[goodthenandnow]

> One thing though, you focus a lot on syscalls, but I think the challenge in recent years has been to find new ways to have kernel <-> userspace interactions _outside_ of syscall, which are cumbersome to use, rigid in structure, and practically speaking, there are only so many entries you can store in an IDT.

Today there is another option for doing the kernel-userspace communication: using an io_uring like interface. Yes, it's a syscall, but it's one with enough extensibility and performance characteristics. It's extensible because it's close to an IPC with the kernel (and it could be changed to be a new IPC mechanism for process-to-process communication if it isn't already). And it's performant because it's based in shared memory and is assyncronous by default.