volt-vmm/rootfs/volt-init/src/sys.rs

// System utilities: signal handling, hostname, kernel cmdline, console

use std::ffi::CString;

/// Set up console I/O by ensuring fd 0/1/2 point to /dev/console or /dev/ttyS0
pub fn setup_console() {
    // Try /dev/console first, then /dev/ttyS0
    let consoles = ["/dev/console", "/dev/ttyS0"];

    for console in &consoles {
        let c_path = CString::new(*console).unwrap();
        let fd = unsafe { libc::open(c_path.as_ptr(), libc::O_RDWR | libc::O_NOCTTY | libc::O_NONBLOCK) };
        if fd >= 0 {
            // Clear O_NONBLOCK now that the open succeeded
            unsafe {
                let flags = libc::fcntl(fd, libc::F_GETFL);
                if flags >= 0 {
                    libc::fcntl(fd, libc::F_SETFL, flags & !libc::O_NONBLOCK);
                }
            }

            // Close existing fds and dup console to 0, 1, 2
            if fd != 0 {
                unsafe {
                    libc::close(0);
                    libc::dup2(fd, 0);
                }
            }
            unsafe {
                libc::close(1);
                libc::dup2(fd, 1);
                libc::close(2);
                libc::dup2(fd, 2);
            }
            if fd > 2 {
                unsafe {
                    libc::close(fd);
                }
            }

            // Make this our controlling terminal
            unsafe {
                libc::ioctl(0, libc::TIOCSCTTY as libc::Ioctl, 1);
            }
            return;
        }
    }
    // If we get here, no console device available — output will be lost
}

/// Install signal handlers for PID 1
pub fn install_signal_handlers() {
    unsafe {
        // SIGCHLD: reap zombies
        libc::signal(
            libc::SIGCHLD,
            sigchld_handler as *const () as libc::sighandler_t,
        );

        // SIGTERM: ignore (PID 1 handles shutdown via shell)
        libc::signal(libc::SIGTERM, libc::SIG_IGN);

        // SIGINT: ignore (Ctrl+C shouldn't kill init)
        libc::signal(libc::SIGINT, libc::SIG_IGN);
    }
}

extern "C" fn sigchld_handler(_sig: libc::c_int) {
    // Reap all zombie children
    unsafe {
        loop {
            let ret = libc::waitpid(-1, std::ptr::null_mut(), libc::WNOHANG);
            if ret <= 0 {
                break;
            }
        }
    }
}

/// Read kernel command line
pub fn read_kernel_cmdline() -> String {
    std::fs::read_to_string("/proc/cmdline")
        .unwrap_or_default()
        .trim()
        .to_string()
}

/// Parse a key=value from kernel cmdline
pub fn parse_cmdline_value(cmdline: &str, key: &str) -> Option<String> {
    let prefix = format!("{}=", key);
    for param in cmdline.split_whitespace() {
        if let Some(value) = param.strip_prefix(&prefix) {
            return Some(value.to_string());
        }
    }
    None
}

/// Set system hostname
pub fn set_hostname(name: &str) {
    let c_name = CString::new(name).unwrap();
    let ret = unsafe { libc::sethostname(c_name.as_ptr(), name.len()) };
    if ret != 0 {
        eprintln!(
            "[volt-init] Failed to set hostname: {}",
            std::io::Error::last_os_error()
        );
    }
}