The Design and Implementation of the Anykernel and Rump Kernels

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For testing and development we added close to 1,000 test cases using rump kernels
as the test backends. The test suite is run against daily NetBSD changes and has
been able to find real regressions, including kernel panics which would have caused
the test suite to fail if testing was done against the test host kernel. Testing against
rump kernels means that a kernel panic is inconsequential to the test run and allows
the test run to complete in constant time irrespective of how many tests cause a
kernel crash. Additionally, when problems are discovered, the test program that
was used to discover the problem can directly be used to debug the relevant kernel
code without the need to set up a separate kernel debugging environment.
6.1 Future Directions and Challenges
The hosting of NetBSD-based rump kernels on other POSIX-style operating systems
such as Linux was analyzed. Running a limited set of applications was possible, but
interfacing between the host and rump namespaces is not yet supported on a general
level. For example, the file status structure is called struct stat in the client and
rump kernel namespaces, but the binary layouts may not match, since the client
uses the host representation and the rump kernel uses the NetBSD representation.
If a reference to a mismatching data structure is passed from the client to the rump
kernel, the rump kernel will access incorrect fields. Data passed over the namespace
boundary need to be translated. NetBSD readily contains system call parameter
translation code for a number of operating systems such as Linux and FreeBSD
under sys/compat. We wish to investigate using this already existing translation
code where possible to enlarge the set of supported client ABIs.
Another approach to widening host platform support is to port rump kernels to a
completely new type of non-POSIX host. Fundamentally, the host must provide
the rump kernel a single memory address space and thread scheduling. Therefore,
existing microkernel interfaces such as L4 and Minix make interesting cases. Again,