fe2f5e1bf8
Alt+1..6 was a worse choice than the Alt+F-keys it replaced, and the reason
is the one that matters: anything the kernel swallows is taken from every
program that will ever run here, permanently.
Alt+<digit> is Meta-digit. zsh's own line editor binds it as digit-argument --
Alt+1 Alt+2 x repeats x twelve times -- and every readline editor does the
same. Yesterday's chord broke that system-wide, which is exactly the failure
mode of picking a chord applications want.
Working the whole space instead of one axis of it:
the HOST takes Alt+F4, Alt+F2, Ctrl+Alt+F1..F6
APPLICATIONS want Alt+anything (Meta), Ctrl+letter, Ctrl+Shift+digit
(Ctrl+Shift+2 types ^@), bare F-keys
the LAYOUT wants AltGr+letter -- Polish diacritics
Ctrl+Alt+Shift+F1..F6 is in none of those sets. Display managers bind the same
chord without Shift, so adding it steps out of the host's way, and no terminal
application binds a triple-modified function key.
Which chords actually reach a guest was measured rather than assumed: a
temporary probe in kbdgetc logged every modified keypress and QEMU's sendkey
fired each candidate at it. Everything reached the guest, Ctrl+Alt+F2
included -- so that conflict is the host's display manager, not QEMU. The same
probe corrected an earlier claim: `sendkey altgr-2` produces no event at all,
so the previous commit's "AltGr+2 did not fire" was never actually tested.
And the escape hatch is real now. VT_SETMODE was accepted and ignored, so a
program could ask to own the chord, be told yes, and still not get it.
VT_PROCESS genuinely stops the kernel switching. Together with the EVIOCGRAB
path -- which kbdgetc already checks before the chord is recognised -- there
are three honest layers: nothing, VT_PROCESS, exclusive grab.
What VT_PROCESS still does not do is the VT_RELDISP handshake; struct vt_mode
carries relsig/acqsig for when Schcom needs to release the GPU before the
screen changes hands.
Verified by screendump hash: Alt+2 reaches zsh as Meta, Ctrl+Alt+F2 and
Ctrl+Shift+F2 leave the screen untouched, Ctrl+Alt+Shift+F2 switches.
schfs-check passes.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VQ7Qx8E1q1M1bbCq8QLHS2
107 lines
5.6 KiB
Markdown
107 lines
5.6 KiB
Markdown
# The system, layer by layer
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What SchOS is today. Everything in this directory is built and running; what is
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merely intended lives in [../plan/](../plan/).
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---
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## The names, and what each one covers
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`uname -s` reports `SchIFT`, the way every Unix reports its kernel rather than
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its distribution.
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| Layer | Name | What it is |
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|---|---|---|
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| System | **SchOS** | The distribution — kernel, userland, tooling |
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| Kernel | **SchIFT** | Multi-core x86-64 kernel with a modular VFS |
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| Filesystem | **SchFS** | Transactional, copy-on-write, the root filesystem |
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| API | **SchAPI** | The native programming interface — *designed, not built* |
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| Compositor | **Schcom** | Owns the display; v0 runs |
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Six virtual terminals sit under all of it -- `/dev/tty1`..`tty6`,
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Ctrl+Alt+Shift+F1..F6 --
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each with its own screen, line discipline and foreground process group. See
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[terminals.md](terminals.md).
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---
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## The stack, bottom to top
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```
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┌─────────────────────────────────────────────────┐
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│ toybox mksh musl first-party cmd/ │ userland
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├─────────────────────────────────────────────────┤
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│ schinit — PID 1, job manifests, supervision │
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├─────────────────────────────────────────────────┤
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│ syscall table — Linux numbering, one .inc file │ ← the ABI seam
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╞═════════════════════════════════════════════════╡
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│ VFS │ sockets │ signals │ mmap │ poll │ procfs │
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├──────┴─────────┴─────────┴──────┴──────┴────────┤
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│ SchFS │ lwIP │ text/gfx │ buffer cache │
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├─────────┴────────┴────────────┴─────────────────┤
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│ device model — class vtables, bus binding │
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├─────────────────────────────────────────────────┤
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│ drivers: xHCI e1000 virtio-gpu VBE IDE PS/2│
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├─────────────────────────────────────────────────┤
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│ scheduler │ paging │ traps │ IRQ │ SMP │ DMA │ SchIFT core
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└─────────────────────────────────────────────────┘
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▲
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UEFI loader (boot/uefi)
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```
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The two seams that matter are the syscall table and the device model. Above the
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first, software is ordinary and portable — musl and toybox are unmodified.
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Below the second, a driver never names its consumer and a consumer never names a
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driver.
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---
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## Where it came from
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SchOS began as [xv6](https://github.com/mit-pdos/xv6-public) and is now mostly
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something else. What survives from xv6 is the *shape* of the process table, the
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sleep/wakeup discipline, and the buffer cache. What has been replaced: the
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scheduler and trap path (rewritten for x86-64 and for more than one processor),
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the memory manager, the entire filesystem, the syscall layer, and every driver.
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That inheritance is worth knowing when reading the code, because the parts that
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still look like xv6 follow xv6's conventions and the parts that do not, do not.
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---
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## The documents
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Read in this order if you are new:
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| [boot.md](boot.md) | Firmware to the first userspace process. The shortest path through the whole system. |
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| [kernel.md](kernel.md) | Memory, processes, scheduling, traps, signals, SMP. |
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| [syscalls.md](syscalls.md) | The one table everything is generated from, and how a musl binary runs unmodified. |
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| [filesystem.md](filesystem.md) | The VFS, the buffer cache, mounts, procfs. |
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| [schfs.md](schfs.md) | The copy-on-write root filesystem. |
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| [devices.md](devices.md) | Buses, classes, binding, and the vtables consumers talk to. |
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| [usb.md](usb.md) | xHCI, the USB core, and the three class drivers. |
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| [graphics.md](graphics.md) | Framebuffer, text rendering, the console, and PSOGM. |
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| [networking.md](networking.md) | NIC drivers, lwIP, and both socket families. |
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| [init.md](init.md) | `schinit` and the job manifests. |
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---
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## Three rules that hold across all of it
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**The kernel and the host tools compile the same SchFS source.** `mkschfs`
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cannot disagree with the kernel about the on-disk format, because there is only
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one implementation. Format bugs are found on the host, where a test takes a
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second instead of a boot.
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**Syscalls are declared in exactly one place.** `kernel/sys/table.inc`.
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The constants, the dispatch table and the Linux translation map are all
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generated from it, so a syscall cannot be half-registered.
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**A list you can read beats a list assembled by side effects.** Drivers are
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written out by hand in `kernel/drivers/registry.c` rather than collected by a
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linker section, and platform devices are registered in one function rather than
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inside each driver's init. The tradeoff is deliberate: self-registration is
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nicer to write, and it means the list of what is in your kernel is not written
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down anywhere you can read.
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