a1c965da1e
Sixty-five headers sat side by side in include/, so `#include "irq.h"` said nothing about where irq.h was or what it belonged to, and errno.h, stat.h and fcntl.h at the top shadowed the system's for any host tool built with -I./include. They are in folders now -- arch/ core/ fs/ dev/ gfx/ net/ uapi/ (and ldls/ for the Linux driver layer) -- and every include names the folder, as Linux's do: "core/proc.h". Done mechanically and checked the hard way: the kernel built from this tree disassembles identically to the one built from the tree before it. The full image boots, and userland is the same set of programs. Paths in docs and comments follow; docs/guides/layout.md has a table of what is where, and tools/fix-includes.py rewrites old-style includes from the folders in the tree, for code written before this. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4
169 lines
7.2 KiB
Markdown
169 lines
7.2 KiB
Markdown
<div align="center">
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<img src="docs/branding/superseded-full-logo.png" alt="SchOS" width="360">
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**A 64-bit operating system, written from the metal up.**
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SMP · copy-on-write filesystem · TCP/IP · PCI, USB and virtio drivers · TrueType text · Linux syscall ABI
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</div>
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---
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SchOS began as [xv6](https://github.com/mit-pdos/xv6-public) and is now mostly
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something else. The scheduler, the memory manager and the trap path have been
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rewritten for x86-64 and for more than one processor; the filesystem has been
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replaced outright; the syscall table speaks Linux numbering so that real
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software — musl, toybox, mksh — runs unmodified.
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It is a hobby system built by one person, and it is honest about that: what
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works below has been *run*, not inferred, and the gaps are listed as plainly as
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the features.
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## The pieces
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| Layer | Name | What it is |
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|---|---|---|
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| System | **SchOS** | The distribution — kernel, userland, tooling |
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| Kernel | **SchIFT** | Multi-core x86-64 kernel with a modular VFS |
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| Filesystem | **SchFS** | Transactional, copy-on-write, the root filesystem |
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| API | **SchAPI** | System programming interface — the stable surface |
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| Compositor | **SchCom** | Display compositor *(planned)* |
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| Window manager | **SchWM** | *(planned)* |
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| Desktop | **SchDE** | *(planned)* |
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`uname -s` reports `SchIFT`, the way every Unix reports its kernel rather than
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its distribution.
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## What works
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**Kernel** — Long mode, 4-level paging, preemptive multitasking. **SMP**: one,
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two and four processors all boot, with CPU enumeration from the ACPI MADT rather
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than the 1994 MP table. Memory sized from the E820 map, so it runs in tens of
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megabytes rather than demanding hundreds.
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**Filesystem** — **SchFS** is the root: a copy-on-write B-tree with a
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uberblock ring, so a crash leaves either the old tree or the new one and there
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is nothing to repair. Free space is derived from the tree rather than stored
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beside it, which removes a whole class of disagreement. `/proc/schfs` shows the
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generation counter advancing as writes commit.
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**Processes** — fork, exec, wait, pipes, signals, sessions and process groups,
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`mmap` (anonymous and file-backed), POSIX shared memory, Unix domain sockets,
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`poll`.
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**Devices** — PCI enumeration with a bus-agnostic device model at
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`/proc/devices`. Drivers for **e1000** networking, **virtio-gpu** and stdvga
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displays, **xHCI** USB with HID, hub and mass-storage class drivers, IDE, PS/2,
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serial. `/dev/fb0` speaks the Linux fbdev interface.
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**Networking** — ARP, IPv4, ICMP, UDP, TCP and DHCP, on lwIP behind a
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driver-agnostic interface class. Verified end to end from the host, both
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directions, rather than by inspection. Names resolve, so `wget http://host/`
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works; `httpd` serves a directory back the other way.
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**Userland** — musl, toybox, mksh and zsh, built from source. 268 applets:
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`ls`, `cat`, `ps`, `top`, `wc`, `cp`, `mount`, `awk`, `bc`, `diff` and the rest
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behave the way you expect, because they are the real programs. `edit` is
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[kilo](https://github.com/antirez/kilo) — arrow keys, Ctrl-S, Ctrl-Q, nothing
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to learn.
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**Text** — a TrueType rasteriser (`glyf` outlines, composite glyphs, cmap
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format 4) replacing the 8×16 cell grid. JetBrains Mono for the terminal, Roboto
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for the desktop layer to come.
