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Section 13
MFDSP$–Master File Directory Service
Package
MFDSP$ retrieves information about files from the master file directory (MFD). A copy
of the MFD is needed before the MFDSP$ routine can be used. The MFD copy is
produced by a call to ER MSCON$ (using the DGET$ or DGETP$ function). Once this
copy of the MFD is in a mass storage file that is assigned to the calling program, the
MFDSP$ routine can be used to retrieve the lead items, main items, and device area
descriptor (DAD) tables of all the files in the MFD. A complete description of how the
ER MSCON$ is used and what information is contained in lead items, main items, and
DAD tables can be found in the Exec Installation and Configuration Guide.
The copy of the MFD can also be obtained by initially calling MFDSP$ with function code
10. MFDSP$ then does an ER MSCON$ DGET$ function to copy the MFD to a scratch
file that MFDSP$ has assigned.
The following subsections describe the packet needed by the MFDSP$ routine, as well
as the MASM calling sequence.
13.1. Packet
The MFDSP$ routine requires that the calling program provide it with a packet. The first
two words of the MFDSP$ packet must contain (in Fieldata LJSF) the internal file name
of the file that holds the output from the ER MSCON$. This file must be assigned
before the call to MFDSP$ can be made. Failure to have the file assigned results in an
I/O error type 01, code 21, contingency 12.
The MFDSP$ routine uses the remainder of the packet as scratch space. Since the
routine does track-size double-buffered I/O, the packet must be large enough to hold two
I/O packets, two track-size buffers, and additional space required by the MFDSP$ routine
for its internal tables. In general, a packet of 4,400 words is an adequate starting size.
Once the ER MSCON$ file is successfully initialized, the exact packet size required is
returned in register A5. The packet length may have to be increased if a 02 error is
returned.
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