Evdev on Kandelo - /dev/input keyboard and pointer, plus an espeak-ng speech demo

[mho22]

Why

Kandelo had no input devices: nothing existed under /dev/input, so evdev consumers — SDL2 (#709), Wayland (#948), Hyprland (#976) up the stack — had no way to read a keyboard or a pointer. This PR is the base layer of the five-PR DRI stack (#698 → #709 → #948 → #976 → #1241). It adds a kernel evdev subsystem fed by host input sources on both hosts, and proves the audio path end-to-end by porting espeak-ng against main's existing OSS /dev/dsp device.

Earlier revisions of this PR added a kernel ALSA subsystem instead. The review recommended against carrying a narrow subset of the ALSA contract under standard ALSA names, and main's /dev/dsp already covers the PCM needs — the ALSA surface is gone from this branch (see Notes).

What changed

• kernel evdev subsystem (crates/kernel/src/input/): /dev/input/event0 (keyboard) and /dev/input/event1 (pointer) devfs nodes with per-OFD InputFdState; EVIOCG* ioctl dispatch, with the length-encoded EVIOC ioctls resolved through a family table; a kernel_input_event export that fans events out to every open fd, with ring overflow handled by SYN_DROPPED resync; sys_read drains the ring and sys_poll gates POLLIN; state is released on close and serialised across fork/exec
• shared ABI: struct input_event plus EV_*/KEY_*/BTN_*/REL_*/ABS_*/EVIOC* constants; linux/input.h and linux/input-event-codes.h vendored into the musl overlay; abi/snapshot.json, host/src/generated/abi.ts, and libc/glue/abi_constants.h regenerated — additive-only, no ABI_VERSION bump
• host input, both hosts: an InputSource interface; BrowserInputSource captures DOM keyboard/pointer events and translates them through a key-code table; NodeInputSource is the headless null source so vitest exercises the same path; ingress routes through the kernel entry gate
• espeak-ng port (packages/registry/espeak-ng/): cross-build recipe with a cmake toolchain file, linked against upstream pcaudiolib 1.3 built with only its OSS backend — that backend opens /dev/dsp, so no pcaudiolib source is patched and no kernel audio code is added; the English-only voice data ships as a resolver-published runtime file; the image builder stages /usr/bin/espeak-ng, /usr/share/espeak-ng-data, and /usr/local/bin/evdev_demo at image-compose time
• demos: kandelo presets "Evdev input log" and "OSS - Espeak-NG" with Playwright specs kandelo-evdev.spec.ts / kandelo-espeak.spec.ts; programs/evdev_demo.c and programs/input-evdev-smoke.c; an evdev-demo package owning evdev_demo.wasm

Notes

• The kernel ALSA surface from earlier revisions (/dev/snd/{pcmC0D0p,controlC0}, the mmap ring, the three kernel_audio_* exports) is removed in cfa1d51. main's audio.rs already answers the OSS quality checklist (blocking write, EAGAIN, GETOSPACE, audio-clock-driven consumption), and this branch's copy was byte-identical to it. The net kernel audio delta vs main is zero.
• host/src/audio/ is also unchanged vs main — the PCM drivers the demo plays through (BrowserPcmDriver, NodePcmDriver) already landed there.

Both hosts

Browser: BrowserInputSource, wired through browser-kernel-host.ts, browser-kernel-protocol.ts, browser-kernel-worker-entry.ts. Node: NodeInputSource, wired through the node counterparts in the same commits. Shared: kernel-worker.ts carries the input fan-in for both. Vitest covers the Node path end-to-end (input-evdev.test.ts: key + pointer + ring overflow) and the browser translation layer (browser-input-source.test.ts); the Playwright specs cover the browser path.

Verification

The stack was verified at its tip 272be070a (explore-dri-omarchy), which contains all 26 commits here:

• cargo test -p kandelo --target aarch64-apple-darwin --lib → 1665 pass, 0 fail
• host typecheck clean; all 48 stack vitest gate files pass, including the seven input/ioctl test files this PR adds
• scripts/run-libc-tests.sh → 0 unexpected failures
• scripts/run-posix-tests.sh → FAIL: 0
• bash scripts/check-abi-version.sh → consistent; this layer is additive at ABI 43, the wayland layer up-stack bumps to 44
• browser-demo verification of the espeak and evdev presets on the rebased branch is pending: it needs a shell.vfs.zst built for the stack's ABI, which is not yet published. The Playwright specs are in the tree but have not run against this rebase.

