Implementing a User-Mode Linux with Minimal Changes from Original Kernel

This paper presents some aspects of implementing a User-Mode Linux with as few changes to the original Linux kernel as possible. To port a Linux kernel to a User-Mode environment, basically all parts of the kernel directly interacting with the hardware must be changed. To accomplish this, we need an environment which simulates some hardware parts. This includes simulation of interfaces to device controllers such as keyboard, IDE, graphics or network controller and other devices such as the real-time-clock. Secondly a solution must be found for replacing the assembler code contained within the original kernel with functions. The implementation of the functions, which are called instead of the assembler code, should not become part of the kernel, but be part of the User-Mode environment, just like the implementation of the assembler instructions is not part of the kernel but part of the CPU.