Towards a catalog of variability evolution patterns: the Linux kernel case

A complete understanding of evolution of variability requires analysis over all project spaces that contain it: source code, build system and the variability model. Aiming at better understanding of how complex variant-rich software evolve, we set to study one, the Linux kernel, in detail. We qualitatively analyze a number of evolution steps in the kernel history and present our findings as a preliminary sample of a catalog of evolution patterns. Our patterns focus on how the variability evolves when features are removed from the variability model, but are kept as part of the software. The identified patterns relate changes to the variability model, the build system, and implementation code. Despite preliminary, they already indicate evolution steps that have not been captured by prior studies, both empirical and theoretical.