10.3. Setting FFIO library parameters (UNICOS systems only)

The UNICOS operating system supports a number of library parameters that can be tuned. Sites can use these parameters to change both the performance of the libraries and some of their limits. Through a similar technique, users can also change these parameters when linking an application.

When SEGLDR is invoked, one of its first actions is to read the /lib/segdirs file, which defines the parameters of SEGLDR; this file contains an LINCLUDE directive for the file /usr/lib/segdirs/def_lib, which by default is empty. An administrator can place directives in this file to modify the SEGLDR behavior.

The following HARDREF directives select optional capabilities of the FFIO package to include in the standard libraries compiled into user programs by default.

Each of these directives refers to a list of function pointers. Each function-pointer list represents the set of routines necessary to process one or more options on the assign(1) command. Some of these layers are tied to specific hardware, such as tape or SDS. Others are foreign conversion options such as ETA System V-format data. Not all of these layers are loaded into user programs by default. As delivered, the UNICOS operating system can read and write data in many different ways, however, only a subset of these capabilities is loaded into user programs by default, so that user executables are smaller.

If UNICOS source code is available, it is better to change the switches in fdcconfig.h, rather than to use these HARDREF directives, primarily because assign still issues warnings to users who use layers disabled in fdcconfig.h. Also, changing fdcconfig.h is the only way to disable layers that are shipped enabled by default.