaction updates for %s journal seq %llu",
+	       trans->fn, trans->journal_res.seq);
+	prt_newline(buf);
+	printbuf_indent_add(buf, 2);
+
+	trans_for_each_update(trans, i) {
+		struct bkey_s_c old = { &i->old_k, i->old_v };
+
+		prt_printf(buf, "update: btree=%s cached=%u %pS",
+		       bch2_btree_id_str(i->btree_id),
+		       i->cached,
+		       (void *) i->ip_allocated);
+		prt_newline(buf);
+
+		prt_printf(buf, "  old ");
+		bch2_bkey_val_to_text(buf, trans->c, old);
+		prt_newline(buf);
+
+		prt_printf(buf, "  new ");
+		bch2_bkey_val_to_text(buf, trans->c, bkey_i_to_s_c(i->k));
+		prt_newline(buf);
+	}
+
+	trans_for_each_wb_update(trans, wb) {
+		prt_printf(buf, "update: btree=%s wb=1 %pS",
+		       bch2_btree_id_str(wb->btree),
+		       (void *) i->ip_allocated);
+		prt_newline(buf);
+
+		prt_printf(buf, "  new ");
+		bch2_bkey_val_to_text(buf, trans->c, bkey_i_to_s_c(&wb->k));
+		prt_newline(buf);
+	}
+
+	printbuf_indent_sub(buf, 2);
+}
+
+noinline __cold
+void bch2_dump_trans_updates(struct btree_trans *trans)
+{
+	struct printbuf buf = PRINTBUF;
+
+	bch2_trans_updates_to_text(&buf, trans);
+	bch2_print_string_as_lines(KERN_ERR, buf.buf);
+	printbuf_exit(&buf);
+}
+
+noinline __cold
+void bch2_btree_path_to_text(struct printbuf *out, struct btree_path *path)
+{
+	prt_printf(out, "path: idx %2u ref %u:%u %c %c btree=%s l=%u pos ",
+		   path->idx, path->ref, path->intent_ref,
+		   path->preserve ? 'P' : ' ',
+		   path->should_be_locked ? 'S' : ' ',
+		   bch2_btree_id_str(path->btree_id),
+		   path->level);
+	bch2_bpos_to_text(out, path->pos);
+
+	prt_printf(out, " locks %u", path->nodes_locked);
+#ifdef TRACK_PATH_ALLOCATED
+	prt_printf(out, " %pS", (void *) path->ip_allocated);
+#endif
+	prt_newline(out);
+}
+
+static noinline __cold
+void __bch2_trans_paths_to_text(struct printbuf *out, struct btree_trans *trans,
+				bool nosort)
+{
+	struct btree_path *path;
+	unsigned idx;
+
+	if (!nosort)
+		btree_trans_sort_paths(trans);
+
+	trans_for_each_path_inorder(trans, path, idx)
+		bch2_btree_path_to_text(out, path);
+}
+
+noinline __cold
+void bch2_trans_paths_to_text(struct printbuf *out, struct btree_trans *trans)
+{
+	__bch2_trans_paths_to_text(out, trans, false);
+}
+
+static noinline __cold
+void __bch2_dump_trans_paths_updates(struct btree_trans *trans, bool nosort)
+{
+	struct printbuf buf = PRINTBUF;
+
+	__bch2_trans_paths_to_text(&buf, trans, nosort);
+	bch2_trans_updates_to_text(&buf, trans);
+
+	bch2_print_string_as_lines(KERN_ERR, buf.buf);
+	printbuf_exit(&buf);
+}
+
+noinline __cold
+void bch2_dump_trans_paths_updates(struct btree_trans *trans)
+{
+	__bch2_dump_trans_paths_updates(trans, false);
+}
+
+noinline __cold
+static void bch2_trans_update_max_paths(struct btree_trans *trans)
+{
+	struct btree_transaction_stats *s = btree_trans_stats(trans);
+	struct printbuf buf = PRINTBUF;
+
+	if (!s)
+		return;
+
+	bch2_trans_paths_to_text(&buf, trans);
+
+	if (!buf.allocation_failure) {
+		mutex_lock(&s->lock);
+		if (s->nr_max_paths < hweight64(trans->paths_allocated)) {
+			s->nr_max_paths = trans->nr_max_paths =
+				hweight64(trans->paths_allocated);
+			swap(s->max_paths_text, buf.buf);
+		}
+		mutex_unlock(&s->lock);
+	}
+
+	printbuf_exit(&buf);
+
+	trans->nr_max_paths = hweight64(trans->paths_allocated);
+}
+
+static noinline void btree_path_overflow(struct btree_trans *trans)
+{
+	bch2_dump_trans_paths_updates(trans);
+	panic("trans path overflow\n");
+}
+
+static inline struct btree_path *btree_path_alloc(struct btree_trans *trans,
+						  struct btree_path *pos)
+{
+	struct btree_path *path;
+	unsigned idx;
+
+	if (unlikely(trans->paths_allocated ==
+		     ~((~0ULL << 1) << (BTREE_ITER_MAX - 1))))
+		btree_path_overflow(trans);
+
+	idx = __ffs64(~trans->paths_allocated);
+
+	/*
+	 * Do this before marking the new path as allocated, since it won't be
+	 * initialized yet:
+	 */
+	if (unlikely(idx > trans->nr_max_paths))
+		bch2_trans_update_max_paths(trans);
+
+	trans->paths_allocated |= 1ULL << idx;
+
+	path = &trans->paths[idx];
+	path->idx		= idx;
+	path->ref		= 0;
+	path->intent_ref	= 0;
+	path->nodes_locked	= 0;
+	path->alloc_seq++;
+
+	btree_path_list_add(trans, pos, path);
+	trans->paths_sorted = false;
+	return path;
+}
+
+struct btree_path *bch2_path_get(struct btree_trans *trans,
+				 enum btree_id btree_id, struct bpos pos,
+				 unsigned locks_want, unsigned level,
+				 unsigned flags, unsigned long ip)
+{
+	struct btree_path *path, *path_pos = NULL;
+	bool cached = flags & BTREE_ITER_CACHED;
+	bool intent = flags & BTREE_ITER_INTENT;
+	int i;
+
+	bch2_trans_verify_not_in_restart(trans);
+	bch2_trans_verify_locks(trans);
+
+	btree_trans_sort_paths(trans);
+
+	trans_for_each_path_inorder(trans, path, i) {
+		if (__btree_path_cmp(path,
+				     btree_id,
+				     cached,
+				     pos,
+				     level) > 0)
+			break;
+
+		path_pos = path;
+	}
+
+	if (path_pos &&
+	    path_pos->cached	== cached &&
+	    path_pos->btree_id	== btree_id &&
+	    path_pos->level	== level) {
+		__btree_path_get(path_pos, intent);
+		path = bch2_btree_path_set_pos(trans, path_pos, pos, intent, ip);
+	} else {
+		path = btree_path_alloc(trans, path_pos);
+		path_pos = NULL;
+
+		__btree_path_get(path, intent);
+		path->pos			= pos;
+		path->btree_id			= btree_id;
+		path->cached			= cached;
+		path->uptodate			= BTREE_ITER_NEED_TRAVERSE;
+		path->should_be_locked		= false;
+		path->level			= level;
+		path->locks_want		= locks_want;
+		path->nodes_locked		= 0;
+		for (i = 0; i < ARRAY_SIZE(path->l); i++)
+			path->l[i].b		= ERR_PTR(-BCH_ERR_no_btree_node_init);
+#ifdef TRACK_PATH_ALLOCATED
+		path->ip_allocated		= ip;
+#endif
+		trans->paths_sorted		= false;
+	}
+
+	if (!(flags & BTREE_ITER_NOPRESERVE))
+		path->preserve = true;
+
+	if (path->intent_ref)
+		locks_want = max(locks_want, level + 1);
+
+	/*
+	 * If the path has locks_want greater than requested, we don't downgrade
+	 * it here - on transaction restart because btree node split needs to
+	 * upgrade locks, we might be putting/getting the iterator again.
+	 * Downgrading iterators only happens via bch2_trans_downgrade(), after
+	 * a successful transaction commit.
