[joveian]

There is a difference between what is possible to do with rump kernels and what NetBSD is currently doing with them. The basic point is to be able to use the same code in different contexts, so in theory you could use rump kernels in implementing a microkernel. However, AFAIK NetBSD currently uses it for (optionally) running filesystems in userland (so you can mount potentially corrupted file systems without crashing the kernel) and for testing. Your (b) is a separate thing that has always been possible in NetBSD (there is also loadable kernel module support). More things could be made to work as userland drivers easily but could still require glue to make it actually work. I don't understand the details but there are multiple ways to make the glue and it can be easier if you are trying to get NetBSD drivers to run in NetBSD userland.

You can also use rump kernels to make an application that runs directly on Xen, KVM, or hardware or that e.g. uses NetBSD file system code on Linux (or Cygwin) userland. Much of this still need some work to do what you want, but less than writing the drivers from scratch, much less maintining them. rumpkernel.org is starting to have packages for some applications. This doesn't require otherwise using NetBSD.

[akavel]

Uh, so only FS for now? That's sure nice, and a nice start, but I really thought there's more to it. Thanks for the clarification & and details.

(I remembered that Haiku got network drivers from some WhatsitBSD, so I thought those are maybe there too, but it seems it was FreeBSD actually, so just some confusion of mine. So no microkernel there, it seems. Bummer.)

As to running on Xen etc, that was what I seemed to vaguely remeber as what rump kernels mean, so I was really confused and surprised to slowly find out that the NetBSD usage of the term seems to diverge quite substantially, as far as I can (or can't?) understand. Hmph.

[joveian]

I just saw this so not sure if you'll actually see this response, but rump kernel doesn't imply Xen or such, that is just a common thing people want to do with them. It just means kernel drivers that can be used outside the kernel. Anykernel refers to a kernel that can be used that way with minimal differences and without modifying individual drivers. So rump kernel is "libkernel" and an anykernel is one way to get a rump kernel.

There is a FAQ with more information at: https://github.com/rumpkernel/wiki/wiki/Info:-FAQ

I'm pretty sure that Antti created these terms, so it is an authoritative definition :).

[akavel]

Thanks. The problem is, I actually have already read the appropriate sections of the FAQ & some rumpkernel.org pages, but I'm still confused. (I've written my original question out of frustration that things didn't become clear after all the reading.) I'm starting to think it may be best to dive in and try reading the "book" referenced in the FAQ (i.e. the Antti's PhD paper). Seems actually very approachable for a regular non-sciency engineer, from first looks. And/or maybe the "tutorial" I've found at https://github.com/rumpkernel/wiki/wiki/Tutorial:-Getting-st...