power outage stash

Cargo.lock

@@ -223,6 +223,7 @@ dependencies = [
  "tracing",
  "tracing-human-layer",
  "tracing-subscriber",
+ "which",
 ]
 
 [[package]]
@@ -851,6 +852,15 @@ version = "0.11.1+wasi-snapshot-preview1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ccf3ec651a847eb01de73ccad15eb7d99f80485de043efb2f370cd654f4ea44b"
 
+[[package]]
+name = "which"
+version = "8.0.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "81995fafaaaf6ae47a7d0cc83c67caf92aeb7e5331650ae6ff856f7c0c60c459"
+dependencies = [
+ "libc",
+]
+
 [[package]]
 name = "windows"
 version = "0.61.3"

Cargo.toml

@@ -47,6 +47,7 @@ tap = "1.0.1"
 tracing = { version = "0.1.44", features = ["attributes"] }
 tracing-human-layer = "0.2.1"
 tracing-subscriber = { version = "0.3.22", default-features = false, features = ["std", "env-filter", "fmt", "ansi", "registry", "parking_lot"] }
+which = "8.0.2"
 
 [profile.dev]
 opt-level = 1
@@ -63,3 +64,21 @@ opt-level = 1
 [profile.release.package."*"]
 debug = true
 debug-assertions = true
+
+[lints.clippy]
+#arithmetic_side_effects = "warn"
+as_ptr_cast_mut = "warn"
+assigning_clones = "warn"
+borrow_as_ptr = "warn"
+#cargo_common_metadata = "warn"
+cast_lossless = "warn"
+#cast_possible_truncation = "warn"
+cast_possible_wrap = "warn"
+cast_ptr_alignment = "warn"
+cast_sign_loss = "warn"
+clear_with_drain = "warn"
+coerce_container_to_any = "warn"
+derive_partial_eq_without_eq = "warn"
+doc_broken_link = "warn"
+doc_comment_double_space_linebreaks = "warn"
+doc_markdown = "warn"

package.nix

@@ -58,6 +58,8 @@ in {
     inherit (self) strictDeps __structuredAttrs;
     inherit (self) doCheck doInstallCheck;
 
+    outputs = [ "out" "doc" ];
+
     src = lib.fileset.toSource {
       root = ./.;
       fileset = lib.fileset.unions [

rustfmt.toml

@@ -4,3 +4,13 @@
 
 match_block_trailing_comma = true
 merge_derives = false
+
+# Unstable options.
+blank_lines_upper_bound = 3
+format_code_in_doc_comments = true
+format_macro_matchers = true
+# When structs, slices, arrays, and block/array-like macros are used as the last argument in an expression list,
+# allow them to overflow (like blocks/closures) instead of being indented on a new line.
+overflow_delimited_expr = true
+# Put `type` and `const` items before methods.
+reorder_impl_items = true

shell.nix

@@ -16,7 +16,21 @@
   fenixLib ? let
     src = fetchTarball "https://github.com/nix-community/fenix/archive/main.tar.gz";
   in import src { inherit pkgs; },
-  fenixToolchain ? fenixLib.latest.toolchain,
+  fenixBaseToolchain ? fenixLib.stable.withComponents [
+    "cargo"
+    "rustc"
+    "llvm-tools"
+    "rust-std"
+    "rust-docs"
+    "rust-src"
+    "rustc-dev"
+    "clippy"
+  ],
+  fenixToolchain ? fenixLib.combine [
+    fenixBaseToolchain
+    # Rustfmt is very handy to have as nightly.
+    fenixLib.latest.rustfmt
+  ],
 }: let
   inherit (pkgs) lib;
 

src/daemon.rs

@@ -1,7 +1,7 @@
 use std::{
     env, io,
-    ops::Deref,
     os::fd::{AsFd, BorrowedFd, IntoRawFd, OwnedFd, RawFd},
+    process::{Command, Stdio},
     sync::{
         Arc, LazyLock,
         atomic::{AtomicUsize, Ordering},
@@ -11,18 +11,31 @@ use std::{
 
 use iddqd::{BiHashMap, IdOrdMap};
 
-use mio::{Events, Interest, Poll, Token, net::UnixListener, unix::SourceFd};
+use mio::{Events, Interest, Poll, Token, event::Event, net::UnixListener, unix::SourceFd};
 
