Right, the hypothetical tiny Linux kernel would probably be built without driver support and have NetBSD's rump kernel drivers in place of both Hurd's DDE and t

Right, the hypothetical tiny Linux kernel would probably be built without driver support and have NetBSD's rump kernel drivers in place of both Hurd's DDE and the monolithic Linux drivers, which keeps the userspace advantage. It's true that a Mach port is quite tricky (particularly the virtual memory semantics). Apparently there was an old abandoned attempt to port Mach on top of POSIX, which if someone obtains the source, might be a useful reference to see what went wrong or is incomplete [1]. It's worth noting that the reverse (Linux on top of Mach) was already done by Apple nearly a couple of decades ago as MkLinux, but they ultimately settled on XNU. [1] https://www.gnu.org/software/hurd/open_issues/mach_on_top_of_posix.html https://www.gnu.org/software/hurd/open_issues/mach_on_top_of...