linux.rs

//! Contains the input/output code for keyboards on Linux.

#![cfg_attr(feature = "simulated_output", allow(dead_code, unused_imports))]

pub use evdev::BusType;
use evdev::{uinput, Device, EventType, InputEvent, PropType, RelativeAxisType};
use inotify::{Inotify, WatchMask};
use mio::{unix::SourceFd, Events, Interest, Poll, Token};
use nix::ioctl_read_buf;
use rustc_hash::FxHashMap as HashMap;
use signal_hook::{
    consts::{SIGINT, SIGTERM, SIGTSTP},
    iterator::Signals,
};

use std::convert::TryFrom;
use std::fs;
use std::io;
use std::os::unix::io::AsRawFd;
use std::path::PathBuf;
use std::sync::atomic::{AtomicU64, Ordering};
use std::thread;

use super::*;
use crate::{kanata::CalculatedMouseMove, oskbd::KeyEvent};
use kanata_parser::cfg::DeviceDetectMode;
use kanata_parser::cfg::UnicodeTermination;
use kanata_parser::custom_action::*;
use kanata_parser::keys::*;

pub struct KbdIn {
    devices: HashMap<Token, (Device, String)>,
    /// Some(_) if devices are explicitly listed, otherwise None.
    missing_device_paths: Option<Vec<String>>,
    poll: Poll,
    events: Events,
    token_counter: usize,
    /// stored to prevent dropping
    _inotify: Inotify,
    include_names: Option<Vec<String>>,
    exclude_names: Option<Vec<String>>,
    device_detect_mode: DeviceDetectMode,
}

const INOTIFY_TOKEN_VALUE: usize = 0;
const INOTIFY_TOKEN: Token = Token(INOTIFY_TOKEN_VALUE);

pub static WAIT_DEVICE_MS: AtomicU64 = AtomicU64::new(200);

impl KbdIn {
    pub fn new(
        dev_paths: &[String],
        continue_if_no_devices: bool,
        include_names: Option<Vec<String>>,
        exclude_names: Option<Vec<String>>,
        device_detect_mode: DeviceDetectMode,
    ) -> Result<Self, io::Error> {
        let poll = Poll::new()?;

        let mut missing_device_paths = None;
        let devices = if !dev_paths.is_empty() {
            missing_device_paths = Some(vec![]);
            devices_from_input_paths(
                dev_paths,
                missing_device_paths.as_mut().expect("initialized"),
            )
        } else {
            discover_devices(
                include_names.as_deref(),
                exclude_names.as_deref(),
                device_detect_mode,
            )
        };
        if devices.is_empty() {
            if continue_if_no_devices {
                log::warn!("no keyboard devices found; kanata is waiting");
            } else {
                return Err(io::Error::new(
                    io::ErrorKind::NotFound,
                    "No keyboard devices were found",
                ));
            }
        }
        let _inotify = watch_devinput().map_err(|e| {
            log::error!("failed to watch files: {e:?}");
            e
        })?;
        poll.registry().register(
            &mut SourceFd(&_inotify.as_raw_fd()),
            INOTIFY_TOKEN,
            Interest::READABLE,
        )?;

        let mut kbdin = Self {
            poll,
            missing_device_paths,
            _inotify,
            events: Events::with_capacity(32),
            devices: HashMap::default(),
            token_counter: INOTIFY_TOKEN_VALUE + 1,
            include_names,
            exclude_names,
            device_detect_mode,
        };

        for (device, dev_path) in devices.into_iter() {
            if let Err(e) = kbdin.register_device(device, dev_path.clone()) {
                log::warn!("found device {dev_path} but could not register it {e:?}");
                if let Some(ref mut missing) = kbdin.missing_device_paths {
                    missing.push(dev_path);
                }
            }
        }

