Example of open and close
=========================

The following program fragment shows how the driver is opened and closed.
The driver must always be opened before any action can be performed::

  void open_test(void)
    { int i:
    
      printf("opening the vcan-driver...\n");
      handle= open("/dev/vcan", O_RDWR, 0666);
      if (handle==-1)
        { printf("opening of the driver failed!\n");
          printf("errno: %d\n", errno);
          return;
        };
      /* perform some commands : */
      do_something_with_the_CAN_bus();
      /* finished */
      i= close(handle);
      if (i==-1)
        { printf("closing failed !\n"); 
          printf("errno: %d\n", errno); 
          return;        
        };
    }