[anttiok]

"a" is sort of orthogonal to rump kernels, but yes, you can run at least file system drivers transparently as userspace servers (just give -o rump to mount(8)). I've also run a USB modem driver as a userspace server, in the "the kernel I'm running doesn't contain support, but a future kernel revision has" fashion.

For "b", rump kernels don't support "compiling out". Rather, the idea is to "link in" only what you need, as in "don't need file systems in that particular application? well don't link in VFS then".

I'm not sure if you're right or wrong, but maybe the rump kernel FAQ at http://wiki.rumpkernel.org/Info:-FAQ will straighten your thoughts. In the regrettable case that it doesn't, you can always suggestion additional questions.

[akavel]

Actually, I've asked my question after trying to do some basic reading on my own, but it only deepened my confusion, unfortunately. I vaguely remembered that "rump kernels" seemed to mean "assume we're on Xen/KVM/... and make use of that", or a notion of "library kernels" -- one of those two, though not 100% sure which one (or both?). But then from some NetBSD docs/wikis/... it started to look to me like they're adding another term "anykernel" here and there, and then naming with that some microkernel-like stuff, like mounting stuff in userspace, but then not sure why naming the option as "rump", etc -- and all of that made me more and more confused, instead of less. And that's what made me ask here.