        Ok(kbdin)
    }

    fn register_device(&mut self, mut dev: Device, path: String) -> Result<(), io::Error> {
        log::info!("registering {path}: {:?}", dev.name().unwrap_or(""));
        wait_for_all_keys_unpressed(&dev)?;
        // NOTE: This grab-ungrab-grab sequence magically fixes an issue with a Lenovo Yoga
        // trackpad not working. No idea why this works.
        dev.grab()?;
        dev.ungrab()?;
        dev.grab()?;

        let tok = Token(self.token_counter);
        self.token_counter += 1;
        let fd = dev.as_raw_fd();
        self.poll
            .registry()
            .register(&mut SourceFd(&fd), tok, Interest::READABLE)?;
        self.devices.insert(tok, (dev, path));
        Ok(())
    }

    pub fn read(&mut self) -> Result<Vec<InputEvent>, io::Error> {
        let mut input_events = vec![];
        loop {
            log::trace!("polling");

            if let Err(e) = self.poll.poll(&mut self.events, None) {
                log::error!("failed poll: {:?}", e);
                return Ok(vec![]);
            }

            let mut do_rediscover = false;
            for event in &self.events {
                if let Some((device, _)) = self.devices.get_mut(&event.token()) {
                    if let Err(e) = device
                        .fetch_events()
                        .map(|evs| evs.into_iter().for_each(|ev| input_events.push(ev)))
                    {
                        // Currently the kind() is uncategorized... not helpful, need to match
                        // on os error (19)
                        match e.raw_os_error() {
                            Some(19) => {
                                self.poll
                                    .registry()
                                    .deregister(&mut SourceFd(&device.as_raw_fd()))?;
                                if let Some((_, path)) = self.devices.remove(&event.token()) {
                                    log::warn!("removing kbd device: {path}");
                                    if let Some(ref mut missing) = self.missing_device_paths {
                                        missing.push(path);
                                    }
                                }
                            }
                            _ => {
                                log::error!("failed fetch events due to {e}, kind: {}", e.kind());
                                return Err(e);
                            }
                        };
                    }
                } else if event.token() == INOTIFY_TOKEN {
                    do_rediscover = true;
                } else {
                    panic!("encountered unexpected epoll event {event:?}");
                }
            }
            if do_rediscover {
                log::info!("watch found file changes, looking for new devices");
                self.rediscover_devices()?;
            }
            if !input_events.is_empty() {
                return Ok(input_events);
            }
        }
    }

    fn rediscover_devices(&mut self) -> Result<(), io::Error> {
        // This function is kinda ugly but the borrow checker doesn't like all this mutation.
        let mut paths_registered = vec![];
        if let Some(ref mut missing) = self.missing_device_paths {
            if missing.is_empty() {
                log::info!("no devices are missing, doing nothing");
                return Ok(());
            }
            log::info!("checking for {missing:?}");
            let discovered_devices = missing
                .iter()
                .filter_map(|dev_path| {
                    for _ in 0..(WAIT_DEVICE_MS.load(Ordering::SeqCst) / 10) {
                        // try a few times with waits in between; device might not be ready
                        if let Ok(device) = Device::open(dev_path) {
                            return Some((device, dev_path.clone()));
                        }
                        std::thread::sleep(std::time::Duration::from_millis(10));
                    }
                    None
                })
                .collect::<Vec<(_, _)>>();
            for (device, dev_path) in discovered_devices {
                if let Err(e) = self.register_device(device, dev_path.clone()) {
                    log::warn!("found device {dev_path} but could not register it {e:?}");
                } else {
                    paths_registered.push(dev_path);
                }
            }
        }
        if let Some(ref mut missing) = self.missing_device_paths {
            missing.retain(|path| !paths_registered.contains(path));
        } else {
            log::info!("sleeping for a moment to let devices become ready");
            std::thread::sleep(std::time::Duration::from_millis(
                WAIT_DEVICE_MS.load(Ordering::SeqCst),
            ));
            discover_devices(
                self.include_names.as_deref(),
                self.exclude_names.as_deref(),
                self.device_detect_mode,
            )
            .into_iter()
            .try_for_each(|(dev, path)| {
                if !self
                    .devices
                    .values()
                    .any(|(_, registered_path)| &path == registered_path)
                {
                    self.register_device(dev, path)
                } else {
                    Ok(())
                }
            })?;
        }
        Ok(())
    }
}

