func: static void fd_chr_update_read_handler(CharDriverState *chr)
  
  {
  
      FDCharDriver *s = chr->opaque;
  
  
  
      if (s->fd_in_tag) {
  
          g_source_remove(s->fd_in_tag);
  
          s->fd_in_tag = 0;
  
      }
  
  
  
      if (s->fd_in) {
  
          s->fd_in_tag = io_add_watch_poll(s->fd_in, fd_chr_read_poll, fd_chr_read, chr);
  
      }
  
  }
  