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clone is a STREAMS software driver that finds and opens an unused minor device on another STREAMS driver. The minor device passed to clone during the open is interpreted as the major device number of another STREAMS driver for which an unused minor device is to be obtained. Each such open results in a separate stream to a previously unused minor device.
The clone driver consists solely of an open function. This open function performs all of the necessary work so that subsequent system calls (including close(S)) require no further involvement of clone.
clone will generate an ENXIO error, without opening the device, if the minor device number provided does not correspond to a valid major device, or if the driver indicated is not a STREAMS driver.
clone will generate an ENODEV error, without opening the device, if a pipe cannot be created.
AT&T STREAMS Programmer's Guide