func: static int mux_chr_can_read(void *opaque)
  
  {
  
      CharDriverState *chr = opaque;
  
      MuxDriver *d = chr->opaque;
  
  
  
      if ((d->prod - d->cons) < MUX_BUFFER_SIZE)
  
          return 1;
  
      if (d->chr_can_read[chr->focus])
  
          return d->chr_can_read[chr->focus](d->ext_opaque[chr->focus]);
  
      return 0;
  
  }
  