a4fbdb7437
The set libwayland's event loop is made of, in kernel/sys/sys_event.c: four kinds of descriptor with no inode, FD_EVENT, that read() drains and poll() reports on. They were table entries returning ENOSYS that read as done. epoll registers (descriptor, file) pairs, so a closed descriptor leaves the set; level- and edge-triggered, EPOLLONESHOT. Waiting is poll()'s, a tick at a time. The old eventfd and signalfd numbers (284, 282) were aliased to the new calls and read flags from a garbage register; they are their own entries now, with epoll_create and epoll_pwait. cmd/evtest checks each, then all four in one set. The plans are brought up to date: everything Wayland was waiting on is built except setsockopt. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4
177 lines
7.6 KiB
Markdown
177 lines
7.6 KiB
Markdown
# The GUI becomes Wayland
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Schcom survives and changes its wire format. SchWM and SchDE are deleted. What
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follows is why that is not a retreat, and what it costs.
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Blocked on [foundations.md](foundations.md). Everything there is built except
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item 4, `setsockopt` that does not lie: descriptor passing, shareable memory,
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sockets in the filesystem, dynamic linking, and the epoll/eventfd/timerfd/
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signalfd set libwayland's event loop is made of.
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---
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## What was deleted
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`projects/schwm/` and `projects/schde/`, both README-only; no code was lost. They
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are **gone from the tree now** rather than marked for deletion — a directory that
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has said "to be deleted" for months is a corner, not a decision. The arguments
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each made are kept below, because they are the part worth keeping.
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### SchWM is not abandoned — Wayland dissolves it
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In X11 the window manager is a separate privileged client because X11 puts
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compositing in the server and policy nowhere. **Wayland's central decision is
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that the compositor *is* the window manager**: there is no protocol by which a
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second process places another's windows, and every attempt to add one has been a
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private extension.
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So SchWM's own argument —
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> *"Compositing is mechanical and must never stall: it runs every frame and a
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> mistake there is a frozen screen. Window management is policy, full of special
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> cases and personal taste, and it changes constantly."*
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— is a real and correct observation **about X11**, which Wayland answers a
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different way. It stays worth honouring, but as a **module boundary inside
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Schcom**, not a process boundary: policy in its own file behind its own
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interface. Do not keep it in its own process, because the protocol to talk to it
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does not exist.
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### SchDE is re-sited rather than abandoned
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A panel, a launcher and a wallpaper are ordinary Wayland clients using
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`wlr-layer-shell` — MIT, an XML file, no dependency. They need no directory of
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their own until one of them is written. SchDE's other observation stands on its
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own and is recorded here so it does not go with the directory: **a GUI terminal
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is not the kernel console with a window around it.** The console parses ANSI
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because it draws straight to the framebuffer; a terminal client parses ANSI
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itself and renders it with proportional-capable text. The two share no code.
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### `projects/schinst/` stays
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Its GUI was the part tied to SchWM, and that part becomes a Wayland client.
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Everything else in it — the `.sip` format, `mksip`, the apply path, the
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installation environment — is untouched by any of this, and remains the
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best-specified unstarted work in the tree.
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---
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## What survives
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**Schcom stays, and keeps its name.** It already owns the display, allocates and
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owns client buffers, implements surface/attach/commit, routes input from
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`/dev/input/eventN`, composites multiple clients bottom-to-top, and cleans up
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after clients that die.
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Its own README says the protocol is deliberately Wayland-shaped — surfaces rather
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than windows, buffers attached and made visible only on commit, the compositor
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telling clients when to draw. That was the right call and this is where it is
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cashed in: **what changes is the wire format and the buffer handle, not the
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architecture.**
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---
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## What has to exist first
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Items 1–4 of [foundations.md](foundations.md), and the first three are absolute —
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libwayland does not start without them.
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The sharpest is descriptor passing. `wl_shm_create_pool` passes a **file
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descriptor**, and there is no path in the protocol that passes an integer
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instead. `struct schcom_surface`'s `handle_kind` field was written precisely so
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that switching would be a new value rather than a protocol break, and it cannot
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help: *our* protocol is the flexible one.