+	 */
+
+	locks_want = min(locks_want, BTREE_MAX_DEPTH);
+	if (locks_want > path->locks_want)
+		bch2_btree_path_upgrade_noupgrade_sibs(trans, path, locks_want, NULL);
+
+	return path;
+}
+
+struct bkey_s_c bch2_btree_path_peek_slot(struct btree_path *path, struct bkey *u)
+{
+
+	struct btree_path_level *l = path_l(path);
+	struct bkey_packed *_k;
+	struct bkey_s_c k;
+
+	if (unlikely(!l->b))
+		return bkey_s_c_null;
+
+	EBUG_ON(path->uptodate != BTREE_ITER_UPTODATE);
+	EBUG_ON(!btree_node_locked(path, path->level));
+
+	if (!path->cached) {
+		_k = bch2_btree_node_iter_peek_all(&l->iter, l->b);
+		k = _k ? bkey_disassemble(l->b, _k, u) : bkey_s_c_null;
+
+		EBUG_ON(k.k && bkey_deleted(k.k) && bpos_eq(k.k->p, path->pos));
+
+		if (!k.k || !bpos_eq(path->pos, k.k->p))
+			goto hole;
+	} else {
+		struct bkey_cached *ck = (void *) path->l[0].b;
+
+		EBUG_ON(ck &&
+			(path->btree_id != ck->key.btree_id ||
+			 !bkey_eq(path->pos, ck->key.pos)));
+		if (!ck || !ck->valid)
+			return bkey_s_c_null;
+
+		*u = ck->k->k;
+		k = bkey_i_to_s_c(ck->k);
+	}
+
+	return k;
+hole:
+	bkey_init(u);
+	u->p = path->pos;
+	return (struct bkey_s_c) { u, NULL };
+}
+
+/* Btree iterators: */
+
+int __must_check
+__bch2_btree_iter_traverse(struct btree_iter *iter)
+{
+	return bch2_btree_path_traverse(iter->trans, iter->path, iter->flags);
+}
+
+int __must_check
+bch2_btree_iter_traverse(struct btree_iter *iter)
+{
+	int ret;
+
+	iter->path = bch2_btree_path_set_pos(iter->trans, iter->path,
+					btree_iter_search_key(iter),
+					iter->flags & BTREE_ITER_INTENT,
+					btree_iter_ip_allocated(iter));
+
+	ret = bch2_btree_path_traverse(iter->trans, iter->path, iter->flags);
+	if (ret)
+		return ret;
+
+	btree_path_set_should_be_locked(iter->path);
+	return 0;
+}
+
+/* Iterate across nodes (leaf and interior nodes) */
+
+struct btree *bch2_btree_iter_peek_node(struct btree_iter *iter)
+{
+	struct btree_trans *trans = iter->trans;
+	struct btree *b = NULL;
+	int ret;
+
+	EBUG_ON(iter->path->cached);
+	bch2_btree_iter_verify(iter);
+
+	ret = bch2_btree_path_traverse(trans, iter->path, iter->flags);
+	if (ret)
+		goto err;
+
+	b = btree_path_node(iter->path, iter->path->level);
+	if (!b)
+		goto out;
+
+	BUG_ON(bpos_lt(b->key.k.p, iter->pos));
+
+	bkey_init(&iter->k);
+	iter->k.p = iter->pos = b->key.k.p;
+
+	iter->path = bch2_btree_path_set_pos(trans, iter->path, b->key.k.p,
+					iter->flags & BTREE_ITER_INTENT,
+					btree_iter_ip_allocated(iter));
+	btree_path_set_should_be_locked(iter->path);
+out:
+	bch2_btree_iter_verify_entry_exit(iter);
+	bch2_btree_iter_verify(iter);
+
+	return b;
+err:
+	b = ERR_PTR(ret);
+	goto out;
+}
+
+struct btree *bch2_btree_iter_peek_node_and_restart(struct btree_iter *iter)
+{
+	struct btree *b;
+
+	while (b = bch2_btree_iter_peek_node(iter),
+	       bch2_err_matches(PTR_ERR_OR_ZERO(b), BCH_ERR_transaction_restart))
+		bch2_trans_begin(iter->trans);
+
+	return b;
+}
+
+struct btree *bch2_btree_iter_next_node(struct btree_iter *iter)
+{
+	struct btree_trans *trans = iter->trans;
+	struct btree_path *path = iter->path;
+	struct btree *b = NULL;
+	int ret;
+
+	bch2_trans_verify_not_in_restart(trans);
+	EBUG_ON(iter->path->cached);
+	bch2_btree_iter_verify(iter);
+
+	/* already at end? */
+	if (!btree_path_node(path, path->level))
+		return NULL;
+
+	/* got to end? */
+	if (!btree_path_node(path, path->level + 1)) {
+		btree_path_set_level_up(trans, path);
+		return NULL;
+	}
+
+	if (!bch2_btree_node_relock(trans, path, path->level + 1)) {
+		__bch2_btree_path_unlock(trans, path);
+		path->l[path->level].b		= ERR_PTR(-BCH_ERR_no_btree_node_relock);
+		path->l[path->level + 1].b	= ERR_PTR(-BCH_ERR_no_btree_node_relock);
+		btree_path_set_dirty(path, BTREE_ITER_NEED_TRAVERSE);
+		trace_and_count(trans->c, trans_restart_relock_next_node, trans, _THIS_IP_, path);
+		ret = btree_trans_restart(trans, BCH_ERR_transaction_restart_relock);
+		goto err;
+	}
+
+	b = btree_path_node(path, path->level + 1);
+
+	if (bpos_eq(iter->pos, b->key.k.p)) {
+		__btree_path_set_level_up(trans, path, path->level++);
+	} else {
+		/*
+		 * Haven't gotten to the end of the parent node: go back down to
+		 * the next child node
+		 */
+		path = iter->path =
+			bch2_btree_path_set_pos(trans, path, bpos_successor(iter->pos),
+					   iter->flags & BTREE_ITER_INTENT,
+					   btree_iter_ip_allocated(iter));
+
+		btree_path_set_level_down(trans, path, iter->min_depth);
+
+		ret = bch2_btree_path_traverse(trans, path, iter->flags);
+		if (ret)
+			goto err;
+
+		b = path->l[path->level].b;
+	}
+
+	bkey_init(&iter->k);
+	iter->k.p = iter->pos = b->key.k.p;
+
+	iter->path = bch2_btree_path_set_pos(trans, iter->path, b->key.k.p,
+					iter->flags & BTREE_ITER_INTENT,
+					btree_iter_ip_allocated(iter));
+	btree_path_set_should_be_locked(iter->path);
+	BUG_ON(iter->path->uptodate);
+out:
+	bch2_btree_iter_verify_entry_exit(iter);
+	bch2_btree_iter_verify(iter);
+
+	return b;
+err:
+	b = ERR_PTR(ret);
+	goto out;
+}
+
+/* Iterate across keys (in leaf nodes only) */
+
+inline bool bch2_btree_iter_advance(struct btree_iter *iter)
+{
+	if (likely(!(iter->flags & BTREE_ITER_ALL_LEVELS))) {
+		struct bpos pos = iter->k.p;
+		bool ret = !(iter->flags & BTREE_ITER_ALL_SNAPSHOTS
+			     ? bpos_eq(pos, SPOS_MAX)
+			     : bkey_eq(pos, SPOS_MAX));
+
+		if (ret && !(iter->flags & BTREE_ITER_IS_EXTENTS))
+			pos = bkey_successor(iter, pos);
+		bch2_btree_iter_set_pos(iter, pos);
+		return ret;
+	} else {
+		if (!btree_path_node(iter->path, iter->path->level))
+			return true;
+
+		iter->advanced = true;
+		return false;
+	}
+}
+
+inline bool bch2_btree_iter_rewind(struct btree_iter *iter)
+{
+	struct bpos pos = bkey_start_pos(&iter->k);
+	bool ret = !(iter->flags & BTREE_ITER_ALL_SNAPSHOTS
+		     ? bpos_eq(pos, POS_MIN)
+		     : bkey_eq(pos, POS_MIN));
+
+	if (ret && !(iter->flags & BTREE_ITER_IS_EXTENTS))
+		pos = bkey_predecessor(iter, pos);
+	bch2_btree_iter_set_pos(iter, pos);
+	return ret;
+}
+
+static noinline
+struct bkey_i *__bch2_btree_trans_peek_updates(struct btree_iter *iter)
+{
+	struct btree_insert_entry *i;
+	struct bkey_i *ret = NULL;
+
+	trans_for_each_update(iter->trans, i) {
+		if (i->btree_id < iter->btree_id)
+			continue;
+		if (i->btree_id > iter->btree_id)
+			break;
+		if (bpos_lt(i->k->k.p, iter->path->pos))
+			continue;
+		if (i->key_cache_already_flushed)
+			continue;
+		if (!ret || bpos_lt(i->k->k.p, ret->k.p))