#[derive(Copy, Clone, Debug, PartialEq, Eq)]
enum DeviceType {
    Keyboard,
    KeyboardMouse,
    Mouse,
    Other,
}

pub fn is_input_device(device: &Device, detect_mode: DeviceDetectMode) -> bool {
    use evdev::Key;
    if device.name() == Some("kanata") {
        return false;
    }
    let is_keyboard = device
        .supported_keys()
        .map_or(false, |keys| keys.contains(Key::KEY_ENTER));
    let is_mouse = device
        .supported_relative_axes()
        .map_or(false, |axes| axes.contains(RelativeAxisType::REL_X));
    let device_type = match (is_keyboard, is_mouse) {
        (true, true) => DeviceType::KeyboardMouse,
        (true, false) => DeviceType::Keyboard,
        (false, true) => DeviceType::Mouse,
        (false, false) => DeviceType::Other,
    };
    let device_name = device.name().unwrap_or("unknown device name");
    match (detect_mode, device_type) {
        (_, DeviceType::Other) => {
            log::debug!("Use for input: false. Non-input device: {}", device_name,);
            false
        }
        (DeviceDetectMode::Any, _)
        | (DeviceDetectMode::KeyboardMice, DeviceType::Keyboard | DeviceType::KeyboardMouse)
        | (DeviceDetectMode::KeyboardOnly, DeviceType::Keyboard) => {
            log::debug!(
                "Use for input: true. detect type {:?}; device type {:?}, device name: {}",
                detect_mode,
                device_type,
                device_name,
            );
            true
        }
        _ => {
            log::debug!(
                "Use for input: false. detect type {:?}; device type {:?}, device name: {}",
                detect_mode,
                device_type,
                device_name,
            );
            true
        }
    }
}

impl TryFrom<InputEvent> for KeyEvent {
    type Error = ();
    fn try_from(item: InputEvent) -> Result<Self, Self::Error> {
        use OsCode::*;
        match item.kind() {
            evdev::InputEventKind::Key(k) => Ok(Self {
                code: OsCode::from_u16(k.0).ok_or(())?,
                value: KeyValue::from(item.value()),
            }),
            evdev::InputEventKind::RelAxis(axis_type) => {
                let dist = item.value();
                let code: OsCode = match axis_type {
                    RelativeAxisType::REL_WHEEL | RelativeAxisType::REL_WHEEL_HI_RES => {
                        if dist > 0 {
                            MouseWheelUp
                        } else {
                            MouseWheelDown
                        }
                    }
                    RelativeAxisType::REL_HWHEEL | RelativeAxisType::REL_HWHEEL_HI_RES => {
                        if dist > 0 {
                            MouseWheelRight
                        } else {
                            MouseWheelLeft
                        }
                    }
                    _ => return Err(()),
                };
                Ok(KeyEvent {
                    code,
                    value: KeyValue::Tap,
                })
            }
            _ => Err(()),
        }
    }
}

impl From<KeyEvent> for InputEvent {
    fn from(item: KeyEvent) -> Self {
        InputEvent::new(EventType::KEY, item.code as u16, item.value as i32)
    }
}

use std::cell::Cell;

#[cfg(all(not(feature = "simulated_output"), not(feature = "passthru_ahk")))]
pub struct KbdOut {
    device: uinput::VirtualDevice,
    accumulated_scroll: u16,
    accumulated_hscroll: u16,
    raw_buf: Vec<InputEvent>,
    pub unicode_termination: Cell<UnicodeTermination>,
    pub unicode_u_code: Cell<OsCode>,
}

#[cfg(all(not(feature = "simulated_output"), not(feature = "passthru_ahk")))]
impl KbdOut {
    pub fn new(
        symlink_path: &Option<String>,
        trackpoint: bool,
        bus_type: BusType,
    ) -> Result<Self, io::Error> {
        // Support pretty much every feature of a Keyboard or a Mouse in a VirtualDevice so that no event from the original input devices gets lost
        // TODO investigate the rare possibility that a device is e.g. a Joystick and a Keyboard or a Mouse at the same time, which could lead to lost events

