The Design and Implementation of the Anykernel and Rump Kernels

193
original
rump kernel backend
FFS SLOC 1748 247
supported file FFS FFS, ext2, FAT,
systems
SysVBFS
FFS effort > 2.5 weeks (100 hours) 2hours
total effort 7weeks(280hours) 2 days (16 hours)
Table 4.2:
makefs implementation effort comparison.
In the original version of makefs all of the phases were implemented in a single C
program. Notably, phase 4 is the only one that requires a duplicate implementation
of features offered by the kernel file system driver.
We implemented makefs using a rump kernel backend for phase 4. We partially
reused code from the original makefs, since we had to analyze the source tree to
determine the image size (phases 1&2). We rely on an external newfs/mkfs program
for creating an empty file system image (phase 3). For phase 4 we use fs-utils to
copy a directory hierarchy to a file system image.
For phase 3, we had to make sure that the mkfs/newfs utility can create an empty
file system in a regular file. Historically, such utilities operate on device special
files. Out of the supported file systems, we had to add support for regular files to
the NetBSD FAT and SysVBFS file system creation utilities. Support for each was
approximately 100 lines of modification.
We obtained the implementation effort for the original implementation from the
author [76] and compare the two implementations in Table 4.2. As can be observed,
over a third of the original effort was for implementing support for a single file system
driver. Furthermore, the time cited is only for the original implementation and does