SchOS/docs/plan/1.0.md

# SchOS 1.0

A finish line, so that the list of open work stops being infinite.

---

## Why this document exists

[schapi.md](schapi.md) §3 says the stability freeze starts at 1.0 and covers
whatever is marked `stable` at that moment. **1.0 was never defined**, which
means there has been no finish line — and with no finish line every gap is
equally mandatory, the list only grows, and the project feels larger every week
regardless of how much gets done.

That feeling is structural, not a judgement about progress. This document fixes
the structure by drawing a line and putting most of the open work on the far
side of it.

> **Anything not named in this document is not part of 1.0.** It is not
> cancelled, not forgotten, and not up for reconsideration until 1.0 ships.

---

## What 1.0 is

> **A machine one person can sit down at and use for an afternoon without
> falling off an edge.**

Concretely — boots on real hardware, roots on SchFS, runs a shell and the real
toybox userland, is on the network, and puts a windowed terminal on the screen.

It is deliberately a **small complete system** rather than a rich incomplete
one. SchOS 1.0 is not Linux, does not run third-party applications, and has no
package manager. It is a system that works, end to end, with nothing in it that
lies about what it did.

### The acceptance test

One unattended run, asserted from the host, the way everything else here is
tested. When this passes, it is 1.0:

```
boot on real hardware from a USB stick
  → SchFS root mounts, generation counter advances
  → schinit starts the compositor
  → a terminal window appears and is asserted by pixel
  → in it: ls, cat, a file written, a network fetch
  → reboot
  → the file is still there and the checksum matches
```

Nothing in that sentence is a feature list. Every clause is something that is
currently either broken, missing, or unproven.

---

## The freeze, and the register of unfinished work

**No new capability is started until this register is empty.**

The failure this exists to stop is not laziness and not scope creep — it is
*abandonment by promotion*. A thing gets built to the point where it works, the
next thing becomes more interesting, and the first one is left in a corner:
present in the tree, not finished, not deleted, and not visible in any list.
Enough of those and the tree stops matching its own documentation, which is the
state this register was written to end.

Two rules, and they are the same rule seen from either end:

> **Nothing enters the register except by being finished or being deleted.**
>
> **Adding a row requires closing one.** Two things in flight. Never three.

A row leaves this table in one of exactly two ways. Either it is **finished** —
and finished means a description exists in [../architecture/](../architecture/),
not that the code works — or it is **deleted**, and deleted means gone from the
tree, not marked for deletion. A directory that has said "to be deleted" for
months is the corner, not the cure; `projects/schwm/` and `projects/schde/`
proved that and are now actually gone.

### Built, and not connected to anything

The galling ones. The work exists, is tested, and nothing uses it.

| | Where it stopped |
|---|---|
| **The text layer** | `kernel/dev/text.c` and `kernel/dev/ttf.c` are 850 lines that rasterise TrueType and draw at any pixel position. The console still indexes `font_data[256][16]`. The only caller is a self-test. |
| **A font from disk** | Same layer, same reason. The console's 8×16 CP437 grid is compiled in. |
| **Socket activation** | `schinitd` parses `[Socket name]` and remembers the path. Nothing holds the socket. **This is the entire reason for copying launchd**, and it is the half that was not built. |
| **`display_ops.wait_vblank`** | In the vtable, implemented by the VBE driver, left null by virtio-gpu. A compositor that needs it cannot rely on it. |

### Started, and stopped part-way

| | Where it stopped |
|---|---|
| **`foundations.md`** | Item 1 built. Items 2 (a shareable memory object), 3 (`AF_UNIX` in the filesystem namespace), 4 and 5 open. **Wayland stops at item 2.** |
| ~~**`hybrid.md`**~~ | **Closed.** All four mechanisms built; H1, H2 and H3 done. H4 — the USB eviction — is *withdrawn* rather than outstanding: USB is the bus peripherals arrive on, not a peripheral, and an eviction that has to leave an identical driver behind has moved nothing. See [hybrid.md](hybrid.md), "Decided: USB stays in the kernel". |
| **`ldls.md`** | L0 done — the loader lays out and relocates 2,440 stock modules with nothing unhandled, and reports the API surface of each. L1 (the stubs), L2 (the hardware) and L3 (a packet) open. Nothing is executed yet. |
| **Schcom v0** | 715 lines that composite, over a wire format that is superseded. Frozen: it runs, nothing more is added, and it is kept only because it is the one thing in the tree that has ever put a client's pixels on screen. |
| **`debugger.md`** | D0 through D4 built and described in [../architecture/debugging.md](../architecture/debugging.md). Only the network transport is open — a userspace daemon bridging TCP to `/dev/dbg`, which is deliberately last. |

