Update bcachefs sources to bee7b5a4fa21 bcachefs: Pin btree cache in ram for random access in fsck

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

36 files changed, 859 insertions, 376 deletions

diff --git a/.bcachefs_revision b/.bcachefs_revision
index d3c500bc..1aa1789b 100644
--- a/.bcachefs_revision
+++ b/.bcachefs_revision
@@ -1 +1 @@
-50847e296b34efabe199e408ec4d72f10a866c39
+bee7b5a4fa2135c9ec9d1c9424018ee494500bb5
diff --git a/include/linux/sort.h b/include/linux/sort.h
index afea0445..17c6ba34 100644
--- a/include/linux/sort.h
+++ b/include/linux/sort.h
@@ -2,6 +2,12 @@
 #define _LINUX_SORT_H
 
 #include <stdlib.h>
+#include <linux/types.h>
+
+void sort_r(void *base, size_t num, size_t size,
+	    cmp_r_func_t cmp_func,
+	    swap_r_func_t swap_func,
+	    const void *priv);
 
 static inline void sort(void *base, size_t num, size_t size,
 			int (*cmp_func)(const void *, const void *),
diff --git a/libbcachefs/backpointers.c b/libbcachefs/backpointers.c
index b4dc319b..23fe9378 100644
--- a/libbcachefs/backpointers.c
+++ b/libbcachefs/backpointers.c
@@ -129,8 +129,7 @@ static noinline int backpointer_mod_err(struct btree_trans *trans,
 	printbuf_exit(&buf);
 
 	if (c->curr_recovery_pass > BCH_RECOVERY_PASS_check_extents_to_backpointers) {
-		bch2_inconsistent_error(c);
-		return -EIO;
+		return bch2_inconsistent_error(c) ? BCH_ERR_erofs_unfixed_errors : 0;
 	} else {
 		return 0;
 	}
@@ -553,60 +552,61 @@ static inline struct bbpos bp_to_bbpos(struct bch_backpointer bp)
 	};
 }
 
-static size_t btree_nodes_fit_in_ram(struct bch_fs *c)
+static u64 mem_may_pin_bytes(struct bch_fs *c)
 {
 	struct sysinfo i;
-	u64 mem_bytes;
-
 	si_meminfo(&i);
-	mem_bytes = i.totalram * i.mem_unit;
-	return div_u64(mem_bytes >> 1, c->opts.btree_node_size);
+
+	u64 mem_bytes = i.totalram * i.mem_unit;
+	return div_u64(mem_bytes * c->opts.fsck_memory_usage_percent, 100);
+}
+
+static size_t btree_nodes_fit_in_ram(struct bch_fs *c)
+{
+	return div_u64(mem_may_pin_bytes(c), c->opts.btree_node_size);
 }
 
 static int bch2_get_btree_in_memory_pos(struct btree_trans *trans,
-					unsigned btree_leaf_mask,
-					unsigned btree_interior_mask,
+					u64 btree_leaf_mask,
+					u64 btree_interior_mask,
 					struct bbpos start, struct bbpos *end)
 {
-	struct btree_iter iter;
-	struct bkey_s_c k;
-	size_t btree_nodes = btree_nodes_fit_in_ram(trans->c);
-	enum btree_id btree;
+	struct bch_fs *c = trans->c;
+	s64 mem_may_pin = mem_may_pin_bytes(c);
 	int ret = 0;
 
-	for (btree = start.btree; btree < BTREE_ID_NR && !ret; btree++) {
-		unsigned depth = ((1U << btree) & btree_leaf_mask) ? 1 : 2;
+	btree_interior_mask |= btree_leaf_mask;
+
+	c->btree_cache.pinned_nodes_leaf_mask		= btree_leaf_mask;
+	c->btree_cache.pinned_nodes_interior_mask	= btree_interior_mask;
+	c->btree_cache.pinned_nodes_start		= start;
+	c->btree_cache.pinned_nodes_end			= *end = BBPOS_MAX;
+
+	for (enum btree_id btree = start.btree;
+	     btree < BTREE_ID_NR && !ret;
+	     btree++) {
+		unsigned depth = ((1U << btree) & btree_leaf_mask) ? 0 : 1;
+		struct btree_iter iter;
+		struct btree *b;
 
 		if (!((1U << btree) & btree_leaf_mask) &&
 		    !((1U << btree) & btree_interior_mask))
 			continue;
 
-		bch2_trans_node_iter_init(trans, &iter, btree,
-					  btree == start.btree ? start.pos : POS_MIN,
-					  0, depth, 0);
-		/*
-		 * for_each_btree_key_contineu() doesn't check the return value
-		 * from bch2_btree_iter_advance(), which is needed when
-		 * iterating over interior nodes where we'll see keys at
-		 * SPOS_MAX:
-		 */
-		do {
-			k = __bch2_btree_iter_peek_and_restart(trans, &iter, 0);
-			ret = bkey_err(k);
-			if (!k.k || ret)
-				break;
-
-			--btree_nodes;
-			if (!btree_nodes) {
-				*end = BBPOS(btree, k.k->p);
+		__for_each_btree_node(trans, iter, btree,
+				      btree == start.btree ? start.pos : POS_MIN,
+				      0, depth, BTREE_ITER_PREFETCH, b, ret) {
+			mem_may_pin -= btree_buf_bytes(b);
+			if (mem_may_pin <= 0) {
+				c->btree_cache.pinned_nodes_end = *end =
+					BBPOS(btree, b->key.k.p);
 				bch2_trans_iter_exit(trans, &iter);
 				return 0;
 			}
-		} while (bch2_btree_iter_advance(&iter));
+		}
 		bch2_trans_iter_exit(trans, &iter);
 	}
 
-	*end = BBPOS_MAX;
 	return ret;
 }
 
@@ -664,62 +664,6 @@ static int bch2_check_extents_to_backpointers_pass(struct btree_trans *trans,
 	return 0;
 }
 
-static struct bpos bucket_pos_to_bp_safe(const struct bch_fs *c,
-					 struct bpos bucket)
-{
-	return bch2_dev_exists2(c, bucket.inode)
-		? bucket_pos_to_bp(c, bucket, 0)
-		: bucket;
-}
-
-static int bch2_get_alloc_in_memory_pos(struct btree_trans *trans,
-					struct bpos start, struct bpos *end)
-{
-	struct btree_iter alloc_iter;
-	struct btree_iter bp_iter;
-	struct bkey_s_c alloc_k, bp_k;
-	size_t btree_nodes = btree_nodes_fit_in_ram(trans->c);
-	bool alloc_end = false, bp_end = false;
-	int ret = 0;
-
-	bch2_trans_node_iter_init(trans, &alloc_iter, BTREE_ID_alloc,
-				  start, 0, 1, 0);
-	bch2_trans_node_iter_init(trans, &bp_iter, BTREE_ID_backpointers,
-				  bucket_pos_to_bp_safe(trans->c, start), 0, 1, 0);
-	while (1) {
-		alloc_k = !alloc_end
-			? __bch2_btree_iter_peek_and_restart(trans, &alloc_iter, 0)
-			: bkey_s_c_null;
-		bp_k = !bp_end
-			? __bch2_btree_iter_peek_and_restart(trans, &bp_iter, 0)
-			: bkey_s_c_null;
-
-		ret = bkey_err(alloc_k) ?: bkey_err(bp_k);
-		if ((!alloc_k.k && !bp_k.k) || ret) {
-			*end = SPOS_MAX;
-			break;
-		}
-
-		--btree_nodes;
-		if (!btree_nodes) {
-			*end = alloc_k.k ? alloc_k.k->p : SPOS_MAX;
-			break;
-		}
-
-		if (bpos_lt(alloc_iter.pos, SPOS_MAX) &&
-		    bpos_lt(bucket_pos_to_bp_safe(trans->c, alloc_iter.pos), bp_iter.pos)) {
-			if (!bch2_btree_iter_advance(&alloc_iter))
-				alloc_end = true;
-		} else {
-			if (!bch2_btree_iter_advance(&bp_iter))
-				bp_end = true;
-		}
-	}
-	bch2_trans_iter_exit(trans, &bp_iter);
-	bch2_trans_iter_exit(trans, &alloc_iter);
-	return ret;
-}
-
 int bch2_check_extents_to_backpointers(struct bch_fs *c)
 {
 	struct btree_trans *trans = bch2_trans_get(c);
@@ -730,10 +674,16 @@ int bch2_check_extents_to_backpointers(struct bch_fs *c)
 	bkey_init(&s.last_flushed.k->k);
 
 	while (1) {
-		ret = bch2_get_alloc_in_memory_pos(trans, s.bucket_start, &s.bucket_end);
+		struct bbpos end;
+		ret = bch2_get_btree_in_memory_pos(trans,
+				BIT_ULL(BTREE_ID_backpointers),
+				BIT_ULL(BTREE_ID_backpointers),
+				BBPOS(BTREE_ID_backpointers, s.bucket_start), &end);
 		if (ret)
 			break;
 
+		s.bucket_end = end.pos;
+
 		if ( bpos_eq(s.bucket_start, POS_MIN) &&
 		    !bpos_eq(s.bucket_end, SPOS_MAX))
 			bch_verbose(c, "%s(): alloc info does not fit in ram, running in multiple passes with %zu nodes per pass",
@@ -761,6 +711,9 @@ int bch2_check_extents_to_backpointers(struct bch_fs *c)
 	bch2_trans_put(trans);
 	bch2_bkey_buf_exit(&s.last_flushed, c);
 
+	c->btree_cache.pinned_nodes_leaf_mask = 0;
+	c->btree_cache.pinned_nodes_interior_mask = 0;
+
 	bch_err_fn(c, ret);
 	return ret;
 }
@@ -866,6 +819,9 @@ int bch2_check_backpointers_to_extents(struct bch_fs *c)
 	}
 	bch2_trans_put(trans);
 
+	c->btree_cache.pinned_nodes_leaf_mask = 0;
+	c->btree_cache.pinned_nodes_interior_mask = 0;
+
 	bch_err_fn(c, ret);
 	return ret;
 }
diff --git a/libbcachefs/bbpos_types.h b/libbcachefs/bbpos_types.h
index 5198e94c..f6389334 100644
--- a/libbcachefs/bbpos_types.h
+++ b/libbcachefs/bbpos_types.h
@@ -13,6 +13,6 @@ static inline struct bbpos BBPOS(enum btree_id btree, struct bpos pos)
 }
 
 #define BBPOS_MIN	BBPOS(0, POS_MIN)
-#define BBPOS_MAX	BBPOS(BTREE_ID_NR - 1, POS_MAX)
+#define BBPOS_MAX	BBPOS(BTREE_ID_NR - 1, SPOS_MAX)
 
 #endif /* _BCACHEFS_BBPOS_TYPES_H */
diff --git a/libbcachefs/bcachefs.h b/libbcachefs/bcachefs.h
index 70369495..b53b321b 100644
--- a/libbcachefs/bcachefs.h
+++ b/libbcachefs/bcachefs.h
@@ -505,6 +505,7 @@ enum gc_phase {
 	GC_PHASE_BTREE_deleted_inodes,
 	GC_PHASE_BTREE_logged_ops,
 	GC_PHASE_BTREE_rebalance_work,
+	GC_PHASE_BTREE_subvolume_children,
 
 	GC_PHASE_PENDING_DELETE,
 };
diff --git a/libbcachefs/bcachefs_format.h b/libbcachefs/bcachefs_format.h
index 14f61361..1bb24aa7 100644
--- a/libbcachefs/bcachefs_format.h
+++ b/libbcachefs/bcachefs_format.h
@@ -840,7 +840,9 @@ struct bch_sb_field_downgrade {
 	x(snapshot_skiplists,		BCH_VERSION(1,  1))		\
 	x(deleted_inodes,		BCH_VERSION(1,  2))		\
 	x(rebalance_work,		BCH_VERSION(1,  3))		\
-	x(member_seq,			BCH_VERSION(1,  4))
+	x(member_seq,			BCH_VERSION(1,  4))		\
+	x(subvolume_fs_parent,		BCH_VERSION(1,  5))		\
+	x(btree_subvolume_children,	BCH_VERSION(1,  6))
 
 enum bcachefs_metadata_version {
 	bcachefs_metadata_version_min = 9,
@@ -1488,7 +1490,9 @@ enum btree_id_flags {
 	  BIT_ULL(KEY_TYPE_logged_op_truncate)|					\
 	  BIT_ULL(KEY_TYPE_logged_op_finsert))					\
 	x(rebalance_work,	18,	BTREE_ID_SNAPSHOT_FIELD,		\
-	  BIT_ULL(KEY_TYPE_set)|BIT_ULL(KEY_TYPE_cookie))
+	  BIT_ULL(KEY_TYPE_set)|BIT_ULL(KEY_TYPE_cookie))			\
+	x(subvolume_children,	19,	0,					\
+	  BIT_ULL(KEY_TYPE_set))
 
 enum btree_id {
 #define x(name, nr, ...) BTREE_ID_##name = nr,
diff --git a/libbcachefs/bkey_methods.h b/libbcachefs/bkey_methods.h
index 03efe8ee..f8217b24 100644
--- a/libbcachefs/bkey_methods.h
+++ b/libbcachefs/bkey_methods.h
@@ -78,6 +78,7 @@ bool bch2_bkey_merge(struct bch_fs *, struct bkey_s, struct bkey_s_c);
 
 enum btree_update_flags {
 	__BTREE_UPDATE_INTERNAL_SNAPSHOT_NODE = __BTREE_ITER_FLAGS_END,
+	__BTREE_UPDATE_SNAPSHOT_WHITEOUT_CHECKS_DONE,
 	__BTREE_UPDATE_NOJOURNAL,
 	__BTREE_UPDATE_KEY_CACHE_RECLAIM,
 