[github-actions]

Phase B-1 matrix build status — pr-698-staging

ABI v15. 62 built, 4 failed, 66 total.

Package	Arch	Status	Sha
libcurl	wasm32	built	05aae726
libcxx	wasm32	built	7924fbe0
libcxx	wasm64	built	cfe94678
libpng	wasm32	built	e11caae0
libxml2	wasm32	built	6db06345
libxml2	wasm64	built	bfabb4ff
openssl	wasm32	built	2708b58d
openssl	wasm64	built	a1be8942
sqlite	wasm32	built	0affae3a
sqlite	wasm64	built	2638b6ad
zlib	wasm32	built	a74da2ed
zlib	wasm64	built	76101599
bc	wasm32	built	46973bfb
bzip2	wasm32	built	ffa5f4c4
coreutils	wasm32	built	4d8239d1
curl	wasm32	built	dca90723
dash	wasm32	built	ad59e65d
diffutils	wasm32	built	d67cb386
dinit	wasm32	built	6780ca3d
fbdoom	wasm32	built	a4dcc46f
file	wasm32	built	d2312c00
findutils	wasm32	built	3767b4e1
gawk	wasm32	built	faedad8e
git	wasm32	built	f50d2974
grep	wasm32	built	b9b6b1e6
gzip	wasm32	built	539fee04
kandelo-sdk	wasm32	built	bdddb4fe
kernel	wasm32	built	51062af5
less	wasm32	built	5180eac9
lsof	wasm32	built	96fa5be8
m4	wasm32	built	0aa7ce01
make	wasm32	built	5cdd9bd8
mariadb	wasm32	built	4c185e36
mariadb	wasm64	built	ec3ea5f8
msmtpd	wasm32	built	aa3de664
nano	wasm32	built	4a52b067
ncurses	wasm32	built	ff1ca5a3
netcat	wasm32	built	20b49fdf
nginx	wasm32	built	5c15a366
php	wasm32	built	f1bfba4b
posix-utils-lite	wasm32	built	df2ce6e9
sed	wasm32	built	80e62002
spidermonkey	wasm32	built	0b3b3066
tar	wasm32	built	0532dd66
tcl	wasm32	built	eba6fe94
unzip	wasm32	built	b4f32850
userspace	wasm32	built	1d4c6a6f
vim	wasm32	built	9895fd65
wget	wasm32	built	6c82e2c4
xz	wasm32	built	7bf9b496
zip	wasm32	built	261d8148
zstd	wasm32	built	0c16fdb0
bash	wasm32	built	15fc009b
mariadb-test	wasm32	built	884a67b1
mariadb-vfs	wasm32	built	dd1e248f
mariadb-vfs	wasm64	built	f3286762
nethack	wasm32	built	73993e86
node	wasm32	built	2e1b58a3
spidermonkey-node	wasm32	built	22cfbf7c
vim-browser-bundle	wasm32	built	0deeb2d2
nethack-browser-bundle	wasm32	built	8561a152
rootfs	wasm32	built	74c566e1
shell	wasm32	failed	—
lamp	wasm32	failed	—
node-vfs	wasm32	failed	—
wordpress	wasm32	failed	—

_{Auto-generated; replaced on each push. Raw data in the publish-status workflow artifact.}

[brandonpayton]

Codex review

This feedback is from Codex (OpenAI), reviewing at Brandon's request.

Summary

I do not recommend adopting this kernel ALSA surface as Kandelo's sound API for the stated SDL goal. The browser AudioWorklet, shared-ring transport, dual-host AudioDriver abstraction, and end-to-end eSpeak demonstration are useful engineering work. However, the demo proves a Kandelo-specific pcaudiolib backend and the host playback path; it does not demonstrate compatibility with SDL's ALSA backend, alsa-lib, or ordinary ALSA applications.

ALSA is a large Linux kernel/userspace contract, not simply a PCM node plus several ioctl numbers. Implementing /dev/snd/* usefully requires the control plane, device/card enumeration, hardware and software parameter negotiation, state and XRUN behavior, poll semantics, read/write and mmap paths, and the ABI details expected by alsa-lib. Carrying a small custom subset under ALSA names risks freezing an interface that looks compatible but is not.