        // For some reason 0..0x300 (max value for a key) doesn't work, the closest that I've got to work is 560
        let keys = evdev::AttributeSet::from_iter((0..560).map(evdev::Key));
        let relative_axes = evdev::AttributeSet::from_iter([
            RelativeAxisType::REL_WHEEL,
            RelativeAxisType::REL_HWHEEL,
            RelativeAxisType::REL_X,
            RelativeAxisType::REL_Y,
            RelativeAxisType::REL_Z,
            RelativeAxisType::REL_RX,
            RelativeAxisType::REL_RY,
            RelativeAxisType::REL_RZ,
            RelativeAxisType::REL_DIAL,
            RelativeAxisType::REL_MISC,
            RelativeAxisType::REL_WHEEL_HI_RES,
            RelativeAxisType::REL_HWHEEL_HI_RES,
        ]);

        let device = uinput::VirtualDeviceBuilder::new()?
            .name("kanata")
            // libinput's "disable while typing" feature don't work when bus_type
            // is set to BUS_USB, but appears to work when it's set to BUS_I8042.
            .input_id(evdev::InputId::new(bus_type, 1, 1, 1))
            .with_keys(&keys)?
            .with_relative_axes(&relative_axes)?;
        let device = if trackpoint {
            device.with_properties(&evdev::AttributeSet::from_iter([PropType::POINTING_STICK]))?
        } else {
            device
        };
        let mut device = device.build()?;
        let devnode = device
            .enumerate_dev_nodes_blocking()?
            .next() // Expect only one. Using fold or calling next again blocks indefinitely
            .ok_or_else(|| io::Error::new(io::ErrorKind::NotFound, "devnode is not found"))??;
        log::info!("Created device {:#?}", devnode);
        let symlink = if let Some(symlink_path) = symlink_path {
            let dest = PathBuf::from(symlink_path);
            let symlink = Symlink::new(devnode, dest)?;
            Some(symlink)
        } else {
            None
        };
        handle_signals(symlink);

        Ok(KbdOut {
            device,
            accumulated_scroll: 0,
            accumulated_hscroll: 0,
            raw_buf: vec![],

            // historically was the only option, so make Enter the default
            unicode_termination: Cell::new(UnicodeTermination::Enter),

            // historically was the only option, so make KEY_U the default
            unicode_u_code: Cell::new(OsCode::KEY_U),
        })
    }

    pub fn update_unicode_termination(&self, t: UnicodeTermination) {
        self.unicode_termination.replace(t);
    }

    pub fn update_unicode_u_code(&self, u: OsCode) {
        self.unicode_u_code.replace(u);
    }

    pub fn write_raw(&mut self, event: InputEvent) -> Result<(), io::Error> {
        if event.event_type() == EventType::SYNCHRONIZATION {
            // Possible codes are:
            //
            // SYN_REPORT: probably the only one we'll ever receive, segments atomic reads
            // SYN_CONFIG: unused
            // SYN_MT_REPORT: same as SYN_REPORT above but for touch devices, which kanata almost
            //     certainly shouldn't be dealing with.
            // SYN_DROPPED: buffer full, events dropped. Not sure what this means or how to handle
            //     this correctly.
            //
            // With this knowledge, seems fine to not bother checking.
            self.device.emit(&self.raw_buf)?;
            self.raw_buf.clear();
        } else {
            self.raw_buf.push(event);
        }
        Ok(())
    }

    pub fn write(&mut self, event: InputEvent) -> Result<(), io::Error> {
        if !self.raw_buf.is_empty() {
            self.device.emit(&self.raw_buf)?;
            self.raw_buf.clear();
        }
        self.device.emit(&[event])?;
        Ok(())
    }

    pub fn write_many(&mut self, events: &[InputEvent]) -> Result<(), io::Error> {
        if !self.raw_buf.is_empty() {
            self.device.emit(&self.raw_buf)?;
            self.raw_buf.clear();
        }
        self.device.emit(events)?;
        Ok(())
    }

