v0.5.1 console key releases: Linux VT and FreeBSD vt(4), with a guard
* linux console source: releases from the console's own keyboard, typed by its keymap SetKeyReport with KeySourceConsole, on a Linux virtual console the game runs on, switches the keyboard to raw keycodes (K_MEDIUMRAW) while releases are reported. The kernel allows the switch on the caller's controlling tty, so no root is needed; a console that refuses is not asked again and the protocol is next. Going back to presses, Fini and EmergencyReset switch it back. Each keycode is typed as the console types it cooked, after drivers/tty/vt/keyboard.c, by the console's own tables read at the switch (KDGKBENT, KDGKBSENT, KDGKBDIACRUC, KDGKBMETA): modifiers and their left and right groups, Caps and Num Lock with their lights kept in step (KDSKBLED), sticky and locked modifiers, Unicode entries, dead keys and compose, the keypad by Num Lock, function strings, Meta as ESC prefix or bit 7, console switching by Alt+Fn and Alt+arrows to consoles in use, and from kernel 7.1 cursor and CSI keys with their modifiers. Translation starts from the console's modifiers and locks (TIOCLINUX 6, KDGKBLED). Each key is held by its keycode; a key typing several keys taps all but its last. Switching to another console ends every hold Lost. Mouse reports are off while the keyboard is raw, since the console types them into the same input, and come back after it. The guard: before the first switch the package runs the binary again, named console-guard, holding the console and the read end of a pipe only the game writes. If the pipe ends while the keyboard is raw (kill -9, the OOM killer, a Go fatal error), the guard switches the keyboard back, restores the termios the game found and shows the cursor, without a reset that would clear the game's last words. A game leading its console's session takes the console with it as it dies; its guard then leads a session of its own and opens the console again once the kernel has hung it up, to restore it. Checked in QEMU on a real VT, kernels 6.8 and 7.2, the game as uid 1000: the same key strokes read identically raw and cooked (Shift released first, Ctrl, Alt, AltGr, Caps and Num Lock, the keypad, function keys, modified cursor keys on 7.2; dead grave and tilde, compose, a euro sign and Cyrillic from a loaded keymap), Alt+F2 away ended the hold Lost and Alt+F1 came back, and the keyboard came back to K_UNICODE with ICANON and ECHO after Fini, a panic with EmergencyReset, kill -9, and kill -9 of a game leading its session (left raw without the guard's own session). Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01B3zCVjspRDuEuMrDTumVhp * freebsd console source: releases from vt(4)'s keyboard, typed by its keymap On FreeBSD's vt(4) console the keyboard switches to keycodes (K_CODE), which vt allows any process with the console open, no root needed. Each keycode types what vt types for it cooked: the keyboard's keymap and accent map (GIO_KEYMAP, GIO_DEADKEYMAP) run through a port of the kernel's genkbd_keyaction, kbdmux's left Alt keypad codes, and vt_processkey's xterm sequences, ESC for Alt and console switching. The locks go back to the keyboard and its lights with KDSKBSTATE. Scroll Lock is inert while raw; with the console's history mode on (Scroll Lock lit) the keyboard stays as it is and the ask reports presses. Shared with the Linux source now: the restore EmergencyReset runs, the guard, which opens again a console revoked or hung up with its session's leader, and what a key asks of the console. A console that can't go raw just now (Scroll Lock on, its guard gone, output not drained) is tried again at the next ask rather than never; a refusal at prepare still holds for good. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01B3zCVjspRDuEuMrDTumVhp * example-keys: show each key event, for trying key releases A viewer for the key events a terminal or console reports: F2 asks for releases from the console or the terminal's protocol, or gives them back, and the report each ask came to shows above the events. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01B3zCVjspRDuEuMrDTumVhp --------- Co-authored-by: Claude <noreply@anthropic.com>
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//go:build freebsd
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package terminal
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import (
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"os"
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"strconv"
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"sync"
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"unsafe"
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"golang.org/x/sys/unix"
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)
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// The FreeBSD console's ioctls (sys/kbio.h, sys/consio.h), which
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// golang.org/x/sys/unix does not define
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const (
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kdGetKeyboardMode = 0x40044B06 // KDGKBMODE
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kdSetKeyboardMode = 0x20044B07 // KDSKBMODE
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kdGetLockState = 0x40044B13 // KDGKBSTATE
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kdSetLockState = 0x20044B14 // KDSKBSTATE
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gioKeymap = 0x20006B06 // GIO_KEYMAP
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gioDeadKeymap = 0x20006B08 // GIO_DEADKEYMAP
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vtActivate = 0x20047605 // VT_ACTIVATE
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vtGetActive = 0x40047607 // VT_GETACTIVE
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vtGetIndex = 0x40047608 // VT_GETINDEX
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)
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// Keyboard modes
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const (
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kXlate = 1 // K_XLATE
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kCode = 2 // K_CODE
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)
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// keymapT is GIO_KEYMAP's keymap_t
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type keymapT struct {
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nKeys uint16
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keys [fbsdNumKeys]fbsdKey
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}
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// accentmapT is GIO_DEADKEYMAP's accentmap_t
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type accentmapT struct {
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nAccs uint16
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accents [fbsdDeadKeys]fbsdAccent
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}
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// freebsdConsole is the vt(4) console the game runs on, its keyboard switched
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// to keycodes (K_CODE) while releases come from it
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type freebsdConsole struct {
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tty *os.File
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fd int
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vt int // the console's number, from 1
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termios *unix.Termios // the termios the backend found, which the guard restores
