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Ways to modify OpenIFS

We do not recommend that the source code in the oifs/src directory is edited directly as this can make it difficult to track changes and update to new versions. We recommend all code changes are maintained outside the main src directory. There are several ways in which code changes to OpenIFS could be managed:

Copy entire source

Copy the entire oifs/src to (for example) oifs/mysrc and work on the copy. The build configuration files can also be copied if required to, say, oifs/mymake. For instance you might make a new version of oifs/make/fcmcfg/oifs.cfg for your own changes.

Multiple copies of the src directory could be used for different experiments.  The use of a version control system is recommended to track changes. The difficulty with this approach is the full source needs to be copied which makes integrating changes different and changed files are hard to see.

Copy only changed/new source

Leave code in oifs/src 'as-is' and place only modified or new code in separate directories but link to pre-compiled code in oifs/make.  This has the advantage that multiple code developments can be maintained in separate directories; code changes are easy to see and integrating new versions of the model source straightforward. A version control system can also be used.

This makes use of a facility provided by the FCM build software called 'inherited builds'. This is explained below in a series of examples.

Inherited builds with FCM

In essence an inherited build is one in which a pre-build (i.e. compilation) of OpenIFS is used or inherited by a new FCM configuration file placed in a separate directory. The new FCM configuration file only needs to specify what's different about the build, either the sources or compilation settings. The rest of the information is obtained by telling FCM to look at the already  compiled OpenIFS. A user may have a number of these separate configuration files each in separate directories for developing or testing independent code changes.