@@ -91,6 +92,8 @@ enum btree_update_flags {
 };
 
 #define BTREE_UPDATE_INTERNAL_SNAPSHOT_NODE (1U << __BTREE_UPDATE_INTERNAL_SNAPSHOT_NODE)
+#define BTREE_UPDATE_SNAPSHOT_WHITEOUT_CHECKS_DONE	\
+					(1U << __BTREE_UPDATE_SNAPSHOT_WHITEOUT_CHECKS_DONE)
 #define BTREE_UPDATE_NOJOURNAL		(1U << __BTREE_UPDATE_NOJOURNAL)
 #define BTREE_UPDATE_KEY_CACHE_RECLAIM	(1U << __BTREE_UPDATE_KEY_CACHE_RECLAIM)
 
diff --git a/libbcachefs/btree_cache.c b/libbcachefs/btree_cache.c
index 9b7ea122..79975046 100644
--- a/libbcachefs/btree_cache.c
+++ b/libbcachefs/btree_cache.c
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 
 #include "bcachefs.h"
+#include "bbpos.h"
 #include "bkey_buf.h"
 #include "btree_cache.h"
 #include "btree_io.h"
@@ -208,6 +209,18 @@ static int __btree_node_reclaim(struct bch_fs *c, struct btree *b, bool flush)
 	int ret = 0;
 
 	lockdep_assert_held(&bc->lock);
+
+	struct bbpos pos = BBPOS(b->c.btree_id, b->key.k.p);
+
+	u64 mask = b->c.level
+		? bc->pinned_nodes_interior_mask
+		: bc->pinned_nodes_leaf_mask;
+
+	if ((mask & BIT_ULL(b->c.btree_id)) &&
+	    bbpos_cmp(bc->pinned_nodes_start, pos) < 0 &&
+	    bbpos_cmp(bc->pinned_nodes_end, pos) >= 0)
+		return -BCH_ERR_ENOMEM_btree_node_reclaim;
+
 wait_on_io:
 	if (b->flags & ((1U << BTREE_NODE_dirty)|
 			(1U << BTREE_NODE_read_in_flight)|
@@ -905,7 +918,7 @@ retry:
 
 	if (unlikely(btree_node_read_error(b))) {
 		six_unlock_type(&b->c.lock, lock_type);
-		return ERR_PTR(-EIO);
+		return ERR_PTR(-BCH_ERR_btree_node_read_error);
 	}
 
 	EBUG_ON(b->c.btree_id != path->btree_id);
@@ -996,7 +1009,7 @@ struct btree *bch2_btree_node_get(struct btree_trans *trans, struct btree_path *
 
 	if (unlikely(btree_node_read_error(b))) {
 		six_unlock_type(&b->c.lock, lock_type);
-		return ERR_PTR(-EIO);
+		return ERR_PTR(-BCH_ERR_btree_node_read_error);
 	}
 
 	EBUG_ON(b->c.btree_id != path->btree_id);
@@ -1079,7 +1092,7 @@ lock_node:
 
 	if (unlikely(btree_node_read_error(b))) {
 		six_unlock_read(&b->c.lock);
-		b = ERR_PTR(-EIO);
+		b = ERR_PTR(-BCH_ERR_btree_node_read_error);
 		goto out;
 	}
 
diff --git a/libbcachefs/btree_gc.c b/libbcachefs/btree_gc.c
index eb92526b..6c52f116 100644
--- a/libbcachefs/btree_gc.c
+++ b/libbcachefs/btree_gc.c
@@ -407,7 +407,7 @@ again:
 		printbuf_reset(&buf);
 		bch2_bkey_val_to_text(&buf, c, bkey_i_to_s_c(cur_k.k));
 
-		if (mustfix_fsck_err_on(ret == -EIO, c,
+		if (mustfix_fsck_err_on(bch2_err_matches(ret, EIO), c,
 				btree_node_unreadable,
 				"Topology repair: unreadable btree node at btree %s level %u:\n"
 				"  %s",
@@ -979,7 +979,7 @@ static int bch2_gc_btree_init_recurse(struct btree_trans *trans, struct btree *b
 						false);
 			ret = PTR_ERR_OR_ZERO(child);
 
-			if (ret == -EIO) {
+			if (bch2_err_matches(ret, EIO)) {
 				bch2_topology_error(c);
 
 				if (__fsck_err(c,
diff --git a/libbcachefs/btree_io.c b/libbcachefs/btree_io.c
index 61b60938..86415701 100644
--- a/libbcachefs/btree_io.c
+++ b/libbcachefs/btree_io.c
@@ -581,8 +581,7 @@ static int __btree_err(int ret,
 		break;
 	case -BCH_ERR_btree_node_read_err_bad_node:
 		bch2_print_string_as_lines(KERN_ERR, out.buf);
-		bch2_topology_error(c);
-		ret = bch2_run_explicit_recovery_pass(c, BCH_RECOVERY_PASS_check_topology) ?: -EIO;
+		ret = bch2_topology_error(c);
 		break;
 	case -BCH_ERR_btree_node_read_err_incompatible:
 		bch2_print_string_as_lines(KERN_ERR, out.buf);
@@ -1737,7 +1736,7 @@ static int __bch2_btree_root_read(struct btree_trans *trans, enum btree_id id,
 		list_move(&b->list, &c->btree_cache.freeable);
 		mutex_unlock(&c->btree_cache.lock);
 
-		ret = -EIO;
+		ret = -BCH_ERR_btree_node_read_error;
 		goto err;
 	}
 
@@ -1841,7 +1840,7 @@ static void btree_node_write_work(struct work_struct *work)
 		bch2_dev_list_has_dev(wbio->wbio.failed, ptr->dev));
 
 	if (!bch2_bkey_nr_ptrs(bkey_i_to_s_c(&wbio->key))) {
-		ret = -BCH_ERR_btree_write_all_failed;
+		ret = -BCH_ERR_btree_node_write_all_failed;
 		goto err;
 	}
 
diff --git a/libbcachefs/btree_iter.c b/libbcachefs/btree_iter.c
index 3aac6ed5..07b1de5c 100644
--- a/libbcachefs/btree_iter.c
+++ b/libbcachefs/btree_iter.c
@@ -2303,7 +2303,7 @@ struct bkey_s_c bch2_btree_iter_peek_prev(struct btree_iter *iter)
 		btree_iter_path(trans, iter)->level);
 
 	if (iter->flags & BTREE_ITER_WITH_JOURNAL)
-		return bkey_s_c_err(-EIO);
+		return bkey_s_c_err(-BCH_ERR_btree_iter_with_journal_not_supported);
 
 	bch2_btree_iter_verify(iter);
 	bch2_btree_iter_verify_entry_exit(iter);
@@ -2501,6 +2501,7 @@ struct bkey_s_c bch2_btree_iter_peek_slot(struct btree_iter *iter)
 			k = bch2_btree_iter_peek_upto(&iter2, end);
 
 			if (k.k && !bkey_err(k)) {
+				swap(iter->key_cache_path, iter2.key_cache_path);
 				iter->k = iter2.k;
 				k.k = &iter->k;
 			}
@@ -2760,6 +2761,9 @@ void bch2_trans_copy_iter(struct btree_iter *dst, struct btree_iter *src)
 	struct btree_trans *trans = src->trans;
 
 	*dst = *src;
+#ifdef TRACK_PATH_ALLOCATED
+	dst->ip_allocated = _RET_IP_;
+#endif
 	if (src->path)
 		__btree_path_get(trans->paths + src->path, src->flags & BTREE_ITER_INTENT);
 	if (src->update_path)
diff --git a/libbcachefs/btree_types.h b/libbcachefs/btree_types.h
index 0d5eecbd..b2ebf143 100644
--- a/libbcachefs/btree_types.h
+++ b/libbcachefs/btree_types.h
@@ -6,6 +6,7 @@
 #include <linux/list.h>
 #include <linux/rhashtable.h>
 
+#include "bbpos_types.h"
 #include "btree_key_cache_types.h"
 #include "buckets_types.h"
 #include "errcode.h"
@@ -173,6 +174,11 @@ struct btree_cache {
 	 */
 	struct task_struct	*alloc_lock;
 	struct closure_waitlist	alloc_wait;
+
+	struct bbpos		pinned_nodes_start;
+	struct bbpos		pinned_nodes_end;
+	u64			pinned_nodes_leaf_mask;
+	u64			pinned_nodes_interior_mask;
 };
 
 struct btree_node_iter {
@@ -654,6 +660,7 @@ const char *bch2_btree_node_type_str(enum btree_node_type);
 	 BIT_ULL(BKEY_TYPE_inodes)|			\
 	 BIT_ULL(BKEY_TYPE_stripes)|			\
 	 BIT_ULL(BKEY_TYPE_reflink)|			\
+	 BIT_ULL(BKEY_TYPE_subvolumes)|			\
 	 BIT_ULL(BKEY_TYPE_btree))
 
 #define BTREE_NODE_TYPE_HAS_ATOMIC_TRIGGERS		\
@@ -727,7 +734,7 @@ struct btree_root {
 	__BKEY_PADDED(key, BKEY_BTREE_PTR_VAL_U64s_MAX);
 	u8			level;
 	u8			alive;
-	s8			error;
+	s16			error;
 };
 
 enum btree_gc_coalesce_fail_reason {
diff --git a/libbcachefs/btree_update.c b/libbcachefs/btree_update.c
index e5193116..d3d625d4 100644
--- a/libbcachefs/btree_update.c
+++ b/libbcachefs/btree_update.c
@@ -82,40 +82,169 @@ static noinline int extent_back_merge(struct btree_trans *trans,
 	return 0;
 }
 
+static struct bkey_s_c peek_slot_including_whiteouts(struct btree_trans *trans, struct btree_iter *iter,
+						     enum btree_id btree, struct bpos pos)
+{
+	struct bkey_s_c k;
+	int ret;
+
+	for_each_btree_key_norestart(trans, *iter, btree, pos,
+			   BTREE_ITER_ALL_SNAPSHOTS|
+			   BTREE_ITER_NOPRESERVE, k, ret) {
+		if (!bkey_eq(k.k->p, pos))
+			break;
+		if (bch2_snapshot_is_ancestor(trans->c, pos.snapshot, k.k->p.snapshot))
+			return k;
+	}
+	bch2_trans_iter_exit(trans, iter);
+
+	return ret ? bkey_s_c_err(ret) : bkey_s_c_null;
+}
+
 /*
  * When deleting, check if we need to emit a whiteout (because we're overwriting
  * something in an ancestor snapshot)
  */
-static int need_whiteout_for_snapshot(struct btree_trans *trans,
-				      enum btree_id btree_id, struct bpos pos)
+static int need_whiteout_for_snapshot(struct btree_trans *trans, enum btree_id btree, struct bpos pos)
+{
+	pos.snapshot = bch2_snapshot_parent(trans->c, pos.snapshot);
+	if (!pos.snapshot)
+		return 0;
+
+	struct btree_iter iter;
+	struct bkey_s_c k = peek_slot_including_whiteouts(trans, &iter, btree, pos);
+	int ret = bkey_err(k) ?: k.k && !bkey_whiteout(k.k);
+	bch2_trans_iter_exit(trans, &iter);
+
+	return ret;
+}
+
+/*
+ * We're overwriting a key at @pos in snapshot @snapshot, so we need to insert a
+ * whiteout: that might be in @snapshot, or if there are overwites in sibling
+ * snapshots, find the common ancestor where @pos is overwritten in every
+ * descendent and insert the whiteout there - which might be at @pos.
+ */
+static int delete_interior_snapshot_key(struct btree_trans *trans,
+					enum btree_id btree,
+					struct bpos whiteout, bool deleting,
+					struct bpos overwrite, bool old_is_whiteout)
 {
+	struct bch_fs *c = trans->c;
+	struct bpos orig_whiteout = whiteout, sib = whiteout;
 	struct btree_iter iter;
 	struct bkey_s_c k;
-	u32 snapshot = pos.snapshot;
 	int ret;
 
-	if (!bch2_snapshot_parent(trans->c, pos.snapshot))
-		return 0;
+	sib.snapshot = bch2_snapshot_sibling(c, sib.snapshot);
 
-	pos.snapshot++;
+	for_each_btree_key_norestart(trans, iter, btree, sib,
+				     BTREE_ITER_ALL_SNAPSHOTS|BTREE_ITER_INTENT, k, ret) {
+		BUG_ON(bpos_gt(k.k->p, overwrite));
 
