3 files changed, 60 insertions, 1 deletions

diff --git a/fs/bcachefs/btree_update.c b/fs/bcachefs/btree_update.c
index 5dac09c98026..48af3d2e3da9 100644
--- a/fs/bcachefs/btree_update.c
+++ b/fs/bcachefs/btree_update.c
@@ -180,8 +180,19 @@ int __bch2_insert_snapshot_whiteouts(struct btree_trans *trans,
 	}
 	bch2_trans_iter_exit(trans, &new_iter);
 	bch2_trans_iter_exit(trans, &old_iter);
-	darray_exit(&s);
 
+	snapshot_id_list s2;
+	ret = bch2_get_snapshot_overwrites(trans, id, old_pos, &s2);
+	if (ret) {
+		darray_exit(&s);
+		return ret;
+	}
+
+	BUG_ON(s.nr != s2.nr);
+	BUG_ON(memcmp(s.data, s2.data, sizeof(s.data[0]) * s.nr));
+
+	darray_exit(&s2);
+	darray_exit(&s);
 	return ret;
 }
 
diff --git a/fs/bcachefs/snapshot.c b/fs/bcachefs/snapshot.c
index 00d62d1190ef..f553fe095f61 100644
--- a/fs/bcachefs/snapshot.c
+++ b/fs/bcachefs/snapshot.c
@@ -1079,6 +1079,35 @@ fsck_err:
 	return ret;
 }
 
+int __bch2_get_snapshot_overwrites(struct btree_trans *trans,
+				   enum btree_id btree, struct bpos pos,
+				   snapshot_id_list *s)
+{
+	struct bch_fs *c = trans->c;
+	struct btree_iter iter;
+	struct bkey_s_c k;
+	int ret = 0;
+
+	for_each_btree_key_reverse_norestart(trans, iter, btree, bpos_predecessor(pos),
+					     BTREE_ITER_all_snapshots, k, ret) {
+		if (!bkey_eq(k.k->p, pos))
+			break;
+
+		if (!bch2_snapshot_is_ancestor(c, k.k->p.snapshot, pos.snapshot) ||
+		    snapshot_list_has_ancestor(c, s, k.k->p.snapshot))
+			continue;
+
+		ret = snapshot_list_add(c, s, k.k->p.snapshot);
+		if (ret)
+			break;
+	}
+	bch2_trans_iter_exit(trans, &iter);
+	if (ret)
+		darray_exit(s);
+
+	return ret;
+}
+
 /*
  * Mark a snapshot as deleted, for future cleanup:
  */
diff --git a/fs/bcachefs/snapshot.h b/fs/bcachefs/snapshot.h
index 382a171f5413..be7b71c06621 100644
--- a/fs/bcachefs/snapshot.h
+++ b/fs/bcachefs/snapshot.h
@@ -258,6 +258,25 @@ static inline int bch2_check_key_has_snapshot(struct btree_trans *trans,
 		: __bch2_check_key_has_snapshot(trans, iter, k);
 }
 
+int __bch2_get_snapshot_overwrites(struct btree_trans *,
+				   enum btree_id, struct bpos,
+				   snapshot_id_list *);
+
+/*
+ * Get a list of snapshot IDs that have overwritten a given key:
+ */
+static inline int bch2_get_snapshot_overwrites(struct btree_trans *trans,
+					       enum btree_id btree, struct bpos pos,
+					       snapshot_id_list *s)
+{
+	darray_init(s);
+
+	return bch2_snapshot_has_children(trans->c, pos.snapshot)
+		? __bch2_get_snapshot_overwrites(trans, btree, pos, s)
+		: 0;
+
+}
+
 int bch2_snapshot_node_set_deleted(struct btree_trans *, u32);
 
 int __bch2_key_has_snapshot_overwrites(struct btree_trans *, enum btree_id, struct bpos);