Daniel Samson
3111c7c5e6
The mechanism behind delegation, which device-manager.md named as the step after hello: the device manager claims what discovery seeded and hands each device to the driver it matched, so assignment stops being first-come-first-served. It is a MOVE, not a copy. A claim is exclusive (driver-model.md, invariant 1), so the giver stops holding the device the instant the receiver starts. That is why this is a new syscall rather than the M13 capability path, where a passed handle is shared refcounted — exclusivity cannot be expressed that way. The kernel's whole rule is that you may give away what you hold. It has no notion of which task is the device manager and deliberately gains none: a binary name inside the kernel is not something that cannot safely live in user space. A recipient that does not exist is refused, because a device moved to nobody would be unreachable for the rest of the boot — nothing un-holds a device but task death. Three errnos, each naming its own rule: ENODEV no such device, EPERM you do not hold it, ESRCH no such recipient. Nothing uses it yet. The five claimants move across one at a time in D4-D5, so the suite stays green throughout and a regression names the driver that caused it. Ten assertions, verified to discriminate: removing the ownership check flips four of them, including the giveaway that an illegal transfer then blocks the legitimate claim behind it. Suite 116 -> 117.
DanOS
Codename: Shodan
A very small resilient operating system.
Zen of DanOS:
- Resilient Micro-Kernel Architecture.
- Every process run in an isolated user space not kernel space.
- Processes cannot take down the entire OS with it when they die or is killed
- Stable public runtime library, private OS ABI.
- Keeps a stable runtime for user space processes between OS versions (great for backwards compatibility)
- Allows the underlying OS to be changed without effecting applications
- Provides a boundary to enable compatibility between OS's e.g. POSIX, MUSL etc
- Drivers are just isolated processes in user space.
- Thin binaries that can be restarted like applications.
- Useful during driver development.
- Drivers can claim MMIO / ports
- Driver resources (e.g. IRQ/Port/MMIO) claims are automatically cleaned up if the driver dies or is killed
- Drivers can also hook into the process lifecycle to clean up or reset hardware
- No legacy to deal with
- Zig code uses a clean coding style (Zen of Zig)
- Favor reading code over writing code.
- No magic numbers.
- No shortened names unless its for ABI compatibility or acronyms
- Inter-Process Communication (IPC)
- Publish and subscribe to Asynchronous Messages
- Talk to services and processes synchronously
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/, the test fixtures under zig-out/test/system/services/,
and the initial-ramdisk at zig-out/boot/.
Release media
zig build release-x86-64
Produces zig-out/danos-x86-64.iso, a hybrid ISO that boots flashed raw to a
USB stick (balenaEtcher, dd) or burned to optical media — see
docs/release-iso.md. zig build check-iso-image
validates it without booting.
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 why behind the code live in
docs/ — start with docs/README.md.
For the hardware needed to run DanOS — minimum specs plus a plain-language guide
matching Intel/AMD CPU generations by name — see
docs/system-requirements.md.
Logo
San Serif Text "Dan OS" with a black karate belt around it.