-	for_each_btree_key_norestart(trans, iter, btree_id, pos,
-			   BTREE_ITER_ALL_SNAPSHOTS|
-			   BTREE_ITER_NOPRESERVE, k, ret) {
-		if (!bkey_eq(k.k->p, pos))
+		if (bpos_lt(k.k->p, sib)) /* unrelated branch - skip */
+			continue;
+		if (bpos_gt(k.k->p, sib)) /* did not find @sib */
 			break;
 
-		if (bch2_snapshot_is_ancestor(trans->c, snapshot,
-					      k.k->p.snapshot)) {
-			ret = !bkey_whiteout(k.k);
+		/* @overwrite is also written in @sib, now check parent */
+		whiteout.snapshot = bch2_snapshot_parent(c, whiteout.snapshot);
+		if (bpos_eq(whiteout, overwrite))
 			break;
-		}
+
+		sib = whiteout;
+		sib.snapshot = bch2_snapshot_sibling(c, sib.snapshot);
 	}
-	bch2_trans_iter_exit(trans, &iter);
 
+	if (ret)
+		goto err;
+
+	if (!deleting && bpos_eq(whiteout, orig_whiteout))
+		goto out;
+
+	if (!bpos_eq(iter.pos, whiteout)) {
+		bch2_trans_iter_exit(trans, &iter);
+		bch2_trans_iter_init(trans, &iter, btree, whiteout, BTREE_ITER_INTENT);
+		k = bch2_btree_iter_peek_slot(&iter);
+		ret = bkey_err(k);
+		if (ret)
+			goto err;
+	}
+
+	iter.flags &= ~BTREE_ITER_ALL_SNAPSHOTS;
+	iter.flags |= BTREE_ITER_FILTER_SNAPSHOTS;
+
+	struct bkey_i *delete = bch2_trans_kmalloc(trans, sizeof(*delete));
+	ret = PTR_ERR_OR_ZERO(delete);
+	if (ret)
+		goto err;
+
+	bkey_init(&delete->k);
+	delete->k.p = whiteout;
+
+	ret = !bpos_eq(whiteout, overwrite)
+		? !old_is_whiteout
+		: need_whiteout_for_snapshot(trans, btree, whiteout);
+	if (ret < 0)
+		goto err;
+	if (ret)
+		delete->k.type = KEY_TYPE_whiteout;
+
+	ret = bch2_trans_update(trans, &iter, delete,
+				BTREE_UPDATE_INTERNAL_SNAPSHOT_NODE|
+				BTREE_UPDATE_SNAPSHOT_WHITEOUT_CHECKS_DONE);
+out:
+err:
+	bch2_trans_iter_exit(trans, &iter);
 	return ret;
 }
 
+/*
+ * We're overwriting a key in a snapshot that has ancestors: if we're
+ * overwriting a key in a different snapshot, we need to check if it is now
+ * fully overritten and can be deleted, and if we're deleting a key in the
+ * current snapshot we need to check if we need to leave a whiteout.
+ */
+static noinline int
+overwrite_interior_snapshot_key(struct btree_trans *trans,
+				struct btree_iter *iter,
+				struct bkey_i *k)
+{
+	struct bkey_s_c old = bch2_btree_iter_peek_slot(iter);
+
+	int ret = bkey_err(old);
+	if (ret)
+		return ret;
+
+	if (!bkey_deleted(old.k)) {
+		if (old.k->p.snapshot != k->k.p.snapshot) {
+			/*
+			 * We're overwriting a key in a different snapshot:
+			 * check if it's also been overwritten in siblings
+			 */
+			ret = delete_interior_snapshot_key(trans, iter->btree_id,
+							   k->k.p,   bkey_deleted(&k->k),
+							   old.k->p, bkey_whiteout(old.k));
+			if (ret)
+				return ret;
+			if (bkey_deleted(&k->k))
+				return 1;
+		} else if (bkey_deleted(&k->k)) {
+			/*
+			 * We're deleting a key in the current snapshot:
+			 * check if we need to leave a whiteout
+			 */
+			ret = need_whiteout_for_snapshot(trans, iter->btree_id, k->k.p);
+			if (unlikely(ret < 0))
+				return ret;
+			if (ret)
+				k->k.type = KEY_TYPE_whiteout;
+		}
+	}
+
+	return 0;
+}
+
 int __bch2_insert_snapshot_whiteouts(struct btree_trans *trans,
 				   enum btree_id id,
 				   struct bpos old_pos,
@@ -503,32 +632,29 @@ static noinline int bch2_trans_update_get_key_cache(struct btree_trans *trans,
 int __must_check bch2_trans_update(struct btree_trans *trans, struct btree_iter *iter,
 				   struct bkey_i *k, enum btree_update_flags flags)
 {
-	btree_path_idx_t path_idx = iter->update_path ?: iter->path;
-	int ret;
-
 	if (iter->flags & BTREE_ITER_IS_EXTENTS)
 		return bch2_trans_update_extent(trans, iter, k, flags);
 
-	if (bkey_deleted(&k->k) &&
-	    !(flags & BTREE_UPDATE_KEY_CACHE_RECLAIM) &&
-	    (iter->flags & BTREE_ITER_FILTER_SNAPSHOTS)) {
-		ret = need_whiteout_for_snapshot(trans, iter->btree_id, k->k.p);
-		if (unlikely(ret < 0))
-			return ret;
-
+	if (!(flags & (BTREE_UPDATE_SNAPSHOT_WHITEOUT_CHECKS_DONE|
+		       BTREE_UPDATE_KEY_CACHE_RECLAIM)) &&
+	    (iter->flags & BTREE_ITER_FILTER_SNAPSHOTS) &&
+	    bch2_snapshot_parent(trans->c, k->k.p.snapshot)) {
+		int ret = overwrite_interior_snapshot_key(trans, iter, k);
 		if (ret)
-			k->k.type = KEY_TYPE_whiteout;
+			return ret < 0 ? ret : 0;
 	}
 
 	/*
 	 * Ensure that updates to cached btrees go to the key cache:
 	 */
+	btree_path_idx_t path_idx = iter->update_path ?: iter->path;
 	struct btree_path *path = trans->paths + path_idx;
+
 	if (!(flags & BTREE_UPDATE_KEY_CACHE_RECLAIM) &&
 	    !path->cached &&
 	    !path->level &&
 	    btree_id_cached(trans->c, path->btree_id)) {
-		ret = bch2_trans_update_get_key_cache(trans, iter, path);
+		int ret = bch2_trans_update_get_key_cache(trans, iter, path);
 		if (ret)
 			return ret;
 
@@ -790,6 +916,27 @@ int bch2_btree_delete_range(struct bch_fs *c, enum btree_id id,
 int bch2_btree_bit_mod(struct btree_trans *trans, enum btree_id btree,
 		       struct bpos pos, bool set)
 {
+	struct bkey_i *k = bch2_trans_kmalloc(trans, sizeof(*k));
+	int ret = PTR_ERR_OR_ZERO(k);
+	if (ret)
+		return ret;
+
+	bkey_init(&k->k);
+	k->k.type = set ? KEY_TYPE_set : KEY_TYPE_deleted;
+	k->k.p = pos;
+
+	struct btree_iter iter;
+	bch2_trans_iter_init(trans, &iter, btree, pos, BTREE_ITER_INTENT);
+
+	ret   = bch2_btree_iter_traverse(&iter) ?:
+		bch2_trans_update(trans, &iter, k, 0);
+	bch2_trans_iter_exit(trans, &iter);
+	return ret;
+}
+
+int bch2_btree_bit_mod_buffered(struct btree_trans *trans, enum btree_id btree,
+				struct bpos pos, bool set)
+{
 	struct bkey_i k;
 
 	bkey_init(&k.k);
diff --git a/libbcachefs/btree_update.h b/libbcachefs/btree_update.h
index b9382b7b..cc7c53e8 100644
--- a/libbcachefs/btree_update.h
+++ b/libbcachefs/btree_update.h
@@ -63,11 +63,12 @@ int bch2_btree_delete_range(struct bch_fs *, enum btree_id,
 			    struct bpos, struct bpos, unsigned, u64 *);
 
 int bch2_btree_bit_mod(struct btree_trans *, enum btree_id, struct bpos, bool);
+int bch2_btree_bit_mod_buffered(struct btree_trans *, enum btree_id, struct bpos, bool);
 
 static inline int bch2_btree_delete_at_buffered(struct btree_trans *trans,
 						enum btree_id btree, struct bpos pos)
 {
-	return bch2_btree_bit_mod(trans, btree, pos, false);
+	return bch2_btree_bit_mod_buffered(trans, btree, pos, false);
 }
 
 int __bch2_insert_snapshot_whiteouts(struct btree_trans *, enum btree_id,
diff --git a/libbcachefs/btree_update_interior.c b/libbcachefs/btree_update_interior.c
index 030291cc..5fbea33f 100644
--- a/libbcachefs/btree_update_interior.c
+++ b/libbcachefs/btree_update_interior.c
@@ -1844,8 +1844,7 @@ int __bch2_foreground_maybe_merge(struct btree_trans *trans,
 			__func__, buf1.buf, buf2.buf);
 		printbuf_exit(&buf1);
 		printbuf_exit(&buf2);
-		bch2_topology_error(c);
-		ret = -EIO;
+		ret = bch2_topology_error(c);
 		goto err;
 	}
 
diff --git a/libbcachefs/buckets.c b/libbcachefs/buckets.c
index 7dca10ba..c2f46b26 100644
--- a/libbcachefs/buckets.c
+++ b/libbcachefs/buckets.c
@@ -1053,7 +1053,8 @@ int bch2_trigger_extent(struct btree_trans *trans,
 			  (int) bch2_bkey_needs_rebalance(c, old);
 
 		if (mod) {
-			int ret = bch2_btree_bit_mod(trans, BTREE_ID_rebalance_work, new.k->p, mod > 0);
+			int ret = bch2_btree_bit_mod_buffered(trans, BTREE_ID_rebalance_work,
+							      new.k->p, mod > 0);
 			if (ret)
 				return ret;
 		}
diff --git a/libbcachefs/dirent.c b/libbcachefs/dirent.c
index 97773cff..b5ee11b5 100644
--- a/libbcachefs/dirent.c
+++ b/libbcachefs/dirent.c
@@ -201,17 +201,17 @@ static struct bkey_i_dirent *dirent_create_key(struct btree_trans *trans,
 }
 
 int bch2_dirent_create_snapshot(struct btree_trans *trans,
-			u64 dir, u32 snapshot,
+			u32 dir_subvol, u64 dir, u32 snapshot,
 			const struct bch_hash_info *hash_info,
 			u8 type, const struct qstr *name, u64 dst_inum,
 			u64 *dir_offset,
 			bch_str_hash_flags_t str_hash_flags)
 {
-	subvol_inum zero_inum = { 0 };
+	subvol_inum dir_inum = { .subvol = dir_subvol, .inum = dir };
 	struct bkey_i_dirent *dirent;
 	int ret;
 
-	dirent = dirent_create_key(trans, zero_inum, type, name, dst_inum);
+	dirent = dirent_create_key(trans, dir_inum, type, name, dst_inum);
 	ret = PTR_ERR_OR_ZERO(dirent);
 	if (ret)
 		return ret;
@@ -220,7 +220,7 @@ int bch2_dirent_create_snapshot(struct btree_trans *trans,
 	dirent->k.p.snapshot	= snapshot;
 
 	ret = bch2_hash_set_in_snapshot(trans, bch2_dirent_hash_desc, hash_info,
-					zero_inum, snapshot,
+					dir_inum, snapshot,
 					&dirent->k_i, str_hash_flags,
 					BTREE_UPDATE_INTERNAL_SNAPSHOT_NODE);
 	*dir_offset = dirent->k.p.offset;
@@ -522,7 +522,7 @@ int bch2_empty_dir_snapshot(struct btree_trans *trans, u64 dir, u32 snapshot)
 			   SPOS(dir, 0, snapshot),
 			   POS(dir, U64_MAX), 0, k, ret)
 		if (k.k->type == KEY_TYPE_dirent) {
-			ret = -ENOTEMPTY;
+			ret = -BCH_ERR_ENOTEMPTY_dir_not_empty;
 			break;
 		}
 	bch2_trans_iter_exit(trans, &iter);
diff --git a/libbcachefs/dirent.h b/libbcachefs/dirent.h
index f1dd7208..34cb8e18 100644
--- a/libbcachefs/dirent.h
+++ b/libbcachefs/dirent.h
@@ -35,7 +35,7 @@ static inline unsigned dirent_val_u64s(unsigned len)
 int bch2_dirent_read_target(struct btree_trans *, subvol_inum,
 			    struct bkey_s_c_dirent, subvol_inum *);
 
