L4/Darwin: Evolving UNIX

UNIX has remained a mainstay of modern computing. With its foundations of security, reliability, performance and configurability, UNIX has adapted to and is used in a vast array of environments. While UNIX fosters robustness, modularity and a “smaller is better” philosophy, that scrutiny is generally not applied to the kernel itself. Modern UNIX kernels have large, unwieldy code bases that do not enjoy the benefits seen in the user environment. Apple’s Darwin kernel is the open-source core of the Mac OS X operating system. Like most modern UNIX systems, the kernel boasts modern features such as 64bit address spaces, robust hot-plug and support for server and workstation workloads. L4/Darwin (Darbat), a virtualised Darwin system running on the L4 microkernel, aims to address the problem of the ever-growing UNIX kernel. Using the highperformance L4 microkernel, Darbat can isolate kernel modules, such as device drivers, using hardware protection while maintaining binary compatibility and performance. This modularisation also allows Darbat to use L4 as an advanced hypervisor to support multiple operating system instances for server consolidation. This paper covers the on-going design and implementation of the Darbat project and the experiences of bringing the strengths of UNIX into the UNIX kernel itself.