For Kandelo's immediate objective, I recommend a smaller implementation-neutral PCM core with a correct OSS-compatible /dev/dsp frontend.

Completeness concerns

1. This does not establish SDL ALSA compatibility. SDL calls a broad libasound API; it does not normally issue these raw kernel ioctls itself. This PR does not port or test alsa-lib, and eSpeak uses a new Kandelo-specific pcaudiolib backend instead. The resulting demo is valuable, but it should not be treated as evidence that SDL or other ALSA software will run unmodified.

2. The control device is intentionally a stub. The PR description says /dev/snd/controlC0 opens but all ioctls fail. A node that passes an existence probe but cannot enumerate or describe a card is not a complete ALSA control implementation and can cause consumers to fail later in less obvious ways.

3. The advertised PCM ABI is only a narrow subset. Capture is absent, the full control/device discovery contract is absent, and compatibility with real alsa-lib read/write and mmap behavior has not been demonstrated. Unsupported functionality should not be advertised under standard ALSA device names unless the supported conformance boundary is explicit and tested.

4. The proof is application-specific. The custom eSpeak backend is coupled to exactly the implemented subset, so it cannot reveal missing behavior that a general ALSA client would exercise. At minimum, a claim of ALSA compatibility would require an unmodified alsa-lib plus representative clients and negative/state-transition tests.

5. Required verification is incomplete. The PR says the musl libc-test and Open POSIX Test Suite were not run. Repository policy requires both before completion, even for an additive change. The full Vitest suite also needs to run, not only selected audio and package-system files.

6. The size cost is not isolated. This PR is merged with large DRI/input work, so its source diff and final kernel artifact do not show the incremental cost of ALSA. Before choosing this API, measure the audio-only delta in raw and compressed kernel Wasm, host/worklet JavaScript, steady-state ring memory, and userspace artifacts such as libraries and test/demo binaries.

Direction Brandon is exploring

Brandon is exploring deeper /dev/dsp support on a clean branch, with the goal of satisfying SDL without implementing the Linux ALSA kernel ABI.

There are strong reasons for that direction:

• Upstream SDL2 and SDL3 already contain an OSS dsp backend. SDL2 primarily relies on blocking write() for pacing; SDL3 additionally uses SNDCTL_DSP_GETOSPACE.
• Kandelo already has /dev/dsp, its SDK header, and an existing non-SDL consumer, so this is an incremental compatibility improvement rather than a second sound ABI.
• FreeBSD's native PCM framework exposes an OSS-compatible /dev/dsp API rather than kernel ALSA. FreeBSD supplies ALSA compatibility in userspace over OSS, which is also a viable later path for Kandelo if Linux-specific applications become important.
• POSIX does not standardize audio. A small Unix device extension does not make Kandelo less POSIX, while ALSA does not make it more POSIX.
• SDL performs application-side conversion and resampling, so the kernel does not need ALSA's full negotiation and plugin model merely to provide useful playback.

The /dev/dsp work should be source/API compatible rather than claiming host binary compatibility. Kandelo should own and ABI-snapshot its wasm32 ioctl values and fixed-width structures such as audio_buf_info.

For SDL-quality playback, the current /dev/dsp implementation still needs real backpressure: blocking writes, O_NONBLOCK/EAGAIN, truthful POLLOUT with wakeups, GETOSPACE, actual drain/reset behavior, audio-clock-driven consumption, and deterministic open-file-description ownership. It must stop dropping the oldest queued audio when full. Playback-only is a reasonable first boundary, but capture opens should then fail rather than advertise a recording device that returns EOF.

Suggested disposition

I would treat this PR as a valuable audio-transport exploration and reuse the sound parts selectively:

• retain the AudioDriver separation and dual-host wiring;
• retain the AudioWorklet-driven browser consumption concept;
• retain deterministic Node pacing and host instrumentation where useful;
• move those pieces behind a generic PCM stream rather than ALSA state/mmap structures;
• do not merge /dev/snd and the partial ALSA UAPI as Kandelo's public sound contract solely for SDL.

If broad compatibility with unmodified Linux ALSA applications later becomes an explicit product requirement, evaluate a userspace alsa-lib OSS/native PCM adapter first. A kernel ALSA implementation should only be undertaken with a defined compatibility target and conformance suite.

— Codex (OpenAI), at Brandon's request