-int bch2_dirent_create_snapshot(struct btree_trans *, u64, u32,
+int bch2_dirent_create_snapshot(struct btree_trans *, u32, u64, u32,
 			const struct bch_hash_info *, u8,
 			const struct qstr *, u64, u64 *,
 			bch_str_hash_flags_t);
diff --git a/libbcachefs/errcode.h b/libbcachefs/errcode.h
index 3fd33b30..fe3fc14d 100644
--- a/libbcachefs/errcode.h
+++ b/libbcachefs/errcode.h
@@ -109,6 +109,8 @@
 	x(ENOENT,			ENOENT_dirent_doesnt_match_inode)	\
 	x(ENOENT,			ENOENT_dev_not_found)			\
 	x(ENOENT,			ENOENT_dev_idx_not_found)		\
+	x(ENOTEMPTY,			ENOTEMPTY_dir_not_empty)		\
+	x(ENOTEMPTY,			ENOTEMPTY_subvol_not_empty)		\
 	x(0,				open_buckets_empty)			\
 	x(0,				freelist_empty)				\
 	x(BCH_ERR_freelist_empty,	no_buckets_found)			\
@@ -178,6 +180,7 @@
 	x(EINVAL,			opt_parse_error)			\
 	x(EINVAL,			remove_with_metadata_missing_unimplemented)\
 	x(EINVAL,			remove_would_lose_data)			\
+	x(EINVAL,			btree_iter_with_journal_not_supported)	\
 	x(EROFS,			erofs_trans_commit)			\
 	x(EROFS,			erofs_no_writes)			\
 	x(EROFS,			erofs_journal_err)			\
@@ -227,7 +230,10 @@
 	x(BCH_ERR_operation_blocked,    nocow_lock_blocked)			\
 	x(EIO,				btree_node_read_err)			\
 	x(EIO,				sb_not_downgraded)			\
-	x(EIO,				btree_write_all_failed)			\
+	x(EIO,				btree_node_write_all_failed)		\
+	x(EIO,				btree_node_read_error)			\
+	x(EIO,				btree_node_read_validate_error)		\
+	x(EIO,				btree_need_topology_repair)		\
 	x(BCH_ERR_btree_node_read_err,	btree_node_read_err_fixable)		\
 	x(BCH_ERR_btree_node_read_err,	btree_node_read_err_want_retry)		\
 	x(BCH_ERR_btree_node_read_err,	btree_node_read_err_must_retry)		\
diff --git a/libbcachefs/error.c b/libbcachefs/error.c
index 70a12539..8ae95b21 100644
--- a/libbcachefs/error.c
+++ b/libbcachefs/error.c
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 #include "bcachefs.h"
 #include "error.h"
+#include "recovery.h"
 #include "super.h"
 #include <linux/thread_with_file.h>
 
@@ -25,11 +26,16 @@ bool bch2_inconsistent_error(struct bch_fs *c)
 	}
 }
 
-void bch2_topology_error(struct bch_fs *c)
+int bch2_topology_error(struct bch_fs *c)
 {
 	set_bit(BCH_FS_topology_error, &c->flags);
-	if (!test_bit(BCH_FS_fsck_running, &c->flags))
+	if (!test_bit(BCH_FS_fsck_running, &c->flags)) {
 		bch2_inconsistent_error(c);
+		return -BCH_ERR_btree_need_topology_repair;
+	} else {
+		return bch2_run_explicit_recovery_pass(c, BCH_RECOVERY_PASS_check_topology) ?:
+			-BCH_ERR_btree_node_read_validate_error;
+	}
 }
 
 void bch2_fatal_error(struct bch_fs *c)
diff --git a/libbcachefs/error.h b/libbcachefs/error.h
index fec17d13..94491190 100644
--- a/libbcachefs/error.h
+++ b/libbcachefs/error.h
@@ -30,7 +30,7 @@ struct work_struct;
 
 bool bch2_inconsistent_error(struct bch_fs *);
 
-void bch2_topology_error(struct bch_fs *);
+int bch2_topology_error(struct bch_fs *);
 
 #define bch2_fs_inconsistent(c, ...)					\
 ({									\
diff --git a/libbcachefs/fs-common.c b/libbcachefs/fs-common.c
index 523507e3..3d43c036 100644
--- a/libbcachefs/fs-common.c
+++ b/libbcachefs/fs-common.c
@@ -107,6 +107,7 @@ int bch2_create_trans(struct btree_trans *trans,
 		u32 new_subvol, dir_snapshot;
 
 		ret = bch2_subvolume_create(trans, new_inode->bi_inum,
+					    dir.subvol,
 					    snapshot_src.subvol,
 					    &new_subvol, &snapshot,
 					    (flags & BCH_CREATE_SNAPSHOT_RO) != 0);
@@ -242,7 +243,7 @@ int bch2_unlink_trans(struct btree_trans *trans,
 		      struct bch_inode_unpacked *dir_u,
 		      struct bch_inode_unpacked *inode_u,
 		      const struct qstr *name,
-		      bool deleting_snapshot)
+		      bool deleting_subvol)
 {
 	struct bch_fs *c = trans->c;
 	struct btree_iter dir_iter = { NULL };
@@ -270,18 +271,25 @@ int bch2_unlink_trans(struct btree_trans *trans,
 	if (ret)
 		goto err;
 
-	if (!deleting_snapshot && S_ISDIR(inode_u->bi_mode)) {
+	if (!deleting_subvol && S_ISDIR(inode_u->bi_mode)) {
 		ret = bch2_empty_dir_trans(trans, inum);
 		if (ret)
 			goto err;
 	}
 
-	if (deleting_snapshot && !inode_u->bi_subvol) {
+	if (deleting_subvol && !inode_u->bi_subvol) {
 		ret = -BCH_ERR_ENOENT_not_subvol;
 		goto err;
 	}
 
-	if (deleting_snapshot || inode_u->bi_subvol) {
+	if (inode_u->bi_subvol) {
+		/* Recursive subvolume destroy not allowed (yet?) */
+		ret = bch2_subvol_has_children(trans, inode_u->bi_subvol);
+		if (ret)
+			goto err;
+	}
+
+	if (deleting_subvol || inode_u->bi_subvol) {
 		ret = bch2_subvolume_unlink(trans, inode_u->bi_subvol);
 		if (ret)
 			goto err;
diff --git a/libbcachefs/fs.c b/libbcachefs/fs.c
index 77ea6109..4445fa2f 100644
--- a/libbcachefs/fs.c
+++ b/libbcachefs/fs.c
@@ -503,7 +503,7 @@ static int bch2_link(struct dentry *old_dentry, struct inode *vdir,
 		bch2_subvol_is_ro(c, inode->ei_subvol) ?:
 		__bch2_link(c, inode, dir, dentry);
 	if (unlikely(ret))
-		return ret;
+		return bch2_err_class(ret);
 
 	ihold(&inode->v);
 	d_instantiate(dentry, &inode->v);
@@ -555,8 +555,9 @@ static int bch2_unlink(struct inode *vdir, struct dentry *dentry)
 	struct bch_inode_info *dir= to_bch_ei(vdir);
 	struct bch_fs *c = dir->v.i_sb->s_fs_info;
 
-	return bch2_subvol_is_ro(c, dir->ei_subvol) ?:
+	int ret = bch2_subvol_is_ro(c, dir->ei_subvol) ?:
 		__bch2_unlink(vdir, dentry, false);
+	return bch2_err_class(ret);
 }
 
 static int bch2_symlink(struct mnt_idmap *idmap,
@@ -591,7 +592,7 @@ static int bch2_symlink(struct mnt_idmap *idmap,
 	return 0;
 err:
 	iput(&inode->v);
-	return ret;
+	return bch2_err_class(ret);
 }
 
 static int bch2_mkdir(struct mnt_idmap *idmap,
diff --git a/libbcachefs/fsck.c b/libbcachefs/fsck.c
index e4a8a14c..dfd54708 100644
--- a/libbcachefs/fsck.c
+++ b/libbcachefs/fsck.c
@@ -252,7 +252,7 @@ create_lostfound:
 		goto err;
 
 	ret =   bch2_dirent_create_snapshot(trans,
-				root_inode.bi_inum, snapshot, &root_hash_info,
+				0, root_inode.bi_inum, snapshot, &root_hash_info,
 				mode_to_type(lostfound->bi_mode),
 				&lostfound_str,
 				lostfound->bi_inum,
@@ -275,9 +275,24 @@ static int reattach_inode(struct btree_trans *trans,
 	char name_buf[20];
 	struct qstr name;
 	u64 dir_offset = 0;
+	u32 dirent_snapshot = inode_snapshot;
 	int ret;
 
-	ret = lookup_lostfound(trans, inode_snapshot, &lostfound);
+	if (inode->bi_subvol) {
+		inode->bi_parent_subvol = BCACHEFS_ROOT_SUBVOL;
+
+		u64 root_inum;
+		ret = subvol_lookup(trans, inode->bi_parent_subvol,
+				    &dirent_snapshot, &root_inum);
+		if (ret)
+			return ret;
+
+		snprintf(name_buf, sizeof(name_buf), "subvol-%u", inode->bi_subvol);
+	} else {
+		snprintf(name_buf, sizeof(name_buf), "%llu", inode->bi_inum);
+	}
+
+	ret = lookup_lostfound(trans, dirent_snapshot, &lostfound);
 	if (ret)
 		return ret;
 
@@ -291,14 +306,16 @@ static int reattach_inode(struct btree_trans *trans,
 
 	dir_hash = bch2_hash_info_init(trans->c, &lostfound);
 
-	snprintf(name_buf, sizeof(name_buf), "%llu", inode->bi_inum);
 	name = (struct qstr) QSTR(name_buf);
 
 	ret = bch2_dirent_create_snapshot(trans,
-				lostfound.bi_inum, inode_snapshot,
+				inode->bi_parent_subvol, lostfound.bi_inum,
+				dirent_snapshot,
 				&dir_hash,
 				inode_d_type(inode),
-				&name, inode->bi_inum, &dir_offset,
+				&name,
+				inode->bi_subvol ?: inode->bi_inum,
+				&dir_offset,
 				BCH_HASH_SET_MUST_CREATE);
 	if (ret)
 		return ret;
@@ -564,13 +581,12 @@ static int get_inodes_all_snapshots(struct btree_trans *trans,
 }
 
 static struct inode_walker_entry *
-lookup_inode_for_snapshot(struct bch_fs *c, struct inode_walker *w,
-			  u32 snapshot, bool is_whiteout)
+lookup_inode_for_snapshot(struct bch_fs *c, struct inode_walker *w, struct bkey_s_c k)
 {
-	struct inode_walker_entry *i;
-
-	snapshot = bch2_snapshot_equiv(c, snapshot);
+	bool is_whiteout = k.k->type == KEY_TYPE_whiteout;
+	u32 snapshot = bch2_snapshot_equiv(c, k.k->p.snapshot);
 
+	struct inode_walker_entry *i;
 	__darray_for_each(w->inodes, i)
 		if (bch2_snapshot_is_ancestor(c, snapshot, i->snapshot))
 			goto found;
@@ -581,20 +597,24 @@ found:
 
 	if (snapshot != i->snapshot && !is_whiteout) {
 		struct inode_walker_entry new = *i;
-		size_t pos;
-		int ret;
 
 		new.snapshot = snapshot;
 		new.count = 0;
 
-		bch_info(c, "have key for inode %llu:%u but have inode in ancestor snapshot %u",
-			 w->last_pos.inode, snapshot, i->snapshot);
+		struct printbuf buf = PRINTBUF;
+		bch2_bkey_val_to_text(&buf, c, k);
+
+		bch_info(c, "have key for inode %llu:%u but have inode in ancestor snapshot %u\n"
+			 "unexpected because we should always update the inode when we update a key in that inode\n"
+			 "%s",
+			 w->last_pos.inode, snapshot, i->snapshot, buf.buf);
+		printbuf_exit(&buf);
 
 		while (i > w->inodes.data && i[-1].snapshot > snapshot)
 			--i;
 
-		pos = i - w->inodes.data;
-		ret = darray_insert_item(&w->inodes, pos, new);
+		size_t pos = i - w->inodes.data;
+		int ret = darray_insert_item(&w->inodes, pos, new);
 		if (ret)
 			return ERR_PTR(ret);
 
@@ -605,21 +625,21 @@ found:
 }
 
 static struct inode_walker_entry *walk_inode(struct btree_trans *trans,
-					     struct inode_walker *w, struct bpos pos,
-					     bool is_whiteout)
+					     struct inode_walker *w,
+					     struct bkey_s_c k)
 {
-	if (w->last_pos.inode != pos.inode) {
-		int ret = get_inodes_all_snapshots(trans, w, pos.inode);
+	if (w->last_pos.inode != k.k->p.inode) {
+		int ret = get_inodes_all_snapshots(trans, w, k.k->p.inode);
 		if (ret)
 			return ERR_PTR(ret);
-	} else if (bkey_cmp(w->last_pos, pos)) {
+	} else if (bkey_cmp(w->last_pos, k.k->p)) {
 		darray_for_each(w->inodes, i)
 			i->seen_this_pos = false;
 	}
 
-	w->last_pos = pos;
+	w->last_pos = k.k->p;
 
-	return lookup_inode_for_snapshot(trans->c, w, pos.snapshot, is_whiteout);
+	return lookup_inode_for_snapshot(trans->c, w, k);
 }
 
 static int __get_visible_inodes(struct btree_trans *trans,
@@ -767,6 +787,43 @@ fsck_err:
 	goto out;
 }
 