-use rustix::{buffer::spare_capacity, net::SocketFlags, process::Uid};
+use rustix::{
+    buffer::spare_capacity,
+    net::SocketFlags,
+    process::{Pid, PidfdFlags, Uid, WaitId, WaitIdOptions},
+};
+
+mod rustix {
+    pub use rustix::process::{getuid, pidfd_open, waitid};
+    pub use rustix::*;
+}
+
+//mod rustix_prelude {
+//    pub use rustix::process::{getuid, pidfd_open, waitid};
+//}
 
-use serde::{Deserialize, Serialize};
 use serde_json::StreamDeserializer;
 
-use crate::{
-    SourceFile, SourceLine,
-    daemon_tokfd::{FdInfo, FdKind},
-    prelude::*,
-};
+use crate::prelude::*;
+
+pub mod api;
+use api::DaemonCmd;
+
+use crate::daemon_tokfd::{FdInfo, FdKind};
 
 use crate::{OwnedFdWithFlags, TokenFd};
 
@@ -43,75 +56,13 @@ pub static TMPDIR: LazyLock<&'static Path> = LazyLock::new(|| {
     Box::leak(dir)
 });
 
-#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
-#[derive(Deserialize, Serialize)]
-#[serde(untagged)]
-pub enum ConvenientAttrPath {
-    Dotted(Box<str>),
-    Split(Box<[Box<str>]>),
-}
-
-impl ConvenientAttrPath {
-    /// Not currently used, but here for completeness.
-    #[expect(dead_code)]
-    pub fn clone_from_dotted(s: &str) -> Self {
-        Self::Dotted(Box::from(s))
-    }
-
-    /// Not currently used, but here for completeness.
-    #[expect(dead_code)]
-    pub fn clone_from_split(s: &[&str]) -> Self {
-        Self::from_str_iter(s.iter().map(Deref::deref))
-    }
-
-    pub fn from_str_iter<'i, I>(iter: I) -> Self
-    where
-        I: Iterator<Item = &'i str>,
-    {
-        let boxed = iter.map(Box::from);
-        Self::Split(Box::from_iter(boxed))
-    }
-
-    pub fn to_nix_decl(&self) -> Box<str> {
-        use ConvenientAttrPath::*;
-        match self {
-            Dotted(s) => s.clone(),
-            Split(path) => {
-                // FIXME: quote if necessary
-                path.join(".").into_boxed_str()
-            },
-        }
-    }
-}
-
-impl<'i> FromIterator<&'i str> for ConvenientAttrPath {
-    fn from_iter<I>(iter: I) -> Self
-    where
-        I: IntoIterator<Item = &'i str>,
-    {
-        Self::from_str_iter(iter.into_iter())
-    }
-}
-
-impl FromIterator<Box<str>> for ConvenientAttrPath {
-    fn from_iter<I>(iter: I) -> Self
-    where
-        I: IntoIterator<Item = Box<str>>,
-    {
-        Self::Split(Box::from_iter(iter))
-    }
-}
-
-#[derive(Debug, Clone, PartialEq)]
-#[derive(serde::Deserialize, serde::Serialize)]
-#[serde(tag = "action", content = "args", rename_all = "snake_case")]
-// FIXME: rename to not confuse with the clap argument type.
-pub enum DaemonCmd {
-    Append {
-        name: ConvenientAttrPath,
-        value: Box<str>,
-    },
-}
+pub static NIXOS_REBUILD: LazyLock<&'static Path> = LazyLock::new(|| {
+    which::which("nixos-rebuild")
+        .inspect_err(|e| error!("couldn't find `nixos-rebuild` in PATH: {e}"))
+        .map(PathBuf::into_boxed_path)
+        .map(|boxed| &*Box::leak(boxed))
+        .unwrap_or(Path::new("/run/current-system/sw/bin/nixos-rebuild"))
+});
 
 const TIMEOUT_NEVER: Option<Duration> = None;
 
@@ -121,12 +72,49 @@ fn next_token() -> Token {
 
     // If the increment wrapped to 0, then we just increment it again.
     if tok == 0 {
-        return Token(NEXT_TOKEN_NUMBER.fetch_add(1, Ordering::SeqCst));
+        warn!("File descriptor token wrapped. That's... a lot.");
+        return next_token();
     }
 
