oi-userland supports incremental builds. They can be activated by setting the BASS_O_MATIC_MODE environment variable to incremental.
Implementation is rather very simple and relies on a fact that every time a component is modified, the Makefile has to be changed and commited. For detecting changes we rely on git and we try to guess the initial commit to look at. By default we scan the GIT_PREVIOUS_SUCCESSFUL_COMMIT environment variable (set by default in Jenkins environments): if the variable is not found, bass-o-matic defaults to 'HEAD~1'.
