The only concern for me is performance. Though I believe the service server provided by the Hurd would outperform FUSE, I'm not sure that it is worth the overhead of all other parts in the entire system. If the performance decrease is negligible, I'll be happy to use the kernel.
Per another comment on this thread the Docker as P9 process is pretty close. But it doesn't share services per se across users in the space. Spring (Sun's research OS) looked at cutting the penalties down for moving kernel/user with some nice 'doors' kinds of things. At the time there was discussion that with enough address space (so that you're VM system got the benefit of warm caches and no page remapping) you could really do some interesting things. Were I retired I would probably spend some time playing with that stuff on a modern 64 bit architecture :-)
five transitions (user->kernel->user->kernel->user)
three (user->kernel->user)
I wonder if it couldn't be accelerated with hardware support...
We are still very far from other industries where reliability is taken seriously.
That is, yes there was a cost to this. However, leaving aside the unknowns of whether there would still be millions in tooling necessary for security even with microkernels, you have to provide some sort of reasonable argument that the current market (> billions) would still exist. You can't just take that for granted.
The difference isn't that IT has some dangerous crap in it. The difference is that you know some of these dangers. And, you feel that it doesn't belong for some reason.
Consider, you probably have highly charged electrical wiring to your house. Fairly high pressure water. Possibly gas. Literally explosive. Several drawers of sharp instruments in your kitchen. Possibly power tools that are literally spinning blades. Of sizes from less than a centimeter to upwards of a meter.
Think of a computer less as a safe device that only gives good results, and more as an extremely powerful tool that does what you tell it to do. Very fast. And then be thankful that it won't take your fingers off if you slip while pushing a board across it.
* Who am I kidding? We still do a fair bit of it. :)
Also... apropos of what? I'm not sure how this followed from my parent post.
QNX, Symbian, L4, PikeOS are just some examples of operating systems with micro-kernels that achieved success on the market.
Only the desktop/server OSs still lag behind due to compatibility with existing software.
I run software that (thanks to poor design, IMO) manages to bottleneck context switching on Linux's monolithic kernel. I can't imagine this not being worse with more of the OS pushed out into userspace, though I'd love to be proven wrong!
The Mill CPU design doesn't have a user/kernel mode split, and it's also single-address-space (still with the same level of protection, just a different mechanism). Protection domain switching is done through portal calls, which are essentially shared library-like indirect calls with metadata for the CPU. Further, saving and restoring things like registers is done asynchronously. That should remove any remaining performance difference (and make monolithic designs faster too).
Their forum has some good responses from the team on follow up questions asked by the community as well.
It can potentially be even better, since you can potentially get more direct access to whatever resource you're contending on.
i also tried installing the debian port on an old desktop but had some driver issues. i guess most people run it in a hypervisor.
there are a lot of architectural advantages to putting all drivers in user space. the hurd isn't really totally comparable to plan 9 (because it runs on a microkernel) or minix (because it's thought of as being independent of the any partciular microkernel). but it seems like the community/political issues -- plus the amount of cruft that's bound to accumulate in a codebase that old -- has nearly slowed to project to a grinding halt, which is a kind of a shame.