Daniel Samson
a64a01a6a9
Add a FAT12/16/32 filesystem the VFS mounts at /mnt/usb, reading and writing a USB stick through the block device. Verified end to end under QEMU: the fat server mounts the volume, the VFS routes /mnt/usb to it, and a client lists the root and reads a file (the ELF magic of /mnt/usb/system/kernel). - engine.zig: the FAT engine over a BlockDevice interface — mount (a bare FAT or, as QEMU's VVFAT and most real sticks present it, an MBR-partitioned disk), FAT chain walk (12/16/32), cluster allocation, directory traversal with long-name read, and file read / write / create. Host-tested against a RAM-backed FAT16 image (create, cluster-spanning write, mid-file overwrite, read-back, list). - on-disk.zig: the align(1) boot-sector / directory / long-name / FSInfo structs and the cluster-count FAT-type detection. - fat.zig: the server — wraps the .block device (a DMA bounce buffer) in a BlockDevice, mounts the FAT, serves the vfs-protocol as a backend, and mounts itself into the VFS at /mnt/usb. Spawned by init as a boot service. - runtime.block: the block-device client (geometry / read / write by physical address, so whole sectors never cross IPC). - Raise the kernel service-name registry (maximum_services) 8 -> 16: it is indexed directly by ServiceId, and fat = 8 was being rejected, so the fat server exited before registering. - VFS: an absolute path with no matching mount is now not-found rather than silently created in the flat ramfs — so /mnt/usb fails cleanly until mounted. Tests: fat-mount (the full stack: block -> FAT -> VFS mount -> list + file read) passes; host units cover the engine and on-disk structs; the vfs, shutdown, and USB regression suite stays green (10/10).
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.