Daniel Samson
547d0ec46b
device-authority.md is rewritten as an implementation design rather than a rival to device-manager.md. The what was already settled there in 2026-07: structure in the manager, authority in the kernel, and delegation as the step after hello. This is the how, plus the two decisions that paragraph leaves open. Decision 1: the manager claims, it is not granted. device-manager.md says "claims (or is granted)"; claiming wins because the manager runs before any driver exists and takes the seeded devices unopposed, leaving nothing unheld to race for. One new call, device_transfer(device_id, task_id), checks only that the caller holds the device — no names in the kernel, no attestation. The alternative put a binary path inside the kernel, and the kernel should hold only what cannot safely live in user space. The residual is stated rather than hidden: authority rests on the manager claiming first, which init.csv makes an operator-visible ordering rather than an attacker- controlled one, and the enforced version arrives with the spawn capability drivers.md already names as missing. Decision 2: the kernel stops holding inventory. It reads three things out of a descriptor — physical ranges, interrupt numbers, one PCI BDF — and stores the rest only so device_enumerate can hand it back. Devices with no resources leave the kernel entirely: a USB device conveys no mapping authority, so there is nothing to enforce. That is also the case which sidesteps containment, and therefore the reason a shared cap existed. Decision 3: no shared ceiling. The table becomes dynamic — it is built after heap.init, so nothing ever prevented it — and the two invented numbers go. A per-holder quota replaces them, because dynamic storage with no bound moves the ceiling to the kernel heap, which is shared and fatal rather than partial. A bound charged to whoever caused it is isolation. Two earlier drafts of this document are gone: one gave init the root grants, the other proposed extracting a firmware-framebuffer driver. Both were wrong and both are recorded as wrong in the run plan's settled list — the framebuffer is not a device, it is where pixels go until a real display driver announces itself. Run 2 is nine steps, ordered so the suite stays green throughout: build and prove the transfer mechanism, move the five claimants across one at a time, then the flag day, then the inventory, then the ceilings.
OS Development
This document explains the architectural decisions behind the operating system.
Written in Zig?
The OS is written in Zig because it has excellent EFI support, so the OS boots quickly without a third-party bootloader.
Zig comes batteries included for systems work — cross-compilation, a build system, and a test runner are all part of the toolchain. Building with -Doptimize=ReleaseSafe keeps runtime safety checks on in the shipped kernel, which removes entire classes of bugs. The built-in test suite, combined with a QEMU integration harness, means every feature is proven to work, before it is shipped.
The codebase of the OS prioritizes readability. The aim is a codebase where someone new to OS development can find their way around without a guide.
A microkernel?
The kernel is a thin layer: it schedules processes and manages memory. Everything else — drivers, file systems, the display — runs in user space as separate, isolated processes.
The payoff is resilience. When a driver crashes, it doesn't take the OS down with it; it gets restarted. That makes this an ideal environment for developing an operating system, because a buggy driver is an ordinary bug: patch it, restart the service, and keep going.
There is a security benefit too. Processes are isolated and talk over Inter-Process Communication (IPC) channels, so compromising one service doesn't hand an attacker the whole machine. Vulnerabilities tend to stay contained in the process they started in.
Other operating systems choose to pack all of these duties into one binary as a Monolithic kernel, mostly for performance: a function call inside the kernel is faster than passing a message between isolated processes. That cost is real — an IPC round-trip is a few microseconds where a function call is nanoseconds — but it is also workload-shaped. Compute-bound programs don't notice it at all. For bulk data like file contents and pixels, the design moves data through shared memory and DMA so it is copied once, the same as a monolithic kernel; only small control messages cross the IPC boundary. What remains is the per-message cost on chatty paths, and the scheduler and memory management are designed to keep that small.
Private ABI
The syscall layer is private. The numbers and structures in abi.zig are an internal detail shared between the kernel and the system's own libraries, and they are free to change between builds.
The public boundary sits one level up: the vDSO that programs call into, and the documented IPC protocols such as the VFS protocol. Programs that stick to those interfaces keep working while the kernel rearranges itself underneath. This is the opposite of the Linux approach, where raw syscall numbers are frozen forever; here, stability is promised at the library and protocol level, and nowhere below it.
Steal the best bits and dump the legacy
The OS is Unix-like, but selectively. It borrows the ideas that have aged well — everything is a file, small services composed over clean interfaces — and skips the parts of POSIX that have caused decades of headaches.
Some concrete choices:
spawn, notfork. Creating a process starts a fresh program and returns the child's id. There is no clone-the-whole-address-space-then-immediately-throw-it-away dance, and none of the subtle state-inheritance bugs that come with it.- Time is a syscall. The kernel owns the clock and timers directly. There is no time daemon to keep alive and no ambiguity about where the truth lives.
- Lifecycle events arrive as messages. A supervisor learns that a child exited through an IPC message on an endpoint it already owns — delivered like any other message, not as an interrupt that can fire between any two instructions.
The test for keeping an idea is simple: does it still pull its weight, or is it only there because it was there in 1979?