This document assumes that you're familiar with how to generate kernels, how to properly configure disks and pseudo-devices in a kernel configuration file.
In order to compile in support for the vnd, you must add a line similar to the following to your kernel configuration file:
pseudo-device vnd # vnode disk driver
To also compile in support for reading compressed disk images, add the following option to your kernel config file:
options VND_COMPRESSION # compressed vnd(4)
Compressed disk images are expected in the cloop2 format, they can be created from "normal" disk images by the vndcompress(1) program.
There is a run-time utility that is used for configuring both compressed and uncompressed vnds. See vnconfig(8) for more information.
/dev/{,r}vnd*