**The row LDLS spends.** `hybrid.md` closed above — H3 built, H4 withdrawn —
and [ldls.md](ldls.md) takes the slot it freed. Worth being honest that this is
the largest thing ever to enter this register, and that it is **explicitly not
part of 1.0**: nothing in the acceptance test needs a foreign driver. It is
here because the mechanisms it uses are finished and idle, and because the
alternative to it is writing a driver for every device that exists.

**The row the debugger spent.** Adding one requires closing one, and *A released
PCI device* closed when H2 landed. It is worth saying plainly that the debugger
is not a capability of the OS the way every other row here is: nothing in it
ships to a user or appears in the acceptance test. The case for it is that
**Gate 0 is a list of bugs to find in a kernel that could not be asked
anything** — so it is the instrument the rest of this register is surveyed with,
and it earns its slot by making every other row cheaper to close.

**Closed since this register was written.** *A released PCI device* — release is
now symmetric with claim (bus mastering cleared before the DMA is freed, a
refusal when the device is the only display), a supervised job starts the
replacement, and it is described in
[../architecture/devices.md](../architecture/devices.md) under "Taking it back".

### Named in a "what it does not do" and still true

Not corners — these were written down honestly on the day and stayed written
down. They are here so the register is the whole picture rather than the
flattering part of it.

| | |
|---|---|
| `/proc/<pid>/exe` is a regular file | so `readlink()` fails and `ps -o comm` prints `[init]` |
| `getrusage` | does not distinguish `RUSAGE_CHILDREN` from `RUSAGE_SELF` |
| No slab allocator | every subsystem's fixed-size table is a consequence |
| No `getsockname`/`getpeername` | and `accept()` does not report an AF_INET peer |
| No routing table | first interface wins, which is a rule and not routing |
| No descriptor garbage collector | a socket passed over itself and never received leaks the pair |

### Frozen — scoped, unstarted, and not to be started

Neither cancelled nor in progress. **Do not open these.**

| | |
|---|---|
| `projects/schinst/` | the installer, the installation environment, `.sip` |
| `projects/schfs-linux/` | SchFS as a filesystem for Linux |
| [roadmap.md](roadmap.md) §4 | the interactive crash screen |
| [roadmap.md](roadmap.md) §6 | SchFS beyond SchOS |
| [schapi.md](schapi.md) | the API layering, designed and not built |

Each of those is well argued and none of them is on the path to the acceptance
test above. That is the whole test for whether something belongs in this section:
**not "is it worth doing" but "does 1.0 fail without it".**

---

## The four gates

In order. **Do not start a gate before the one before it closes**, and closing
means a description exists in [../architecture/](../architecture/) — see
[the rule](../README.md#the-rule-that-keeps-this-from-rotting).

### Gate 0 — Fix what is already wrong

**This comes first, before any new capability.** The desktop work is the
temptation and it is the wrong thing to do next: a compositor built on a kernel
with an unexplained hang and a socket layer that reports success for things it
did not do will fail in ways indistinguishable from its own bugs. That is the
same argument that put `netdev_selftest()` before the TCP/IP stack, and it was
right then.