+			ret = i->k;
+	}
+
+	return ret;
+}
+
+static inline struct bkey_i *btree_trans_peek_updates(struct btree_iter *iter)
+{
+	return iter->flags & BTREE_ITER_WITH_UPDATES
+		? __bch2_btree_trans_peek_updates(iter)
+		: NULL;
+}
+
+static struct bkey_i *bch2_btree_journal_peek(struct btree_trans *trans,
+					      struct btree_iter *iter,
+					      struct bpos end_pos)
+{
+	struct bkey_i *k;
+
+	if (bpos_lt(iter->path->pos, iter->journal_pos))
+		iter->journal_idx = 0;
+
+	k = bch2_journal_keys_peek_upto(trans->c, iter->btree_id,
+					iter->path->level,
+					iter->path->pos,
+					end_pos,
+					&iter->journal_idx);
+
+	iter->journal_pos = k ? k->k.p : end_pos;
+	return k;
+}
+
+static noinline
+struct bkey_s_c btree_trans_peek_slot_journal(struct btree_trans *trans,
+					      struct btree_iter *iter)
+{
+	struct bkey_i *k = bch2_btree_journal_peek(trans, iter, iter->path->pos);
+
+	if (k) {
+		iter->k = k->k;
+		return bkey_i_to_s_c(k);
+	} else {
+		return bkey_s_c_null;
+	}
+}
+
+static noinline
+struct bkey_s_c btree_trans_peek_journal(struct btree_trans *trans,
+					 struct btree_iter *iter,
+					 struct bkey_s_c k)
+{
+	struct bkey_i *next_journal =
+		bch2_btree_journal_peek(trans, iter,
+				k.k ? k.k->p : path_l(iter->path)->b->key.k.p);
+
+	if (next_journal) {
+		iter->k = next_journal->k;
+		k = bkey_i_to_s_c(next_journal);
+	}
+
+	return k;
+}
+
+/*
+ * Checks btree key cache for key at iter->pos and returns it if present, or
+ * bkey_s_c_null:
+ */
+static noinline
+struct bkey_s_c btree_trans_peek_key_cache(struct btree_iter *iter, struct bpos pos)
+{
+	struct btree_trans *trans = iter->trans;
+	struct bch_fs *c = trans->c;
+	struct bkey u;
+	struct bkey_s_c k;
+	int ret;
+
+	if ((iter->flags & BTREE_ITER_KEY_CACHE_FILL) &&
+	    bpos_eq(iter->pos, pos))
+		return bkey_s_c_null;
+
+	if (!bch2_btree_key_cache_find(c, iter->btree_id, pos))
+		return bkey_s_c_null;
+
+	if (!iter->key_cache_path)
+		iter->key_cache_path = bch2_path_get(trans, iter->btree_id, pos,
+						     iter->flags & BTREE_ITER_INTENT, 0,
+						     iter->flags|BTREE_ITER_CACHED|
+						     BTREE_ITER_CACHED_NOFILL,
+						     _THIS_IP_);
+
+	iter->key_cache_path = bch2_btree_path_set_pos(trans, iter->key_cache_path, pos,
+					iter->flags & BTREE_ITER_INTENT,
+					btree_iter_ip_allocated(iter));
+
+	ret =   bch2_btree_path_traverse(trans, iter->key_cache_path,
+					 iter->flags|BTREE_ITER_CACHED) ?:
+		bch2_btree_path_relock(trans, iter->path, _THIS_IP_);
+	if (unlikely(ret))
+		return bkey_s_c_err(ret);
+
+	btree_path_set_should_be_locked(iter->key_cache_path);
+
+	k = bch2_btree_path_peek_slot(iter->key_cache_path, &u);
+	if (k.k && !bkey_err(k)) {
+		iter->k = u;
+		k.k = &iter->k;
+	}
+	return k;
+}
+
+static struct bkey_s_c __bch2_btree_iter_peek(struct btree_iter *iter, struct bpos search_key)
+{
+	struct btree_trans *trans = iter->trans;
+	struct bkey_i *next_update;
+	struct bkey_s_c k, k2;
+	int ret;
+
+	EBUG_ON(iter->path->cached);
+	bch2_btree_iter_verify(iter);
+
+	while (1) {
+		struct btree_path_level *l;
+
+		iter->path = bch2_btree_path_set_pos(trans, iter->path, search_key,
+					iter->flags & BTREE_ITER_INTENT,
+					btree_iter_ip_allocated(iter));
+
+		ret = bch2_btree_path_traverse(trans, iter->path, iter->flags);
+		if (unlikely(ret)) {
+			/* ensure that iter->k is consistent with iter->pos: */
+			bch2_btree_iter_set_pos(iter, iter->pos);
+			k = bkey_s_c_err(ret);
+			goto out;
+		}
+
+		l = path_l(iter->path);
+
+		if (unlikely(!l->b)) {
+			/* No btree nodes at requested level: */
+			bch2_btree_iter_set_pos(iter, SPOS_MAX);
+			k = bkey_s_c_null;
+			goto out;
+		}
+
+		btree_path_set_should_be_locked(iter->path);
+
+		k = btree_path_level_peek_all(trans->c, l, &iter->k);
+
+		if (unlikely(iter->flags & BTREE_ITER_WITH_KEY_CACHE) &&
+		    k.k &&
+		    (k2 = btree_trans_peek_key_cache(iter, k.k->p)).k) {
+			k = k2;
+			ret = bkey_err(k);
+			if (ret) {
+				bch2_btree_iter_set_pos(iter, iter->pos);
+				goto out;
+			}
+		}
+
+		if (unlikely(iter->flags & BTREE_ITER_WITH_JOURNAL))
+			k = btree_trans_peek_journal(trans, iter, k);
+
+		next_update = btree_trans_peek_updates(iter);
+
+		if (next_update &&
+		    bpos_le(next_update->k.p,
+			    k.k ? k.k->p : l->b->key.k.p)) {
+			iter->k = next_update->k;
+			k = bkey_i_to_s_c(next_update);
+		}
+
+		if (k.k && bkey_deleted(k.k)) {
+			/*
+			 * If we've got a whiteout, and it's after the search
+			 * key, advance the search key to the whiteout instead
+			 * of just after the whiteout - it might be a btree
+			 * whiteout, with a real key at the same position, since
+			 * in the btree deleted keys sort before non deleted.
+			 */
+			search_key = !bpos_eq(search_key, k.k->p)
+				? k.k->p
+				: bpos_successor(k.k->p);
+			continue;
+		}
+
+		if (likely(k.k)) {
+			break;
+		} else if (likely(!bpos_eq(l->b->key.k.p, SPOS_MAX))) {
+			/* Advance to next leaf node: */
+			search_key = bpos_successor(l->b->key.k.p);
+		} else {
+			/* End of btree: */
+			bch2_btree_iter_set_pos(iter, SPOS_MAX);
+			k = bkey_s_c_null;
+			goto out;
+		}
+	}
+out:
+	bch2_btree_iter_verify(iter);
+
+	return k;
+}
+
+/**
+ * bch2_btree_iter_peek_upto() - returns first key greater than or equal to
+ * iterator's current position
+ * @iter:	iterator to peek from
+ * @end:	search limit: returns keys less than or equal to @end
+ *
+ * Returns:	key if found, or an error extractable with bkey_err().
+ */
+struct bkey_s_c bch2_btree_iter_peek_upto(struct btree_iter *iter, struct bpos end)
+{
+	struct btree_trans *trans = iter->trans;
+	struct bpos search_key = btree_iter_search_key(iter);
+	struct bkey_s_c k;
+	struct bpos iter_pos;
+	int ret;
+
+	EBUG_ON(iter->flags & BTREE_ITER_ALL_LEVELS);
+	EBUG_ON((iter->flags & BTREE_ITER_FILTER_SNAPSHOTS) && bkey_eq(end, POS_MAX));
+
+	if (iter->update_path) {
+		bch2_path_put_nokeep(trans, iter->update_path,
+				     iter->flags & BTREE_ITER_INTENT);
+		iter->update_path = NULL;
+	}
+
+	bch2_btree_iter_verify_entry_exit(iter);
+
+	while (1) {
+		k = __bch2_btree_iter_peek(iter, search_key);
+		if (unlikely(!k.k))
+			goto end;
+		if (unlikely(bkey_err(k)))
+			goto out_no_locked;
+
+		/*
+		 * We need to check against @end before FILTER_SNAPSHOTS because
+		 * if we get to a different inode that requested we might be
+		 * seeing keys for a different snapshot tree that will all be
+		 * filtered out.
