if (fd == 87 || fd == 88) (new Throwable()).printStackTrace();
  public static int close(int fd) {    if (VM.TraceFileSystem) VM.sysWrite("VM_FileSystem.close: fd=" + fd + "\n");    VM_BootRecord bootRecord = VM_BootRecord.the_boot_record;    return VM.sysCall1(bootRecord.sysCloseIP, fd);  }