+static struct bkey_s_c_dirent dirent_get_by_pos(struct btree_trans *trans,
+						struct btree_iter *iter,
+						struct bpos pos)
+{
+	return bch2_bkey_get_iter_typed(trans, iter, BTREE_ID_dirents, pos, 0, dirent);
+}
+
+static struct bkey_s_c_dirent inode_get_dirent(struct btree_trans *trans,
+					       struct btree_iter *iter,
+					       struct bch_inode_unpacked *inode,
+					       u32 *snapshot)
+{
+	if (inode->bi_subvol) {
+		u64 inum;
+		int ret = subvol_lookup(trans, inode->bi_parent_subvol, snapshot, &inum);
+		if (ret)
+			return ((struct bkey_s_c_dirent) { .k = ERR_PTR(ret) });
+	}
+
+	return dirent_get_by_pos(trans, iter, SPOS(inode->bi_dir, inode->bi_dir_offset, *snapshot));
+}
+
+static bool inode_points_to_dirent(struct bch_inode_unpacked *inode,
+				   struct bkey_s_c_dirent d)
+{
+	return  inode->bi_dir		== d.k->p.inode &&
+		inode->bi_dir_offset	== d.k->p.offset;
+}
+
+static bool dirent_points_to_inode(struct bkey_s_c_dirent d,
+				   struct bch_inode_unpacked *inode)
+{
+	return d.v->d_type == DT_SUBVOL
+		? le32_to_cpu(d.v->d_child_subvol)	== inode->bi_subvol
+		: le64_to_cpu(d.v->d_inum)		== inode->bi_inum;
+}
+
 static int check_inode_deleted_list(struct btree_trans *trans, struct bpos p)
 {
 	struct btree_iter iter;
@@ -779,6 +836,49 @@ static int check_inode_deleted_list(struct btree_trans *trans, struct bpos p)
 	return k.k->type == KEY_TYPE_set;
 }
 
+static int check_inode_dirent_inode(struct btree_trans *trans, struct bkey_s_c inode_k,
+				    struct bch_inode_unpacked *inode,
+				    u32 inode_snapshot, bool *write_inode)
+{
+	struct bch_fs *c = trans->c;
+	struct printbuf buf = PRINTBUF;
+
+	struct btree_iter dirent_iter = {};
+	struct bkey_s_c_dirent d = inode_get_dirent(trans, &dirent_iter, inode, &inode_snapshot);
+	int ret = bkey_err(d);
+	if (ret && !bch2_err_matches(ret, ENOENT))
+		return ret;
+
+	if (fsck_err_on(ret,
+			c, inode_points_to_missing_dirent,
+			"inode points to missing dirent\n%s",
+			(bch2_bkey_val_to_text(&buf, c, inode_k), buf.buf)) ||
+	    fsck_err_on(!ret && !dirent_points_to_inode(d, inode),
+			c, inode_points_to_wrong_dirent,
+			"inode points to dirent that does not point back:\n%s",
+			(bch2_bkey_val_to_text(&buf, c, inode_k),
+			 prt_newline(&buf),
+			 bch2_bkey_val_to_text(&buf, c, d.s_c), buf.buf))) {
+		/*
+		 * We just clear the backpointer fields for now. If we find a
+		 * dirent that points to this inode in check_dirents(), we'll
+		 * update it then; then when we get to check_path() if the
+		 * backpointer is still 0 we'll reattach it.
+		 */
+		inode->bi_dir = 0;
+		inode->bi_dir_offset = 0;
+		inode->bi_flags &= ~BCH_INODE_backptr_untrusted;
+		*write_inode = true;
+	}
+
+	ret = 0;
+fsck_err:
+	bch2_trans_iter_exit(trans, &dirent_iter);
+	printbuf_exit(&buf);
+	bch_err_fn(c, ret);
+	return ret;
+}
+
 static int check_inode(struct btree_trans *trans,
 		       struct btree_iter *iter,
 		       struct bkey_s_c k,
@@ -923,6 +1023,22 @@ static int check_inode(struct btree_trans *trans,
 		do_update = true;
 	}
 
+	if (u.bi_dir || u.bi_dir_offset) {
+		ret = check_inode_dirent_inode(trans, k, &u, k.k->p.snapshot, &do_update);
+		if (ret)
+			goto err;
+	}
+
+	if (fsck_err_on(u.bi_parent_subvol &&
+			(u.bi_subvol == 0 ||
+			 u.bi_subvol == BCACHEFS_ROOT_SUBVOL),
+			c, inode_bi_parent_nonzero,
+			"inode %llu:%u has subvol %u but nonzero parent subvol %u",
+			u.bi_inum, k.k->p.snapshot, u.bi_subvol, u.bi_parent_subvol)) {
+		u.bi_parent_subvol = 0;
+		do_update = true;
+	}
+
 	if (u.bi_subvol) {
 		struct bch_subvolume s;
 
@@ -980,28 +1096,6 @@ int bch2_check_inodes(struct bch_fs *c)
 	return ret;
 }
 
-static struct bkey_s_c_dirent dirent_get_by_pos(struct btree_trans *trans,
-						struct btree_iter *iter,
-						struct bpos pos)
-{
-	return bch2_bkey_get_iter_typed(trans, iter, BTREE_ID_dirents, pos, 0, dirent);
-}
-
-static bool inode_points_to_dirent(struct bch_inode_unpacked *inode,
-				   struct bkey_s_c_dirent d)
-{
-	return  inode->bi_dir		== d.k->p.inode &&
-		inode->bi_dir_offset	== d.k->p.offset;
-}
-
-static bool dirent_points_to_inode(struct bkey_s_c_dirent d,
-				   struct bch_inode_unpacked *inode)
-{
-	return d.v->d_type == DT_SUBVOL
-		? le32_to_cpu(d.v->d_child_subvol)	== inode->bi_subvol
-		: le64_to_cpu(d.v->d_inum)		== inode->bi_inum;
-}
-
 static int check_i_sectors(struct btree_trans *trans, struct inode_walker *w)
 {
 	struct bch_fs *c = trans->c;
@@ -1310,7 +1404,7 @@ static int check_extent(struct btree_trans *trans, struct btree_iter *iter,
 			goto err;
 	}
 
-	i = walk_inode(trans, inode, equiv, k.k->type == KEY_TYPE_whiteout);
+	i = walk_inode(trans, inode, k);
 	ret = PTR_ERR_OR_ZERO(i);
 	if (ret)
 		goto err;
@@ -1489,84 +1583,82 @@ fsck_err:
 	return ret ?: trans_was_restarted(trans, restart_count);
 }
 
-static int check_inode_backpointer(struct btree_trans *trans,
+static int check_dirent_inode_dirent(struct btree_trans *trans,
 				   struct btree_iter *iter,
 				   struct bkey_s_c_dirent d,
 				   struct bch_inode_unpacked *target,
 				   u32 target_snapshot)
 {
 	struct bch_fs *c = trans->c;
-	struct btree_iter bp_iter = { NULL };
 	struct printbuf buf = PRINTBUF;
 	int ret = 0;
 
+	if (inode_points_to_dirent(target, d))
+		return 0;
+
 	if (!target->bi_dir &&
 	    !target->bi_dir_offset) {
 		target->bi_dir		= d.k->p.inode;
 		target->bi_dir_offset	= d.k->p.offset;
-
-		ret = __bch2_fsck_write_inode(trans, target, target_snapshot);
-		if (ret)
-			goto err;
+		return __bch2_fsck_write_inode(trans, target, target_snapshot);
 	}
 
-	if (!inode_points_to_dirent(target, d)) {
-		struct bkey_s_c_dirent bp_dirent = dirent_get_by_pos(trans, &bp_iter,
-				      SPOS(target->bi_dir, target->bi_dir_offset, target_snapshot));
-		ret = bkey_err(bp_dirent);
-		if (ret && !bch2_err_matches(ret, ENOENT))
-			goto err;
-
-		bool backpointer_exists = !ret;
-		ret = 0;
-
-		bch2_bkey_val_to_text(&buf, c, d.s_c);
-		prt_newline(&buf);
-		if (backpointer_exists)
-			bch2_bkey_val_to_text(&buf, c, bp_dirent.s_c);
+	struct btree_iter bp_iter = { NULL };
+	struct bkey_s_c_dirent bp_dirent = dirent_get_by_pos(trans, &bp_iter,
+			      SPOS(target->bi_dir, target->bi_dir_offset, target_snapshot));
+	ret = bkey_err(bp_dirent);
+	if (ret && !bch2_err_matches(ret, ENOENT))
+		goto err;
 
-		if (fsck_err_on(S_ISDIR(target->bi_mode) && backpointer_exists,
-				c, inode_dir_multiple_links,
-				"directory %llu:%u with multiple links\n%s",
-				target->bi_inum, target_snapshot, buf.buf)) {
-			ret = __remove_dirent(trans, d.k->p);
-			goto out;
-		}
+	bool backpointer_exists = !ret;
+	ret = 0;
+
+	if (fsck_err_on(!backpointer_exists,
+			c, inode_wrong_backpointer,
+			"inode %llu:%u has wrong backpointer:\n"
+			"got       %llu:%llu\n"
+			"should be %llu:%llu",
+			target->bi_inum, target_snapshot,
+			target->bi_dir,
+			target->bi_dir_offset,
+			d.k->p.inode,
+			d.k->p.offset)) {
+		target->bi_dir		= d.k->p.inode;
+		target->bi_dir_offset	= d.k->p.offset;
+		ret = __bch2_fsck_write_inode(trans, target, target_snapshot);
+		goto out;
+	}
 
-		/*
-		 * hardlinked file with nlink 0:
-		 * We're just adjusting nlink here so check_nlinks() will pick
-		 * it up, it ignores inodes with nlink 0
-		 */
-		if (fsck_err_on(backpointer_exists && !target->bi_nlink,
-				c, inode_multiple_links_but_nlink_0,
-				"inode %llu:%u type %s has multiple links but i_nlink 0\n%s",
-				target->bi_inum, target_snapshot, bch2_d_types[d.v->d_type], buf.buf)) {
-			target->bi_nlink++;
-			target->bi_flags &= ~BCH_INODE_unlinked;
-
-			ret = __bch2_fsck_write_inode(trans, target, target_snapshot);
-			if (ret)
-				goto err;
-		}
+	bch2_bkey_val_to_text(&buf, c, d.s_c);
+	prt_newline(&buf);
+	if (backpointer_exists)
+		bch2_bkey_val_to_text(&buf, c, bp_dirent.s_c);
+
+	if (fsck_err_on(backpointer_exists &&
+			(S_ISDIR(target->bi_mode) ||
+			 target->bi_subvol),
+			c, inode_dir_multiple_links,
+			"%s %llu:%u with multiple links\n%s",
+			S_ISDIR(target->bi_mode) ? "directory" : "subvolume",
+			target->bi_inum, target_snapshot, buf.buf)) {
+		ret = __remove_dirent(trans, d.k->p);
+		goto out;
+	}
 
-		if (fsck_err_on(!backpointer_exists,
-				c, inode_wrong_backpointer,
-				"inode %llu:%u has wrong backpointer:\n"
-				"got       %llu:%llu\n"
-				"should be %llu:%llu",
-				target->bi_inum, target_snapshot,
-				target->bi_dir,
-				target->bi_dir_offset,
-				d.k->p.inode,
-				d.k->p.offset)) {
-			target->bi_dir		= d.k->p.inode;
-			target->bi_dir_offset	= d.k->p.offset;
-
-			ret = __bch2_fsck_write_inode(trans, target, target_snapshot);
-			if (ret)
-				goto err;
-		}
+	/*
+	 * hardlinked file with nlink 0:
+	 * We're just adjusting nlink here so check_nlinks() will pick
+	 * it up, it ignores inodes with nlink 0
+	 */
+	if (fsck_err_on(backpointer_exists && !target->bi_nlink,
+			c, inode_multiple_links_but_nlink_0,
+			"inode %llu:%u type %s has multiple links but i_nlink 0\n%s",
+			target->bi_inum, target_snapshot, bch2_d_types[d.v->d_type], buf.buf)) {
+		target->bi_nlink++;
+		target->bi_flags &= ~BCH_INODE_unlinked;
+		ret = __bch2_fsck_write_inode(trans, target, target_snapshot);
+		if (ret)
+			goto err;
 	}
 out:
 err:
@@ -1588,7 +1680,7 @@ static int check_dirent_target(struct btree_trans *trans,
 	struct printbuf buf = PRINTBUF;
 	int ret = 0;
 
-	ret = check_inode_backpointer(trans, iter, d, target, target_snapshot);
+	ret = check_dirent_inode_dirent(trans, iter, d, target, target_snapshot);
 	if (ret)
 		goto err;
 