+		 *
+		 * But we can't do the full check here, because bkey_start_pos()
+		 * isn't monotonically increasing before FILTER_SNAPSHOTS, and
+		 * that's what we check against in extents mode:
+		 */
+		if (k.k->p.inode > end.inode)
+			goto end;
+
+		if (iter->update_path &&
+		    !bkey_eq(iter->update_path->pos, k.k->p)) {
+			bch2_path_put_nokeep(trans, iter->update_path,
+					     iter->flags & BTREE_ITER_INTENT);
+			iter->update_path = NULL;
+		}
+
+		if ((iter->flags & BTREE_ITER_FILTER_SNAPSHOTS) &&
+		    (iter->flags & BTREE_ITER_INTENT) &&
+		    !(iter->flags & BTREE_ITER_IS_EXTENTS) &&
+		    !iter->update_path) {
+			struct bpos pos = k.k->p;
+
+			if (pos.snapshot < iter->snapshot) {
+				search_key = bpos_successor(k.k->p);
+				continue;
+			}
+
+			pos.snapshot = iter->snapshot;
+
+			/*
+			 * advance, same as on exit for iter->path, but only up
+			 * to snapshot
+			 */
+			__btree_path_get(iter->path, iter->flags & BTREE_ITER_INTENT);
+			iter->update_path = iter->path;
+
+			iter->update_path = bch2_btree_path_set_pos(trans,
+						iter->update_path, pos,
+						iter->flags & BTREE_ITER_INTENT,
+						_THIS_IP_);
+			ret = bch2_btree_path_traverse(trans, iter->update_path, iter->flags);
+			if (unlikely(ret)) {
+				k = bkey_s_c_err(ret);
+				goto out_no_locked;
+			}
+		}
+
+		/*
+		 * We can never have a key in a leaf node at POS_MAX, so
+		 * we don't have to check these successor() calls:
+		 */
+		if ((iter->flags & BTREE_ITER_FILTER_SNAPSHOTS) &&
+		    !bch2_snapshot_is_ancestor(trans->c,
+					       iter->snapshot,
+					       k.k->p.snapshot)) {
+			search_key = bpos_successor(k.k->p);
+			continue;
+		}
+
+		if (bkey_whiteout(k.k) &&
+		    !(iter->flags & BTREE_ITER_ALL_SNAPSHOTS)) {
+			search_key = bkey_successor(iter, k.k->p);
+			continue;
+		}
+
+		/*
+		 * iter->pos should be mononotically increasing, and always be
+		 * equal to the key we just returned - except extents can
+		 * straddle iter->pos:
+		 */
+		if (!(iter->flags & BTREE_ITER_IS_EXTENTS))
+			iter_pos = k.k->p;
+		else
+			iter_pos = bkey_max(iter->pos, bkey_start_pos(k.k));
+
+		if (unlikely(!(iter->flags & BTREE_ITER_IS_EXTENTS)
+			     ? bkey_gt(iter_pos, end)
+			     : bkey_ge(iter_pos, end)))
+			goto end;
+
+		break;
+	}
+
+	iter->pos = iter_pos;
+
+	iter->path = bch2_btree_path_set_pos(trans, iter->path, k.k->p,
+				iter->flags & BTREE_ITER_INTENT,
+				btree_iter_ip_allocated(iter));
+
+	btree_path_set_should_be_locked(iter->path);
+out_no_locked:
+	if (iter->update_path) {
+		ret = bch2_btree_path_relock(trans, iter->update_path, _THIS_IP_);
+		if (unlikely(ret))
+			k = bkey_s_c_err(ret);
+		else
+			btree_path_set_should_be_locked(iter->update_path);
+	}
+
+	if (!(iter->flags & BTREE_ITER_ALL_SNAPSHOTS))
+		iter->pos.snapshot = iter->snapshot;
+
+	ret = bch2_btree_iter_verify_ret(iter, k);
+	if (unlikely(ret)) {
+		bch2_btree_iter_set_pos(iter, iter->pos);
+		k = bkey_s_c_err(ret);
+	}
+
+	bch2_btree_iter_verify_entry_exit(iter);
+
+	return k;
+end:
+	bch2_btree_iter_set_pos(iter, end);
+	k = bkey_s_c_null;
+	goto out_no_locked;
+}
+
+/**
+ * bch2_btree_iter_peek_all_levels() - returns the first key greater than or
+ * equal to iterator's current position, returning keys from every level of the
+ * btree. For keys at different levels of the btree that compare equal, the key
+ * from the lower level (leaf) is returned first.
+ * @iter:	iterator to peek from
+ *
+ * Returns:	key if found, or an error extractable with bkey_err().
+ */
+struct bkey_s_c bch2_btree_iter_peek_all_levels(struct btree_iter *iter)
+{
+	struct btree_trans *trans = iter->trans;
+	struct bkey_s_c k;
+	int ret;
+
+	EBUG_ON(iter->path->cached);
+	bch2_btree_iter_verify(iter);
+	BUG_ON(iter->path->level < iter->min_depth);
+	BUG_ON(!(iter->flags & BTREE_ITER_ALL_SNAPSHOTS));
+	EBUG_ON(!(iter->flags & BTREE_ITER_ALL_LEVELS));
+
+	while (1) {
+		iter->path = bch2_btree_path_set_pos(trans, iter->path, iter->pos,
+					iter->flags & BTREE_ITER_INTENT,
+					btree_iter_ip_allocated(iter));
+
+		ret = bch2_btree_path_traverse(trans, iter->path, iter->flags);
+		if (unlikely(ret)) {
+			/* ensure that iter->k is consistent with iter->pos: */
+			bch2_btree_iter_set_pos(iter, iter->pos);
+			k = bkey_s_c_err(ret);
+			goto out_no_locked;
+		}
+
+		/* Already at end? */
+		if (!btree_path_node(iter->path, iter->path->level)) {
+			k = bkey_s_c_null;
+			goto out_no_locked;
+		}
+
+		k = btree_path_level_peek_all(trans->c,
+				&iter->path->l[iter->path->level], &iter->k);
+
+		/* Check if we should go up to the parent node: */
+		if (!k.k ||
+		    (iter->advanced &&
+		     bpos_eq(path_l(iter->path)->b->key.k.p, iter->pos))) {
+			iter->pos = path_l(iter->path)->b->key.k.p;
+			btree_path_set_level_up(trans, iter->path);
+			iter->advanced = false;
+			continue;
+		}
+
+		/*
+		 * Check if we should go back down to a leaf:
+		 * If we're not in a leaf node, we only return the current key
+		 * if it exactly matches iter->pos - otherwise we first have to
+		 * go back to the leaf:
+		 */
+		if (iter->path->level != iter->min_depth &&
+		    (iter->advanced ||
+		     !k.k ||
+		     !bpos_eq(iter->pos, k.k->p))) {
+			btree_path_set_level_down(trans, iter->path, iter->min_depth);
+			iter->pos = bpos_successor(iter->pos);
+			iter->advanced = false;
+			continue;
+		}
+
+		/* Check if we should go to the next key: */
+		if (iter->path->level == iter->min_depth &&
+		    iter->advanced &&
+		    k.k &&
+		    bpos_eq(iter->pos, k.k->p)) {
+			iter->pos = bpos_successor(iter->pos);
+			iter->advanced = false;
+			continue;
+		}
+
+		if (iter->advanced &&
+		    iter->path->level == iter->min_depth &&
+		    !bpos_eq(k.k->p, iter->pos))
+			iter->advanced = false;
+
+		BUG_ON(iter->advanced);
+		BUG_ON(!k.k);
+		break;
+	}
+
+	iter->pos = k.k->p;
+	btree_path_set_should_be_locked(iter->path);
+out_no_locked:
+	bch2_btree_iter_verify(iter);
+
+	return k;
+}
+
+/**
+ * bch2_btree_iter_next() - returns first key greater than iterator's current
+ * position
+ * @iter:	iterator to peek from
+ *
+ * Returns:	key if found, or an error extractable with bkey_err().
+ */
+struct bkey_s_c bch2_btree_iter_next(struct btree_iter *iter)
+{
+	if (!bch2_btree_iter_advance(iter))
+		return bkey_s_c_null;
+
+	return bch2_btree_iter_peek(iter);
+}
+
+/**
+ * bch2_btree_iter_peek_prev() - returns first key less than or equal to
+ * iterator's current position
+ * @iter:	iterator to peek from
+ *
+ * Returns:	key if found, or an error extractable with bkey_err().
