7c0f7c7d01
Third guess at a chord, and the third one would have been wrong too: a display
manager that grabs Ctrl+Alt+F<n> matches loosely, so Ctrl+Alt+Shift+F2 never
reaches the guest either. Extra modifiers do not get past a loose grab.
The real problem is that this is not knowable from inside. A key the host
swallowed is indistinguishable from a key nobody pressed, so the guest cannot
probe for a free combination, and there is no combination that is free
everywhere:
the HOST takes Alt+F4, Alt+F2, Ctrl+Alt+F1..F6 (loosely matched),
Ctrl+Alt+digit (QEMU's own console tabs)
APPLICATIONS want Alt+anything (Meta -- zsh binds Meta-digit as
digit-argument), Ctrl+letter, Ctrl+Shift+digit
(Ctrl+Shift+2 types ^@), bare F-keys
the LAYOUT wants AltGr+letter
So it is a setting. VT_SETCHORD/VT_GETCHORD, and in userspace:
chvt -c ctrl+shift+F Ctrl+Shift+F1..F6 (the new default)
chvt -c ctrl+alt+shift+F
chvt -c alt+1
chvt -c off no chord; chvt N is then the only way
chvt report the active terminal and the chord
`off` is a legitimate setting rather than a failure mode. On a machine whose
host grabs everything worth binding, `chvt N` is the honest answer.
The default moved to Ctrl+Shift+F1..F6: display managers bind Ctrl+Alt+F<n>,
not Ctrl+Shift+F<n>, and Ctrl+Shift with a *function* key is not a character
on any layout -- unlike Ctrl+Shift+digit, which is.
Caught while writing it: VTC_RALT was 0x08 while kbd.h's RALT is (1<<7), since
(1<<3) is CAPSLOCK. A chord set from userspace with AltGr would simply never
have matched, and the only symptom would have been a key that does nothing.
A _Static_assert now holds the two headers together.
Verified: Ctrl+Alt+F2 leaves the screen byte-identical, Ctrl+Shift+F2 switches,
Ctrl+Shift+F1 returns to a pixel-identical tty1, and chvt -c round-trips
through alt+1 and off and back. 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`, `chvt N`
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or a settable chord --
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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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