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**When it dies** — PSOGM, the Purple Screen of Guru Meditation: stop code,
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fault address, call chain, and a QR code containing a text copy of the whole
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report.
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## Quick start
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```sh
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make # kernel + UEFI loader + root filesystem
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make qemu # build it and boot it
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make iso # a bootable ISO for VMware or real hardware
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```
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Builds on **Linux, macOS, FreeBSD/OpenBSD/NetBSD and Windows** (Git Bash). The
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toolchain is clang + lld everywhere — it is a cross-compiler by construction, so
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one LLVM install targets the bare-metal kernel, the 16-bit boot code and musl
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userland from any host. See **[docs/guides/building.md](docs/guides/building.md)** for
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prerequisites per platform, and
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**[docs/history/moving-to-linux.md](docs/history/moving-to-linux.md)** for moving a checkout
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between machines.
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## Testing
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Booting to a prompt proves nothing: a filesystem can mount and still fail the
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first real command, and that has happened here. So the test harness drives the
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serial console and asserts on what comes back.
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```sh
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tools/windows/bootcheck.ps1 # boot, run real commands, check the answers
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tools/windows/bootcheck.ps1 -Tty -Ps # terminal behaviour, process enumeration
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make schfs-check # SchFS B-tree, object and image suites
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```
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`bootcheck` is PowerShell because `pwsh` runs on every supported host.
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## Layout
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```
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kernel/ arch/ core/ dev/ drivers/ fs/ net/ proc/ sys/
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fs/schfs/ the filesystem -- same source the host tools compile
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include/ kernel and userland headers, by subsystem (arch/ core/ fs/ dev/ ...)
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boot/ uefi/ (PE loader) common/ (shared loader UI)
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lib/ cmd/ first-party userland runtime and programs
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ports/ third-party software built from source
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tools/ windows/ (.ps1) posix/ (.sh) python/ (.py) and .c/.pl
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docs/ architecture/ (what it is) plan/ (what's next)
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guides/ (how to work on it) history/ (why it's like this)
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```
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**[docs/README.md](docs/README.md)** is the index. If you are reading the tree
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for the first time, [docs/architecture/README.md](docs/architecture/README.md)
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is the system layer by layer.
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One rule worth knowing: **the kernel and the host tools compile the same SchFS
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source**. `mkschfs` cannot disagree with the kernel about the on-disk format,
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because there is only one implementation — found and fixed on the host, where a
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test takes a second instead of a boot.
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Another: **syscalls are declared in exactly one place**,
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`kernel/sys/table.inc`. Everything else is generated from it.
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## Not there yet
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- **No desktop.** Schcom composites and routes input; the plan is now to put it
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on Wayland and delete the homegrown protocol. See
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[docs/plan/wayland.md](docs/plan/wayland.md).
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- **No descriptor passing.** No `sendmsg`/`recvmsg`, so no `SCM_RIGHTS` — which
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is what the GUI work stops at. [docs/plan/foundations.md](docs/plan/foundations.md).
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- **No dynamic linking.** `exec` handles static `ET_EXEC` only.
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- **No page cache**, so writable `MAP_SHARED` of a file is refused rather than
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faked.
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- **A USB disk cannot be booted from** — the root device is compiled in rather
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than selectable.
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- SchFS has no Linux driver yet; the plan is on-disk format version first, then
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FUSE, then a kernel module.
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- CFF/OpenType outlines and TrueType hinting are deliberately out of scope.
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## Licensing
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**GPL-2.0-or-later**, copyright Nexoniarz. See [LICENSE](LICENSE).
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The kernel derives from xv6, which is MIT — see [LICENSE.MIT](LICENSE.MIT).
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Third-party code redistributed in a built image (musl, toybox, mksh, zsh, kilo,
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the fonts) keeps its own licence; [NOTICE](NOTICE) carries the attributions.
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See [docs/licensing.md](docs/licensing.md).
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Drivers may be adapted from BSD sources and, since the move to the GPL, from
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Linux — GPL-2.0-only code combines with GPL-2.0-or-later, and the result ships
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under GPLv2. Best of all is still the public specification — xHCI, virtio,
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AHCI, e1000 — which carries no licence on what you write from it.
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---
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<div align="center">
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<sub>Built with stubbornness and a serial console.</sub>
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</div>
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