dbb88064c1
README's layout predated the BIOS/UEFI split. moving-to-linux.md now says what is gitignored and therefore absent from a clone: dist/ holds 61 MB of upstream tarballs, so copy it or let the build re-fetch them -- make ports verifies each against a known SHA-256 either way.
150 lines
6.1 KiB
Markdown
150 lines
6.1 KiB
Markdown
<div align="center">
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<img src="Assets/SchOS%20Full%20Logo.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 · 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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**Userland** — musl, toybox and mksh, built from source. `ls`, `cat`, `ps`,
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`top`, `wc`, `cp`, `mount` and the rest behave the way you expect, because they
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are the real programs.
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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 + bootloader + root filesystem -> schos.img
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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/building.md](docs/building.md)** for
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prerequisites per platform, and
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**[docs/moving-to-linux.md](docs/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
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boot/ bios/ (MBR, stage 2, VBE splash) uefi/ (PE loader)
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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, roadmap, licensing, building
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```
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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 TCP/IP. The decision is made — port lwIP rather than write one — but it is
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not done. The e1000 driver works; nothing speaks to it yet.
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- No compositor, window manager or desktop. That is the next large piece.
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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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**Apache-2.0**, 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, the fonts)
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keeps its own licence; [NOTICE](NOTICE) carries the attributions.
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Drivers may be adapted from BSD sources, which are compatible. Linux drivers are
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not: GPL-2.0-only and Apache-2.0 cannot be combined and redistributed. Reading
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Linux to understand hardware is fine; translating a driver is not. Best of all
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is the public specification — xHCI, virtio, AHCI, e1000 — which carries no
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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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