The Design and Implementation of the Anykernel and Rump Kernels

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ule directory tree from /stand on the host mapped into the rump kernel namespace
so that a rump kernel could read kernel module binaries from the host.
3.8 Attaching Components
A rump kernel’s initial configuration is defined by the components that are linked in
when the rump kernel is bootstrapped. At bootstrap time, the rump kernel needs
to detect which components were included in the initial configuration and attach
them. If drivers are loaded at runtime, they need to be attached to the rump kernel
as well.
In this section we go over how loading and attaching components in a rump kernel
is similar to a regular kernel and how it is different. The host may support static
linking, dynamic linking or both. We include both alternatives in the discussion.
There are two methods for attaching components, called kernel modules and rump
components. We will discuss both and point out the differences. We start the
discussion with kernel modules.
3.8.1 Kernel Modules
In NetBSD terminology, a driver which can be loaded and unloaded at runtime is
said to be modular. The loadable binary image containing the driver is called a
kernel module, ormodule for short. We adapt the terminology for our discussion.
The infrastructure for supporting modular drivers on NetBSD has been available
since NetBSD 5.0 12 . Some drivers offered by NetBSD are modular, and others are
12 NetBSD 5.0 was released in 2009. Versions prior to 5.0 provided kernel modules through
a different mechanism called Loadable Kernel Modules (LKM ). The modules available from 5.0