rust-kernel

//! The console "tty": keyboard input, and the `File` behind file
//! descriptors 0, 1 and 2.
//!
//! Two input modes, like a Linux terminal:
//!
//! * **cooked** (canonical, the default): typed characters are echoed and
//!   collected in a line buffer (Backspace edits it); only when Enter is
//!   pressed does the whole line become readable from fd 0. So `read(0)`
//!   gets a complete, already-edited line. Programs like `cat` use this.
//! * **raw**: every key goes to the reader immediately and nothing is echoed;
//!   arrow keys arrive as ANSI escape sequences (`ESC [ A` = up). The shell
//!   switches to raw while it edits its command line, so it can do its own
//!   echo, Backspace and up-arrow history. (Linux: `tcsetattr` / `ioctl`.)
//!
//! In cooked mode Ctrl+C and Ctrl+Z don't become input: they send SIGINT /
//! SIGTSTP to the *foreground process group* (set by the shell with
//! ioctl TIOCSPGRP) -- that's how Ctrl+C stops the running program but not
//! the shell. (The virtio console, hvc0, has no job control.)
//!
//! Output (`Console::write`) understands two control characters besides
//! '\n': '\x08' erases the character before the cursor, and '\x0c' (form
//! feed) clears the screen.

use crate::errno::Errno;
use crate::fs::file::{File, KIND_CONSOLE, Stat};
use crate::signal;
use crate::thread::WaitQueue;
use crate::{print, serial_print, vga_buffer};
use alloc::string::String;
use conquer_once::spin::OnceCell;
use core::sync::atomic::{AtomicBool, AtomicU64, Ordering};
use crossbeam_queue::ArrayQueue;
use pc_keyboard::KeyCode;
use spin::Mutex;

/// The line being typed in cooked mode (not yet readable).
static LINE: Mutex<String> = Mutex::new(String::new());
/// Bytes waiting for `read(0, ...)`: finished lines (cooked) or keys (raw).
static INPUT: OnceCell<ArrayQueue<u8>> = OnceCell::uninit();
/// Raw mode on?
static RAW: AtomicBool = AtomicBool::new(false);
/// pid of the process that switched raw mode on (0 = none). If it exits
/// without switching back, the console goes back to cooked mode.
static RAW_OWNER: AtomicU64 = AtomicU64::new(0);

/// The foreground process group: Ctrl+C / Ctrl+Z signal it (0 = none).
/// The shell sets it to each job it runs, and back to itself after.
static FOREGROUND: AtomicU64 = AtomicU64::new(0);

pub fn foreground() -> u64 {
    FOREGROUND.load(Ordering::SeqCst)
}

pub fn set_foreground(pgid: u64) {
    FOREGROUND.store(pgid, Ordering::SeqCst);
}

/// Threads blocked in `Console::read`, waiting for input.
static INPUT_WAIT: WaitQueue = WaitQueue::new();

fn input() -> &'static ArrayQueue<u8> {
    INPUT.get_or_init(|| ArrayQueue::new(4096))
}

/// Switch between raw (`true`) and cooked mode for process `pid`. Returns
/// the old mode.
pub fn set_raw(raw: bool, pid: u64) -> bool {
    LINE.lock().clear(); // a half-typed cooked line doesn't survive a switch
    RAW_OWNER.store(if raw { pid } else { 0 }, Ordering::SeqCst);
    RAW.swap(raw, Ordering::SeqCst)
}

/// A process ended: if it left the console in raw mode, undo that (so the
/// next program, or a respawned shell, gets normal line input).
pub fn process_exited(pid: u64) {
    if RAW_OWNER.compare_exchange(pid, 0, Ordering::SeqCst, Ordering::SeqCst).is_ok() {
        RAW.store(false, Ordering::SeqCst);
    }
}

pub fn is_raw() -> bool {
    RAW.load(Ordering::SeqCst)
}

/// Make `bytes` readable and wake readers. (Queue full: drop -- nobody reads.)
fn deliver(bytes: &[u8]) {
    for &b in bytes {
        let _ = input().push(b);
    }
    INPUT_WAIT.wake_all();
}

