57aff40228
docs/ was ten files where a plan, a description, a guide and a bug report all
sat next to each other. It is now architecture/ (what SchOS is), plan/ (what it
will be), guides/ (how to work on it) and history/ (why it is like this), with
an index that states the one rule holding it together: 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 ticked checkbox says the work happened. It does not say what the work
*produced*, and six months later the checkbox is all that is left. The network
stack proved the point: finished, verified end to end, and for a month the only
description of it anywhere was a checkbox four levels of indentation deep.
So roadmap.md went from 534 lines to 181 -- nothing deleted, the done work
graduated. Seven subsystems that were finished and undescribed now have
descriptions: boot, kernel, syscalls, filesystem, networking, graphics, usb,
init. Every one ends with "What it does not do", which is the section that pays;
a document listing only strengths is marketing, and the reader who needs it most
is the one about to trip over a limitation nobody wrote down.
schfs.md still opened with "phases 1 through 3 1/2 are done, phase 4 is next"
long after all five had landed. It is a description now, with the phase record
and the hard-won bugs moved to history/.
Three corrections found on the way, all load-bearing:
* projects/schcom/README.md claimed SCM_RIGHTS was done. There is no
sendmsg/recvmsg in the kernel at all, and an entire GUI plan rested on it.
* The root README said "No TCP/IP" months after the stack landed.
* history/kernel.md sec.7 was marked "in progress" on a problem that process
groups solved.
Also adds plan/1.0.md, which draws a finish line so the open list stops being
infinite, and marks schwm/ and schde/ superseded: in Wayland the compositor is
the window manager, so that split dissolves rather than being abandoned.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VQ7Qx8E1q1M1bbCq8QLHS2
92 lines
4.7 KiB
Markdown
92 lines
4.7 KiB
Markdown
---
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name: schunix-device-model
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description: "The bus-agnostic device model behind /proc/devices, and the settled decision on how Linux drivers may be used."
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metadata:
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node_type: memory
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type: project
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originSessionId: 9d8a2aef-bcf0-47a0-96c6-f706efab4a95
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modified: 2026-08-08T18:05:13.551Z
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---
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Built 2026-08-08. `include/device.h` + `kernel/dev/device.c`, readable at
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`/proc/devices`. Written up in `docs/architecture/devices.md`. Supersedes the two separate
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arrays in `kernel/drivers/registry.c` as the answer to "what is attached".
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**Bus is provenance, class is capability** — keep them separate. `bus` is
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`platform`/`pci`/`usb`; `class` is `display`/`input`/`storage`/`net`/`bus`. A USB
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disk and a SATA disk are both `storage`. `device_find_class()` is how a consumer
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asks for "the display" without naming a driver, which is what stops the next
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display driver requiring edits to every consumer.
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Where a driver claims a device, **the driver's opinion beats the descriptor's**:
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`struct usb_driver` gained a `devclass` field distinct from the USB interface
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class, because the descriptor says what the device claims to be and the driver
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knows what it made of it. A USB driver that forgets to set it lands in `other`.
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Registration is automatic in `pci_bind()` and `usb_bind_all()` so a driver
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cannot forget; platform devices are registered by hand in
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`platform_register_devices()` in registry.c, in one readable block, matching
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that file's existing "a list you can read beats a list assembled by side
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effects" reasoning.
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Flat list with a bus tag, **not a device tree** — nothing walks a hierarchy yet.
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No lock: everything is added during single-threaded boot. **USB hotplug would
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break both assumptions** and needs a spinlock plus a reader lock in procfs.
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## The display class
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`include/display.h` + ops in `kernel/dev/vga.c`, published on the device by
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`vga_pci_driver.ops`. `struct pci_driver` gained an `ops` field for this —
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**it has to live on the driver, not be set inside probe()**, because
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`pci_bind()` registers the device *after* probe returns.
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Ops: `mode`, `acquire`, `present(x,y,w,h)`, `wait_vblank`. The wrappers in
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device.c null-check every op so consumers are not each written around a
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maybe-absent vtable.
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- **Back buffer comes from `dma_alloc()`, which is the wrong pool** and is used
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because it is the only *physically contiguous* allocator in the kernel —
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kalloc hands out single pages. 1.9 MB of a 4 MB arena meant for device rings.
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Allocated lazily on first `acquire()`, never at boot. The real fix travels
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with the E820 work ([[schunix-smp-and-memory-bugs]]).
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- **vblank is the 1987 VGA port 0x3DA bit 3**, not VBE — VBE's protected-mode
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interface for this is optional and usually absent. Two loops (wait for the
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current retrace to *end*, then for the next to begin), or you return
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immediately having just missed one. Both loops are bounded so hardware that
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never reports retrace cannot hang a caller holding the console lock.
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`echo d > /proc/sysrq` runs `display_selftest()`; `tools/dispshot.ps1`
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photographs it to `build/dispshot.ppm` — it was derived from crashshot.ps1 and
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originally kept its output path, so the two silently overwrote each other and
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`crashqr.py` then failed on a capture that was not a crash screen. The pattern is designed to fail visibly: quadrants slant on a
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stride error, change colour on a bpp error, and the 1px inset frame clips on an
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off-by-one in the present rectangle. Verified 2026-08-08.
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The console still writes *directly* to the framebuffer; the two paths coexist
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deliberately. Routing text through the back buffer would mean presenting per
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character.
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## Linux drivers — settled 2026-08-08
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Nexoniarz's decision, and the reasoning is correct: **not shipped, ever**; the
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user installs one themselves through a device manager and Schunix loads it.
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- *Distribution* is what triggers the GPL. A user obtaining and loading a driver
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on their own machine is their act, not ours.
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- Implementing a *loader* from published documentation is clean-room and fine —
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it stays clean-room only if written from docs, not transcribed from Linux
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source. See [[schunix-licensing]].
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Also worth keeping separate when this resumes: "loadable modules" (a stable ABI
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plus a linker/loader, on top of this model) and "drivers out of kernel"
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(user-space processes, DriverKit-style — needs IPC and mmap, both of which
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already exist). They get bundled together in conversation and are different
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projects.
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## Adding /proc files
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Three places, all needed: a `PROC_*` id and a case in `proc_gen_global()` in
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`kernel/dev/procfs.c`, and a row in the `globals[]` table in
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`kernel/fs/procfs.c`. Miss the third and the file exists but cannot be opened by
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name. `sb_pad()` exists there now for column layout — cprintf has no width
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specifier.
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