     Token(tok)
 }
 
+trait EventExt {
+    type Display;
+
+    fn display(&self) -> Self::Display;
+}
+
+#[derive(Copy)]
+#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+struct EventDisplay {
+    token: Token,
+    error: bool,
+    writable: bool,
+    write_closed: bool,
+    readable: bool,
+    read_closed: bool,
+}
+impl EventExt for Event {
+    type Display = EventDisplay;
+
+    fn display(&self) -> Self::Display {
+        EventDisplay {
+            token: self.token(),
+            error: self.is_error(),
+            writable: self.is_writable(),
+            write_closed: self.is_write_closed(),
+            readable: self.is_readable(),
+            read_closed: self.is_read_closed(),
+        }
+    }
+}
+impl Display for EventDisplay {
+    fn fmt(&self, f: &mut Formatter) -> FmtResult {
+        todo!()
+    }
+}
+
 #[derive(Debug)]
 pub struct Daemon {
     config_path: Arc<Path>,
@@ -199,6 +187,32 @@ impl Daemon {
         token
     }
 
+    fn register_with_name<S>(&mut self, fd: RawFd, kind: FdKind, name: Box<OsStr>) -> Token {
+        let token = next_token();
+
+        debug!(
+            "Registering new {} FdInfo for {fd} ({}) with token {token:?}",
+            name.to_string_lossy(),
+            kind.name_str(),
+        );
+
+        self.fd_info
+            .insert_unique(FdInfo::new_with_name(fd, kind, name))
+            .unwrap();
+
+        self.tokfd
+            .insert_unique(TokenFd { token, fd })
+            .unwrap_or_else(|e| todo!("{e}"));
+
+        let mut source = SourceFd(&fd);
+        self.poller
+            .registry()
+            .register(&mut source, token, Interest::READABLE)
+            .unwrap_or_else(|e| unreachable!("registering {fd:?} with poller failed: {e}"));
+
+        token
+    }
+
     fn deregister(&mut self, fd: RawFd) {
         let info = self
             .fd_info
@@ -342,9 +356,36 @@ impl Daemon {
         self.fd.as_fd()
     }
 }
+const DAEMON: Token = Token(0);
 
 /// Private helpers.
 impl Daemon {
+    //fn proxy_stdio(&mut self, fd: &BorrowedFd) -> Result<(), IoError> {
+    //    let info = self.fd_info.get(&fd.as_raw_fd()).unwrap();
+    //    let label = match info.kind {
+    //        FdKind::ChildStdout => "stdout",
+    //        FdKind::ChildStderr => "stderr",
+    //        other => unreachable!("child stdio cannot have kind {other:?}"),
+    //    };
+    //    // FIXME: don't use a new allocation every time.
+    //    let mut buffer: Vec<u8> = Vec::with_capacity(1024);
+    //    // FIXME: handle line buffering correctly.
+    //    loop {
+    //        let count = rustix::io::read(fd, spare_capacity(&mut buffer))
+    //            .inspect_err(|e| error!("read() on child stdio fd {fd:?} failed: {e}"))?;
+    //
+    //        if count == 0 {
+    //            break;
+    //        }
+    //
+    //        for line in buffer.lines() {
+    //            debug!("[child {label}]: {}", line.as_bstr())
+    //        }
+    //    }
+    //
+    //    Ok(())
+    //}
+
     fn read_cmd(&mut self, fd: &BorrowedFd) -> Result<(), IoError> {
         // FIXME: don't use a new allocation every time.
         let mut cmd_buffer: Vec<u8> = Vec::with_capacity(1024);
@@ -383,42 +424,63 @@ impl Daemon {
     }
 
     fn dispatch_cmd(&mut self, cmd: DaemonCmd) -> Result<(), IoError> {
+        // Write the new file...
         let (name, value) = match cmd {
             DaemonCmd::Append { name, value } => (name, value),
         };
-        let mut opts = File::options();
-        opts.read(true)
-            .write(true)
-            .create(false)
-            .custom_flags(libc::O_CLOEXEC);
-        let source_file = SourceFile::open_from(self.config_path.clone(), opts)?;
+        let source_file = crate::open_source_file(self.config_path.clone())?;
         let pri = crate::get_where(source_file.clone()).unwrap_or_else(|e| todo!("{e}"));
         let new_pri = pri - 1;
-        //let new_pri_line =
-        //    crate::get_next_prio_line(source_file.clone(), Arc::from(name), Arc::from(value));
         // Get next priority line.
-        let source_lines = source_file.lines()?;
-        let penultimate = source_lines.get(source_lines.len() - 2);
-        // FIXME: don't rely on whitespace lol
-        debug_assert_eq!(penultimate.map(SourceLine::text).as_deref(), Some("  ];"));
-        let penultimate = penultimate.unwrap();
-        let new_generation = 0 - new_pri;
-        let new_line = SourceLine {
-            line: penultimate.line,
-            path: source_file.path(),
-            text: Arc::from(format!(
-                "      {} = lib.mkOverride ({}) ({}); # DYNIX GENERATION {}",
-                name.to_nix_decl(),
-                new_pri,
-                value,
-                new_generation,
-            )),
-        };
-
-        drop(source_lines);
+        let opt_name = name.to_nix_decl();
+        let new_line = crate::get_next_prio_line(source_file.clone(), &opt_name, new_pri, &value)
+            .unwrap_or_else(|e| panic!("someone is holding a reference to source.lines(): {e}"));
 