@@ -1606,27 +1698,12 @@ static int check_dirent_target(struct btree_trans *trans,
 
 		bkey_reassemble(&n->k_i, d.s_c);
 		n->v.d_type = inode_d_type(target);
-
-		ret = bch2_trans_update(trans, iter, &n->k_i, 0);
-		if (ret)
-			goto err;
-
-		d = dirent_i_to_s_c(n);
-	}
-
-	if (fsck_err_on(d.v->d_type == DT_SUBVOL &&
-			target->bi_parent_subvol != le32_to_cpu(d.v->d_parent_subvol),
-			c, dirent_d_parent_subvol_wrong,
-			"dirent has wrong d_parent_subvol field: got %u, should be %u",
-			le32_to_cpu(d.v->d_parent_subvol),
-			target->bi_parent_subvol)) {
-		n = bch2_trans_kmalloc(trans, bkey_bytes(d.k));
-		ret = PTR_ERR_OR_ZERO(n);
-		if (ret)
-			goto err;
-
-		bkey_reassemble(&n->k_i, d.s_c);
-		n->v.d_parent_subvol = cpu_to_le32(target->bi_parent_subvol);
+		if (n->v.d_type == DT_SUBVOL) {
+			n->v.d_parent_subvol = target->bi_parent_subvol;
+			n->v.d_child_subvol = target->bi_subvol;
+		} else {
+			n->v.d_inum = target->bi_inum;
+		}
 
 		ret = bch2_trans_update(trans, iter, &n->k_i, 0);
 		if (ret)
@@ -1641,45 +1718,113 @@ fsck_err:
 	return ret;
 }
 
-static int check_subvol_dirent(struct btree_trans *trans, struct btree_iter *iter,
-			       struct bkey_s_c_dirent d)
+/* find a subvolume that's a descendent of @snapshot: */
+static int find_snapshot_subvol(struct btree_trans *trans, u32 snapshot, u32 *subvolid)
+{
+	struct btree_iter iter;
+	struct bkey_s_c k;
+	int ret;
+
+	for_each_btree_key_norestart(trans, iter, BTREE_ID_subvolumes, POS_MIN, 0, k, ret) {
+		if (k.k->type != KEY_TYPE_subvolume)
+			continue;
+
+		struct bkey_s_c_subvolume s = bkey_s_c_to_subvolume(k);
+		if (bch2_snapshot_is_ancestor(trans->c, le32_to_cpu(s.v->snapshot), snapshot)) {
+			bch2_trans_iter_exit(trans, &iter);
+			*subvolid = k.k->p.offset;
+			goto found;
+		}
+	}
+	if (!ret)
+		ret = -ENOENT;
+found:
+	bch2_trans_iter_exit(trans, &iter);
+	return ret;
+}
+
+static int check_dirent_to_subvol(struct btree_trans *trans, struct btree_iter *iter,
+				  struct bkey_s_c_dirent d)
 {
 	struct bch_fs *c = trans->c;
+	struct btree_iter subvol_iter = {};
 	struct bch_inode_unpacked subvol_root;
+	u32 parent_subvol = le32_to_cpu(d.v->d_parent_subvol);
 	u32 target_subvol = le32_to_cpu(d.v->d_child_subvol);
-	u32 target_snapshot;
-	u64 target_inum;
+	u32 parent_snapshot;
+	u64 parent_inum;
+	struct printbuf buf = PRINTBUF;
 	int ret = 0;
 
-	ret = subvol_lookup(trans, target_subvol,
-			      &target_snapshot, &target_inum);
+	ret = subvol_lookup(trans, parent_subvol, &parent_snapshot, &parent_inum);
 	if (ret && !bch2_err_matches(ret, ENOENT))
 		return ret;
 
-	if (fsck_err_on(ret, c, dirent_to_missing_subvol,
-			"dirent points to missing subvolume %u",
-			le32_to_cpu(d.v->d_child_subvol)))
-		return __remove_dirent(trans, d.k->p);
+	if (fsck_err_on(ret, c, dirent_to_missing_parent_subvol,
+			"dirent parent_subvol points to missing subvolume\n%s",
+			(bch2_bkey_val_to_text(&buf, c, d.s_c), buf.buf)) ||
+	    fsck_err_on(!ret && !bch2_snapshot_is_ancestor(c, parent_snapshot, d.k->p.snapshot),
+			c, dirent_not_visible_in_parent_subvol,
+			"dirent not visible in parent_subvol (not an ancestor of subvol snap %u)\n%s",
+			parent_snapshot,
+			(bch2_bkey_val_to_text(&buf, c, d.s_c), buf.buf))) {
+		u32 new_parent_subvol;
+		ret = find_snapshot_subvol(trans, d.k->p.snapshot, &new_parent_subvol);
+		if (ret)
+			goto err;
 
-	ret = lookup_inode(trans, target_inum,
-			   &subvol_root, &target_snapshot);
+		struct bkey_i_dirent *new_dirent = bch2_bkey_make_mut_typed(trans, iter, &d.s_c, 0, dirent);
+		ret = PTR_ERR_OR_ZERO(new_dirent);
+		if (ret)
+			goto err;
+
+		new_dirent->v.d_parent_subvol = cpu_to_le32(new_parent_subvol);
+	}
+
+	struct bkey_s_c_subvolume s =
+		bch2_bkey_get_iter_typed(trans, &subvol_iter,
+					 BTREE_ID_subvolumes, POS(0, target_subvol),
+					 0, subvolume);
+	ret = bkey_err(s.s_c);
 	if (ret && !bch2_err_matches(ret, ENOENT))
 		return ret;
 
-	if (fsck_err_on(ret, c, subvol_to_missing_root,
-			"subvolume %u points to missing subvolume root %llu",
-			target_subvol,
-			target_inum)) {
-		bch_err(c, "repair not implemented yet");
-		return -EINVAL;
+	if (ret) {
+		if (fsck_err(c, dirent_to_missing_subvol,
+			     "dirent points to missing subvolume\n%s",
+			     (bch2_bkey_val_to_text(&buf, c, d.s_c), buf.buf)))
+			return __remove_dirent(trans, d.k->p);
+		ret = 0;
+		goto out;
 	}
 
-	if (fsck_err_on(subvol_root.bi_subvol != target_subvol,
-			c, subvol_root_wrong_bi_subvol,
-			"subvol root %llu has wrong bi_subvol field: got %u, should be %u",
+	if (fsck_err_on(le32_to_cpu(s.v->fs_path_parent) != parent_subvol,
+			c, subvol_fs_path_parent_wrong,
+			"subvol with wrong fs_path_parent, should be be %u\n%s",
+			parent_subvol,
+			(bch2_bkey_val_to_text(&buf, c, s.s_c), buf.buf))) {
+		struct bkey_i_subvolume *n =
+			bch2_bkey_make_mut_typed(trans, &subvol_iter, &s.s_c, 0, subvolume);
+		ret = PTR_ERR_OR_ZERO(n);
+		if (ret)
+			goto err;
+
+		n->v.fs_path_parent = le32_to_cpu(parent_subvol);
+	}
+
+	u64 target_inum = le64_to_cpu(s.v->inode);
+	u32 target_snapshot = le32_to_cpu(s.v->snapshot);
+
+	ret = lookup_inode(trans, target_inum, &subvol_root, &target_snapshot);
+	if (ret && !bch2_err_matches(ret, ENOENT))
+		return ret;
+
+	if (fsck_err_on(parent_subvol != subvol_root.bi_parent_subvol,
+			c, inode_bi_parent_wrong,
+			"subvol root %llu has wrong bi_parent_subvol: got %u, should be %u",
 			target_inum,
-			subvol_root.bi_subvol, target_subvol)) {
-		subvol_root.bi_subvol = target_subvol;
+			subvol_root.bi_parent_subvol, parent_subvol)) {
+		subvol_root.bi_parent_subvol = parent_subvol;
 		ret = __bch2_fsck_write_inode(trans, &subvol_root, target_snapshot);
 		if (ret)
 			return ret;
@@ -1689,7 +1834,11 @@ static int check_subvol_dirent(struct btree_trans *trans, struct btree_iter *ite
 				  target_snapshot);
 	if (ret)
 		return ret;
+out:
+err:
 fsck_err:
+	bch2_trans_iter_exit(trans, &subvol_iter);
+	printbuf_exit(&buf);
 	return ret;
 }
 
@@ -1731,7 +1880,7 @@ static int check_dirent(struct btree_trans *trans, struct btree_iter *iter,
 
 	BUG_ON(!btree_iter_path(trans, iter)->should_be_locked);
 
-	i = walk_inode(trans, dir, equiv, k.k->type == KEY_TYPE_whiteout);
+	i = walk_inode(trans, dir, k);
 	ret = PTR_ERR_OR_ZERO(i);
 	if (ret < 0)
 		goto err;
@@ -1777,7 +1926,7 @@ static int check_dirent(struct btree_trans *trans, struct btree_iter *iter,
 	d = bkey_s_c_to_dirent(k);
 
 	if (d.v->d_type == DT_SUBVOL) {
-		ret = check_subvol_dirent(trans, iter, d);
+		ret = check_dirent_to_subvol(trans, iter, d);
 		if (ret)
 			goto err;
 	} else {
@@ -1858,7 +2007,7 @@ static int check_xattr(struct btree_trans *trans, struct btree_iter *iter,
 	if (ret)
 		return ret;
 
-	i = walk_inode(trans, inode, k.k->p, k.k->type == KEY_TYPE_whiteout);
+	i = walk_inode(trans, inode, k);
 	ret = PTR_ERR_OR_ZERO(i);
 	if (ret)
 		return ret;
@@ -1997,62 +2146,52 @@ static int path_down(struct bch_fs *c, pathbuf *p,
  *
  * XXX: we should also be verifying that inodes are in the right subvolumes
  */
-static int check_path(struct btree_trans *trans,
-		      pathbuf *p,
-		      struct bch_inode_unpacked *inode,
-		      u32 snapshot)
+static int check_path(struct btree_trans *trans, pathbuf *p, struct bkey_s_c inode_k)
 {
 	struct bch_fs *c = trans->c;
+	struct btree_iter inode_iter = {};
+	struct bch_inode_unpacked inode;
+	struct printbuf buf = PRINTBUF;
+	u32 snapshot = bch2_snapshot_equiv(c, inode_k.k->p.snapshot);
 	int ret = 0;
 
-	snapshot = bch2_snapshot_equiv(c, snapshot);
 	p->nr = 0;
 
-	while (!(inode->bi_inum == BCACHEFS_ROOT_INO &&
-		 inode->bi_subvol == BCACHEFS_ROOT_SUBVOL)) {
+	BUG_ON(bch2_inode_unpack(inode_k, &inode));
+
+	while (!(inode.bi_inum == BCACHEFS_ROOT_INO &&
+		 inode.bi_subvol == BCACHEFS_ROOT_SUBVOL)) {
 		struct btree_iter dirent_iter;
 		struct bkey_s_c_dirent d;
 		u32 parent_snapshot = snapshot;
 
-		if (inode->bi_subvol) {
-			u64 inum;
-
-			ret = subvol_lookup(trans, inode->bi_parent_subvol,
-					    &parent_snapshot, &inum);
-			if (ret)
-				break;
-		}
-
-		d = dirent_get_by_pos(trans, &dirent_iter,
-				      SPOS(inode->bi_dir, inode->bi_dir_offset,
-					   parent_snapshot));
+		d = inode_get_dirent(trans, &dirent_iter, &inode, &parent_snapshot);
 		ret = bkey_err(d.s_c);
 		if (ret && !bch2_err_matches(ret, ENOENT))
 			break;
 
-		if (!ret && !dirent_points_to_inode(d, inode)) {
+		if (!ret && !dirent_points_to_inode(d, &inode)) {
 			bch2_trans_iter_exit(trans, &dirent_iter);
 			ret = -BCH_ERR_ENOENT_dirent_doesnt_match_inode;
 		}
 
 		if (bch2_err_matches(ret, ENOENT)) {
-			if (fsck_err(c,  inode_unreachable,
-				     "unreachable inode %llu:%u, type %s nlink %u backptr %llu:%llu",
-				     inode->bi_inum, snapshot,
-				     bch2_d_type_str(inode_d_type(inode)),
-				     inode->bi_nlink,
-				     inode->bi_dir,
-				     inode->bi_dir_offset))
-				ret = reattach_inode(trans, inode, snapshot);
-			break;
+			ret = 0;
+			if (fsck_err(c, inode_unreachable,
+				     "unreachable inode\n%s",
+				     (printbuf_reset(&buf),
+				      bch2_bkey_val_to_text(&buf, c, inode_k),
+				      buf.buf)))
+				ret = reattach_inode(trans, &inode, snapshot);
+			goto out;
 		}
 
 		bch2_trans_iter_exit(trans, &dirent_iter);
 
-		if (!S_ISDIR(inode->bi_mode))
+		if (!S_ISDIR(inode.bi_mode))
 			break;
 
-		ret = path_down(c, p, inode->bi_inum, snapshot);
+		ret = path_down(c, p, inode.bi_inum, snapshot);
 		if (ret) {
 			bch_err(c, "memory allocation failure");
 			return ret;
@@ -2060,7 +2199,12 @@ static int check_path(struct btree_trans *trans,
 
 		snapshot = parent_snapshot;
 
