tty: Ctrl+Alt+Shift+F1..F6, and VT_SETMODE actually works
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
This commit is contained in:
Nexoniarz
parent
91a6d440d6
commit
fe2f5e1bf8
9 changed files with 170 additions and 58 deletions
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@ -36,32 +36,40 @@
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#define KEY_INS 0xE8
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#define KEY_DEL 0xE9
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// Alt+1..Alt+6 -- 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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// Alt+1..Alt+6 -- switch virtual terminal.
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// Ctrl+Alt+Shift+F1..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 would be typed into
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// the terminal instead of switching away from it.
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//
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// The number row rather than the function keys, and left Alt rather than
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// either, because everything else was already taken:
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// Choosing this took two wrong answers. Anything the kernel swallows is taken
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// from every program that will ever run here, permanently, and the obvious
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// candidates are all spoken for on one side or the other:
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//
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// Alt+F4 the host window manager closes the QEMU window
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// Alt+F2 GNOME and KDE open a run dialog
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// Ctrl+Alt+F1..F6 the host switches its *own* virtual terminals
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// AltGr+anything Polish diacritics, and AltGr is Ctrl+Alt on some setups
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// Ctrl+Shift+key widely bound inside applications
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// HOST takes it, before the guest ever sees it
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// Alt+F4 the window manager closes the QEMU window
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// Alt+F2 GNOME and KDE open a run dialog
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// Ctrl+Alt+F1..F6 the display manager switches its *own* terminals
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//
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// Alt+digit survives all of that. It is matched exactly -- Ctrl+Alt+1 and
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// AltGr+1 do nothing -- so a chord meant for the host never reaches here.
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#define KEY_ALT_F1 0x120
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#define SCAN_1 0x02 // 1..6 are scancodes 0x02..0x07
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// APPLICATIONS want it, and would never get it again
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// Alt+<anything> Meta. zsh's own line editor binds Meta-digit as
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// digit-argument; every readline editor does too
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// Ctrl+<letter> control characters
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// Ctrl+Shift+<digit> types a character -- Ctrl+Shift+2 is ^@
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// F1..F6 alone help, and whatever a full-screen program wants
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//
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// THE KEYBOARD LAYOUT wants it
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// AltGr+<letter> Polish diacritics, and on some setups AltGr is
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// delivered as Ctrl+Alt
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//
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// Ctrl+Alt+Shift+F1..F6 is in none of those sets. Display managers bind the
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// same chord *without* Shift, so adding it steps out of the host's way, and
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// no terminal application binds a triple-modified function key. Four keys is
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// more than one wants to press, which is correct for something done rarely
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// and deliberately -- and `chvt N` is there for everything else.
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#define KEY_VT_SWITCH 0x120
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#define SCAN_F1 0x3B // F1..F6 are scancodes 0x3B..0x40
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// C('A') == Control-A
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#define C(x) (x - '@')
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@ -133,6 +133,21 @@ struct rlimit {
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#define VT_ACTIVATE 0x5606
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#define VT_WAITACTIVE 0x5607
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// VT_SETMODE modes. VT_AUTO is the kernel switching on its own; VT_PROCESS
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// means a program has taken switching over and the kernel must keep its hands
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// off the keyboard.
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#define VT_AUTO 0x00
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#define VT_PROCESS 0x01
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#define VT_ACKACQ 0x02
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struct vt_mode {
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char mode; // VT_AUTO or VT_PROCESS
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char waitv; // unused here
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short relsig; // signal on release -- not delivered yet
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short acqsig; // signal on acquire -- not delivered yet
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short frsig; // unused
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};
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struct vt_stat {
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uint16 v_active; // active terminal, 1-based
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uint16 v_signal; // unused; Linux keeps it for VT_SETMODE
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@ -118,6 +118,10 @@ struct vt {
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int sid; // session that owns this terminal, 0 = none
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int opened; // times it has been opened, for /dev/tty
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// VT_AUTO or VT_PROCESS. In VT_PROCESS a program has claimed switching and
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// the kernel stops acting on the chord -- see vt_kernel_switches().
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int mode;
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};
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// The active terminal, and the one the framebuffer is showing.
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@ -142,5 +146,6 @@ void vt_repaint(struct vt *v); // grid -> framebuffer, if active
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uint32 vt_rgb(uint8 idx); // palette index -> RGB
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int vt_index(struct vt *v); // 0-based number of a terminal
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int vt_kernel_switches(void); // 0 if a program owns switching
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#endif // VT_H
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