         crate::write_next_prio(source_file, new_line).unwrap_or_else(|e| todo!("{e}"));
 
+        // Rebuild and switch.
+        // FIXME: allow passing additional args.
+        let child = Command::new(*NIXOS_REBUILD)
+            .arg("switch")
+            .arg("--log-format")
+            .arg("raw-with-logs")
+            .arg("--no-reexec")
+            .arg("-v")
+            .stdout(Stdio::piped())
+            .stderr(Stdio::piped())
+            .spawn()
+            .inspect_err(|e| {
+                error!("failed to spawn `nixos-rebuild` command: {e}");
+            })?;
+
+        debug!("Spanwed child process {}", child.id());
+
+        let pid = Pid::from_child(&child);
+
+        let stdout = child.stdout.unwrap_or_else(|| {
+            unreachable!("`child` is given `.stdout(Stdio::piped())`");
+        });
+        let stderr = child.stderr.unwrap_or_else(|| {
+            unreachable!("`child` is given `.stderr(Stdio::piped())`");
+        });
+
+        let _token = self.register(stdout.into_raw_fd(), FdKind::ChildStdout);
+        let _token = self.register(stderr.into_raw_fd(), FdKind::ChildStderr);
+
+        match rustix::process::pidfd_open(pid, PidfdFlags::NONBLOCK) {
+            Ok(pidfd) => {
+                debug!("Opened pidfd {pidfd:?}, for process {pid}");
+                self.register(pidfd.into_raw_fd(), FdKind::Pid(pid));
+            },
+            Err(e) if e.kind() == IoErrorKind::NotFound => {
+                warn!("child {pid} not found; died before we could open it?");
+            },
+            Err(e) => {
+                error!("Error opening pidfd for child {pid}: {e}");
+                return Err(e)?;
+            },
+        }
+
         Ok(())
     }
 
@@ -436,7 +498,6 @@ impl Daemon {
             );
         }
         let mut daemon_source = SourceFd(&raw_fd);
-        const DAEMON: Token = Token(0);
         self.tokfd
             .insert_unique(TokenFd {
                 token: DAEMON,
@@ -453,103 +514,167 @@ impl Daemon {
 
         loop {
             if tracing::enabled!(tracing::Level::DEBUG) {
-                //
-                trace!("Daemon loop iteration, with file descriptors: ");
+                debug!("Daemon loop iteration, with file descriptors: ");
                 for info in &self.fd_info {
-                    trace!("- {}", info.display());
+                    debug!("- {}", info.display());
                 }
             }
 