    pub fn write_key(&mut self, key: OsCode, value: KeyValue) -> Result<(), io::Error> {
        let key_ev = KeyEvent::new(key, value);
        let input_ev = key_ev.into();
        log::debug!("send to uinput: {:?}", input_ev);
        self.device.emit(&[input_ev])?;
        Ok(())
    }

    pub fn write_code(&mut self, code: u32, value: KeyValue) -> Result<(), io::Error> {
        let event = InputEvent::new(EventType::KEY, code as u16, value as i32);
        self.device.emit(&[event])?;
        Ok(())
    }

    pub fn press_key(&mut self, key: OsCode) -> Result<(), io::Error> {
        self.write_key(key, KeyValue::Press)
    }

    pub fn release_key(&mut self, key: OsCode) -> Result<(), io::Error> {
        self.write_key(key, KeyValue::Release)
    }

    /// Send using C-S-u + <unicode hex number> + spc
    pub fn send_unicode(&mut self, c: char) -> Result<(), io::Error> {
        log::debug!("sending unicode {c}");
        let hex = format!("{:x}", c as u32);
        self.press_key(OsCode::KEY_LEFTCTRL)?;
        self.press_key(OsCode::KEY_LEFTSHIFT)?;
        self.press_key(self.unicode_u_code.get())?;
        self.release_key(self.unicode_u_code.get())?;
        self.release_key(OsCode::KEY_LEFTSHIFT)?;
        self.release_key(OsCode::KEY_LEFTCTRL)?;
        let mut s = String::new();
        for c in hex.chars() {
            s.push(c);
            let osc = str_to_oscode(&s).expect("valid keycodes for unicode");
            s.clear();
            self.press_key(osc)?;
            self.release_key(osc)?;
        }
        match self.unicode_termination.get() {
            UnicodeTermination::Enter => {
                self.press_key(OsCode::KEY_ENTER)?;
                self.release_key(OsCode::KEY_ENTER)?;
            }
            UnicodeTermination::Space => {
                self.press_key(OsCode::KEY_SPACE)?;
                self.release_key(OsCode::KEY_SPACE)?;
            }
            UnicodeTermination::SpaceEnter => {
                self.press_key(OsCode::KEY_SPACE)?;
                self.release_key(OsCode::KEY_SPACE)?;
                self.press_key(OsCode::KEY_ENTER)?;
                self.release_key(OsCode::KEY_ENTER)?;
            }
            UnicodeTermination::EnterSpace => {
                self.press_key(OsCode::KEY_ENTER)?;
                self.release_key(OsCode::KEY_ENTER)?;
                self.press_key(OsCode::KEY_SPACE)?;
                self.release_key(OsCode::KEY_SPACE)?;
            }
        }
        Ok(())
    }

    pub fn click_btn(&mut self, btn: Btn) -> Result<(), io::Error> {
        self.press_key(btn.into())
    }

    pub fn release_btn(&mut self, btn: Btn) -> Result<(), io::Error> {
        self.release_key(btn.into())
    }

    pub fn scroll(
        &mut self,
        direction: MWheelDirection,
        hi_res_distance: u16,
    ) -> Result<(), io::Error> {
        log::debug!("scroll: {direction:?} {hi_res_distance:?}");

        let mut lo_res_distance = hi_res_distance / HI_RES_SCROLL_UNITS_IN_LO_RES;
        let leftover_hi_res_distance = hi_res_distance % HI_RES_SCROLL_UNITS_IN_LO_RES;

        match direction {
            MWheelDirection::Up | MWheelDirection::Down => {
                self.accumulated_scroll += leftover_hi_res_distance;
                lo_res_distance += self.accumulated_scroll / HI_RES_SCROLL_UNITS_IN_LO_RES;
                self.accumulated_scroll %= HI_RES_SCROLL_UNITS_IN_LO_RES;
            }
            MWheelDirection::Left | MWheelDirection::Right => {
                self.accumulated_hscroll += leftover_hi_res_distance;
                lo_res_distance += self.accumulated_hscroll / HI_RES_SCROLL_UNITS_IN_LO_RES;
                self.accumulated_hscroll %= HI_RES_SCROLL_UNITS_IN_LO_RES;
            }
        }

