1c1b0c9570
/dev/tty1..tty6, Alt+F1..F6 or `chvt N`. Each is an independent terminal --
its own screen, cursor, line discipline, foreground process group and
session. Two shells on two terminals are unrelated processes that share a
keyboard and a screen.
What made it possible is a backing store. The console drew straight into the
framebuffer and scrolled by moving pixels, which works exactly as long as
nothing else wants the screen: there was nowhere to put terminal 2 while
terminal 1 was visible, and nothing to repaint terminal 1 from. Each terminal
owns a grid of cells now and the framebuffer shows whichever grid is active,
so vt_switch() is set-index, repaint, return -- nothing is saved on the way
out because the outgoing grid has been current all along.
The rule the layer is built on: a terminal does not know whether it is
visible. Writes land in the grid, the cursor moves, the grid scrolls, all
unconditionally; drawing is one question asked at the bottom of vt.c. Every
alternative spreads "am I on screen" through the escape parser, and then a
terminal switched away from mid-sequence comes back wrong.
Everything that was a single global is per-terminal now: tty_fg_pgrp (deleted),
termios, the input ring, the escape parser, the UTF-8 decoder, and the cursor
-- which also stops being pixels in gfx.c and becomes cells in the terminal.
TIOCSCTTY was `return 0` and now records proc->ctty, which is what /dev/tty
resolves through; /dev/tty was an alias for /dev/console with the same minor,
and they are different questions.
kbd.c names Alt+F1..F6 as KEY_ALT_F1+n, above 0xFF on purpose -- every byte
value is already a character or a UTF-8 continuation, and a chord colliding
with one would be typed into the terminal instead of switching away from it.
What the chord means is decided in console.c, where the terminals are.
VT_ACTIVATE / VT_WAITACTIVE / VT_GETSTATE / VT_OPENQRY, Linux's numbers.
The argument to ACTIVATE is by value, not a pointer -- same shape as TCFLSH.
Two bugs found by screenshotting the result rather than reading the log:
- zsh emits 0x0F to leave alt-charset mode, because that is what the `linux`
terminfo says rmacs is, and the console drew CP437 glyph 0x0F: a sun, in
the prompt, on every line. A terminal never draws a C0 control character.
- SGR 7 was unimplemented, so zsh's partial-line marker rendered as a bare
'#' instead of a reversed block. Reverse video swaps the colours at draw
time, not at store time, so turning it off restores what was underneath.
Verified by screendump: tty1 and tty2 show different screens, and switching
back repaints tty1's earlier content from its grid. schfs-check passes.
docs/architecture/terminals.md, including what it does not do -- no
scrollback, no reflow, no VT_PROCESS mode for a display server to veto a
switch, which Schcom will need before it owns Alt+F7.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VQ7Qx8E1q1M1bbCq8QLHS2
32 lines
1.3 KiB
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32 lines
1.3 KiB
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# The interactive shell on /dev/tty1, the first virtual terminal.
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Label = os.schos.console-shell
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# zsh, not /bin/sh. mksh stays as /bin/sh and is what schinit falls back to
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# when no manifest loads -- so if zsh ever fails to start, the recovery shell
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# is a different program rather than the same broken one. See ports/zsh.
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Program = /bin/zsh
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Args = -zsh
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RunAtLoad = yes
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KeepAlive = yes
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# The environment this job's shell starts with. Until schinit grew an
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# Environment key, every process on SchOS started with an empty environment --
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# the kernel built one and exec threw it away. $TERM is the one that matters
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# most: a line editor with no TERM cannot ask terminfo how to move a cursor.
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Environment = TERM=linux
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Environment = PATH=/bin:/usr/bin
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Environment = HOME=/root
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Environment = SHELL=/bin/zsh
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# This job reads the console, so it has to own it: schinit puts every job in
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# its own session, and a session with no controlling terminal is not delivered
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# terminal input at all. Without this the shell echoes and executes nothing.
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ControllingTerminal = yes
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StandardIn = /dev/tty1
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StandardOut = /dev/tty1
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StandardError = /dev/tty1
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# Seconds between respawns. Guards against a shell that dies instantly
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# defaults to 10. One is enough for a shell someone just exited on purpose.
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ThrottleInterval = 1
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