Open

a request to open the printer device

The open routine grants access to a device. There are two fields in the iORequest block that will be filled in: the IO_DEVICE field has already been initialized by OpenDevice; the Open routine will to initialize the IO_UNIT field as appropriate.

The device open count will be incremented. The device cannot be expunged unless this open is matched by a Close device.

If the open was unsuccessful, IO_ERROR will be set, IO_UNIT and IO_DEVICE will not be valid.