RedBear-OS/init/src/service.rs

use std::collections::{BTreeMap, BTreeSet};
use std::ffi::OsString;
use std::fs::File;
use std::io::{self, Read};
use std::os::fd::{AsRawFd, FromRawFd, OwnedFd};
use std::os::unix::process::CommandExt;
use std::process::Command;
use std::env;

use serde::Deserialize;

use crate::color::{init_error, init_warn, status_fail};
use crate::script::subst_env;

#[derive(Clone, Debug, Deserialize)]
#[serde(deny_unknown_fields)]
pub struct Service {
    pub cmd: String,
    #[serde(default)]
    pub args: Vec<String>,
    #[serde(default)]
    pub envs: BTreeMap<String, String>,
    #[serde(default)]
    pub inherit_envs: BTreeSet<String>,
    #[serde(rename = "type")]
    pub type_: ServiceType,
    #[serde(default, rename = "ConditionPathExists")]
    pub condition_path_exists: Option<String>,
}

#[derive(Clone, Debug, Default, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum ServiceType {
    #[default]
    Notify,
    Scheme(String),
    Oneshot,
    OneshotAsync,
}

impl Service {
    /// systemd-style ConditionPathExists gate. A leading `!` negates the
    /// test: the service starts only when the path does NOT exist.
    pub fn condition_met(&self) -> bool {
        let Some(cond) = &self.condition_path_exists else {
            return true;
        };
        let (negated, path) = match cond.strip_prefix('!') {
            Some(rest) => (true, rest),
            None => (false, cond.as_str()),
        };
        std::path::Path::new(path).exists() != negated
    }
}

fn create_pipe() -> io::Result<(File, OwnedFd)> {
    let mut fds = [0i32; 2];
    // Use libc::pipe2() which goes through relibc's FILETABLE-managed path
    // (FdGuard::open → SYS_OPENAT_INTO), keeping the userspace file table in
    // sync with the kernel's file table. Using raw syscall::openat()
    // (SYS_OPENAT) here would bypass the FILETABLE and create phantom fds
    // that later cause EEXIST collisions when relibc's own pipe2() (called
    // during Command::spawn fork+exec) tries to insert at a position the
    // FILETABLE incorrectly thinks is free.
    let ret = unsafe { libc::pipe2(fds.as_mut_ptr(), libc::O_CLOEXEC) };
    if ret != 0 {
        return Err(io::Error::last_os_error());
    }
    let rd = unsafe { File::from_raw_fd(fds[0]) };
    let wr = unsafe { OwnedFd::from_raw_fd(fds[1]) };
    Ok((rd, wr))
}

impl Service {
    pub fn spawn(&self, base_envs: &BTreeMap<String, OsString>) {
        let mut command = Command::new(&self.cmd);
        command.args(self.args.iter().map(|arg| subst_env(arg)));
        command.env_clear();
        for env in &self.inherit_envs {
            if let Some(value) = env::var_os(env) {
                command.env(env, value);
            }
        }
        command.envs(base_envs).envs(&self.envs);

        let (mut read_pipe, write_pipe) = create_pipe()
            .unwrap_or_else(|e| panic!("pipe() failed in service.spawn for {}: {}", self.cmd, e));
        unsafe { pass_fd(&mut command, "INIT_NOTIFY", write_pipe.into()) };

        let mut child = match command.spawn() {
            Ok(child) => child,
            Err(err) => {
                status_fail(&format!("failed to execute {:?}: {}", command, err));
                return;
            }
        };

        match &self.type_ {
            ServiceType::Notify => {
                match read_pipe.read_exact(&mut [0]) {
                    Ok(()) => {}
                    Err(err) if err.kind() == io::ErrorKind::UnexpectedEof => {
                        init_warn(&format!("{:?} exited without notifying readiness", command));
                    }
                    Err(err) => {
                        init_error(&format!("failed to wait for {:?}: {}", command, err));
                    }
                }
            }
            ServiceType::Scheme(scheme) => {
                let mut new_fd = usize::MAX;
                loop {
                    match syscall::call_ro(
                        read_pipe.as_raw_fd() as usize,
                        unsafe { plain::as_mut_bytes(&mut new_fd) },
                        syscall::CallFlags::FD | syscall::CallFlags::FD_UPPER,
                        &[],
                    ) {
                        Err(syscall::Error {
                            errno: syscall::EINTR,
                        }) => continue,
                        Ok(0) => {
                            init_warn(&format!("{:?} exited without notifying readiness", command));
                            return;
                        }
                        Ok(1) => {
                            break;
                        }
                        Ok(n) => {
                            init_error(&format!("incorrect amount of fds {} returned", n));
                            return;
                        }
                        Err(err) => {
                            init_error(&format!("failed to wait for {:?}: {}", command, err));
                            return;
                        }
                    }
                }

                let current_namespace_fd = libredox::call::getns().expect("TODO");
                libredox::call::register_scheme_to_ns(current_namespace_fd, scheme, new_fd)
                    .expect("TODO");
            }
            ServiceType::Oneshot => {
                drop(read_pipe);
                match child.wait() {
                    Ok(exit_status) => {
                        if !exit_status.success() {
                            status_fail(&format!("{:?} failed with {}", command, exit_status));
                        }
                    }
                    Err(err) => {
                        init_error(&format!("failed to wait for {:?}: {}", command, err))
                    }
                }
            }
            ServiceType::OneshotAsync => {}
        }
    }
}

unsafe fn pass_fd(cmd: &mut Command, env: &str, fd: OwnedFd) {
    cmd.env(env, format!("{}", fd.as_raw_fd()));
    unsafe {
        cmd.pre_exec(move || {
            // Pass notify pipe to child
            if libc::fcntl(fd.as_raw_fd(), libc::F_SETFD, 0) == -1 {
                Err(io::Error::last_os_error())
            } else {
                Ok(())
            }
        });
    }
}