+ */
+struct bkey_s_c bch2_btree_iter_peek_prev(struct btree_iter *iter)
+{
+	struct btree_trans *trans = iter->trans;
+	struct bpos search_key = iter->pos;
+	struct btree_path *saved_path = NULL;
+	struct bkey_s_c k;
+	struct bkey saved_k;
+	const struct bch_val *saved_v;
+	int ret;
+
+	EBUG_ON(iter->path->cached || iter->path->level);
+	EBUG_ON(iter->flags & BTREE_ITER_WITH_UPDATES);
+
+	if (iter->flags & BTREE_ITER_WITH_JOURNAL)
+		return bkey_s_c_err(-EIO);
+
+	bch2_btree_iter_verify(iter);
+	bch2_btree_iter_verify_entry_exit(iter);
+
+	if (iter->flags & BTREE_ITER_FILTER_SNAPSHOTS)
+		search_key.snapshot = U32_MAX;
+
+	while (1) {
+		iter->path = bch2_btree_path_set_pos(trans, iter->path, search_key,
+						iter->flags & BTREE_ITER_INTENT,
+						btree_iter_ip_allocated(iter));
+
+		ret = bch2_btree_path_traverse(trans, iter->path, iter->flags);
+		if (unlikely(ret)) {
+			/* ensure that iter->k is consistent with iter->pos: */
+			bch2_btree_iter_set_pos(iter, iter->pos);
+			k = bkey_s_c_err(ret);
+			goto out_no_locked;
+		}
+
+		k = btree_path_level_peek(trans, iter->path,
+					  &iter->path->l[0], &iter->k);
+		if (!k.k ||
+		    ((iter->flags & BTREE_ITER_IS_EXTENTS)
+		     ? bpos_ge(bkey_start_pos(k.k), search_key)
+		     : bpos_gt(k.k->p, search_key)))
+			k = btree_path_level_prev(trans, iter->path,
+						  &iter->path->l[0], &iter->k);
+
+		if (likely(k.k)) {
+			if (iter->flags & BTREE_ITER_FILTER_SNAPSHOTS) {
+				if (k.k->p.snapshot == iter->snapshot)
+					goto got_key;
+
+				/*
+				 * If we have a saved candidate, and we're no
+				 * longer at the same _key_ (not pos), return
+				 * that candidate
+				 */
+				if (saved_path && !bkey_eq(k.k->p, saved_k.p)) {
+					bch2_path_put_nokeep(trans, iter->path,
+						      iter->flags & BTREE_ITER_INTENT);
+					iter->path = saved_path;
+					saved_path = NULL;
+					iter->k	= saved_k;
+					k.v	= saved_v;
+					goto got_key;
+				}
+
+				if (bch2_snapshot_is_ancestor(iter->trans->c,
+							      iter->snapshot,
+							      k.k->p.snapshot)) {
+					if (saved_path)
+						bch2_path_put_nokeep(trans, saved_path,
+						      iter->flags & BTREE_ITER_INTENT);
+					saved_path = btree_path_clone(trans, iter->path,
+								iter->flags & BTREE_ITER_INTENT);
+					saved_k = *k.k;
+					saved_v = k.v;
+				}
+
+				search_key = bpos_predecessor(k.k->p);
+				continue;
+			}
+got_key:
+			if (bkey_whiteout(k.k) &&
+			    !(iter->flags & BTREE_ITER_ALL_SNAPSHOTS)) {
+				search_key = bkey_predecessor(iter, k.k->p);
+				if (iter->flags & BTREE_ITER_FILTER_SNAPSHOTS)
+					search_key.snapshot = U32_MAX;
+				continue;
+			}
+
+			break;
+		} else if (likely(!bpos_eq(iter->path->l[0].b->data->min_key, POS_MIN))) {
+			/* Advance to previous leaf node: */
+			search_key = bpos_predecessor(iter->path->l[0].b->data->min_key);
+		} else {
+			/* Start of btree: */
+			bch2_btree_iter_set_pos(iter, POS_MIN);
+			k = bkey_s_c_null;
+			goto out_no_locked;
+		}
+	}
+
+	EBUG_ON(bkey_gt(bkey_start_pos(k.k), iter->pos));
+
+	/* Extents can straddle iter->pos: */
+	if (bkey_lt(k.k->p, iter->pos))
+		iter->pos = k.k->p;
+
+	if (iter->flags & BTREE_ITER_FILTER_SNAPSHOTS)
+		iter->pos.snapshot = iter->snapshot;
+
+	btree_path_set_should_be_locked(iter->path);
+out_no_locked:
+	if (saved_path)
+		bch2_path_put_nokeep(trans, saved_path, iter->flags & BTREE_ITER_INTENT);
+
+	bch2_btree_iter_verify_entry_exit(iter);
+	bch2_btree_iter_verify(iter);
+
+	return k;
+}
+
+/**
+ * bch2_btree_iter_prev() - returns first key less than iterator's current
+ * position
+ * @iter:	iterator to peek from
+ *
+ * Returns:	key if found, or an error extractable with bkey_err().
+ */
+struct bkey_s_c bch2_btree_iter_prev(struct btree_iter *iter)
+{
+	if (!bch2_btree_iter_rewind(iter))
+		return bkey_s_c_null;
+
+	return bch2_btree_iter_peek_prev(iter);
+}
+
+struct bkey_s_c bch2_btree_iter_peek_slot(struct btree_iter *iter)
+{
+	struct btree_trans *trans = iter->trans;
+	struct bpos search_key;
+	struct bkey_s_c k;
+	int ret;
+
+	bch2_btree_iter_verify(iter);
+	bch2_btree_iter_verify_entry_exit(iter);
+	EBUG_ON(iter->flags & BTREE_ITER_ALL_LEVELS);
+	EBUG_ON(iter->path->level && (iter->flags & BTREE_ITER_WITH_KEY_CACHE));
+
+	/* extents can't span inode numbers: */
+	if ((iter->flags & BTREE_ITER_IS_EXTENTS) &&
+	    unlikely(iter->pos.offset == KEY_OFFSET_MAX)) {
+		if (iter->pos.inode == KEY_INODE_MAX)
+			return bkey_s_c_null;
+
+		bch2_btree_iter_set_pos(iter, bpos_nosnap_successor(iter->pos));
+	}
+
+	search_key = btree_iter_search_key(iter);
+	iter->path = bch2_btree_path_set_pos(trans, iter->path, search_key,
+					iter->flags & BTREE_ITER_INTENT,
+					btree_iter_ip_allocated(iter));
+
+	ret = bch2_btree_path_traverse(trans, iter->path, iter->flags);
+	if (unlikely(ret)) {
+		k = bkey_s_c_err(ret);
+		goto out_no_locked;
+	}
+
+	if ((iter->flags & BTREE_ITER_CACHED) ||
+	    !(iter->flags & (BTREE_ITER_IS_EXTENTS|BTREE_ITER_FILTER_SNAPSHOTS))) {
+		struct bkey_i *next_update;
+
+		if ((next_update = btree_trans_peek_updates(iter)) &&
+		    bpos_eq(next_update->k.p, iter->pos)) {
+			iter->k = next_update->k;
+			k = bkey_i_to_s_c(next_update);
+			goto out;
+		}
+
+		if (unlikely(iter->flags & BTREE_ITER_WITH_JOURNAL) &&
+		    (k = btree_trans_peek_slot_journal(trans, iter)).k)
+			goto out;
+
+		if (unlikely(iter->flags & BTREE_ITER_WITH_KEY_CACHE) &&
+		    (k = btree_trans_peek_key_cache(iter, iter->pos)).k) {
+			if (!bkey_err(k))
+				iter->k = *k.k;
+			/* We're not returning a key from iter->path: */
+			goto out_no_locked;
+		}
+
+		k = bch2_btree_path_peek_slot(iter->path, &iter->k);
+		if (unlikely(!k.k))
+			goto out_no_locked;
+	} else {
+		struct bpos next;
+		struct bpos end = iter->pos;
+
+		if (iter->flags & BTREE_ITER_IS_EXTENTS)
+			end.offset = U64_MAX;
+
+		EBUG_ON(iter->path->level);
+
+		if (iter->flags & BTREE_ITER_INTENT) {
+			struct btree_iter iter2;
+
+			bch2_trans_copy_iter(&iter2, iter);
+			k = bch2_btree_iter_peek_upto(&iter2, end);
+
+			if (k.k && !bkey_err(k)) {
+				iter->k = iter2.k;
+				k.k = &iter->k;
+			}
+			bch2_trans_iter_exit(trans, &iter2);
+		} else {
+			struct bpos pos = iter->pos;
+
+			k = bch2_btree_iter_peek_upto(iter, end);
+			if (unlikely(bkey_err(k)))
+				bch2_btree_iter_set_pos(iter, pos);
+			else
+				iter->pos = pos;
+		}
+
+		if (unlikely(bkey_err(k)))
+			goto out_no_locked;
+
+		next = k.k ? bkey_start_pos(k.k) : POS_MAX;
+
+		if (bkey_lt(iter->pos, next)) {
+			bkey_init(&iter->k);
+			iter->k.p = iter->pos;
+
+			if (iter->flags & BTREE_ITER_IS_EXTENTS) {
+				bch2_key_resize(&iter->k,
