return (*handler) (fd, request, arg);
{  int save = errno; int result = (*handler) (fd, request, arg); if (result != -1 || errno != ENOTTY) return result;   errno = save; }
DEFUN(__ioctl, (fd, request),      int fd AND unsigned long int request DOTS){  /* Map individual type fields to Mach IPC types.  */  static const int mach_types[] =    { MACH_MSG_TYPE_CHAR, MACH_MSG_TYPE_INTEGER_16, MACH_MSG_TYPE_INTEGER_32,      -1 };#define io2mach_type(count, type) \  ((mach_msg_type_t) { mach_types[type], typesize (type) * 8, count, 1, 0, 0 })  /* Extract the type information encoded in the request.  */  unsigned int type = _IOC_TYPE (request);  /* Message buffer.  */  struct    {      mig_reply_header_t header;      char data[3 * sizeof (mach_msg_type_t) +		_IOT_COUNT0 (type) * typesize (_IOT_TYPE0 (type)) +		_IOT_COUNT1 (type) * typesize (_IOT_TYPE1 (type)) +		_IOT_COUNT2 (type) * typesize (_IOT_TYPE2 (type))];    } msg;  mach_msg_header_t *const m = &msg.header.Head;  mach_msg_type_t *t = &msg.header.RetCodeType;  mach_msg_id_t msgid;  unsigned int reply_size;  void *arg;  error_t err;  /* Send the RPC already packed up in MSG to IOPORT     and decode the return value.  */  error_t send_rpc (io_t ioport)    {      error_t err;      m->msgh_size = (char *) t - (char *) &msg;      m->msgh_remote_port = ioport;      m->msgh_local_port = __mig_get_reply_port ();      m->msgh_seqno = 0;      m->msgh_id = msgid;      m->msgh_bits = MACH_MSGH_BITS (MACH_MSG_TYPE_COPY_SEND,				     MACH_MSG_TYPE_MAKE_SEND_ONCE);      err = _hurd_intr_rpc_mach_msg (m, MACH_SEND_MSG|MACH_RCV_MSG,				     m->msgh_size, sizeof (msg),				     m->msgh_local_port,				     MACH_MSG_TIMEOUT_NONE,				     MACH_PORT_NULL);      switch (err)	{	case MACH_MSG_SUCCESS:	  break;	case MACH_SEND_INVALID_REPLY:	case MACH_RCV_INVALID_NAME:	  __mig_dealloc_reply_port (m->msgh_local_port);	default:	  return err;	}      if ((m->msgh_bits & MACH_MSGH_BITS_COMPLEX))	{	  /* Allow no ports or VM.  */	  __mach_msg_destroy (m);	  /* Want to return a different error below for a different msgid.  */	  if (m->msgh_id == msgid + 100)	    return MIG_TYPE_ERROR;	}      if (m->msgh_id != msgid + 100)	return (m->msgh_id == MACH_NOTIFY_SEND_ONCE ?		MIG_SERVER_DIED : MIG_REPLY_MISMATCH);      if (m->msgh_size != reply_size &&	  m->msgh_size != sizeof (mig_reply_header_t))	return MIG_TYPE_ERROR;      if (*(int *) &msg.header.RetCodeType !=	  ((union { mach_msg_type_t t; int i; })	   { t: io2mach_type (1, _IOTS (sizeof msg.header.RetCode)) }).i)	return MIG_TYPE_ERROR;      return msg.header.RetCode;    }  va_list ap;  va_start (ap, request);  arg = va_arg (ap, void *);  va_end (ap);  {    /* Check for a registered handler for REQUEST.  */    ioctl_handler_t handler = _hurd_lookup_ioctl_handler (request);    if (handler)      /* This handler groks REQUEST.  Se lo puntamonos.  */      return (*handler) (fd, request, arg);  }  /* Compute the Mach message ID for the RPC from the group and command     parts of the ioctl request.  */  msgid = 100000 + ((_IOC_GROUP (request) - 'f') * 4000); /* Base subsystem */  /* Because of MiG's poorly chosen algorithm of adding 100 to a request     msgid to produce the reply msgid, we cannot just add the command part     of the ioctl request to the subsystem base msgid.  