It's pretty simple: almost all efforts to duplicate POSIX in a safe language failed. The commercial practice is porting a POSIX or Linux API in C to a virtualized partition that runs on microkernel. Safety-critical apps run either directly on the microkernel or on a minimal, language-specific runtime running directly on kernel. Keeps TCB tiny. Overall app/system is split with untrusted components in POSIX/Linux system & security-critical stuff in the minimal partitions. Unlike safe POSIX, this is a proven model done by many small teams.
In this case, it would be a RTOS or user-mode Linux, plus a custom runtime or target for Rust apps, and IPC/middleware to connect the two. Way easier to build. POSIX comes later if effort comes along.
And for the Rust half, that's exactly what's in our roadmap and introduction :) Robigo (the POSIX environment) is a long-term stretch goal so that I can run my own OS on a RISC-V laptop of my own devising and still run traditional UNIX programs like GNU. I think we're in violent agreement.
Im on mobile and didnt realize you were project head when I first replied. Id have been more helpful. My bad.
Im glad your doing it gradually with intermediates. That will let it benefit spinoff projects or even products hopefully. Plus keep you from getting overloaded.
I also like that RISC-V is in your long-term vision. Keeping that in mind early will help avoid architectural mistakes early on. Id say use the ISA closest to it in meantime so little change is necessary.
Far as overall scheme, I'll email you some reference work if your interested in prior work on safe runtimes, split apps, high-security dev techniques, and so on. Might be able to integrate that into idiomatic Rust. That's your call though.
I'd be very interested in that! I don't have a lot of experience in this area, it's just something I'm interested in and started hacking away at. Email is in my profile.
In this case, it would be a RTOS or user-mode Linux, plus a custom runtime or target for Rust apps, and IPC/middleware to connect the two. Way easier to build. POSIX comes later if effort comes along.