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
121 lines
3.9 KiB
C
121 lines
3.9 KiB
C
// PC keyboard interface constants
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#define KBSTATP 0x64 // kbd controller status port(I)
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#define KBS_DIB 0x01 // kbd data in buffer
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#define KBDATAP 0x60 // kbd data port(I)
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#define NO 0
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#define SHIFT (1<<0)
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#define CTL (1<<1)
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#define ALT (1<<2)
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#define CAPSLOCK (1<<3)
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#define NUMLOCK (1<<4)
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#define SCROLLLOCK (1<<5)
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#define E0ESC (1<<6)
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// Special keycodes
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#define KEY_HOME 0xE0
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#define KEY_END 0xE1
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#define KEY_UP 0xE2
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#define KEY_DN 0xE3
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#define KEY_LF 0xE4
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#define KEY_RT 0xE5
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#define KEY_PGUP 0xE6
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#define KEY_PGDN 0xE7
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#define KEY_INS 0xE8
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#define KEY_DEL 0xE9
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// Alt+F1..Alt+F6 -- switch virtual terminal.
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//
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// Above 0xFF deliberately. kbdgetc returns an int and consoleintr takes one,
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// and every value that fits in a byte is already either a character or a
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// UTF-8 continuation byte. A chord that collided with one of those would be
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// typed into the terminal instead of switching away from it.
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#define KEY_ALT_F1 0x120
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#define SCAN_F1 0x3B // F1..F6 are 0x3B..0x40
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// C('A') == Control-A
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#define C(x) (x - '@')
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static uchar shiftcode[256] =
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{
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[0x1D] CTL,
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[0x2A] SHIFT,
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[0x36] SHIFT,
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[0x38] ALT,
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[0x9D] CTL,
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[0xB8] ALT
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};
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static uchar togglecode[256] =
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{
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[0x3A] CAPSLOCK,
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[0x45] NUMLOCK,
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[0x46] SCROLLLOCK
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};
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static uchar normalmap[256] =
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{
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NO, 0x1B, '1', '2', '3', '4', '5', '6', // 0x00
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'7', '8', '9', '0', '-', '=', '\b', '\t',
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'q', 'w', 'e', 'r', 't', 'y', 'u', 'i', // 0x10
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'o', 'p', '[', ']', '\n', NO, 'a', 's',
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'd', 'f', 'g', 'h', 'j', 'k', 'l', ';', // 0x20
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'\'', '`', NO, '\\', 'z', 'x', 'c', 'v',
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'b', 'n', 'm', ',', '.', '/', NO, '*', // 0x30
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NO, ' ', NO, NO, NO, NO, NO, NO,
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NO, NO, NO, NO, NO, NO, NO, '7', // 0x40
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'8', '9', '-', '4', '5', '6', '+', '1',
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'2', '3', '0', '.', NO, NO, NO, NO, // 0x50
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[0x9C] '\n', // KP_Enter
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[0xB5] '/', // KP_Div
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[0xC8] KEY_UP, [0xD0] KEY_DN,
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[0xC9] KEY_PGUP, [0xD1] KEY_PGDN,
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[0xCB] KEY_LF, [0xCD] KEY_RT,
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[0x97] KEY_HOME, [0xCF] KEY_END,
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[0xD2] KEY_INS, [0xD3] KEY_DEL
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};
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static uchar shiftmap[256] =
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{
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NO, 033, '!', '@', '#', '$', '%', '^', // 0x00
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'&', '*', '(', ')', '_', '+', '\b', '\t',
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'Q', 'W', 'E', 'R', 'T', 'Y', 'U', 'I', // 0x10
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'O', 'P', '{', '}', '\n', NO, 'A', 'S',
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'D', 'F', 'G', 'H', 'J', 'K', 'L', ':', // 0x20
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'"', '~', NO, '|', 'Z', 'X', 'C', 'V',
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'B', 'N', 'M', '<', '>', '?', NO, '*', // 0x30
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NO, ' ', NO, NO, NO, NO, NO, NO,
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NO, NO, NO, NO, NO, NO, NO, '7', // 0x40
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'8', '9', '-', '4', '5', '6', '+', '1',
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'2', '3', '0', '.', NO, NO, NO, NO, // 0x50
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[0x9C] '\n', // KP_Enter
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[0xB5] '/', // KP_Div
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[0xC8] KEY_UP, [0xD0] KEY_DN,
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[0xC9] KEY_PGUP, [0xD1] KEY_PGDN,
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[0xCB] KEY_LF, [0xCD] KEY_RT,
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[0x97] KEY_HOME, [0xCF] KEY_END,
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[0xD2] KEY_INS, [0xD3] KEY_DEL
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};
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static uchar ctlmap[256] =
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{
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NO, NO, NO, NO, NO, NO, NO, NO,
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NO, NO, NO, NO, NO, NO, NO, NO,
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C('Q'), C('W'), C('E'), C('R'), C('T'), C('Y'), C('U'), C('I'),
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C('O'), C('P'), NO, NO, '\r', NO, C('A'), C('S'),
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C('D'), C('F'), C('G'), C('H'), C('J'), C('K'), C('L'), NO,
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NO, NO, NO, C('\\'), C('Z'), C('X'), C('C'), C('V'),
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C('B'), C('N'), C('M'), NO, NO, C('/'), NO, NO,
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[0x9C] '\r', // KP_Enter
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[0xB5] C('/'), // KP_Div
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[0xC8] KEY_UP, [0xD0] KEY_DN,
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[0xC9] KEY_PGUP, [0xD1] KEY_PGDN,
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[0xCB] KEY_LF, [0xCD] KEY_RT,
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[0x97] KEY_HOME, [0xCF] KEY_END,
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[0xD2] KEY_INS, [0xD3] KEY_DEL
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};
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