The L4 Microkernel Presented by: Martin Roehricht Nirav Mehta Matthew Garland Chris Schulze

2 Introduction to L4 L4 is a Microkernel Developed at IBM and University of Karlsruhe (Germany) by Jochen Liedtke † Supported Operating Systems –L 4 Linux –GNU HURD –Windows XP in development Open Source (BSD license)

3 What is a Microkernel? Alternative to commonly used “Monolithic” Kernels (Linux, Windows) Main design goal: to keep only the essential functionality inside the kernel –All other functions provided by OS used File system, Hardware drivers, etc… These are implemented using “servers”

4 Comparison between Microkernel and Monolithic kernel

5 Characteristics of the L4 Microkernel Robustness –Faulty drivers fixed without system crash Security –Root privileges used less frequently File system and drivers in user space Performance –Heavily dependent on IPC –Real-time capability

6 The Design of L4 Threads –Basic entity in execution –Basis for Scheduling Tasks –One or more threads –Virtual address space –Communication ports –Cascading hierarchy

7 Inter-Process Communication (IPC) Clan – a group of related tasks Chief – one per clan. Responsible for communication between two clans

8 Conclusion Microkernel research – very hot topic Characteristics –Robustness –Security –Performance –Portability Could be the “wave of the future”