d0f7acf9eb
An x86-64 operating system built from xv6, now largely rewritten: SMP, a copy-on-write root filesystem (SchFS), PCI/USB/virtio drivers, a TTF rasteriser, and a Linux-numbered syscall ABI. No history before this point -- the tree was never under version control. This commit exists so the rename that follows has something to undo to.
42 lines
1.8 KiB
Markdown
42 lines
1.8 KiB
Markdown
# Schcom — the Schunix Compositor
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Owns the display. Every pixel that reaches the screen goes through it.
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Clients do not draw to the framebuffer; they draw into their own buffers and
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hand them over. Schcom decides what is on top of what, composites the result,
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and presents it. It also owns input: it reads the raw event devices and sends
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each event to whichever client should have it.
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That is the whole job. Window *placement* is not part of it — that is SchWM's,
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and Schcom exposes a protocol for it rather than implementing policy itself.
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## Status
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Not started. Scoped only.
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## What it needs from the kernel first
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| Need | State |
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|---|---|
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| Shared memory (`shmget`/`shmat`/`shmdt`) | done |
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| `mmap` of `/dev/fb0` | done |
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| Framebuffer geometry via the fbdev ioctls | done |
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| **Unix domain sockets**, with `SCM_RIGHTS` | **missing** — `socket()` is a `NO_LINUX` stub |
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| **Raw input events** — key down/up with modifiers | **missing** — input only arrives cooked, through the tty line discipline |
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| Mode setting and double buffering | **missing** — needs the virtio-gpu driver |
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The two marked missing are hard blockers, not inconveniences. A client and
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the compositor have to pass a buffer handle between them, and a pipe cannot
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carry one. And a compositor that reads the tty gets line-buffered text
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delivered to a single foreground process, which is not input in any sense it
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can use.
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## Design notes, so far
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- **Buffers are shared memory, not pipes.** A pipe means copying every frame;
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at 800×600×32 that is 1.9 MB per frame per client. shm exists for this.
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- **One protocol, versioned from the start.** SchWM and SchDE are separate
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programs, so the protocol is a real compatibility surface from day one, not
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after the fact.
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- **Policy belongs to SchWM.** If Schcom starts deciding where windows go, the
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split has already failed.
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