/// Called by the keyboard task for every typed character.
pub fn input_char(c: char) {
    if is_raw() {
        let mut utf8 = [0; 4];
        deliver(c.encode_utf8(&mut utf8).as_bytes());
        return;
    }
    let mut line = LINE.lock();
    match c {
        '\u{8}' => {
            // Backspace: only erase what's in the current line.
            if line.pop().is_some() {
                vga_buffer::backspace();
                serial_print!("\x08"); // uart_16550 turns this into "\x08 \x08"
            }
        }
        '\n' => {
            print!("\n");
            serial_print!("\n");
            line.push('\n');
            deliver(line.as_bytes());
            line.clear();
        }
        // Ctrl+C / Ctrl+Z: the "line discipline" turns them into signals
        // for the foreground job (Linux: the ISIG flag of termios). Raw mode
        // passes them through as bytes 3 / 26 instead (above).
        '\u{3}' | '\u{1a}' => {
            let (echo, sig) = if c == '\u{3}' { ("^C\n", signal::SIGINT) } else { ("^Z\n", signal::SIGTSTP) };
            print!("{}", echo);
            serial_print!("{}", echo);
            line.clear(); // the half-typed line is thrown away
            drop(line);
            let fg = foreground();
            if fg != 0 {
                crate::process::signal_group(fg, sig);
            }
        }
        c if (c as u32) < 0x20 && c != '\t' => {} // other control keys: ignore
        c => {
            print!("{}", c);
            serial_print!("{}", c);
            line.push(c);
        }
    }
}

/// Called by the keyboard task for keys that aren't characters (arrows...).
pub fn input_key(key: KeyCode) {
    if is_raw() {
        // The ANSI/VT100 sequences a Linux terminal would send.
        let seq: &[u8] = match key {
            KeyCode::ArrowUp => b"\x1b[A",
            KeyCode::ArrowDown => b"\x1b[B",
            KeyCode::ArrowRight => b"\x1b[C",
            KeyCode::ArrowLeft => b"\x1b[D",
            KeyCode::Home => b"\x1b[H",
            KeyCode::End => b"\x1b[F",
            KeyCode::Delete => b"\x1b[3~",
            _ => return,
        };
        deliver(seq);
    } else {
        print!("<{:?}>", key);
        serial_print!("<{:?}>", key);
    }
}

/// The console as a file: reading gets keyboard input, writing prints to the
/// screen and serial port.
pub struct Console;

/// Held for the whole of one console `write` (see `Console::write`).
static CONSOLE_WRITE: spin::Mutex<()> = spin::Mutex::new(());

impl File for Console {
    /// Blocks until input is available. Cooked: returns up to `buf.len()`
    /// bytes of a line, stopping after its '\n'. Raw: whatever keys are there.
    fn read(&self, buf: &mut [u8]) -> Result<usize, Errno> {
        if buf.is_empty() {
            return Ok(0);
        }
        // Block until input arrives: the thread is parked on INPUT_WAIT
        // (using no CPU) and `deliver` wakes it. The closure runs with
        // interrupts off; the ArrayQueue is lock-free, so that's fine.
        INPUT_WAIT.wait_until_intr(|| {
            let mut n = 0;
            while n < buf.len() {
                let Some(b) = input().pop() else { break };
                buf[n] = b;
                n += 1;
                if b == b'\n' {
                    break;
                }
            }
            if n > 0 { Some(n) } else { None }
        })
    }

    fn write(&self, buf: &[u8]) -> Result<usize, Errno> {
        // One write = one unbroken piece of output, even when programs on
        // other CPUs write at the same time. Taken in thread context only
        // (never in an interrupt handler), so while waiting we just yield.
        let _turn = loop {
            match CONSOLE_WRITE.try_lock() {
                Some(guard) => break guard,
                None => crate::thread::yield_now(),
            }
        };
        // Print valid UTF-8 as is, anything else as '?'. Control characters
        // are handled one by one.
        for chunk in buf.utf8_chunks() {
            for piece in chunk.valid().split_inclusive(['\x08', '\x0c']) {
                let (text, control) = match piece.strip_suffix(['\x08', '\x0c']) {
                    Some(text) => (text, piece.chars().last()),
                    None => (piece, None),
                };
                print!("{}", text);
                serial_print!("{}", text);
                match control {
                    Some('\x08') => {
                        vga_buffer::backspace();
                        serial_print!("\x08");
                    }
                    Some(_) => vga_buffer::clear_screen(), // serial: nothing to clear
                    None => {}
                }
            }
            if !chunk.invalid().is_empty() {
                print!("?");
                serial_print!("?");
            }
        }
        Ok(buf.len())
    }

    fn stat(&self) -> Result<Stat, Errno> {
        Ok(Stat { kind: KIND_CONSOLE, size: 0, mode: 0 })
    }
}