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mu sync.Mutex
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isRaw bool
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km fbsdKeymap
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kb fbsdKeys
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away bool // another console had the keyboard when last asked
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guard *keyGuard
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}
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// openConsole is the console tty is, nil unless it is one: a vt(4) console,
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// not a pty, a serial line or syscons
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func openConsole(tty *os.File, cooked *unix.Termios) keyConsole {
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if vty, err := unix.Sysctl("kern.vty"); cooked == nil || err != nil || vty != "vt" {
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return nil
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}
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fd := int(tty.Fd())
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vt, err := unix.IoctlGetInt(fd, vtGetIndex)
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if err != nil || vt < 1 {
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return nil
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}
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if _, err := unix.IoctlGetInt(fd, kdGetKeyboardMode); err != nil {
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return nil
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}
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c := &freebsdConsole{tty: tty, fd: fd, vt: vt, termios: cooked}
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c.kb.km = &c.km
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return c
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}
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// prepare reads the keymap and starts the guard; a keyboard some other
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// program has raw is left alone
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func (c *freebsdConsole) prepare() bool {
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c.mu.Lock()
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defer c.mu.Unlock()
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if c.isRaw {
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return true
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}
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mode, err := unix.IoctlGetInt(c.fd, kdGetKeyboardMode)
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if err != nil || mode != kXlate || !c.readKeymap() {
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return false
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}
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if c.guard == nil {
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if c.guard, err = startGuard(c.tty); err != nil {
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return false
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}
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}
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return true
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}
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// readKeymap reads the keyboard's keymap and accents, and whether vt takes
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// right Alt for AltGr
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func (c *freebsdConsole) readKeymap() bool {
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var km keymapT
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if ioctlPtr(c.fd, gioKeymap, unsafe.Pointer(&km)) != nil {
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return false
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}
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c.km.keys = km.keys
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var am accentmapT
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c.km.nAccents = 0
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if ioctlPtr(c.fd, gioDeadKeymap, unsafe.Pointer(&am)) == nil {
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c.km.accents, c.km.nAccents = am.accents, min(int(am.nAccs), fbsdDeadKeys)
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}
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altGr, err := unix.SysctlUint32("kern.vt.enable_altgr")
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c.km.altGr = err != nil || altGr != 0
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return true
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}
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// raw arms the guard and switches the keyboard to keycodes, which vt allows
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// whoever has the console open. Scroll Lock on is the console's history mode,
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// which takes every key but its own: the keyboard stays as it is then.
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func (c *freebsdConsole) raw() bool {
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c.mu.Lock()
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defer c.mu.Unlock()
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if c.isRaw {
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return true
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}
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if c.guard == nil || !c.guard.arm(kXlate, c.termios) {
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c.dropGuard()
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return false
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}
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locks, err := unix.IoctlGetInt(c.fd, kdGetLockState)
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if err != nil || locks&fbsdSLKED != 0 || unix.IoctlSetInt(c.fd, kdSetKeyboardMode, kCode) != nil {
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c.guard.disarm()
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return false
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}
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// What was typed cooked would read as keycodes
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flushInput(c.fd)
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c.kb.seed(uint32(locks))
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c.away, c.isRaw = false, true
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rawConsoleKeys.Store(&consoleRestore{fd: c.fd, mode: kXlate, guard: c.guard})
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return true
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}
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// cooked switches the keyboard back
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func (c *freebsdConsole) cooked() {
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c.mu.Lock()
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defer c.mu.Unlock()
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c.cookedLocked()
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}
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// cookedLocked switches the keyboard back, dropping keycodes not yet read; a
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// console that refuses keeps the guard armed. Caller MUST hold mu.