+						min_t(u64, KEY_SIZE_MAX,
+						      (next.inode == iter->pos.inode
+						       ? next.offset
+						       : KEY_OFFSET_MAX) -
+						      iter->pos.offset));
+				EBUG_ON(!iter->k.size);
+			}
+
+			k = (struct bkey_s_c) { &iter->k, NULL };
+		}
+	}
+out:
+	btree_path_set_should_be_locked(iter->path);
+out_no_locked:
+	bch2_btree_iter_verify_entry_exit(iter);
+	bch2_btree_iter_verify(iter);
+	ret = bch2_btree_iter_verify_ret(iter, k);
+	if (unlikely(ret))
+		return bkey_s_c_err(ret);
+
+	return k;
+}
+
+struct bkey_s_c bch2_btree_iter_next_slot(struct btree_iter *iter)
+{
+	if (!bch2_btree_iter_advance(iter))
+		return bkey_s_c_null;
+
+	return bch2_btree_iter_peek_slot(iter);
+}
+
+struct bkey_s_c bch2_btree_iter_prev_slot(struct btree_iter *iter)
+{
+	if (!bch2_btree_iter_rewind(iter))
+		return bkey_s_c_null;
+
+	return bch2_btree_iter_peek_slot(iter);
+}
+
+struct bkey_s_c bch2_btree_iter_peek_and_restart_outlined(struct btree_iter *iter)
+{
+	struct bkey_s_c k;
+
+	while (btree_trans_too_many_iters(iter->trans) ||
+	       (k = bch2_btree_iter_peek_type(iter, iter->flags),
+		bch2_err_matches(bkey_err(k), BCH_ERR_transaction_restart)))
+		bch2_trans_begin(iter->trans);
+
+	return k;
+}
+
+/* new transactional stuff: */
+
+#ifdef CONFIG_BCACHEFS_DEBUG
+static void btree_trans_verify_sorted_refs(struct btree_trans *trans)
+{
+	struct btree_path *path;
+	unsigned i;
+
+	BUG_ON(trans->nr_sorted != hweight64(trans->paths_allocated));
+
+	trans_for_each_path(trans, path) {
+		BUG_ON(path->sorted_idx >= trans->nr_sorted);
+		BUG_ON(trans->sorted[path->sorted_idx] != path->idx);
+	}
+
+	for (i = 0; i < trans->nr_sorted; i++) {
+		unsigned idx = trans->sorted[i];
+
+		EBUG_ON(!(trans->paths_allocated & (1ULL << idx)));
+		BUG_ON(trans->paths[idx].sorted_idx != i);
+	}
+}
+
+static void btree_trans_verify_sorted(struct btree_trans *trans)
+{
+	struct btree_path *path, *prev = NULL;
+	unsigned i;
+
+	if (!bch2_debug_check_iterators)
+		return;
+
+	trans_for_each_path_inorder(trans, path, i) {
+		if (prev && btree_path_cmp(prev, path) > 0) {
+			__bch2_dump_trans_paths_updates(trans, true);
+			panic("trans paths out of order!\n");
+		}
+		prev = path;
+	}
+}
+#else
+static inline void btree_trans_verify_sorted_refs(struct btree_trans *trans) {}
+static inline void btree_trans_verify_sorted(struct btree_trans *trans) {}
+#endif
+
+void __bch2_btree_trans_sort_paths(struct btree_trans *trans)
+{
+	int i, l = 0, r = trans->nr_sorted, inc = 1;
+	bool swapped;
+
+	btree_trans_verify_sorted_refs(trans);
+
+	if (trans->paths_sorted)
+		goto out;
+
+	/*
+	 * Cocktail shaker sort: this is efficient because iterators will be
+	 * mostly sorted.
+	 */
+	do {
+		swapped = false;
+
+		for (i = inc > 0 ? l : r - 2;
+		     i + 1 < r && i >= l;
+		     i += inc) {
+			if (btree_path_cmp(trans->paths + trans->sorted[i],
+					   trans->paths + trans->sorted[i + 1]) > 0) {
+				swap(trans->sorted[i], trans->sorted[i + 1]);
+				trans->paths[trans->sorted[i]].sorted_idx = i;
+				trans->paths[trans->sorted[i + 1]].sorted_idx = i + 1;
+				swapped = true;
+			}
+		}
+
+		if (inc > 0)
+			--r;
+		else
+			l++;
+		inc = -inc;
+	} while (swapped);
+
+	trans->paths_sorted = true;
+out:
+	btree_trans_verify_sorted(trans);
+}
+
+static inline void btree_path_list_remove(struct btree_trans *trans,
+					  struct btree_path *path)
+{
+	unsigned i;
+
+	EBUG_ON(path->sorted_idx >= trans->nr_sorted);
+#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
+	trans->nr_sorted--;
+	memmove_u64s_down_small(trans->sorted + path->sorted_idx,
+				trans->sorted + path->sorted_idx + 1,
+				DIV_ROUND_UP(trans->nr_sorted - path->sorted_idx, 8));
+#else
+	array_remove_item(trans->sorted, trans->nr_sorted, path->sorted_idx);
+#endif
+	for (i = path->sorted_idx; i < trans->nr_sorted; i++)
+		trans->paths[trans->sorted[i]].sorted_idx = i;
+
+	path->sorted_idx = U8_MAX;
+}
+
+static inline void btree_path_list_add(struct btree_trans *trans,
+				       struct btree_path *pos,
+				       struct btree_path *path)
+{
+	unsigned i;
+
+	path->sorted_idx = pos ? pos->sorted_idx + 1 : trans->nr_sorted;
+
+#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
+	memmove_u64s_up_small(trans->sorted + path->sorted_idx + 1,
+			      trans->sorted + path->sorted_idx,
+			      DIV_ROUND_UP(trans->nr_sorted - path->sorted_idx, 8));
+	trans->nr_sorted++;
+	trans->sorted[path->sorted_idx] = path->idx;
+#else
+	array_insert_item(trans->sorted, trans->nr_sorted, path->sorted_idx, path->idx);
+#endif
+
+	for (i = path->sorted_idx; i < trans->nr_sorted; i++)
+		trans->paths[trans->sorted[i]].sorted_idx = i;
+
+	btree_trans_verify_sorted_refs(trans);
+}
+
+void bch2_trans_iter_exit(struct btree_trans *trans, struct btree_iter *iter)
+{
+	if (iter->update_path)
+		bch2_path_put_nokeep(trans, iter->update_path,
+			      iter->flags & BTREE_ITER_INTENT);
+	if (iter->path)
+		bch2_path_put(trans, iter->path,
+			      iter->flags & BTREE_ITER_INTENT);
+	if (iter->key_cache_path)
+		bch2_path_put(trans, iter->key_cache_path,
+			      iter->flags & BTREE_ITER_INTENT);
+	iter->path = NULL;
+	iter->update_path = NULL;
+	iter->key_cache_path = NULL;
+}
+
+void bch2_trans_iter_init_outlined(struct btree_trans *trans,
+			  struct btree_iter *iter,
+			  enum btree_id btree_id, struct bpos pos,
+			  unsigned flags)
+{
+	bch2_trans_iter_init_common(trans, iter, btree_id, pos, 0, 0,
+			       bch2_btree_iter_flags(trans, btree_id, flags),
+			       _RET_IP_);
+}
+
+void bch2_trans_node_iter_init(struct btree_trans *trans,
+			       struct btree_iter *iter,
+			       enum btree_id btree_id,
+			       struct bpos pos,
+			       unsigned locks_want,
+			       unsigned depth,
+			       unsigned flags)
+{
+	flags |= BTREE_ITER_NOT_EXTENTS;
+	flags |= __BTREE_ITER_ALL_SNAPSHOTS;
+	flags |= BTREE_ITER_ALL_SNAPSHOTS;
+
+	bch2_trans_iter_init_common(trans, iter, btree_id, pos, locks_want, depth,
+			       __bch2_btree_iter_flags(trans, btree_id, flags),
+			       _RET_IP_);
+
+	iter->min_depth	= depth;
+
+	BUG_ON(iter->path->locks_want	 < min(locks_want, BTREE_MAX_DEPTH));
+	BUG_ON(iter->path->level	!= depth);
+	BUG_ON(iter->min_depth		!= depth);
+}
+
+void bch2_trans_copy_iter(struct btree_iter *dst, struct btree_iter *src)
+{
+	*dst = *src;
+	if (src->path)
+		__btree_path_get(src->path, src->flags & BTREE_ITER_INTENT);
+	if (src->update_path)
+		__btree_path_get(src->update_path, src->flags & BTREE_ITER_INTENT);
+	dst->key_cache_path = NULL;
+}
+
+void *__bch2_trans_kmalloc(struct btree_trans *trans, size_t size)
+{
