125a3b4993
An HCD programs a bus-master engine: it needs a descriptor ring that is physically contiguous, at a physical address it knows, uncacheable, and pinned. mmap gives none of those. Add dma_alloc(len, flags) -> vaddr (rax), paddr (rdx) and dma_free(vaddr, len): grant contiguous, zeroed, pinned, strong-uncacheable memory in a per-process DMA arena (PML4[228]) and hand back both addresses. Pieces: pmm.allocContiguous(count, max_phys) finds a run of contiguous free frames below a cap (dma_below_4g for 32-bit engines); mapUserDmaInto maps them uncacheable (PCD|PWT) but WITHOUT device_grant, so unlike an MMIO grant these frames are real RAM and freeSubtree returns them on teardown — a driver that dies leaks nothing. dma_free is bounded to the DMA arena so it can never unmap the caller's stack/heap/MMIO. dma_write_combining is accepted but falls back to coherent (WC needs PAT programming). Runtime: runtime.dma.alloc/free (a two-return-value stub, like replyWait). New `dma` kernel test drives the mechanism directly — contiguity, the below-4G cap, coherent mapping, and reclaim-on-teardown (no leak). The thin syscall wrappers follow the tested mmap/mmio_map shape and land their first real use with the first DMA driver. Suite 38/38 plus host tests. |
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| boot | ||
| docs | ||
| library | ||
| system | ||
| test | ||
| tools | ||
| .gitignore | ||
| .zig-version | ||
| README.md | ||
| build.zig | ||
| build.zig.zon | ||
README.md
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.