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func (c *freebsdConsole) cookedLocked() {
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if !c.isRaw {
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return
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}
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c.isRaw = false
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rawConsoleKeys.Store(nil)
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if unix.IoctlSetInt(c.fd, kdSetKeyboardMode, kXlate) == nil {
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flushInput(c.fd)
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c.guard.disarm()
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}
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}
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// keys translates raw keycodes: one byte each, bit 7 set on release
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func (c *freebsdConsole) keys(data []byte, key func(code uint32, action KeyAction, typed []byte)) {
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c.mu.Lock()
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defer c.mu.Unlock()
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if !c.isRaw {
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return
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}
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for _, b := range data {
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code, down := int(b&0x7f), b&0x80 == 0
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if code == 0 {
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continue
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}
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action := KeyRelease
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if down {
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action = KeyPress
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if c.kb.isDown(code) {
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action = KeyRepeat
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}
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}
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typed, act := c.kb.key(code, down)
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c.act(act)
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key(uint32(code), action, typed)
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}
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}
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// act does what a key asks of the console: the locks it toggled kept with the
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// keyboard and its lights, and a switch to another console. Caller MUST hold
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// mu.
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func (c *freebsdConsole) act(a consoleAct) {
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if a.leds {
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unix.IoctlSetInt(c.fd, kdSetLockState, int(c.kb.state&fbsdLockMask))
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}
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if a.vt != 0 {
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c.switchTo(a.vt)
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}
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}
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// switchTo switches to console vt, or the one before or after the one on
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// screen, as vt does for a key cooked; vt itself refuses a console no one has
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// open
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func (c *freebsdConsole) switchTo(vt int) {
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cur, err := unix.IoctlGetInt(c.fd, vtGetActive)
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if err != nil {
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return
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}
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switch vt {
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case vtNext:
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vt = cur%fbsdWindows + 1
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case vtPrev:
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vt = (cur+fbsdWindows-2)%fbsdWindows + 1
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}
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if vt != cur {
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unix.IoctlSetInt(c.fd, vtActivate, vt)
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}
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}
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// front is whether this console is on screen; back on it, translation starts
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// again from the console's locks, its modifiers having moved elsewhere
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func (c *freebsdConsole) front() bool {
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c.mu.Lock()
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defer c.mu.Unlock()
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active, err := unix.IoctlGetInt(c.fd, vtGetActive)
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if !c.isRaw || err != nil {
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return true
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}
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front := active == c.vt
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if front && c.away {
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locks, _ := unix.IoctlGetInt(c.fd, kdGetLockState)
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c.kb.seed(uint32(locks))
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}
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c.away = !front
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return front
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}
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// close switches the keyboard back and ends the guard
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func (c *freebsdConsole) close() {
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c.mu.Lock()
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defer c.mu.Unlock()
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c.cookedLocked()
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c.dropGuard()
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}
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// dropGuard ends the guard, which the next prepare starts again. Caller MUST
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// hold mu.
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func (c *freebsdConsole) dropGuard() {
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if c.guard != nil {
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c.guard.close()
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c.guard = nil
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}
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}
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// flushInput drops the console's pending input as its keyboard switches:
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// keycodes would read as characters, and characters as keycodes
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func flushInput(fd int) {
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unix.IoctlSetPointerInt(fd, unix.TIOCFLUSH, unix.TCIFLUSH) // FREAD, which TCIFLUSH equals here
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}
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// guardExecutable is this program's binary, which runs again as the guard
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func guardExecutable() (string, error) { return os.Executable() }
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// nameGuard leaves the guard's process name as it is: FreeBSD names a process
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// after its binary, and the guard's arguments name it
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func nameGuard() {}
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// consolePath is the console's device, for the guard to open it again
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func consolePath(tty *os.File) string {
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vt, err := unix.IoctlGetInt(int(tty.Fd()), vtGetIndex)
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if err != nil || vt < 1 {
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return ""
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}
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return "/dev/ttyv" + strconv.FormatInt(int64(vt-1), 32)
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}
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// guardRestore switches the console keyboard back for the guard, then has
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// rest restore the console's tty. A session whose leader ends revokes its
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// console, the game's leaving with it, which then takes no ioctl (ENOTTY):
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// the guard opens it again, which vt needs no more of to switch the keyboard.
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func guardRestore(tty *os.File, path string, mode int, rest func(fd int)) {
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fd := int(tty.Fd())
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switch err := unix.IoctlSetInt(fd, kdSetKeyboardMode, mode); err {
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case unix.ENOTTY, unix.ENXIO, unix.EBADF:
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guardReopen(path, mode, func(fd int) {
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flushInput(fd)
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rest(fd)
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})
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case nil:
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flushInput(fd)
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fallthrough
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default:
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rest(fd)
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}
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}
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