1 files changed, 329 insertions, 49 deletions

diff --git a/fs/bcachefs/subvolume.c b/fs/bcachefs/subvolume.c
index 7c67c28d3ef8..b7b96283c316 100644
--- a/fs/bcachefs/subvolume.c
+++ b/fs/bcachefs/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 +55,72 @@ 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,
+			trans, 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,
+				trans, 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;
+	ret = bch2_inode_find_by_inum_nowarn_trans(trans,
+				    (subvol_inum) { k.k->p.offset, le64_to_cpu(subvol.v->inode) },
+				    &inode);
+	if (!ret) {
+		if (fsck_err_on(inode.bi_subvol != subvol.k->p.offset,
+				trans, subvol_root_wrong_bi_subvol,
+				"subvol root %llu:%u has wrong bi_subvol field: got %u, should be %llu",
+				inode.bi_inum, inode.bi_snapshot,
+				inode.bi_subvol, subvol.k->p.offset)) {
+			inode.bi_subvol = subvol.k->p.offset;
+			inode.bi_snapshot = le32_to_cpu(subvol.v->snapshot);
+			ret = __bch2_fsck_write_inode(trans, &inode);
+			if (ret)
+				goto err;
+		}
+	} else if (bch2_err_matches(ret, ENOENT)) {
+		if (fsck_err(trans, subvol_to_missing_root,
+			     "subvolume %llu points to missing subvolume root %llu:%u",
+			     k.k->p.offset, le64_to_cpu(subvol.v->inode),
+			     le32_to_cpu(subvol.v->snapshot))) {
+			ret = bch2_subvolume_delete(trans, iter->pos.offset);
+			bch_err_msg(c, ret, "deleting subvolume %llu", iter->pos.offset);
+			ret = ret ?: -BCH_ERR_transaction_restart_nested;
+			goto err;
+		}
+	} else {
+		goto err;
+	}
+
 	if (!BCH_SUBVOLUME_SNAP(subvol.v)) {
 		u32 snapshot_root = bch2_snapshot_root(c, le32_to_cpu(subvol.v->snapshot));
 		u32 snapshot_tree;
@@ -57,23 +136,25 @@ static int check_subvol(struct btree_trans *trans,
 				"%s: snapshot tree %u not found", __func__, snapshot_tree);
 
 		if (ret)
-			return ret;
+			goto err;
 
 		if (fsck_err_on(le32_to_cpu(st.master_subvol) != subvol.k->p.offset,
-				c, subvol_not_master_and_not_snapshot,
+				trans, subvol_not_master_and_not_snapshot,
 				"subvolume %llu is not set as snapshot but is not master subvolume",
 				k.k->p.offset)) {
 			struct bkey_i_subvolume *s =
 				bch2_bkey_make_mut_typed(trans, iter, &subvol.s_c, 0, subvolume);
 			ret = PTR_ERR_OR_ZERO(s);
 			if (ret)
-				return ret;
+				goto err;
 
 			SET_BCH_SUBVOLUME_SNAP(&s->v, true);
 		}
 	}
-
+err:
 fsck_err:
+	bch2_trans_iter_exit(trans, &subvol_children_iter);
+	printbuf_exit(&buf);
 	return ret;
 }
 
@@ -81,24 +162,68 @@ int bch2_check_subvols(struct bch_fs *c)
 {
 	int ret = bch2_trans_run(c,
 		for_each_btree_key_commit(trans, iter,
-				BTREE_ID_subvolumes, POS_MIN, BTREE_ITER_PREFETCH, k,
+				BTREE_ID_subvolumes, POS_MIN, BTREE_ITER_prefetch, k,
 				NULL, NULL, BCH_TRANS_COMMIT_no_enospc,
 			check_subvol(trans, &iter, k)));
 	bch_err_fn(c, ret);
 	return ret;
 }
 
+static int check_subvol_child(struct btree_trans *trans,
+			      struct btree_iter *child_iter,
+			      struct bkey_s_c child_k)
+{
+	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,
+			trans, 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,
-			   enum bkey_invalid_flags flags, struct printbuf *err)
+int bch2_subvolume_validate(struct bch_fs *c, struct bkey_s_c k,
+			    struct bkey_validate_context from)
 {
+	struct bkey_s_c_subvolume subvol = bkey_s_c_to_subvolume(k);
 	int ret = 0;
 
