Daniel Samson
56110b0019
Retire the kernel's spawn-every-initial-ramdisk-binary loop, resolving the
service/driver split into a real three-level supervision hierarchy:
kernel -> spawns init (PID 1) only, and publishes the initial-ramdisk
init -> the service supervisor: spawns the system services (vfs, device-manager)
device-manager -> spawns the drivers it matches (hpet)
The kernel now only hands the initial-ramdisk image to the process layer
(publishInitialRamdisk) so user space can system_spawn from it; it launches nothing
bundled itself. init gains a boot-services list ("vfs", "device-manager") and spawns
them best-effort before settling into its heartbeat — policy lives in user space,
where a microkernel keeps it. Drivers are absent from that list on purpose: the
device manager owns them. Test-only binaries (vfs-test, bus) no longer run at boot;
their kernel self-tests still spawn them directly.
This removes increment 2's transitional double-spawn: a real boot now brings hpet up
exactly once (verified — kernel -> init -> vfs/device-manager -> hpet, zero "claim
failed"). The automated suite is unaffected: test builds run their case and halt
before the normal boot path, so each already spawns its own binaries. Suite 36/36
plus host tests; normal boot verified by hand under QEMU.
DanOS
Codename: Shodan Version: 1
A small operating system, written from scratch in Zig — a bootloader (boot/)
and a microkernel (system/kernel/), sharing a neutral handoff contract (system/boot-handoff.zig).
It boots x86-64 via UEFI, and so far has a framebuffer console, a physical frame
allocator, its own paging with W^X permissions, interrupt/exception handling, a
LAPIC timer, a kernel heap, a fixed-priority preemptive scheduler, and in-kernel IPC
channels. See docs/ for how each piece works.
Prerequisites
- Zig 0.16.x — the build is pinned to this line (
.zig-version); other minor versions are rejected, because Zig makes breaking changes between releases pre-1.0. A toolchain manager such as zvm orzigupwill pick up.zig-versionautomatically. - QEMU (
qemu-system-x86_64) — to run and test the kernel. On macOS,brew install qemualso bundles the OVMF firmware below. - OVMF UEFI firmware — the
edk2-ovmfpackage (Arch),ovmf(Debian/Ubuntu), oredk2-ovmf(Fedora); on macOS it ships inside the Homebrewqemuformula. Both the build and the test harness probe the known Arch/Debian/Fedora/macOS layouts and use the first that exists, so no configuration is normally needed. Override with-Dovmf-code=/-Dovmf-vars=(build) if yours lives elsewhere. - Python 3 — for the QEMU integration test harness.
Build
zig build
Produces a FHS-shaped zig-out/ that is the danos filesystem and the boot volume:
the UEFI bootloader at zig-out/EFI/BOOT/BOOTX64.efi, the kernel at
zig-out/system/kernel, init at zig-out/system/services/init, drivers under
zig-out/system/drivers/, and the initial-ramdisk at zig-out/boot/.
Run
Boot it in QEMU with OVMF (opens a display window):
zig build run-x86-64
# distro with OVMF elsewhere:
zig build run-x86-64 -Dovmf-code=/path/OVMF_CODE.fd -Dovmf-vars=/path/OVMF_VARS.fd
Test
zig build test # host unit tests (the platform-independent shared code)
python3 test/qemu_test.py # QEMU integration tests: boots the kernel and asserts
# on its serial output (see docs/testing.md)
The integration harness builds and boots the kernel once per test case, checking memory, the frame allocator, paging (incl. NX and the null guard), the heap, interrupts, and exception handling. It exits non-zero on any failure, so it drops straight into CI.
Documentation
Design notes explaining the why behind the code live in
docs/ — start with docs/README.md.
Logo
San Serif Text "Dan OS" with a black karate belt around it.