+	unsigned new_top = trans->mem_top + size;
+	size_t old_bytes = trans->mem_bytes;
+	size_t new_bytes = roundup_pow_of_two(new_top);
+	int ret;
+	void *new_mem;
+	void *p;
+
+	trans->mem_max = max(trans->mem_max, new_top);
+
+	WARN_ON_ONCE(new_bytes > BTREE_TRANS_MEM_MAX);
+
+	new_mem = krealloc(trans->mem, new_bytes, GFP_NOWAIT|__GFP_NOWARN);
+	if (unlikely(!new_mem)) {
+		bch2_trans_unlock(trans);
+
+		new_mem = krealloc(trans->mem, new_bytes, GFP_KERNEL);
+		if (!new_mem && new_bytes <= BTREE_TRANS_MEM_MAX) {
+			new_mem = mempool_alloc(&trans->c->btree_trans_mem_pool, GFP_KERNEL);
+			new_bytes = BTREE_TRANS_MEM_MAX;
+			kfree(trans->mem);
+		}
+
+		if (!new_mem)
+			return ERR_PTR(-BCH_ERR_ENOMEM_trans_kmalloc);
+
+		trans->mem = new_mem;
+		trans->mem_bytes = new_bytes;
+
+		ret = bch2_trans_relock(trans);
+		if (ret)
+			return ERR_PTR(ret);
+	}
+
+	trans->mem = new_mem;
+	trans->mem_bytes = new_bytes;
+
+	if (old_bytes) {
+		trace_and_count(trans->c, trans_restart_mem_realloced, trans, _RET_IP_, new_bytes);
+		return ERR_PTR(btree_trans_restart(trans, BCH_ERR_transaction_restart_mem_realloced));
+	}
+
+	p = trans->mem + trans->mem_top;
+	trans->mem_top += size;
+	memset(p, 0, size);
+	return p;
+}
+
+static inline void check_srcu_held_too_long(struct btree_trans *trans)
+{
+	WARN(trans->srcu_held && time_after(jiffies, trans->srcu_lock_time + HZ * 10),
+	     "btree trans held srcu lock (delaying memory reclaim) for %lu seconds",
+	     (jiffies - trans->srcu_lock_time) / HZ);
+}
+
+void bch2_trans_srcu_unlock(struct btree_trans *trans)
+{
+	if (trans->srcu_held) {
+		struct bch_fs *c = trans->c;
+		struct btree_path *path;
+
+		trans_for_each_path(trans, path)
+			if (path->cached && !btree_node_locked(path, 0))
+				path->l[0].b = ERR_PTR(-BCH_ERR_no_btree_node_srcu_reset);
+
+		check_srcu_held_too_long(trans);
+		srcu_read_unlock(&c->btree_trans_barrier, trans->srcu_idx);
+		trans->srcu_held = false;
+	}
+}
+
+void bch2_trans_srcu_lock(struct btree_trans *trans)
+{
+	if (!trans->srcu_held) {
+		trans->srcu_idx = srcu_read_lock(&trans->c->btree_trans_barrier);
+		trans->srcu_lock_time	= jiffies;
+		trans->srcu_held = true;
+	}
+}
+
+/**
+ * bch2_trans_begin() - reset a transaction after a interrupted attempt
+ * @trans: transaction to reset
+ *
+ * Returns:	current restart counter, to be used with trans_was_restarted()
+ *
+ * While iterating over nodes or updating nodes a attempt to lock a btree node
+ * may return BCH_ERR_transaction_restart when the trylock fails. When this
+ * occurs bch2_trans_begin() should be called and the transaction retried.
+ */
+u32 bch2_trans_begin(struct btree_trans *trans)
+{
+	struct btree_path *path;
+	u64 now;
+
+	bch2_trans_reset_updates(trans);
+
+	trans->restart_count++;
+	trans->mem_top			= 0;
+
+	trans_for_each_path(trans, path) {
+		path->should_be_locked = false;
+
+		/*
+		 * If the transaction wasn't restarted, we're presuming to be
+		 * doing something new: dont keep iterators excpt the ones that
+		 * are in use - except for the subvolumes btree:
+		 */
+		if (!trans->restarted && path->btree_id != BTREE_ID_subvolumes)
+			path->preserve = false;
+
+		/*
+		 * XXX: we probably shouldn't be doing this if the transaction
+		 * was restarted, but currently we still overflow transaction
+		 * iterators if we do that
+		 */
+		if (!path->ref && !path->preserve)
+			__bch2_path_free(trans, path);
+		else
+			path->preserve = false;
+	}
+
+	now = local_clock();
+	if (!trans->restarted &&
+	    (need_resched() ||
+	     now - trans->last_begin_time > BTREE_TRANS_MAX_LOCK_HOLD_TIME_NS)) {
+		drop_locks_do(trans, (cond_resched(), 0));
+		now = local_clock();
+	}
+	trans->last_begin_time = now;
+
+	if (unlikely(trans->srcu_held &&
+		     time_after(jiffies, trans->srcu_lock_time + msecs_to_jiffies(10))))
+		bch2_trans_srcu_unlock(trans);
+
+	trans->last_begin_ip = _RET_IP_;
+	if (trans->restarted) {
+		bch2_btree_path_traverse_all(trans);
+		trans->notrace_relock_fail = false;
+	}
+
+	return trans->restart_count;
+}
+
+static struct btree_trans *bch2_trans_alloc(struct bch_fs *c)
+{
+	struct btree_trans *trans;
+
+	if (IS_ENABLED(__KERNEL__)) {
+		trans = this_cpu_xchg(c->btree_trans_bufs->trans, NULL);
+		if (trans)
+			return trans;
+	}
+
+	trans = mempool_alloc(&c->btree_trans_pool, GFP_NOFS);
+	/*
+	 * paths need to be zeroed, bch2_check_for_deadlock looks at
+	 * paths in other threads
+	 */
+	memset(&trans->paths, 0, sizeof(trans->paths));
+	return trans;
+}
+
+const char *bch2_btree_transaction_fns[BCH_TRANSACTIONS_NR];
+
+unsigned bch2_trans_get_fn_idx(const char *fn)
+{
+	unsigned i;
+
+	for (i = 0; i < ARRAY_SIZE(bch2_btree_transaction_fns); i++)
+		if (!bch2_btree_transaction_fns[i] ||
+		    bch2_btree_transaction_fns[i] == fn) {
+			bch2_btree_transaction_fns[i] = fn;
+			return i;
+		}
+
+	pr_warn_once("BCH_TRANSACTIONS_NR not big enough!");
+	return i;
+}
+
+struct btree_trans *__bch2_trans_get(struct bch_fs *c, unsigned fn_idx)
+	__acquires(&c->btree_trans_barrier)
+{
+	struct btree_trans *trans;
+	struct btree_transaction_stats *s;
+
+	trans = bch2_trans_alloc(c);
+
+	memset(trans, 0, sizeof(*trans));
+	trans->c		= c;
+	trans->fn		= fn_idx < ARRAY_SIZE(bch2_btree_transaction_fns)
+		? bch2_btree_transaction_fns[fn_idx] : NULL;
+	trans->last_begin_time	= local_clock();
+	trans->fn_idx		= fn_idx;
+	trans->locking_wait.task = current;
+	trans->journal_replay_not_finished =
+		unlikely(!test_bit(JOURNAL_REPLAY_DONE, &c->journal.flags)) &&
+		atomic_inc_not_zero(&c->journal_keys.ref);
+	closure_init_stack(&trans->ref);
+
+	s = btree_trans_stats(trans);
+	if (s && s->max_mem) {
+		unsigned expected_mem_bytes = roundup_pow_of_two(s->max_mem);
+
+		trans->mem = kmalloc(expected_mem_bytes, GFP_KERNEL);
+
+		if (!unlikely(trans->mem)) {
+			trans->mem = mempool_alloc(&c->btree_trans_mem_pool, GFP_KERNEL);
+			trans->mem_bytes = BTREE_TRANS_MEM_MAX;
+		} else {
+			trans->mem_bytes = expected_mem_bytes;
+		}
+	}
+
+	if (s) {
+		trans->nr_max_paths = s->nr_max_paths;
+		trans->wb_updates_size = s->wb_updates_size;
+	}
+
+	trans->srcu_idx		= srcu_read_lock(&c->btree_trans_barrier);
+	trans->srcu_lock_time	= jiffies;
+	trans->srcu_held	= true;
+
+	if (IS_ENABLED(CONFIG_BCACHEFS_DEBUG_TRANSACTIONS)) {
+		struct btree_trans *pos;
+
+		seqmutex_lock(&c->btree_trans_lock);
+		list_for_each_entry(pos, &c->btree_trans_list, list) {
+			/*
+			 * We'd much prefer to be stricter here and completely
+			 * disallow multiple btree_trans in the same thread -
+			 * but the data move path calls bch2_write when we
+			 * already have a btree_trans initialized.
