Kerneluserland

Kerneluserland is a term used in operating system design to describe architectures or implementations in which the traditional boundary between kernel space and user space is reinterpreted, softened, or restructured. It is not a single standardized technology, but rather a family of approaches that explore different ways to integrate or separate kernel functionality from user-level software.

In practice, kerneluserland can refer to several related patterns. One pattern is running certain kernel services or interfaces in user space, with controlled communication to a minimal kernel, as seen in experiments like user-mode Linux. Another pattern involves arranging systems so that components traditionally part of the kernel operate within a single address space alongside applications, or as user-space servers that provide kernel-like services through well-defined interfaces. A further pattern is the use of user-space drivers and services to reduce kernel complexity and improve fault isolation, sometimes at the cost of performance or deeper integration.

Proponents argue that kerneluserland designs can enhance fault isolation, portability, and security by containing bugs and vulnerabilities within isolated compartments or by enabling easier experimentation and rapid iteration. They can also enable more flexible development workflows and simpler deployment in certain environments.

Challenges include potential performance overhead from additional context switches and IPC, the difficulty of maintaining strong security boundaries between kernel-like services and user processes, and compatibility with existing APIs and software ecosystems. Kerneluserland remains a niche concept, often discussed in the context of research OSes, unikernels, microkernel-like systems, and experimental platforms. Related topics include kernel-space versus user-space, UML, MINIX 3, Genode, and various unikernel projects.