SCSI Pass-Through Programmer's Guide

3. Dup capability on SPT device files
A ‘dup’ function has been introduced for SPT device files to duplicate them and thus have
multiple forked processes making SPT calls. SPT calls are made as described in the previous
section (please see appendix A for a program listing). Child processes can be created after
opening the SPT device file using the fork() call. This enhancement is available via patch
MPENX04A for MPE/iX release C.75.00
4. Using SPT Device files across system boots
The SPT ioctl call results in direct communication between the device managers (software)
and SCSI devices (hardware) via the ‘port’ number of the DM instead of the unique
(constant) LDEV number. A ‘Port’ is the low level medium for inter process communication
in MPE/iX. There is a possibility of the port assigned to each DM getting changed with each
system boot. As a consequence, these device files may not be valid across boots.
MPE/iX is now modified to create SPT device files that "store" the physical path of the
corresponding device instead of the DM port number. This path is converted to the current
DM port dynamically and the I/O happens. This change will make the device files valid
across boots. Application Programmers, hence, need not create the SPT device file each time.
The new user callable routine HPLDEVTOIOPATH can be used to map LDEV numbers to
the physical path to be used for the one-time creation of the SPT device file.
CAUTION: If you change a device’s SCSI ID, or move it from one HBA to another, the
physical path to that device also changes which would require creating a new device file for
that new path. Further, if you then add a new device at the old location the old device file
will be able to access it (unless you purge the old file at the time you moved the old device).
Therefore it is a good idea to purge and rebuild device files when configuration changes of
this sort are made on a system. Patch MPENX04A provides this enhancement for MPE/iX
release C.75.00.
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