Well, I've created a new filesystem, essentially a derivative of the ufs/ffs
layers. I'm better off putting in my chancements separately, as additional filesystem to be applied only to a test partition, in case my features turn out
like Microsoft bugs^Wfeatures. Now how exactly do I convince the kernel build
to include it? All the necessary code is in there, as far as I can tell, but
in the config file, I see these file-system entries. If I try adding my own
with the file-system statement, it vigorously complains that there is no such
filesystem.

I can't figure out what else I need to do. Pointers?

Valentin