Daniel Samson
a32eed877d
The FAT engine could create, read, write, and grow files, but never free clusters or make directories — so overwriting a shorter file left a stale tail (a real bug: corrupt boot-log re-flushes, and later corrupt compiler cache/.o files). This adds the mutation half of the engine, with the corruption fix wired all the way through. Engine (system/services/fat/engine.zig), all host-tested: - freeChain: return a cluster chain to the pool (bounded against a corrupt cycle) — the shared primitive under truncate and remove. - truncate: free the chain and zero the entry's size/first-cluster (O_TRUNC). - createDirectory (mkdir): allocate + initialise a cluster with "." and ".." and add the directory entry to the parent. - removeFile (unlink): free the chain and mark the 8.3 entry plus any preceding long-name entries deleted, so a reused slot can't inherit an orphaned long name. Refuses directories. - createFile now shares a common addEntry helper with createDirectory. O_TRUNC wired end to end: a truncate open-flag (vfs protocol) that the router already forwards; runtime.fs.OpenOptions.truncate; and fat's handleOpen calls engine.truncate on an existing file. The boot-log flush (log-flush + init) now opens with truncate, so a shorter log on a later boot of the same stick leaves no stale tail — closing the caveat from the boot-log work. mkdir/unlink are engine-complete and host-tested but not yet exposed as VFS operations / runtime.fs methods (they are new path-based ops needing router cases); rename and the richer stat (mtime/mode, blocked on wall-clock) remain. See docs/zig-self-hosting.md (Phase 2). Verified: zig build, zig build test (8 engine host tests, incl. truncate, the overwrite-no-stale-tail regression, remove, and mkdir), zig build check-fat-image, and a sequential QEMU sweep — fat-mount, log-flush (DANOS.LOG read back at 11804 bytes, clean, with the truncate-based final flush), vfs, vfs-client-death, usb-storage, orderly-shutdown, initial-ramdisk, smoke — all green.
DanOS
Codename: Shodan Version: 1
A small resilient operating system, written from scratch in Zig.
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 lifecyle 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 shortend 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/, 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 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.