-		ret = lookup_inode(trans, inode->bi_dir, inode, &snapshot);
+		bch2_trans_iter_exit(trans, &inode_iter);
+		inode_k = bch2_bkey_get_iter(trans, &inode_iter, BTREE_ID_inodes,
+					     SPOS(0, inode.bi_dir, snapshot), 0);
+		ret = bkey_err(inode_k) ?:
+			!bkey_is_inode(inode_k.k) ? -BCH_ERR_ENOENT_inode
+			: bch2_inode_unpack(inode_k, &inode);
 		if (ret) {
 			/* Should have been caught in dirents pass */
 			if (!bch2_err_matches(ret, BCH_ERR_transaction_restart))
@@ -2068,30 +2212,35 @@ static int check_path(struct btree_trans *trans,
 			break;
 		}
 
-		if (path_is_dup(p, inode->bi_inum, snapshot)) {
+		snapshot = inode_k.k->p.snapshot;
+
+		if (path_is_dup(p, inode.bi_inum, snapshot)) {
 			/* XXX print path */
 			bch_err(c, "directory structure loop");
 
 			darray_for_each(*p, i)
 				pr_err("%llu:%u", i->inum, i->snapshot);
-			pr_err("%llu:%u", inode->bi_inum, snapshot);
+			pr_err("%llu:%u", inode.bi_inum, snapshot);
 
 			if (!fsck_err(c, dir_loop, "directory structure loop"))
 				return 0;
 
-			ret = remove_backpointer(trans, inode);
+			ret = remove_backpointer(trans, &inode);
 			if (ret && !bch2_err_matches(ret, BCH_ERR_transaction_restart))
 				bch_err_msg(c, ret, "removing dirent");
 			if (ret)
 				break;
 
-			ret = reattach_inode(trans, inode, snapshot);
+			ret = reattach_inode(trans, &inode, snapshot);
 			if (ret && !bch2_err_matches(ret, BCH_ERR_transaction_restart))
-				bch_err_msg(c, ret, "reattaching inode %llu", inode->bi_inum);
+				bch_err_msg(c, ret, "reattaching inode %llu", inode.bi_inum);
 			break;
 		}
 	}
+out:
 fsck_err:
+	bch2_trans_iter_exit(trans, &inode_iter);
+	printbuf_exit(&buf);
 	bch_err_fn(c, ret);
 	return ret;
 }
@@ -2103,7 +2252,6 @@ fsck_err:
  */
 int bch2_check_directory_structure(struct bch_fs *c)
 {
-	struct bch_inode_unpacked u;
 	pathbuf path = { 0, };
 	int ret;
 
@@ -2116,12 +2264,10 @@ int bch2_check_directory_structure(struct bch_fs *c)
 			if (!bkey_is_inode(k.k))
 				continue;
 
-			BUG_ON(bch2_inode_unpack(k, &u));
-
-			if (u.bi_flags & BCH_INODE_unlinked)
+			if (bch2_inode_flags(k) & BCH_INODE_unlinked)
 				continue;
 
-			check_path(trans, &path, &u, iter.pos.snapshot);
+			check_path(trans, &path, k);
 		})));
 	darray_exit(&path);
 
diff --git a/libbcachefs/inode.c b/libbcachefs/inode.c
index dbe37ccc..414aebe1 100644
--- a/libbcachefs/inode.c
+++ b/libbcachefs/inode.c
@@ -620,7 +620,8 @@ int bch2_trigger_inode(struct btree_trans *trans,
 		bool old_deleted = bkey_is_deleted_inode(old);
 		bool new_deleted = bkey_is_deleted_inode(new.s_c);
 		if (old_deleted != new_deleted) {
-			int ret = bch2_btree_bit_mod(trans, BTREE_ID_deleted_inodes, new.k->p, new_deleted);
+			int ret = bch2_btree_bit_mod_buffered(trans, BTREE_ID_deleted_inodes,
+							      new.k->p, new_deleted);
 			if (ret)
 				return ret;
 		}
@@ -1169,7 +1170,7 @@ fsck_err:
 	bch2_trans_iter_exit(trans, &inode_iter);
 	return ret;
 delete:
-	ret = bch2_btree_bit_mod(trans, BTREE_ID_deleted_inodes, pos, false);
+	ret = bch2_btree_bit_mod_buffered(trans, BTREE_ID_deleted_inodes, pos, false);
 	goto out;
 }
 
diff --git a/libbcachefs/inode.h b/libbcachefs/inode.h
index 9a9353c0..05629805 100644
--- a/libbcachefs/inode.h
+++ b/libbcachefs/inode.h
@@ -177,6 +177,20 @@ static inline u8 inode_d_type(struct bch_inode_unpacked *inode)
 	return inode->bi_subvol ? DT_SUBVOL : mode_to_type(inode->bi_mode);
 }
 
+static inline u32 bch2_inode_flags(struct bkey_s_c k)
+{
+	switch (k.k->type) {
+	case KEY_TYPE_inode:
+		return le32_to_cpu(bkey_s_c_to_inode(k).v->bi_flags);
+	case KEY_TYPE_inode_v2:
+		return le64_to_cpu(bkey_s_c_to_inode_v2(k).v->bi_flags);
+	case KEY_TYPE_inode_v3:
+		return le64_to_cpu(bkey_s_c_to_inode_v3(k).v->bi_flags);
+	default:
+		return 0;
+	}
+}
+
 /* i_nlink: */
 
 static inline unsigned nlink_bias(umode_t mode)
diff --git a/libbcachefs/lru.c b/libbcachefs/lru.c
index 7a4ca5a2..ed7577cd 100644
--- a/libbcachefs/lru.c
+++ b/libbcachefs/lru.c
@@ -44,8 +44,8 @@ static int __bch2_lru_set(struct btree_trans *trans, u16 lru_id,
 			  u64 dev_bucket, u64 time, bool set)
 {
 	return time
-		? bch2_btree_bit_mod(trans, BTREE_ID_lru,
-				     lru_pos(lru_id, dev_bucket, time), set)
+		? bch2_btree_bit_mod_buffered(trans, BTREE_ID_lru,
+					      lru_pos(lru_id, dev_bucket, time), set)
 		: 0;
 }
 
diff --git a/libbcachefs/opts.h b/libbcachefs/opts.h
index 9a4b7faa..f8c2341e 100644
--- a/libbcachefs/opts.h
+++ b/libbcachefs/opts.h
@@ -332,6 +332,11 @@ enum fsck_err_opts {
 	  OPT_BOOL(),							\
 	  BCH2_NO_SB_OPT,		false,				\
 	  NULL,		"Run fsck on mount")				\
+	x(fsck_memory_usage_percent,	u8,				\
+	  OPT_FS|OPT_MOUNT,						\
+	  OPT_UINT(20, 70),						\
+	  BCH2_NO_SB_OPT,		50,				\
+	  NULL,		"Maximum percentage of system ram fsck is allowed to pin")\
 	x(fix_errors,			u8,				\
 	  OPT_FS|OPT_MOUNT,						\
 	  OPT_FN(bch2_opt_fix_errors),					\
diff --git a/libbcachefs/recovery.c b/libbcachefs/recovery.c
index 9127d0e3..4f8782d6 100644
--- a/libbcachefs/recovery.c
+++ b/libbcachefs/recovery.c
@@ -264,7 +264,7 @@ static int journal_replay_entry_early(struct bch_fs *c,
 			bkey_copy(&r->key, (struct bkey_i *) entry->start);
 			r->error = 0;
 		} else {
-			r->error = -EIO;
+			r->error = -BCH_ERR_btree_node_read_error;
 		}
 		r->alive = true;
 		break;
diff --git a/libbcachefs/recovery_types.h b/libbcachefs/recovery_types.h
index fa0c8efd..f0fc1dbb 100644
--- a/libbcachefs/recovery_types.h
+++ b/libbcachefs/recovery_types.h
@@ -34,6 +34,7 @@
 	x(check_snapshot_trees,			18, PASS_ONLINE|PASS_FSCK)	\
 	x(check_snapshots,			19, PASS_ONLINE|PASS_FSCK)	\
 	x(check_subvols,			20, PASS_ONLINE|PASS_FSCK)	\
+	x(check_subvol_children,		35, PASS_ONLINE|PASS_FSCK)	\
 	x(delete_dead_snapshots,		21, PASS_ONLINE|PASS_FSCK)	\
 	x(fs_upgrade_for_subvolumes,		22, 0)				\
 	x(resume_logged_ops,			23, PASS_ALWAYS)		\
diff --git a/libbcachefs/sb-downgrade.c b/libbcachefs/sb-downgrade.c
index 626eaaea..3337419f 100644
--- a/libbcachefs/sb-downgrade.c
+++ b/libbcachefs/sb-downgrade.c
@@ -46,7 +46,13 @@
 	  BIT_ULL(BCH_RECOVERY_PASS_check_inodes),		\
 	  BCH_FSCK_ERR_unlinked_inode_not_on_deleted_list)	\
 	x(rebalance_work,					\
-	  BIT_ULL(BCH_RECOVERY_PASS_set_fs_needs_rebalance))
+	  BIT_ULL(BCH_RECOVERY_PASS_set_fs_needs_rebalance))	\
+	x(subvolume_fs_parent,					\
+	  BIT_ULL(BCH_RECOVERY_PASS_check_dirents),		\
+	  BCH_FSCK_ERR_subvol_fs_path_parent_wrong)		\
+	x(btree_subvolume_children,				\
+	  BIT_ULL(BCH_RECOVERY_PASS_check_subvols),		\
+	  BCH_FSCK_ERR_subvol_children_not_set)
 
 #define DOWNGRADE_TABLE()
 
diff --git a/libbcachefs/sb-errors_types.h b/libbcachefs/sb-errors_types.h
index 63f18c7f..1530bd35 100644
--- a/libbcachefs/sb-errors_types.h
+++ b/libbcachefs/sb-errors_types.h
@@ -231,7 +231,7 @@
 	x(dirent_name_dot_or_dotdot,				223)	\
 	x(dirent_name_has_slash,				224)	\
 	x(dirent_d_type_wrong,					225)	\
-	x(dirent_d_parent_subvol_wrong,				226)	\
+	x(inode_bi_parent_wrong,				226)	\
 	x(dirent_in_missing_dir_inode,				227)	\
 	x(dirent_in_non_dir_inode,				228)	\
 	x(dirent_to_missing_inode,				229)	\
@@ -253,7 +253,16 @@
 	x(reflink_p_front_pad_bad,				245)	\
 	x(journal_entry_dup_same_device,			246)	\
 	x(inode_bi_subvol_missing,				247)	\
-	x(inode_bi_subvol_wrong,				248)
+	x(inode_bi_subvol_wrong,				248)	\
+	x(inode_points_to_missing_dirent,			249)	\
+	x(inode_points_to_wrong_dirent,				250)	\
+	x(inode_bi_parent_nonzero,				251)	\
+	x(dirent_to_missing_parent_subvol,			252)	\
+	x(dirent_not_visible_in_parent_subvol,			253)	\
+	x(subvol_fs_path_parent_wrong,				254)	\
+	x(subvol_root_fs_path_parent_nonzero,			255)	\
+	x(subvol_children_not_set,				256)	\
+	x(subvol_children_bad,					257)
 
 enum bch_sb_error_id {
 #define x(t, n) BCH_FSCK_ERR_##t = n,
diff --git a/libbcachefs/subvolume.c b/libbcachefs/subvolume.c
index e7ee52c3..ce7aed12 100644
--- a/libbcachefs/subvolume.c
+++ b/libbcachefs/subvolume.c
@@ -13,13 +13,26 @@
 
 static int bch2_subvolume_delete(struct btree_trans *, u32);
 
+static struct bpos subvolume_children_pos(struct bkey_s_c k)
+{
+	if (k.k->type != KEY_TYPE_subvolume)
+		return POS_MIN;
+
+	struct bkey_s_c_subvolume s = bkey_s_c_to_subvolume(k);
+	if (!s.v->fs_path_parent)
+		return POS_MIN;
+	return POS(le32_to_cpu(s.v->fs_path_parent), s.k->p.offset);
+}
+
 static int check_subvol(struct btree_trans *trans,
 			struct btree_iter *iter,
 			struct bkey_s_c k)
 {
 	struct bch_fs *c = trans->c;
 	struct bkey_s_c_subvolume subvol;
+	struct btree_iter subvol_children_iter = {};
 	struct bch_snapshot snapshot;
+	struct printbuf buf = PRINTBUF;
 	unsigned snapid;
 	int ret = 0;
 
@@ -42,6 +55,42 @@ static int check_subvol(struct btree_trans *trans,
 		return ret ?: -BCH_ERR_transaction_restart_nested;
 	}
 