+			 */
+			BUG_ON(trans->locking_wait.task->pid == pos->locking_wait.task->pid &&
+			       bch2_trans_locked(pos));
+
+			if (trans->locking_wait.task->pid < pos->locking_wait.task->pid) {
+				list_add_tail(&trans->list, &pos->list);
+				goto list_add_done;
+			}
+		}
+		list_add_tail(&trans->list, &c->btree_trans_list);
+list_add_done:
+		seqmutex_unlock(&c->btree_trans_lock);
+	}
+
+	return trans;
+}
+
+static void check_btree_paths_leaked(struct btree_trans *trans)
+{
+#ifdef CONFIG_BCACHEFS_DEBUG
+	struct bch_fs *c = trans->c;
+	struct btree_path *path;
+
+	trans_for_each_path(trans, path)
+		if (path->ref)
+			goto leaked;
+	return;
+leaked:
+	bch_err(c, "btree paths leaked from %s!", trans->fn);
+	trans_for_each_path(trans, path)
+		if (path->ref)
+			printk(KERN_ERR "  btree %s %pS\n",
+			       bch2_btree_id_str(path->btree_id),
+			       (void *) path->ip_allocated);
+	/* Be noisy about this: */
+	bch2_fatal_error(c);
+#endif
+}
+
+void bch2_trans_put(struct btree_trans *trans)
+	__releases(&c->btree_trans_barrier)
+{
+	struct btree_insert_entry *i;
+	struct bch_fs *c = trans->c;
+	struct btree_transaction_stats *s = btree_trans_stats(trans);
+
+	bch2_trans_unlock(trans);
+
+	if (IS_ENABLED(CONFIG_BCACHEFS_DEBUG_TRANSACTIONS)) {
+		seqmutex_lock(&c->btree_trans_lock);
+		list_del(&trans->list);
+		seqmutex_unlock(&c->btree_trans_lock);
+	}
+
+	closure_sync(&trans->ref);
+
+	if (s)
+		s->max_mem = max(s->max_mem, trans->mem_max);
+
+	trans_for_each_update(trans, i)
+		__btree_path_put(i->path, true);
+	trans->nr_updates		= 0;
+
+	check_btree_paths_leaked(trans);
+
+	if (trans->srcu_held) {
+		check_srcu_held_too_long(trans);
+		srcu_read_unlock(&c->btree_trans_barrier, trans->srcu_idx);
+	}
+
+	kfree(trans->extra_journal_entries.data);
+
+	if (trans->fs_usage_deltas) {
+		if (trans->fs_usage_deltas->size + sizeof(trans->fs_usage_deltas) ==
+		    REPLICAS_DELTA_LIST_MAX)
+			mempool_free(trans->fs_usage_deltas,
+				     &c->replicas_delta_pool);
+		else
+			kfree(trans->fs_usage_deltas);
+	}
+
+	if (unlikely(trans->journal_replay_not_finished))
+		bch2_journal_keys_put(c);
+
+	if (trans->mem_bytes == BTREE_TRANS_MEM_MAX)
+		mempool_free(trans->mem, &c->btree_trans_mem_pool);
+	else
+		kfree(trans->mem);
+
+	/* Userspace doesn't have a real percpu implementation: */
+	if (IS_ENABLED(__KERNEL__))
+		trans = this_cpu_xchg(c->btree_trans_bufs->trans, trans);
+	if (trans)
+		mempool_free(trans, &c->btree_trans_pool);
+}
+
+static void __maybe_unused
+bch2_btree_bkey_cached_common_to_text(struct printbuf *out,
+				      struct btree_bkey_cached_common *b)
+{
+	struct six_lock_count c = six_lock_counts(&b->lock);
+	struct task_struct *owner;
+	pid_t pid;
+
+	rcu_read_lock();
+	owner = READ_ONCE(b->lock.owner);
+	pid = owner ? owner->pid : 0;
+	rcu_read_unlock();
+
+	prt_tab(out);
+	prt_printf(out, "%px %c l=%u %s:", b, b->cached ? 'c' : 'b',
+		   b->level, bch2_btree_id_str(b->btree_id));
+	bch2_bpos_to_text(out, btree_node_pos(b));
+
+	prt_tab(out);
+	prt_printf(out, " locks %u:%u:%u held by pid %u",
+		   c.n[0], c.n[1], c.n[2], pid);
+}
+
+void bch2_btree_trans_to_text(struct printbuf *out, struct btree_trans *trans)
+{
+	struct btree_path *path;
+	struct btree_bkey_cached_common *b;
+	static char lock_types[] = { 'r', 'i', 'w' };
+	unsigned l, idx;
+
+	if (!out->nr_tabstops) {
+		printbuf_tabstop_push(out, 16);
+		printbuf_tabstop_push(out, 32);
+	}
+
+	prt_printf(out, "%i %s\n", trans->locking_wait.task->pid, trans->fn);
+
+	trans_for_each_path_safe(trans, path, idx) {
+		if (!path->nodes_locked)
+			continue;
+
+		prt_printf(out, "  path %u %c l=%u %s:",
+		       path->idx,
+		       path->cached ? 'c' : 'b',
+		       path->level,
+		       bch2_btree_id_str(path->btree_id));
+		bch2_bpos_to_text(out, path->pos);
+		prt_newline(out);
+
+		for (l = 0; l < BTREE_MAX_DEPTH; l++) {
+			if (btree_node_locked(path, l) &&
+			    !IS_ERR_OR_NULL(b = (void *) READ_ONCE(path->l[l].b))) {
+				prt_printf(out, "    %c l=%u ",
+					   lock_types[btree_node_locked_type(path, l)], l);
+				bch2_btree_bkey_cached_common_to_text(out, b);
+				prt_newline(out);
+			}
+		}
+	}
+
+	b = READ_ONCE(trans->locking);
+	if (b) {
+		prt_printf(out, "  blocked for %lluus on",
+			   div_u64(local_clock() - trans->locking_wait.start_time,
+				   1000));
+		prt_newline(out);
+		prt_printf(out, "    %c", lock_types[trans->locking_wait.lock_want]);
+		bch2_btree_bkey_cached_common_to_text(out, b);
+		prt_newline(out);
+	}
+}
+
+void bch2_fs_btree_iter_exit(struct bch_fs *c)
+{
+	struct btree_transaction_stats *s;
+	struct btree_trans *trans;
+	int cpu;
+
+	trans = list_first_entry_or_null(&c->btree_trans_list, struct btree_trans, list);
+	if (trans)
+		panic("%s leaked btree_trans\n", trans->fn);
+
+	if (c->btree_trans_bufs)
+		for_each_possible_cpu(cpu)
+			kfree(per_cpu_ptr(c->btree_trans_bufs, cpu)->trans);
+	free_percpu(c->btree_trans_bufs);
+
+	for (s = c->btree_transaction_stats;
+	     s < c->btree_transaction_stats + ARRAY_SIZE(c->btree_transaction_stats);
+	     s++) {
+		kfree(s->max_paths_text);
+		bch2_time_stats_exit(&s->lock_hold_times);
+	}
+
+	if (c->btree_trans_barrier_initialized)
+		cleanup_srcu_struct(&c->btree_trans_barrier);
+	mempool_exit(&c->btree_trans_mem_pool);
+	mempool_exit(&c->btree_trans_pool);
+}
+
+void bch2_fs_btree_iter_init_early(struct bch_fs *c)
+{
+	struct btree_transaction_stats *s;
+
+	for (s = c->btree_transaction_stats;
+	     s < c->btree_transaction_stats + ARRAY_SIZE(c->btree_transaction_stats);
+	     s++) {
+		bch2_time_stats_init(&s->lock_hold_times);
+		mutex_init(&s->lock);
+	}
+
+	INIT_LIST_HEAD(&c->btree_trans_list);
+	seqmutex_init(&c->btree_trans_lock);
+}
+
+int bch2_fs_btree_iter_init(struct bch_fs *c)
+{
+	int ret;
+
+	c->btree_trans_bufs = alloc_percpu(struct btree_trans_buf);
+	if (!c->btree_trans_bufs)
+		return -ENOMEM;
+
+	ret   = mempool_init_kmalloc_pool(&c->btree_trans_pool, 1,
+					  sizeof(struct btree_trans)) ?:
+		mempool_init_kmalloc_pool(&c->btree_trans_mem_pool, 1,
+					  BTREE_TRANS_MEM_MAX) ?:
+		init_srcu_struct(&c->btree_trans_barrier);
+	if (!ret)
+		c->btree_trans_barrier_initialized = true;
+	return ret;
+}