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SchOS/docs/plan/roadmap.md
Nexoniarz d3c37f82b6 docs: the tree moved and the documentation did not 
The site and several documents still described the system as it was before
virtual terminals, the new schinit, the hybrid work and descriptor passing.

docs/architecture/init.md described the wrong program. It documented a single
schinit that parses manifests and supervises jobs, which has not been true since
PID 1 was split: PID 1 forks a supervisor, spawns jobs on its behalf and reaps;
the job table lives in /proc/schinit; a heartbeat runs both ways; and
proc_reincarnate() re-execs PID 1 in place rather than panicking. Rewritten
around what exists, keeping the reasoning that is still load-bearing -- the five
failures of the sibling-init scheme, the escalation ladder, and the three bugs in
the reincarnation path that each had to happen before they were obvious.

docs/plan/init.md is deleted, which is the tree's own rule for finished work and
had not been applied. Fourteen source comments referenced it by part number, so
they are repointed at the architecture doc by section name rather than left
dangling -- a deleted document nobody notices is worse than a stale one.

docs/architecture/devices.md gained the section it has been missing since
/dev/pci existed: what a driver needs from a kernel, why mmap is checked against
the caller's claims, why DMA is a call and not a mapping, and why the write back
after an interrupt is not optional. Also that a released device does not come
back by itself, which is true and was nowhere.

docs/architecture/networking.md gained a descriptor-passing section, and
docs/architecture/README.md's stack diagram gained the two layers and the third
seam it was missing. "Two seams hold the whole thing together" has not been true
since /dev/pci.

docs/plan/README.md said the hybrid work was deliberately last, on the argument
that an interface with no consumer is wrong in ways nobody can see. The argument
was right; the conclusion was not, and the document now says why it changed --
the alternative to a driver compatibility layer is writing a driver for every
device that exists, and the original objection is answered rather than ignored
because SchOS's own drivers are the consumers.

The site: a Hybrid section with the eviction transcript, cards for virtual
terminals, schinit and drivers outside the kernel, and the numbers remeasured
rather than estimated -- 46,961 lines, 207 syscalls. The boot log in app.js is
from a boot taken today, and the lines are trimmed to what the console can show
without clipping, each still a verbatim prefix of real output.

Two small rendering fixes found by looking at the pages rather than assuming:
.console pre's min-height is now scoped to the hero, so a static transcript sizes
to its content instead of reserving eight lines it does not have; and the docs
reader's contents panel strips inline marks from headings, so a heading written
`proc_reincarnate()` no longer carries its backticks into the sidebar.

Every intra-doc link checked; none broken.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VQ7Qx8E1q1M1bbCq8QLHS2
2026-09-13 20:05:06 +02:00

