presto-hive/src/main/java/io/prestosql/plugin/hive/util/HiveWriteUtils.java/HiveWriteUtils/getRawFileSystem
class HiveWriteUtils:    private static FileSystem getRawFileSystem(FileSystem fileSystem)
    {
        if (fileSystem instanceof FilterFileSystem) {
            return getRawFileSystem(((FilterFileSystem) fileSystem).getRawFileSystem());
        }
        return fileSystem;
    }