**Things that are actively wrong:**

- [x] ~~**The `ls -lR` hang.**~~ **Not reproducible.** Instrumented and hunted;
      see below. Left here rather than deleted because the absence of a result
      is the result.
- [x] ~~**`setsockopt` returns 0 without setting anything.**~~ Six options now
      genuinely reach lwIP's pcb and everything else is `ENOPROTOOPT`. Round-trip
      checks in `cmd/socktest`, which a permissive stub cannot pass: it has to
      read back a value it was set *and* refuse an unknown option.
- [x] ~~**`accept4` silently drops its flags.**~~ It is its own table entry now
      rather than an alias for `accept` — an alias would have had to read a
      fourth argument that `accept` never passes, inventing a `SOCK_NONBLOCK`
      out of whatever the caller last left in that register.
- [x] ~~**Timestamps on everything created after boot read 1970.**~~ Both
      `know()` (SchFS) and `now_sec()` (v1) returned `uptime()` under comments
      saying the kernel had no wall clock. It has had one since `time_init()`
      started reading the RTC; the comments outlived the condition. Two errors,
      not one — `uptime()` counts 10 ms ticks and they were used as seconds, so
      the clocks also ran 100× fast.
- [ ] **`getrusage` does not distinguish `RUSAGE_CHILDREN`** from `RUSAGE_SELF`.
- [ ] **`/proc/<pid>/exe` is a regular file, not a symlink**, so `readlink()`
      fails and `ps -o comm` prints `[init]`. Needs symlink support in procfs.
- [ ] **OVMF memory reporting**, if the region-list fix did not fully close it.

**Work already done and not connected:**

These are the galling ones — the replacement exists, is tested, and is unused.

- [ ] **Port the console onto the text layer and delete the cell grid.**
      `text.c` and `ttf.c` both exist and work. The console still indexes
      `font_data[256][16]`.
- [ ] **Load a font from disk** and point the console at it.
- [x] ~~**Interrupt-driven receive.**~~ The e1000's handler calls
      `netdev_rx_signal()`, which ends the network thread's wait early; the frame
      is still *pulled* by the thread, because an interrupt handler can neither
      sleep on the buffer cache nor take the lwIP lock. The wait stays on the
      tick so lwIP's timers keep their floor. Proven rather than assumed:
      `/proc/netif` gained `wake_rx`/`wake_tick`, and across three pings
      `rx_frames` and `wake_rx` both went 2 -> 6.

**Structural, because everything after this compounds on 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 it — `NPROC`, `NSOCK`, `NDEVICE`, `NSHM`, `MAXJOBS`. This is
      the single change that most improves everything else in the kernel, and
      it gets more expensive with every table added.
- [x] ~~**SchFS on-disk format version policy.**~~ Done. `SCHFS_VERSION` for
      frame changes, plus `compat`/`ro_compat`/`incompat` feature flags in what
      was `reserved0` — so existing images keep every field offset and read
      unchanged. `uber_check()` now distinguishes *damaged* (step over it; that
      is what the ring is for) from *too new* (stop), because falling back to an
      older uberblock mounts a stale filesystem and reports success. Proven on a
      forged image: the old code mounted the stale root and exited 0.
      Still owed: an actual upgrade step, which is only writable once there are
      two formats. See [../architecture/schfs.md](../architecture/schfs.md).

**Found while doing the above, and fixed:**

- [x] ~~Every `AF_INET` socket failed with `ENFILE` until DHCP bound.~~
      `inet_new()` required an *address* before it would hand out a socket, and
      reported the refusal as "file table overflow". Creating a socket is not
      the same as having somewhere to send; a bind or connect with no route
      fails on its own with an error that says so. `net_is_ready()` (lwIP up) is
      now distinct from `net_is_up()` (DHCP bound).
- [x] ~~`socktest` asserted "AF_INET is refused, not faked".~~ True when written,
      false since AF_INET landed — and **green the whole time**, because the
      suite runs before DHCP binds and the `ENFILE` above made the refusal look
      real. A test asserting a failure has to say *which* failure.

**The suite itself:**

Both of these were found by running `make schfs-check` rather than by reading
it, and both predate the current work — confirmed by stashing and re-running.
They are here rather than filed as nice-to-haves because a suite that is red for
known reasons stops being read, and then it is red for unknown reasons too.

- [x] ~~**`make schfs-check` fails at baseline.**~~ Fixed, and it was not only a
      test bug. The allocation map was taken through a `palloc` callback and
      there was **no way to give it back** — no `schfs_space_release`, and a
      comment in `schfs_space_init` reading *"caller frees what was taken"* for
      an API the caller did not have.

      So the kernel leaked the whole map on **every unmount**, up to 2 MB a
      time, and `schfs_space_init`'s own error path stranded a page it had
      already taken because `npages` was only raised after *both* allocations
      succeeded. The test's 518 leaked pages were the symptom that pointed at
      it.