 	bkey_fsck_err_on(bkey_lt(k.k->p, SUBVOL_POS_MIN) ||
-			 bkey_gt(k.k->p, SUBVOL_POS_MAX), c, err,
-			 subvol_pos_bad,
+			 bkey_gt(k.k->p, SUBVOL_POS_MAX),
+			 c, subvol_pos_bad,
 			 "invalid pos");
+
+	bkey_fsck_err_on(!subvol.v->snapshot,
+			 c, subvol_snapshot_bad,
+			 "invalid snapshot");
+
+	bkey_fsck_err_on(!subvol.v->inode,
+			 c, subvol_inode_bad,
+			 "invalid inode");
 fsck_err:
 	return ret;
 }
@@ -112,18 +237,60 @@ 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,
+			   enum btree_iter_update_trigger_flags 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
 bch2_subvolume_get_inlined(struct btree_trans *trans, unsigned subvol,
 			   bool inconsistent_if_not_found,
-			   int iter_flags,
 			   struct bch_subvolume *s)
 {
 	int ret = bch2_bkey_get_val_typed(trans, BTREE_ID_subvolumes, POS(0, subvol),
-					  iter_flags, subvolume, s);
+					  BTREE_ITER_cached|
+					  BTREE_ITER_with_updates, subvolume, s);
 	bch2_fs_inconsistent_on(bch2_err_matches(ret, ENOENT) &&
 				inconsistent_if_not_found,
 				trans->c, "missing subvolume %u", subvol);
@@ -132,16 +299,15 @@ bch2_subvolume_get_inlined(struct btree_trans *trans, unsigned subvol,
 
 int bch2_subvolume_get(struct btree_trans *trans, unsigned subvol,
 		       bool inconsistent_if_not_found,
-		       int iter_flags,
 		       struct bch_subvolume *s)
 {
-	return bch2_subvolume_get_inlined(trans, subvol, inconsistent_if_not_found, iter_flags, s);
+	return bch2_subvolume_get_inlined(trans, subvol, inconsistent_if_not_found, s);
 }
 
 int bch2_subvol_is_ro_trans(struct btree_trans *trans, u32 subvol)
 {
 	struct bch_subvolume s;
-	int ret = bch2_subvolume_get_inlined(trans, subvol, true, 0, &s);
+	int ret = bch2_subvolume_get_inlined(trans, subvol, true, &s);
 	if (ret)
 		return ret;
 
@@ -152,8 +318,7 @@ int bch2_subvol_is_ro_trans(struct btree_trans *trans, u32 subvol)
 
 int bch2_subvol_is_ro(struct bch_fs *c, u32 subvol)
 {
-	return bch2_trans_do(c, NULL, NULL, 0,
-		bch2_subvol_is_ro_trans(trans, subvol));
+	return bch2_trans_do(c, bch2_subvol_is_ro_trans(trans, subvol));
 }
 
 int bch2_snapshot_get_subvol(struct btree_trans *trans, u32 snapshot,
@@ -162,11 +327,11 @@ int bch2_snapshot_get_subvol(struct btree_trans *trans, u32 snapshot,
 	struct bch_snapshot snap;
 
 	return  bch2_snapshot_lookup(trans, snapshot, &snap) ?:
-		bch2_subvolume_get(trans, le32_to_cpu(snap.subvol), true, 0, subvol);
+		bch2_subvolume_get(trans, le32_to_cpu(snap.subvol), true, subvol);
 }
 
-int bch2_subvolume_get_snapshot(struct btree_trans *trans, u32 subvolid,
-				u32 *snapid)
+int __bch2_subvolume_get_snapshot(struct btree_trans *trans, u32 subvolid,
+				  u32 *snapid, bool warn)
 {
 	struct btree_iter iter;
 	struct bkey_s_c_subvolume subvol;
@@ -174,10 +339,11 @@ int bch2_subvolume_get_snapshot(struct btree_trans *trans, u32 subvolid,
 
 	subvol = bch2_bkey_get_iter_typed(trans, &iter,
 					  BTREE_ID_subvolumes, POS(0, subvolid),
-					  BTREE_ITER_CACHED|BTREE_ITER_WITH_UPDATES,
+					  BTREE_ITER_cached|BTREE_ITER_with_updates,
 					  subvolume);
 	ret = bkey_err(subvol);
-	bch2_fs_inconsistent_on(bch2_err_matches(ret, ENOENT), trans->c,
+
+	bch2_fs_inconsistent_on(warn && bch2_err_matches(ret, ENOENT), trans->c,
 				"missing subvolume %u", subvolid);
 
 	if (likely(!ret))
@@ -186,6 +352,12 @@ int bch2_subvolume_get_snapshot(struct btree_trans *trans, u32 subvolid,
 	return ret;
 }
 
