use almost anything that uses libufs(3) against a file as an unprivileged user, e.g.
tunefs(8) and dumpfs(8) against a makefs(8)-created image.
Prodded by: kensmith
getino(3)/putino(3), inode.c has been reworked in Perforce to the point
where a manual page may not be accurate. Certainly putino(3) has not
even been merged back yet.
These will need a lot of improvement for most applications, but they
document the API enough to get someone on their feet, most likely. The
best documentation still exists in the form of libufs(3) consumers in the
base system.