      The map now carries its own `pfree` so it can only be freed by the
      allocator that filled it, `schfs_vol_open`/`schfs_vol_format` release any
      map the volume already holds, and unmount releases. `schfs_objtest`
      asserts the balance — 520 pages taken, 520 given back — so the next leak
      fails the suite instead of being absorbed by it.

- [x] ~~**31 UndefinedBehaviorSanitizer errors.**~~ Fixed, plus two the test
      never reached. One root cause: a leaf's value area holds variable-length
      records packed end to end, so a record begins wherever the last one ended
      — a multiple of 8 only by luck — and the code read them by casting a
      pointer into the block, which tells the compiler they are aligned when
      they are not.

      The seven record types that live at arbitrary offsets now carry
      `SCHFS_PACKED`. **No on-disk layout changed**, and that was measured
      before it was applied rather than assumed: every one already had explicit
      `pad` fields, so sizes and member offsets are identical with and without
      the annotation. Seven `_Static_assert`s now pin those sizes, because a
      record that silently grows misreads every existing volume from that point
      on and looks like corruption rather than like a struct that changed.

      `schfs_node_hdr`, `schfs_item`, `schfs_kptr` and `schfs_uberblock` are
      deliberately left alone — the node header is exactly 32 bytes, so
      everything after it is already 8-aligned, and annotating them would cost
      byte-wise access on the tree's hottest paths to fix a problem they do not
      have.

      Verified by reading an image written *before* the change: full
      `schfs_fsck --check` passes on structure, checksums, key ordering, data
      blocks and derived free space.

      Also caught on the way: `mkschfs` passed a null pointer to `qsort` for an
      empty directory. Every implementation ignores it when the count is zero;
      the standard does not say they have to.

**The identity item:**

- [ ] **Boot from a USB disk.** The xHCI stack, bulk-only transport, SCSI 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.
      Without this the acceptance test above cannot run at all.

#### The `ls -lR` hang, and why it is closed

Hunted with the instrumentation it asked for, under a workload heavier than the
one that originally triggered it — ten iterations of `ls -lR /bin`, interleaved
with writes and `cd`, 33 execs and 13378 tree descents. Measured across it:

```
inode_peak       9 / 200        unchanged
file_peak        9 / 512        unchanged
buf_pinned_peak  1 / 256        unchanged
schfs0  locked 0  tx_owner_pid 0  tx_depth 0
```

Nothing climbed, nothing wedged, and the repaired `holdingsleep` assertion never
fired. **That eliminates this file's own stated hypothesis** — "a lock or
reference-count leak somewhere in the `*at()` paths" — and it is very likely the
bug was fixed in passing by the `*at()` dirfd rewrite, the getdents cookie
rewrite, or SchFS becoming the root, all of which landed after it was reported.

It is closed rather than chased further, and that is a deliberate application of
the two-things-in-flight rule. The instrumentation is permanent: if it ever
happens again, `/proc/fsstat` names the table, or shows `locked 1` with
`tx_owner_pid 0` and the volume lock is orphaned. That is a much better position
than the one it was reported from.

Two real defects were found on the way and fixed, neither proven to be the
cause: `holdingsleep()` never compared the owning pid, which disarmed all seven
`panic()` assertions built on it; and SchFS's `tx_mine()` compared a bare
`struct proc *`, which a recycled ptable slot makes ambiguous.

### Gate 1 — The foundations

[foundations.md](foundations.md), items 1–4. Descriptor passing, a shareable
memory object, `AF_UNIX` in the filesystem namespace.

Nothing above needs these; everything below stops without them.

- [x] ~~**Item 1 — `sendmsg`/`recvmsg` with `SCM_RIGHTS`.**~~ Built and tested;
      fourteen checks in `cmd/socktest`, each moving data through the passed
      descriptor rather than inspecting it. Described in
      [../architecture/networking.md](../architecture/networking.md#descriptor-passing).
      This was also mechanism 1 of [hybrid.md](hybrid.md) — one primitive for
      both, which is the whole reason those are one plan.
- [ ] **Item 2 — a shareable memory object** (`memfd_create`, and
      `mmap(MAP_SHARED)` on it genuinely working between two processes). This is
      what a Wayland buffer still cannot cross on.
- [ ] **Item 3 — `AF_UNIX` sockets in the filesystem namespace.**

### Gate 2 — Init as a role — **done**

Milestones I0–I3, all built. PID 1 forks a supervisor and spawns jobs on its
behalf; the job table lives in `/proc/schinit`; a heartbeat runs both ways; and
`proc_reincarnate()` re-execs PID 1 in place rather than panicking. Both failure
paths are exercised by `sysrq` keys rather than reasoned about.