        let hi_res_scroll_event = InputEvent::new(
            EventType::RELATIVE,
            match direction {
                MWheelDirection::Up | MWheelDirection::Down => RelativeAxisType::REL_WHEEL_HI_RES.0,
                MWheelDirection::Left | MWheelDirection::Right => {
                    RelativeAxisType::REL_HWHEEL_HI_RES.0
                }
            },
            match direction {
                MWheelDirection::Up | MWheelDirection::Right => i32::from(hi_res_distance),
                MWheelDirection::Down | MWheelDirection::Left => -i32::from(hi_res_distance),
            },
        );

        if lo_res_distance > 0 {
            self.write_many(&[
                hi_res_scroll_event,
                InputEvent::new(
                    EventType::RELATIVE,
                    match direction {
                        MWheelDirection::Up | MWheelDirection::Down => {
                            RelativeAxisType::REL_WHEEL.0
                        }
                        MWheelDirection::Left | MWheelDirection::Right => {
                            RelativeAxisType::REL_HWHEEL.0
                        }
                    },
                    match direction {
                        MWheelDirection::Up | MWheelDirection::Right => i32::from(lo_res_distance),
                        MWheelDirection::Down | MWheelDirection::Left => {
                            -i32::from(lo_res_distance)
                        }
                    },
                ),
            ])
        } else {
            self.write(hi_res_scroll_event)
        }
    }

    pub fn move_mouse(&mut self, mv: CalculatedMouseMove) -> Result<(), io::Error> {
        let (axis, distance) = match mv.direction {
            MoveDirection::Up => (RelativeAxisType::REL_Y, -i32::from(mv.distance)),
            MoveDirection::Down => (RelativeAxisType::REL_Y, i32::from(mv.distance)),
            MoveDirection::Left => (RelativeAxisType::REL_X, -i32::from(mv.distance)),
            MoveDirection::Right => (RelativeAxisType::REL_X, i32::from(mv.distance)),
        };
        self.write(InputEvent::new(EventType::RELATIVE, axis.0, distance))
    }

    pub fn move_mouse_many(&mut self, moves: &[CalculatedMouseMove]) -> Result<(), io::Error> {
        let mut events = vec![];
        for mv in moves {
            let (axis, distance) = match mv.direction {
                MoveDirection::Up => (RelativeAxisType::REL_Y, -i32::from(mv.distance)),
                MoveDirection::Down => (RelativeAxisType::REL_Y, i32::from(mv.distance)),
                MoveDirection::Left => (RelativeAxisType::REL_X, -i32::from(mv.distance)),
                MoveDirection::Right => (RelativeAxisType::REL_X, i32::from(mv.distance)),
            };
            events.push(InputEvent::new(EventType::RELATIVE, axis.0, distance));
        }
        self.write_many(&events)
    }

    pub fn set_mouse(&mut self, _x: u16, _y: u16) -> Result<(), io::Error> {
        log::warn!("setmouse does not work in Linux yet. Maybe try out warpd:\n\thttps://github.com/rvaiya/warpd");
        Ok(())
    }
}

fn devices_from_input_paths(
    dev_paths: &[String],
    missing_device_paths: &mut Vec<String>,
) -> Vec<(Device, String)> {
    dev_paths
        .iter()
        .map(|dev_path| (dev_path, Device::open(dev_path)))
        .filter_map(|(dev_path, open_result)| match open_result {
            Ok(d) => Some((d, dev_path.clone())),
            Err(e) => {
                log::warn!("failed to open device '{dev_path}': {e:?}");
                missing_device_paths.push(dev_path.clone());
                None
            }
        })
        .collect()
}