For ioctl requests     past 99, we must skip blocks of 100 msgids to allow for the reply     msgids corresponding to the earlier requests.  */  if (_IOC_COMMAND (request) >= 100)    msgid += 100;  if (_IOC_COMMAND (request) >= 200)    msgid += 100;  msgid += _IOC_COMMAND (request);  if (_IOC_INOUT (request) & IOC_IN)    {      /* Pack an argument into the message buffer.  */      void in (unsigned int count, enum __ioctl_datum type)	{	  if (count > 0)	    {	      void *p = &t[1];	      const size_t len = count * typesize ((unsigned int) type);	      *t = io2mach_type (count, type);	      memcpy (p, arg, len);	      arg += len;	      p += len;	      p = (void *) (((unsigned long int) p + sizeof (*t) - 1)			    & ~(sizeof (*t) - 1));	      t = p;	    }	}      /* Pack the argument data.  */      in (_IOT_COUNT0 (type), _IOT_TYPE0 (type));      in (_IOT_COUNT1 (type), _IOT_TYPE1 (type));      in (_IOT_COUNT2 (type), _IOT_TYPE2 (type));    }  else if (_IOC_INOUT (request) == IOC_VOID)    {      /* The RPC takes a single integer_t argument.	 Rather than pointing to the value, ARG is the value itself.  */      *t++ = io2mach_type (1, _IOTS (int));      *((int *) t)++ = (int) arg;    }  /* Compute the expected size of the reply.  There is a standard header     consisting of the message header and the reply code.  Then, for out     and in/out ioctls, there come the data with their type headers.  */  reply_size = sizeof (mig_reply_header_t);  if (_IOC_INOUT (request) & IOC_OUT)    {      inline void figure_reply (unsigned int count, enum __ioctl_datum type)	{	  if (count > 0)	    {	      /* Add the size of the type and data.  */	      reply_size += sizeof (mach_msg_type_t) + typesize (type) * count;	      /* Align it to word size.  */	      reply_size += sizeof (mach_msg_type_t) - 1;	      reply_size &= ~(sizeof (mach_msg_type_t) - 1);	    }	}      figure_reply (_IOT_COUNT0 (type), _IOT_TYPE0 (type));      figure_reply (_IOT_COUNT1 (type), _IOT_TYPE1 (type));      figure_reply (_IOT_COUNT2 (type), _IOT_TYPE2 (type));    }  err = HURD_DPORT_USE (fd, _hurd_ctty_output (port, ctty, send_rpc));  t = (mach_msg_type_t *) msg.data;  switch (err)    {      /* Unpack the message buffer into the argument location.  */      int out (unsigned int count, unsigned int type,	       void *store, void **update)	{	  if (count > 0)	    {	      const size_t len = count * typesize (type);	      union { mach_msg_type_t t; int i; } ipctype;	      ipctype.t = io2mach_type (count, type);	      if (*(int *) t != ipctype.i)		return 1;	      ++t;	      memcpy (store, t, len);	      if (update != NULL)		*update += len;	      t = (void *) (((unsigned long int) t + len + sizeof (*t) - 1)			    & ~(sizeof (*t) - 1));	    }	  return 0;	}    case 0:      if (m->msgh_size != reply_size ||	  ((_IOC_INOUT (request) & IOC_OUT) &&	   (out (_IOT_COUNT0 (type), _IOT_TYPE0 (type), arg, &arg) ||	    out (_IOT_COUNT1 (type), _IOT_TYPE1 (type), arg, &arg) ||	    out (_IOT_COUNT2 (type), _IOT_TYPE2 (type), arg, &arg))))	return __hurd_fail (MIG_TYPE_ERROR);      return 0;    case MIG_BAD_ID:    case EOPNOTSUPP:      /* The server didn't understand the RPC.  */      err = ENOTTY;    default:      return __hurd_fail (err);    }}