+	if (fsck_err_on(subvol.k->p.offset == BCACHEFS_ROOT_SUBVOL &&
+			subvol.v->fs_path_parent,
+			c, subvol_root_fs_path_parent_nonzero,
+			"root subvolume has nonzero fs_path_parent\n%s",
+			(bch2_bkey_val_to_text(&buf, c, k), buf.buf))) {
+		struct bkey_i_subvolume *n =
+			bch2_bkey_make_mut_typed(trans, iter, &subvol.s_c, 0, subvolume);
+		ret = PTR_ERR_OR_ZERO(n);
+		if (ret)
+			goto err;
+
+		n->v.fs_path_parent = 0;
+	}
+
+	if (subvol.v->fs_path_parent) {
+		struct bpos pos = subvolume_children_pos(k);
+
+		struct bkey_s_c subvol_children_k =
+			bch2_bkey_get_iter(trans, &subvol_children_iter,
+					   BTREE_ID_subvolume_children, pos, 0);
+		ret = bkey_err(subvol_children_k);
+		if (ret)
+			goto err;
+
+		if (fsck_err_on(subvol_children_k.k->type != KEY_TYPE_set,
+				c, subvol_children_not_set,
+				"subvolume not set in subvolume_children btree at %llu:%llu\n%s",
+				pos.inode, pos.offset,
+				(printbuf_reset(&buf),
+				 bch2_bkey_val_to_text(&buf, c, k), buf.buf))) {
+			ret = bch2_btree_bit_mod(trans, BTREE_ID_subvolume_children, pos, true);
+			if (ret)
+				goto err;
+		}
+	}
+
 	struct bch_inode_unpacked inode;
 	struct btree_iter inode_iter = {};
 	ret = bch2_inode_peek_nowarn(trans, &inode_iter, &inode,
@@ -102,9 +151,10 @@ static int check_subvol(struct btree_trans *trans,
 			SET_BCH_SUBVOLUME_SNAP(&s->v, true);
 		}
 	}
-
 err:
 fsck_err:
+	bch2_trans_iter_exit(trans, &subvol_children_iter);
+	printbuf_exit(&buf);
 	return ret;
 }
 
@@ -119,6 +169,42 @@ int bch2_check_subvols(struct bch_fs *c)
 	return ret;
 }
 
+static int check_subvol_child(struct btree_trans *trans,
+			      struct btree_iter *child_iter,
+			      struct bkey_s_c child_k)
+{
+	struct bch_fs *c = trans->c;
+	struct bch_subvolume s;
+	int ret = bch2_bkey_get_val_typed(trans, BTREE_ID_subvolumes, POS(0, child_k.k->p.offset),
+					  0, subvolume, &s);
+	if (ret && !bch2_err_matches(ret, ENOENT))
+		return ret;
+
+	if (fsck_err_on(ret ||
+			le32_to_cpu(s.fs_path_parent) != child_k.k->p.inode,
+			c, subvol_children_bad,
+			"incorrect entry in subvolume_children btree %llu:%llu",
+			child_k.k->p.inode, child_k.k->p.offset)) {
+		ret = bch2_btree_delete_at(trans, child_iter, 0);
+		if (ret)
+			goto err;
+	}
+err:
+fsck_err:
+	return ret;
+}
+
+int bch2_check_subvol_children(struct bch_fs *c)
+{
+	int ret = bch2_trans_run(c,
+		for_each_btree_key_commit(trans, iter,
+				BTREE_ID_subvolume_children, POS_MIN, BTREE_ITER_PREFETCH, k,
+				NULL, NULL, BCH_TRANS_COMMIT_no_enospc,
+			check_subvol_child(trans, &iter, k)));
+	bch_err_fn(c, ret);
+	return 0;
+}
+
 /* Subvolumes: */
 
 int bch2_subvolume_invalid(struct bch_fs *c, struct bkey_s_c k,
@@ -143,8 +229,50 @@ void bch2_subvolume_to_text(struct printbuf *out, struct bch_fs *c,
 		   le64_to_cpu(s.v->inode),
 		   le32_to_cpu(s.v->snapshot));
 
-	if (bkey_val_bytes(s.k) > offsetof(struct bch_subvolume, parent))
-		prt_printf(out, " parent %u", le32_to_cpu(s.v->parent));
+	if (bkey_val_bytes(s.k) > offsetof(struct bch_subvolume, creation_parent)) {
+		prt_printf(out, " creation_parent %u", le32_to_cpu(s.v->creation_parent));
+		prt_printf(out, " fs_parent %u", le32_to_cpu(s.v->fs_path_parent));
+	}
+}
+
+static int subvolume_children_mod(struct btree_trans *trans, struct bpos pos, bool set)
+{
+	return !bpos_eq(pos, POS_MIN)
+		? bch2_btree_bit_mod(trans, BTREE_ID_subvolume_children, pos, set)
+		: 0;
+}
+
+int bch2_subvolume_trigger(struct btree_trans *trans,
+			   enum btree_id btree_id, unsigned level,
+			   struct bkey_s_c old, struct bkey_s new,
+			   unsigned flags)
+{
+	if (flags & BTREE_TRIGGER_TRANSACTIONAL) {
+		struct bpos children_pos_old = subvolume_children_pos(old);
+		struct bpos children_pos_new = subvolume_children_pos(new.s_c);
+
+		if (!bpos_eq(children_pos_old, children_pos_new)) {
+			int ret = subvolume_children_mod(trans, children_pos_old, false) ?:
+				  subvolume_children_mod(trans, children_pos_new, true);
+			if (ret)
+				return ret;
+		}
+	}
+
+	return 0;
+}
+
+int bch2_subvol_has_children(struct btree_trans *trans, u32 subvol)
+{
+	struct btree_iter iter;
+
+	bch2_trans_iter_init(trans, &iter, BTREE_ID_subvolume_children, POS(subvol, 0), 0);
+	struct bkey_s_c k = bch2_btree_iter_peek(&iter);
+	bch2_trans_iter_exit(trans, &iter);
+
+	return bkey_err(k) ?: k.k && k.k->p.inode == subvol
+		? -BCH_ERR_ENOTEMPTY_subvol_not_empty
+		: 0;
 }
 
 static __always_inline int
@@ -228,8 +356,8 @@ static int bch2_subvolume_reparent(struct btree_trans *trans,
 	if (k.k->type != KEY_TYPE_subvolume)
 		return 0;
 
-	if (bkey_val_bytes(k.k) > offsetof(struct bch_subvolume, parent) &&
-	    le32_to_cpu(bkey_s_c_to_subvolume(k).v->parent) != old_parent)
+	if (bkey_val_bytes(k.k) > offsetof(struct bch_subvolume, creation_parent) &&
+	    le32_to_cpu(bkey_s_c_to_subvolume(k).v->creation_parent) != old_parent)
 		return 0;
 
 	s = bch2_bkey_make_mut_typed(trans, iter, &k, 0, subvolume);
@@ -237,7 +365,7 @@ static int bch2_subvolume_reparent(struct btree_trans *trans,
 	if (ret)
 		return ret;
 
-	s->v.parent = cpu_to_le32(new_parent);
+	s->v.creation_parent = cpu_to_le32(new_parent);
 	return 0;
 }
 
@@ -260,7 +388,7 @@ static int bch2_subvolumes_reparent(struct btree_trans *trans, u32 subvolid_to_d
 				BTREE_ID_subvolumes, POS_MIN, BTREE_ITER_PREFETCH, k,
 				NULL, NULL, BCH_TRANS_COMMIT_no_enospc,
 			bch2_subvolume_reparent(trans, &iter, k,
-					subvolid_to_delete, le32_to_cpu(s.parent)));
+					subvolid_to_delete, le32_to_cpu(s.creation_parent)));
 }
 
 /*
@@ -391,6 +519,7 @@ int bch2_subvolume_unlink(struct btree_trans *trans, u32 subvolid)
 }
 
 int bch2_subvolume_create(struct btree_trans *trans, u64 inode,
+			  u32 parent_subvolid,
 			  u32 src_subvolid,
 			  u32 *new_subvolid,
 			  u32 *new_snapshotid,
@@ -447,12 +576,13 @@ int bch2_subvolume_create(struct btree_trans *trans, u64 inode,
 	if (ret)
 		goto err;
 
-	new_subvol->v.flags	= 0;
-	new_subvol->v.snapshot	= cpu_to_le32(new_nodes[0]);
-	new_subvol->v.inode	= cpu_to_le64(inode);
-	new_subvol->v.parent	= cpu_to_le32(src_subvolid);
-	new_subvol->v.otime.lo	= cpu_to_le64(bch2_current_time(c));
-	new_subvol->v.otime.hi	= 0;
+	new_subvol->v.flags		= 0;
+	new_subvol->v.snapshot		= cpu_to_le32(new_nodes[0]);
+	new_subvol->v.inode		= cpu_to_le64(inode);
+	new_subvol->v.creation_parent	= cpu_to_le32(src_subvolid);
+	new_subvol->v.fs_path_parent	= cpu_to_le32(parent_subvolid);
+	new_subvol->v.otime.lo		= cpu_to_le64(bch2_current_time(c));
+	new_subvol->v.otime.hi		= 0;
 
 	SET_BCH_SUBVOLUME_RO(&new_subvol->v, ro);
 	SET_BCH_SUBVOLUME_SNAP(&new_subvol->v, src_subvolid != 0);
diff --git a/libbcachefs/subvolume.h b/libbcachefs/subvolume.h
index 3ca1d183..4045a180 100644
--- a/libbcachefs/subvolume.h
+++ b/libbcachefs/subvolume.h
@@ -7,17 +7,22 @@
 enum bkey_invalid_flags;
 
 int bch2_check_subvols(struct bch_fs *);
+int bch2_check_subvol_children(struct bch_fs *);
 
 int bch2_subvolume_invalid(struct bch_fs *, struct bkey_s_c,
 			   enum bkey_invalid_flags, struct printbuf *);
 void bch2_subvolume_to_text(struct printbuf *, struct bch_fs *, struct bkey_s_c);
+int bch2_subvolume_trigger(struct btree_trans *, enum btree_id, unsigned,
+			   struct bkey_s_c, struct bkey_s, unsigned);
 
 #define bch2_bkey_ops_subvolume ((struct bkey_ops) {		\
 	.key_invalid	= bch2_subvolume_invalid,		\
 	.val_to_text	= bch2_subvolume_to_text,		\
+	.trigger	= bch2_subvolume_trigger,		\
 	.min_val_size	= 16,					\
 })
 
+int bch2_subvol_has_children(struct btree_trans *, u32);
 int bch2_subvolume_get(struct btree_trans *, unsigned,
 		       bool, int, struct bch_subvolume *);
 int bch2_subvolume_get_snapshot(struct btree_trans *, u32, u32 *);
@@ -29,8 +34,7 @@ int bch2_delete_dead_snapshots(struct bch_fs *);
 void bch2_delete_dead_snapshots_async(struct bch_fs *);
 
 int bch2_subvolume_unlink(struct btree_trans *, u32);
-int bch2_subvolume_create(struct btree_trans *, u64, u32,
-			  u32 *, u32 *, bool);
+int bch2_subvolume_create(struct btree_trans *, u64, u32, u32, u32 *, u32 *, bool);
 
 int bch2_fs_subvolumes_init(struct bch_fs *);
 
diff --git a/libbcachefs/subvolume_format.h b/libbcachefs/subvolume_format.h
index af79134b..e029df7b 100644
--- a/libbcachefs/subvolume_format.h
+++ b/libbcachefs/subvolume_format.h
@@ -19,8 +19,8 @@ struct bch_subvolume {
 	 * This is _not_ necessarily the subvolume of the directory containing
 	 * this subvolume:
 	 */
-	__le32			parent;
-	__le32			pad;
+	__le32			creation_parent;
+	__le32			fs_path_parent;
 	bch_le128		otime;
 };
 
diff --git a/linux/mean_and_variance.c b/linux/mean_and_variance.c
index b93d150d..21ec6afc 100644
--- a/linux/mean_and_variance.c
+++ b/linux/mean_and_variance.c
@@ -102,6 +102,8 @@ EXPORT_SYMBOL_GPL(mean_and_variance_get_stddev);
  * mean_and_variance_weighted_update() - exponentially weighted variant of mean_and_variance_update()
  * @s: mean and variance number of samples and their sums
  * @x: new value to include in the &mean_and_variance_weighted
+ * @initted: caller must track whether this is the first use or not
+ * @weight: ewma weight
  *
  * see linked pdf: function derived from equations 140-143 where alpha = 2^w.
  * values are stored bitshifted for performance and added precision.
@@ -132,6 +134,7 @@ EXPORT_SYMBOL_GPL(mean_and_variance_weighted_update);
 /**
  * mean_and_variance_weighted_get_mean() - get mean from @s
  * @s: mean and variance number of samples and their sums
+ * @weight: ewma weight
  */
 s64 mean_and_variance_weighted_get_mean(struct mean_and_variance_weighted s,
 		u8 weight)
@@ -143,6 +146,7 @@ EXPORT_SYMBOL_GPL(mean_and_variance_weighted_get_mean);
 /**
  * mean_and_variance_weighted_get_variance() -- get variance from @s
  * @s: mean and variance number of samples and their sums
+ * @weight: ewma weight
  */
 u64 mean_and_variance_weighted_get_variance(struct mean_and_variance_weighted s,
 		u8 weight)
@@ -155,6 +159,7 @@ EXPORT_SYMBOL_GPL(mean_and_variance_weighted_get_variance);
 /**
  * mean_and_variance_weighted_get_stddev() - get standard deviation from @s
  * @s: mean and variance number of samples and their sums
+ * @weight: ewma weight
  */
 u32 mean_and_variance_weighted_get_stddev(struct mean_and_variance_weighted s,
 		u8 weight)