The Design and Implementation of the Anykernel and Rump Kernels

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The straightforward use of existing data structures has its limitations: the system
the client is hosted on must share the same ABI with the system hosting the rump
kernel. Extending support for systems which are not ABI-compatible is beyond the
scope of our work. However, working remote client support shows that it is possible
to build distributed systems out of a Unix codebase without the need for a new
design and codebase such as Plan 9 [93].
2.6 Summary
A rump kernel is a partial virtualization of an operating system kernel with the virtualization
target being the drivers. To be as lightweight as possible, a rump kernel
relies on two features: relegating support functionality to the host where possible
and an anykernel codebase where different units of the kernel (e.g. networking and
file systems) are disjoint enough to be usable in configurations where all parties are
not present.
Rump kernels support three types of clients: local, microkernel and remote. Each
client type has its unique properties and varies for example in access rights to a
rump kernel, the mechanism for making requests, and performance characteristics.
Remote clients are able to access a rump kernel over the Internet.
For drivers to function, a rump kernel must possess runtime context information.
This information consists of the process/thread context and a unique rump kernel
CPU that each thread is associated with. A rump kernel does not assume virtual
memory, and does not provide support for page faults or memory protection. Virtual
memory protection and page faults, where necessary, are always left to be performed
by the host of the rump kernel client.