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---
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## Port libwayland. Do not port Weston.
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**libwayland is the small piece**: a wire protocol, an object map, and an event
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loop, needing `libffi` and — for the build-time scanner, on the host only —
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`libexpat`. A real port, but a bounded one.
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**Weston is the trap.** It arrives welded to `libinput`, `udev`, `libdrm`,
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`logind`-shaped seat management and a GL renderer, and porting it means porting
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Linux's device management first and finding the compositor somewhere underneath.
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This is precisely the lesson already recorded twice in this tree — about
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FreeBSD's `sys/dev/usb` (100k lines welded to newbus) and about FreeBSD's
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`sys/netinet` (not a library; reaches into mbufs, epoch, netisr, VNET and uma).
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> The tree has learned this twice. It should not pay to learn it a third time.
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So **Schcom links `libwayland-server` and remains ours.** Input comes from
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`/dev/input/eventN`, which already works, rather than from libinput. Output goes
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through `display_ops`, which already exists.
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### Software rendering first, and probably for a long time
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`pixman` for composition, `wl_shm` for buffers. Mesa means EGL means `dlopen`
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means a dynamic loader -- which now exists (see [foundations.md](foundations.md)
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item 5), so it is no longer what stands in the way of Mesa; a GPU driver is.
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Static binaries are still enough to reach a working desktop, and the desktop's
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own programs can stay static until something concrete demands otherwise.
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### One sharp edge
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`wl_keyboard` hands the client **a keymap as an XKB text blob over a file
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descriptor**. A compositor cannot avoid xkbcommon by having simpler opinions
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about keyboards — the protocol requires the blob.
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The cheap route is one precompiled keymap string shipped in the binary, with
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xkbcommon and `xkeyboard-config` deferred until more than one layout is wanted.
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---
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## Licensing
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Checked before anything is fetched — the standing rule is that the licence goes
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in `NOTICE` **before** the file is committed, not after.
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| wayland, wayland-protocols | MIT |
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| `wlr-layer-shell` | MIT |
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| pixman | MIT |
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| libffi | MIT |
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| libxkbcommon | MIT |
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| xkeyboard-config | MIT |
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All GPL-2.0-or-later compatible, all needing only a `NOTICE` entry. The
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Wayland ecosystem is permissively licensed almost throughout, so nothing here
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raises a licensing question at all.
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---
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## Milestones
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| **W0** | [foundations.md](foundations.md) items 1–4, with the combined test that passes a descriptor *and* shares a `memfd` *and* binds a socket at a real path. |
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| **W1** | libwayland builds and installs into the sysroot. `wayland-scanner` runs on the host. |
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| **W2** | Schcom serves `wl_compositor`, `wl_shm`, `wl_surface`, `xdg_shell`. A client draws one window. |
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| **W3** | `wl_seat`: keyboard and pointer, from the evdev path that exists. |
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| **W4** | Two clients, focus, stacking, move and resize. **This is where SchWM's policy lives, as a file.** |
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| **W5** | `wlr-layer-shell`, and a panel. This is SchDE's first pixel. |
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Every milestone from W2 on is asserted **from the host, by pixel**, the way
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`schcom-test` already does. The compositor's own report that it composited
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something proves nothing.
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---
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## What it will still not do
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- **No hardware acceleration.** Software rendering only, until Mesa, which is
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not on this plan. Dynamic linking, which it also needs, is in.
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- **No XWayland**, so no X11 clients, ever, unless someone ports it.
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- **No mode setting.** Resolution stays whatever the loader asked for — see
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[hybrid.md](hybrid.md), where the GPU driver's eviction is also where a modeset
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API would arrive.
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- **No damage tracking beyond "repaint everything"**, no multiple outputs, no
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subsurfaces. Schcom's README already lists these; they are additions rather
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than rewrites, which is the reason for committing to the surface/commit model
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now.
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- **One keyboard layout**, until xkbcommon is ported.
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- **No clipboard, no drag and drop, no screen capture protocol**, none of which
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W0–W5 touches.
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