The Design and Implementation of the Anykernel and Rump Kernels

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which were discovered during writing tests or which were found by running the test
suite prior to commit are not included. Arguably, the full test suite should always
be run prior to commit so that regressions would never hit the public tree, but doing
so is not always practical for small changes.
• VFS changes causing invariants to no longer be valid.
• Leak of vnode objects by changes to file system rename routines.
• Regression of a BPF fix which would cause it to accept programs which
execute a divide-by-zero.
• Locking problem where the kernel giant lock was released in the networking
stack although it was not held.
Although the test suite in 5.99.48 covers only a fraction of the kernel, it is capable
of detecting real regressions. As tests accumulate, this capability will increase.
Additionally, the tests using rump kernels stress the host system enough to be the
only tests to catch some host bugs, such as a kernel race condition from when TLS
support was introduced to NetBSD. In case tests are hosted on a NetBSD system,
multiple layers of bugs in NetBSD will be exercised: bugs in the host system, bugs
in the kernel code under test in a rump kernel and bugs in rump kernel support.
The benefits of using rump kernels for testing do not apply to the first set of bugs,
which again shows what we already mentioned in Section 4.4: a rump kernel cannot
make up for the deficiencies of layers below it.