The Design and Implementation of the Anykernel and Rump Kernels

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e.g. the routine for mapping a process ID number (pid_t) to the structure describing
it (struct proc *). We were interested in being able to extract this code. However,
the same file also contained the definition of the lwp0 variable. Since that definition
included references to the scheduler (“concept not supported in a rump kernel”), we
could not extract the file as such. However, after moving the definition of lwp0 to
kern_lwp.c, where it arguably belongs, kern_proc.c could be extracted.
3.1.2 Providing Components
On a POSIX system, the natural way to provide components to be linked together
is with libraries. Rump kernel components are compiled as part of the regular
system build and installed as libraries into /usr/lib. The kernel base library is
called librump and the hypervisor library is called librumpuser. The factions
are installed with the names librumpdev, librumpnet and librumpvfs for dev,
net and vfs, respectively. The driver components are named with the pattern
librump_driver, e.g. librumpfs_nfs (NFS client driver). The faction
part of the name is an indication of what type of driver is in question, but it does
not convey definitive information on what the driver’s dependencies are. For example,
consider the NFS client: while it is a file system driver, it also depends on
networking.
By default, NetBSD installs two production variants of each library: a static library
and a shared library. The system default is to produce dynamically linked executables
which use shared libraries, and this approach is also used when linking rump
kernels. In custom built rump kernels the choice is up to the user. Shared libraries
allow the host to load the components into physical memory only once irrespective
of how many rump kernel instances are started, but shared libraries have worse performance
due to indirection [39]. Figure 3.1 illustrates the speed penalty inherent
to the position independent code in shared libraries by measuring the time it takes