fn discover_devices(
    include_names: Option<&[String]>,
    exclude_names: Option<&[String]>,
    device_detect_mode: DeviceDetectMode,
) -> Vec<(Device, String)> {
    log::info!("looking for devices in /dev/input");
    let devices: Vec<_> = evdev::enumerate()
        .map(|(path, device)| {
            (
                device,
                path.to_str()
                    .expect("non-utf8 path found for device")
                    .to_owned(),
            )
        })
        .filter(|pd| {
            is_input_device(&pd.0, device_detect_mode)
                && match include_names {
                    None => true,
                    Some(include_names) => {
                        let name = pd.0.name().unwrap_or("");
                        if include_names.iter().any(|include| name == include) {
                            log::info!("device [{}:{name}] is included", &pd.1);
                            true
                        } else {
                            log::info!("device [{}:{name}] is ignored", &pd.1);
                            false
                        }
                    }
                }
                && match exclude_names {
                    None => true,
                    Some(exclude_names) => {
                        let name = pd.0.name().unwrap_or("");
                        if exclude_names.iter().any(|exclude| name == exclude) {
                            log::info!("device [{}:{name}] is excluded", &pd.1);
                            false
                        } else {
                            true
                        }
                    }
                }
        })
        .collect();
    devices
}

fn watch_devinput() -> Result<Inotify, io::Error> {
    let inotify = Inotify::init().expect("Failed to initialize inotify");
    inotify.watches().add("/dev/input", WatchMask::CREATE)?;
    Ok(inotify)
}

#[derive(Clone)]
struct Symlink {
    dest: PathBuf,
}

impl Symlink {
    fn new(source: PathBuf, dest: PathBuf) -> Result<Self, io::Error> {
        if let Ok(metadata) = fs::symlink_metadata(&dest) {
            if metadata.file_type().is_symlink() {
                fs::remove_file(&dest)?;
            } else {
                return Err(io::Error::new(
                    io::ErrorKind::AlreadyExists,
                    format!(
                        "Cannot create a symlink at \"{}\": path already exists.",
                        dest.to_string_lossy()
                    ),
                ));
            }
        }
        std::os::unix::fs::symlink(&source, &dest)?;
        log::info!("Created symlink {:#?} -> {:#?}", dest, source);
        Ok(Self { dest })
    }
}

fn handle_signals(symlink: Option<Symlink>) {
    thread::spawn(|| {
        let mut signals = Signals::new([SIGINT, SIGTERM, SIGTSTP]).expect("signals register");
        if let Some(signal) = (&mut signals).into_iter().next() {
            match signal {
                SIGINT | SIGTERM => {
                    drop(symlink);
                    signal_hook::low_level::emulate_default_handler(signal)
                        .expect("run original sighandlers");
                    unreachable!();
                }
                SIGTSTP => {
                    drop(symlink);
                    log::warn!("got SIGTSTP, exiting instead of pausing so keyboards don't hang");
                    std::process::exit(SIGTSTP);
                }
                _ => unreachable!(),
            }
        }
    });
}

// Note for allow: the ioctl_read_buf triggers this clippy lint.
// Note: CI does not yet support this lint, so also allowing unknown lints.
#[allow(unknown_lints)]
#[allow(clippy::manual_slice_size_calculation)]
fn wait_for_all_keys_unpressed(dev: &Device) -> Result<(), io::Error> {
    let mut pending_release = false;
    const KEY_MAX: usize = OsCode::KEY_MAX as usize;
    let mut keystate = [0u8; KEY_MAX / 8 + 1];
    loop {
        let mut n_pressed_keys = 0;
        ioctl_read_buf!(read_keystates, 'E', 0x18, u8);
        unsafe { read_keystates(dev.as_raw_fd(), &mut keystate) }
            .map_err(|_| io::Error::last_os_error())?;
        for i in 0..=KEY_MAX {
            if (keystate[i / 8] >> (i % 8)) & 0x1 > 0 {
                n_pressed_keys += 1;
            }
        }
        match n_pressed_keys {
            0 => break,
            _ => pending_release = true,
        }
    }
    if pending_release {
        std::thread::sleep(std::time::Duration::from_micros(100));
    }
    Ok(())
}

impl Drop for Symlink {
    fn drop(&mut self) {
        let _ = fs::remove_file(&self.dest);
        log::info!("Deleted symlink {:#?}", self.dest);
    }
}