+int bch2_subvolume_get_snapshot(struct btree_trans *trans, u32 subvolid,
+				u32 *snapid)
+{
+	return __bch2_subvolume_get_snapshot(trans, subvolid, snapid, true);
+}
+
 static int bch2_subvolume_reparent(struct btree_trans *trans,
 				   struct btree_iter *iter,
 				   struct bkey_s_c k,
@@ -197,8 +369,8 @@ 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);
@@ -206,7 +378,7 @@ 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;
 }
 
@@ -223,13 +395,12 @@ static int bch2_subvolumes_reparent(struct btree_trans *trans, u32 subvolid_to_d
 	struct bch_subvolume s;
 
 	return lockrestart_do(trans,
-			bch2_subvolume_get(trans, subvolid_to_delete, true,
-				   BTREE_ITER_CACHED, &s)) ?:
+			bch2_subvolume_get(trans, subvolid_to_delete, true, &s)) ?:
 		for_each_btree_key_commit(trans, iter,
-				BTREE_ID_subvolumes, POS_MIN, BTREE_ITER_PREFETCH, k,
+				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)));
 }
 
 /*
@@ -238,26 +409,61 @@ static int bch2_subvolumes_reparent(struct btree_trans *trans, u32 subvolid_to_d
  */
 static int __bch2_subvolume_delete(struct btree_trans *trans, u32 subvolid)
 {
-	struct btree_iter iter;
-	struct bkey_s_c_subvolume subvol;
-	u32 snapid;
-	int ret = 0;
+	struct btree_iter subvol_iter = {}, snapshot_iter = {}, snapshot_tree_iter = {};
 
-	subvol = bch2_bkey_get_iter_typed(trans, &iter,
+	struct bkey_s_c_subvolume subvol =
+		bch2_bkey_get_iter_typed(trans, &subvol_iter,
 				BTREE_ID_subvolumes, POS(0, subvolid),
-				BTREE_ITER_CACHED|BTREE_ITER_INTENT,
+				BTREE_ITER_cached|BTREE_ITER_intent,
 				subvolume);
-	ret = bkey_err(subvol);
+	int ret = bkey_err(subvol);
 	bch2_fs_inconsistent_on(bch2_err_matches(ret, ENOENT), trans->c,
 				"missing subvolume %u", subvolid);
 	if (ret)
-		return ret;
+		goto err;
 
-	snapid = le32_to_cpu(subvol.v->snapshot);
+	u32 snapid = le32_to_cpu(subvol.v->snapshot);
+
+	struct bkey_s_c_snapshot snapshot =
+		bch2_bkey_get_iter_typed(trans, &snapshot_iter,
+				BTREE_ID_snapshots, POS(0, snapid),
+				0, snapshot);
+	ret = bkey_err(snapshot);
+	bch2_fs_inconsistent_on(bch2_err_matches(ret, ENOENT), trans->c,
+				"missing snapshot %u", snapid);
+	if (ret)
+		goto err;
+
+	u32 treeid = le32_to_cpu(snapshot.v->tree);
+
+	struct bkey_s_c_snapshot_tree snapshot_tree =
+		bch2_bkey_get_iter_typed(trans, &snapshot_tree_iter,
+				BTREE_ID_snapshot_trees, POS(0, treeid),
+				0, snapshot_tree);
+	ret = bkey_err(snapshot_tree);
+	bch2_fs_inconsistent_on(bch2_err_matches(ret, ENOENT), trans->c,
+				"missing snapshot tree %u", treeid);
+	if (ret)
+		goto err;
+
+	if (le32_to_cpu(snapshot_tree.v->master_subvol) == subvolid) {
+		struct bkey_i_snapshot_tree *snapshot_tree_mut =
+			bch2_bkey_make_mut_typed(trans, &snapshot_tree_iter,
+						 &snapshot_tree.s_c,
+						 0, snapshot_tree);
+		ret = PTR_ERR_OR_ZERO(snapshot_tree_mut);
+		if (ret)
+			goto err;
 
-	ret =   bch2_btree_delete_at(trans, &iter, 0) ?:
+		snapshot_tree_mut->v.master_subvol = 0;
+	}
+
+	ret =   bch2_btree_delete_at(trans, &subvol_iter, 0) ?:
 		bch2_snapshot_node_set_deleted(trans, snapid);
-	bch2_trans_iter_exit(trans, &iter);
+err:
+	bch2_trans_iter_exit(trans, &snapshot_tree_iter);
+	bch2_trans_iter_exit(trans, &snapshot_iter);
+	bch2_trans_iter_exit(trans, &subvol_iter);
 	return ret;
 }
 