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# Roadmap — everything else still open
The three current decisions have their own documents; see
[README.md](README.md). This file holds what is left: work that is scoped,
agreed and unstarted, with nothing in it that is finished.
**Finished work is not here.** It moved to
[../architecture/](../architecture/) and was rewritten as a description of what
it produced — see [the rule](../README.md#the-rule-that-keeps-this-from-rotting).
What used to be phases 1 through 4 of this file, several hundred lines of ticked
boxes, is now `usb`, `networking.md`, `graphics.md` and `devices.md` over there.
---
## 1. Storage and the boot path
**Make a USB disk mountable and bootable.** The xHCI stack, the bulk-only
transport, the SCSI layer and the block device all work — a superblock reads back
through `bread()`. What is missing is that **the root device is compiled in
rather than selectable**, so nothing can be told to mount it.
This is also the first piece of the installer, and it is the single change that
would most enlarge what SchOS can boot from.
## 2. Graphics
- **A `/dev/dri`-style device with mode setting**, so resolution stops being
whatever the loader asked for. This was to be done *with*
[hybrid.md](hybrid.md)'s GPU eviction, and that eviction has now happened —
`cmd/vgpud` drives virtio-gpu from userspace. The modeset API is the next thing
it makes affordable, and is milestone H3 over there rather than here.
- **Double buffering and vblank.** `display_ops` specifies both and no driver
implements either. Schcom needs both to not tear.
- **Port the console onto the text layer and delete the cell grid.** The layer
exists, the rasteriser exists, and the console still indexes `font_data[256][16]`.
- **Load a font from disk** and point the console at it.
- **CFF/Type 2 charstrings**, so OTF fonts work. A separate `font_ops` provider
and a bytecode interpreter, *not* an extension of the `glyf` path.
- **Text layout** — advance widths, kerning — as a library in `lib/`, so the
terminal and the file manager are not each solving it.
The console keeps its fixed grid until the first item above; proportional text
belongs to the GUI.
## 3. Networking
Two things the stack owed on the day it landed, both still owed:
- **`accept()` does not report the peer's address**, and there is no
`getsockname`/`getpeername`. Nothing has needed them yet; a server that wants
to log who connected will.
- **No routing table.** With two interfaces up, the first is the default route
and the second is reachable only by an address on its own subnet. That is a
rule rather than an accident, and it is not routing.
Two that were on this list are now done and described in
[../architecture/networking.md](../architecture/networking.md): `setsockopt`
honours six options and refuses the rest, and `sendmsg`/`recvmsg` carry
`SCM_RIGHTS`. A third is closer than it was — toybox's `ping` needed `recvmsg`
*and* `IP_RECVTTL`, and only the second is still missing.
## 4. The interactive crash screen
PSOGM renders and stops. The idea is *a small OS inside the crash*, and the
framing decides the design:
> At panic time the kernel is the only thing running, which is exactly why it can
> offer what a live system cannot: walk the stack, read another process's memory,
> dump page tables, inspect the process table — with no scheduler and no locking
> to respect, because nothing else can race you.
What makes it a *system* rather than a print statement is that it keeps the base
machine's drivers. Concretely, the ones that work with interrupts off: the
framebuffer (`gfx_draw_pixel` is a plain memory write), the PS/2 keyboard
(pollable via ports 0x60/0x64), and the serial port. **Those three are a complete
console.**
Everything else — IDE, USB, the timer, anything that sleeps or takes a
sleeplock — is off limits, because the lock it needs may be precisely the one
held by the CPU that just died.
So the shape is a **polled event loop over preallocated state**: no `kalloc`, no
`sleep`/`wakeup`, no `acquire` on anything a live path might hold, one static
command buffer, and that driver set. **That restriction is not a limitation to
work around later; it is the invariant that makes the mode trustworthy when
everything else is not.** Anything wanting more should be answered by rebooting
into a recovery environment.
A useful precedent to read but not copy: DDB, the BSD in-kernel debugger, is
exactly this, and its hard-won rule is the same one — *a debugger that can
deadlock is worse than no debugger.*
## 5. The installer and `.sip`
Scoped in [`projects/schinst/README.md`](../../projects/schinst/README.md),
which holds the detail. In short:
- [ ] `.sip` format specification, **written down before any code**
- [ ] `tools/mksip` — capture a directory tree into a package
- [ ] The apply path
- [ ] An installation environment that boots from the ISO, partitions, applies
the `.sip`, and installs the loader
`.sip` is modelled on WIM, and the thing worth copying from WIM is that it is
**file-based, not block-based**: one file holds a whole filesystem, applies to a
partition of any size, and several images can share their common files.
**Most of this already exists.** `tools/mkschfs.c` and `tools/mkfs.c` both do
content dedup with an `(st_dev, st_ino)` fast path, and SchFS's B-tree is content
addressed. `mksip` should share that code rather than reimplement it — that is
the reason the dedup was factored the way it was.
Open questions, all wanting a decision before code:
- **Compression.** Something with a small decompressor is worth more than
something with a good ratio, because the decompressor runs in the installation
environment.
- **Multiple images per `.sip`** — WIM's real trick, install/recovery/boot
sharing one blob store. Worth the complexity now, or not?
- **Can the kernel mount a `.sip` read-only directly?** It is close to a
filesystem already, and if it can, the installation environment's root can
simply *be* the `.sip`.
The GUI for this is a Wayland client; see [wayland.md](wayland.md).
## 6. SchFS beyond SchOS
In the order they should happen.
**~~An on-disk format version~~, and an upgrade path.** The version policy is
done — see [../architecture/schfs.md](../architecture/schfs.md). What remains is
the **upgrade step**, and it cannot be written until there are two formats to
convert between; the first bump is when that becomes real work rather than
speculation.
The format is now pinned, which is what the other two items were waiting on.
**A Linux implementation, FUSE first.** Three reasons in order of weight: it can
be tested with `fsx` and `xfstests`, which are far harsher than anything written
alongside the code; it carries no licence entanglement, since libfuse is LGPL and
used across a process boundary; and it can reuse the read/write logic already in
`tools/mkschfs` and `tools/schfs_fsck` rather than being written twice and having
the two disagree.
A kernel module is a different project, comes only after FUSE passes `xfstests`,
and carries the licence problem [../licensing.md](../licensing.md) describes.
**The missing features**, listed honestly before adding any: no journal replay
across an unclean shutdown beyond what copy-on-write gives for free, no
snapshots, no sparse-file support, and no online `fsck`. **Snapshots are the one
where the existing design already pays for most of the cost** — the B-tree is
copy-on-write, which is most of the machinery; nothing takes or names a snapshot.
## 7. The kernel's own gaps
Not phases, and each one improves everything above it:
- **A slab or pool allocator.** `kalloc` hands out one page at a time, and every
subsystem written since has invented its own fixed-size table to work around
that. This is the single change that would most improve the rest of the kernel.
- **A page cache**, which is what a general writable `MAP_SHARED` needs.
[foundations.md](foundations.md) delivers a `memfd` instead, which is narrower
and sufficient for the GUI.
- **Symlinks in procfs**, so `/proc/<pid>/exe` can be one and `ps -o comm` stops
printing `[init]`. Belongs with the rest of the VFS work rather than on its own.
- **The `ls -lR` hang** — **not reproducible**, and kept here because the absence
of a result is a result. Instrumented and hunted at length; see Gate 0 of
[1.0.md](1.0.md). Two real defects were found on the way and fixed, neither
proven to be the cause.
- **No garbage collector for descriptors in flight.** An `AF_UNIX` socket passed
over itself and never received leaks the pair. Bounded at thirty-two sockets,
and nothing in the tree does it — but a third-party program could.
---
## Kept out of scope on purpose
- Anything that needs pushing or publishing. This work stays local.
- TrueType hinting.
- XWayland.
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