vcan_request
============

Here is the definition::

  typedef struct
    { vcan_message_tag    tag          CDEP_NOALIGN_ATTR;
      void                *ptr         CDEP_NOALIGN_ATTR; /* (multi purpose
                                                              pointer) */
      vcan_message        message CDEP_NOALIGN_ATTR;
    } vcan_request;

This driver-call-structure is used to issue a vcan-request. A request is
given as driver-call-data to the system-functions ``read`` or a ``write``.
This structure consists of a tag, describing the kind of the request, a
vcan-message ``message`` and a pointer ``ptr``. The ``ptr`` field is a
multi-purpose pointer and is currently only needed by the VCAN_READ_MANY``
and the ``VCAN_WRITETIMED``-driver-functions. 

In the case of ``VCAN_READ_MANY``, ``ptr`` is a pointer to an array of
integers, the first one is the timeout, all the following are CAN-Id's. The
list of CAN-Id's is finished with a ``-1``.

In the case of ``VCAN_WRITETIMED``, ``ptr`` is a pointer to a variable of the
type ``unsigned long`` that contains the inhibit-time at the start of the
function and the remaining wait-time at the end of the function.  See also the
description of ``VCAN_WRITETIMED``, which is part of the ``vcan_message_tag``
data-type.

tag
  This is the tag that defines the kind of the request.

ptr
  The multi-purpose pointer, see description above.

message
  The vcan-message.