@@ -346,7 +552,7 @@ int bch2_subvolume_unlink(struct btree_trans *trans, u32 subvolid)
 
 	n = bch2_bkey_get_mut_typed(trans, &iter,
 			BTREE_ID_subvolumes, POS(0, subvolid),
-			BTREE_ITER_CACHED, subvolume);
+			BTREE_ITER_cached, subvolume);
 	ret = PTR_ERR_OR_ZERO(n);
 	if (unlikely(ret)) {
 		bch2_fs_inconsistent_on(bch2_err_matches(ret, ENOENT), trans->c,
@@ -360,6 +566,7 @@ 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,
@@ -387,7 +594,7 @@ int bch2_subvolume_create(struct btree_trans *trans, u64 inode,
 
 		src_subvol = bch2_bkey_get_mut_typed(trans, &src_iter,
 				BTREE_ID_subvolumes, POS(0, src_subvolid),
-				BTREE_ITER_CACHED, subvolume);
+				BTREE_ITER_cached, subvolume);
 		ret = PTR_ERR_OR_ZERO(src_subvol);
 		if (unlikely(ret)) {
 			bch2_fs_inconsistent_on(bch2_err_matches(ret, ENOENT), c,
@@ -416,12 +623,13 @@ 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);
@@ -434,6 +642,78 @@ err:
 	return ret;
 }
 
+int bch2_initialize_subvolumes(struct bch_fs *c)
+{
+	struct bkey_i_snapshot_tree	root_tree;
+	struct bkey_i_snapshot		root_snapshot;
+	struct bkey_i_subvolume		root_volume;
+	int ret;
+
+	bkey_snapshot_tree_init(&root_tree.k_i);
+	root_tree.k.p.offset		= 1;
+	root_tree.v.master_subvol	= cpu_to_le32(1);
+	root_tree.v.root_snapshot	= cpu_to_le32(U32_MAX);
+
+	bkey_snapshot_init(&root_snapshot.k_i);
+	root_snapshot.k.p.offset = U32_MAX;
+	root_snapshot.v.flags	= 0;
+	root_snapshot.v.parent	= 0;
+	root_snapshot.v.subvol	= cpu_to_le32(BCACHEFS_ROOT_SUBVOL);
+	root_snapshot.v.tree	= cpu_to_le32(1);
+	SET_BCH_SNAPSHOT_SUBVOL(&root_snapshot.v, true);
+
+	bkey_subvolume_init(&root_volume.k_i);
+	root_volume.k.p.offset = BCACHEFS_ROOT_SUBVOL;
+	root_volume.v.flags	= 0;
+	root_volume.v.snapshot	= cpu_to_le32(U32_MAX);
+	root_volume.v.inode	= cpu_to_le64(BCACHEFS_ROOT_INO);
+
+	ret =   bch2_btree_insert(c, BTREE_ID_snapshot_trees,	&root_tree.k_i, NULL, 0, 0) ?:
+		bch2_btree_insert(c, BTREE_ID_snapshots,	&root_snapshot.k_i, NULL, 0, 0) ?:
+		bch2_btree_insert(c, BTREE_ID_subvolumes,	&root_volume.k_i, NULL, 0, 0);
+	bch_err_fn(c, ret);
+	return ret;
+}
+
+static int __bch2_fs_upgrade_for_subvolumes(struct btree_trans *trans)
+{
+	struct btree_iter iter;
+	struct bkey_s_c k;
+	struct bch_inode_unpacked inode;
+	int ret;
+
+	k = bch2_bkey_get_iter(trans, &iter, BTREE_ID_inodes,
+			       SPOS(0, BCACHEFS_ROOT_INO, U32_MAX), 0);
+	ret = bkey_err(k);
+	if (ret)
+		return ret;
+
+	if (!bkey_is_inode(k.k)) {
+		bch_err(trans->c, "root inode not found");
+		ret = -BCH_ERR_ENOENT_inode;
+		goto err;
+	}
+
+	ret = bch2_inode_unpack(k, &inode);
+	BUG_ON(ret);
+
+	inode.bi_subvol = BCACHEFS_ROOT_SUBVOL;
+
+	ret = bch2_inode_write(trans, &iter, &inode);
+err:
+	bch2_trans_iter_exit(trans, &iter);
+	return ret;
+}
+
+/* set bi_subvol on root inode */
+int bch2_fs_upgrade_for_subvolumes(struct bch_fs *c)
+{
+	int ret = bch2_trans_commit_do(c, NULL, NULL, BCH_TRANS_COMMIT_no_enospc,
+				       __bch2_fs_upgrade_for_subvolumes(trans));
+	bch_err_fn(c, ret);
+	return ret;
+}
+
 int bch2_fs_subvolumes_init(struct bch_fs *c)
 {
 	INIT_WORK(&c->snapshot_delete_work, bch2_delete_dead_snapshots_work);