SchOS/docs

SchOS documentation

Four kinds of document, kept in four directories, because they answer four different questions and go stale at four different rates.

architecture/	What SchOS is	Present tense. Describes what is built and working.
plan/	What SchOS will be	Future tense. Everything here is unbuilt.
guides/	How to work on it	Imperative. Build it, test it, add to it.
history/	Why it is the way it is	Past tense. Bugs whose cause is not visible from the fix.

Plus two that belong to no category and apply to everything: licensing.md — read it before copying anyone else's code in — and branding/, which holds the marks and the rules for using them.

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The rule that keeps this from rotting

When something is finished, it moves from plan/ to architecture/ and is rewritten as a description of the thing rather than a record of building it.

A completed item is not a ticked checkbox. A ticked checkbox says the work happened; it does not say what the work produced, and six months later the checkbox is the only thing left and it explains nothing.

So finishing a piece of work has three steps, and the third is not optional:

1. The code works and is tested.
2. The plan entry is deleted.
3. A description exists in architecture/ written for somebody who was not there — what it does, what shape it has, what it costs, and what it still does not do.

This is not bookkeeping. The tree has already proved it necessary: the network stack was finished, verified end to end, and for a month afterwards the only description of it anywhere was a checkbox in a roadmap, four levels of indentation deep, written in the past tense of somebody arguing for the work rather than explaining the result.

The "what it does not do" section is the one that pays. Every description in architecture/ ends with one. A document that only lists a subsystem's strengths is marketing, and the reader who most needs the document is the one about to trip over a limitation nobody wrote down.

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Start here

New to the tree → architecture/README.md, the system layer by layer, then guides/layout.md for where the files are.

Trying to build it → guides/building.md.

Wondering what happens next → plan/1.0.md, which is the finish line and the register of everything half-built. Then plan/README.md for the order.

About to start something new → the register, first. Nothing new starts while it has rows in it, and a row leaves only by being finished or deleted.

Something is broken and it feels familiar → history/. There is a good chance it is in there.

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architecture/ — what SchOS is

README	The system, layer by layer. Read first.
boot.md	Firmware to the first userspace process, and where the loader puts the kernel.
kernel.md	SchIFT: memory, processes and threads, traps, signals, SMP.
scheduler.md	Fair share by virtual runtime, slices, and nice.
syscalls.md	The call table, and the Linux personality that lets real software run.
filesystem.md	The VFS, the buffer cache, procfs, sysfs, devtmpfs, mounts.
schfs.md	SchFS: the copy-on-write root filesystem.
scff.md	SCFF: the compressed image the live root ships as.
fat.md	FAT12/16/32 with long names: USB sticks, SD cards, the ESP.
devices.md	The device model, driver binding, the class vtables, and drivers that live in a process.
ldls.md	Running Linux's drivers: a .ko in a process, reaching hardware through /dev/pci.
usb.md	xHCI, the USB core, and the class drivers.
graphics.md	Framebuffer, /dev/fb0, text rendering, the console, PSOGM and GMMOS.
terminals.md	The twelve virtual terminals, ptys, and handing one to a display server.
audio.md	/dev/dsp, AudioEngine, AC'97, and ALSA over OSS.
networking.md	NIC drivers, lwIP, sockets — Unix, INET and netlink.
init.md	schinit, PID 1 as a role, and the job manifests.
packages.md	The apk root: Alpine's packages, and SchOS as one of them.
desktop.md	Xorg on the framebuffer, Window Maker, and what they stand on.
debugging.md	Symbols, a log that outlives the kernel, and asking the kernel a question.

plan/ — what SchOS will be

README	What is here, what used to be, and the order.
1.0.md	The finish line, and the freeze. What 1.0 contains, where it stands, and the register of every half-built thing in the tree.
roadmap.md	Everything else scoped and still open.
gpu.md	Linux's amdgpu through LDLS, and /dev/dri served by a process.
finch.md	The author's language for SchOS's own programs.
schapi.md	The long-term API layering, and the compatibility promise.

guides/ — how to work on it

building.md	Prerequisites and the build, per host.
testing.md	The harnesses, and what each one actually proves.
layout.md	Repository map, and how to add a program or a port.
adding-a-driver.md	Writing one, binding it, publishing its class vtable.
hardware-report.md	hwreport: describing a machine onto a USB stick, for whoever fixes it.

branding/ — the marks

README	Shift, the one mark: what it is for, the colour rule, why an icon and a mascot were removed, and why a raster is committed next to its SVG.

history/ — why it is the way it is

README	What belongs in here and what does not.
kernel.md	Bugs whose cause was nowhere near their symptom.
schfs.md	The filesystem's own, from the same period as its design.
moving-to-linux.md	The Windows-to-Fedora move, kept for the parts that recur.

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Writing one of these

Four conventions, all of them observable in the existing files:

State the cost. Every design choice gave something up. A document that does not say what is a document that will be argued with later by somebody who only sees the downside.

Prefer the measured number to the remembered one. "500 of 3565 files carry the advertising clause" is worth more than "some do", and it was worth the minute it took to count.

Write down the bug that shaped it. Half the non-obvious code in this tree is non-obvious because something failed once. If a design is strange, the strangeness is load-bearing and the reader deserves to know why before changing it.

No dates in headings. A date in a heading turns a description into a changelog, and the description is the thing with a long life. Dates belong in history/, where they mean something.