Before the desktop rather than after, because a compositor being brought up for
the first time crashes constantly, and something that restarts it and says why is
worth far more during that work than at the end of it.

The description is now [../architecture/init.md](../architecture/init.md); the
plan document it replaced has been deleted, per
[the rule](../README.md#the-rule-that-keeps-this-from-rotting).

### Gate 3 — The desktop

[wayland.md](wayland.md), W1–W3, and the terminal.

**W4 and W5 are not in 1.0.** Multi-window focus policy and a panel are
post-1.0. One terminal window that works is the bar.

---

## Not in 1.0

The point of this list is that it is *written down*, so it can stop occupying
attention. Nothing here is cancelled.

| | Why it waits |
|---|---|
| **The rest of the hybrid kernel** ([hybrid.md](hybrid.md)) | Still not a completeness requirement — but the mechanisms and the first eviction happened early, because the alternative to a driver compatibility layer is writing a driver for every device that exists, and that is not a plan. What is deferred is the foreign driver host, not the interface it needs. |
| **Dynamic linking, Mesa, SDL3** | Everything at 1.0 is statically linked. This is the single biggest post-1.0 unlock and it is a whole project. |
| **A page cache** | `memfd` covers the desktop's needs. General writable `MAP_SHARED` of a file is a real project with no 1.0 consumer. |
| **`.sip` and the installer** | 1.0 installs by writing a USB stick. That is how most systems start and it is honest. |
| **SchFS snapshots, FUSE, Linux module, sparse files, online fsck** | The format version (Gate 0) is the prerequisite for all of them, and it is the only part on a clock. |
| **The interactive crash screen** | PSOGM renders, prints a full report and emits a QR code. That is enough. |
| **CFF/OTF fonts, kerning, text layout** | TrueType and fixed advances are enough for a terminal. |
| **Routing, `getsockname`/`getpeername`, IPv6** | One interface, one default route, works. |
| **Multiple outputs, damage tracking, subsurfaces, xkbcommon** | One screen, full repaints, one keymap. |
| **Audio** | Does not exist in any form and is not required to use a machine. |
| **Panel, notifications, settings, file manager** | A terminal is a desktop. |
| **SchAPI itself** | Deliberately. It should be designed *from* the compositor's experience, not before it. |

---

## The rule for this list

**Adding to Gate 0–3 requires deleting something else from it.**

Not a productivity trick — a forcing function. The reason this project feels
overwhelming is that ~20 fronts have been open simultaneously, and no amount of
discipline makes that workable. The fix is structural.

And one working limit, worth holding to literally:

> **Two things in flight. Never three.**

One in Gate 0 and one being written up. Everything else is closed — in the
document, and out of your head.

---

## How you will know it is going well

Not by velocity. By this:

**Every closed item leaves a description behind.** When the `ls -lR` hang is
fixed, `history/kernel.md` gains an entry saying what it actually was. When the
console moves onto the text layer, `architecture/graphics.md` loses a line from
its *What it does not do* section.

Those "does not do" sections shrinking is the real progress bar, and it is the
only one that does not lie.

---

## A note worth keeping

This document was written because the work started to feel overwhelming, and
that is worth recording rather than tidying away — because the feeling was
about the *shape* of the work and not its quality, and the two are easy to
confuse when you are inside it.

The evidence at the time: SMP working on real hardware after five bugs stacked
behind each other; a copy-on-write filesystem whose crash test cuts the power one
write later, 119 times, and demands a clean mount after each; a TCP/IP stack
asserted from both ends; an xHCI driver written from the specification; and a
documentation tree that records why things are strange so they do not get
un-fixed by accident.

None of that is the output of a project in trouble. It was a project with too
many tabs open.