-            match self.poller.poll(&mut events, TIMEOUT_NEVER) {
-                Ok(_) => {
-                    trace!(
-                        "mio::Poller::poll() got events: {:?}",
-                        events.iter().size_hint().0,
-                    );
-                    if events.is_empty() {
-                        unreachable!(
-                            "epoll_wait() with a \"forever\" timeout should never give empty events",
-                        );
-                    }
-
-                    let _ = self.fd_error_pop(self.poller.as_raw_fd());
-                },
-                Err(e) if e.kind() == IoErrorKind::Interrupted => {
-                    // EINTR is silly.
-                    continue;
-                },
-                Err(e) => {
-                    if let Some(Errno::BADF) = e.raw_os_error().map(Errno::from_raw_os_error) {
-                        unreachable!("EBADF on poller fd; IO safety violation?");
-                    }
-                    warn!("mio Poll::poll() error: {e}");
-                    self.fd_error_push(self.poller.as_raw_fd(), e)
-                        .tap_err(|e| {
-                            error!("accumulated too many errors for mio::Poll::poll(): {e}")
-                        })?;
-                },
-            }
-
-            for event in &events {
-                trace!("event is {event:?}");
-                match event.token() {
-                    DAEMON => {
-                        let is_sock = self.main_fd_info().kind == FdKind::Socket;
-                        if !is_sock {
-                            // SAFETY: oh boy: disjoint borrows with extra steps.
-                            let file_fd = unsafe { BorrowedFd::borrow_raw(self.fd.as_raw_fd()) };
-                            self.read_cmd(&file_fd).unwrap();
-                            continue;
-                        }
-
-                        // Accept, first.
-                        let flags = SocketFlags::NONBLOCK | SocketFlags::CLOEXEC;
-                        let stream_fd = match rustix::net::accept_with(&self.fd, flags) {
-                            Ok(stream) => {
-                                debug!(
-                                    "Accepted connection from socket {:?} as stream {:?}",
-                                    self.fd, stream,
-                                );
-                                stream
-                            },
-                            Err(e) => {
-                                error!("accept4 on daemon socket failed: {e}");
-                                self.fd_error_push(self.fd.as_raw_fd(), e.into())
-                                    .tap_err(|e| {
-                                        error!(
-                                            "Accumulated too many errors for daemon fd {:?}: {e}",
-                                            self.fd
-                                        )
-                                    })?;
-                                continue;
-                            },
-                        };
-
-                        // Add this stream to our poll interest list.
-                        // NOTE: `stream_fd` is now effectively `ManuallyDrop`.
-                        let stream_fd = stream_fd.into_raw_fd();
-                        let _token = self.register(stream_fd, FdKind::SockStream);
-
-                        // Wait for the next poll to handle.
-                    },
-                    other_token => {
-                        // This must be a stream fd.
-                        let stream_fd = self.fd_for_token(other_token).unwrap_or_else(|| {
-                            unreachable!("tried to get fd for no-existent token? {other_token:?}")
-                        });
-
-                        if event.is_read_closed() {
-                            self.deregister(stream_fd);
-                        } else {
-                            // SAFETY: oh boy.
-                            let stream_fd = unsafe { BorrowedFd::borrow_raw(stream_fd) };
-                            self.read_cmd(&stream_fd).unwrap();
-                        }
-                    },
-                }
-            }
+            let poll_result = self.poller.poll(&mut events, TIMEOUT_NEVER);
+            self.handle_poll(poll_result, &events)?;
         }
     }
+
+    fn handle_poll(
+        &mut self,
+        poll_result: Result<(), IoError>,
+        events: &Events,
+    ) -> Result<(), IoError> {
+        match poll_result {
+            Ok(()) => {
+                trace!(
+                    "mio::Poller::poll() got events: {:?}",
+                    events.iter().size_hint().0,
+                );
+                if events.is_empty() {
+                    unreachable!(
+                        "epoll_wait() with a \"forever\" timeout should never give empty events",
+                    );
+                }
+
+                let _ = self.fd_error_pop(self.poller.as_raw_fd());
+            },
+            Err(e) if e.kind() == IoErrorKind::Interrupted => {
+                // EINTR is silly.
+                // Return early, and poll() again.
+                return Ok(());
+            },
+            Err(e) => {
+                if let Some(Errno::BADF) = e.raw_os_error().map(Errno::from_raw_os_error) {
+                    panic!("EBADF on poller fd; IO safety violation?");
+                }
+                warn!("mio Poll::poll() error: {e}");
+                self.fd_error_push(self.poller.as_raw_fd(), e)
+                    .tap_err(|e| {
+                        error!("accumulated too many errors for mio::Poll::poll(): {e}")
+                    })?;
+            },
+        }
+
+        for event in events {
+            self.handle_event(event)?;
+        }
+
+        Ok(())
+    }
+
+    fn handle_event(&mut self, event: &Event) -> Result<(), IoError> {
+        trace!("Handling event {event:#?}");
+
+        match event.token() {
+            DAEMON => {
+                let is_sock = self.main_fd_info().kind == FdKind::Socket;
+                if !is_sock {
+                    // SAFETY: oh boy: disjoint borrows with extra steps.
+                    let file_fd = unsafe { BorrowedFd::borrow_raw(self.fd.as_raw_fd()) };
+                    self.read_cmd(&file_fd).unwrap();
+
+                    return Ok(());
+                }
+
+                // Accept, first.
+                let flags = SocketFlags::NONBLOCK | SocketFlags::CLOEXEC;
+                let stream_fd = match rustix::net::accept_with(&self.fd, flags) {
+                    Ok(stream) => {
+                        debug!(
+                            "Accepted connection from socket {:?} as stream {:?}",
+                            self.fd, stream,
+                        );
+                        stream
+                    },
+                    Err(e) => {
+                        error!("accept4 on daemon socket failed: {e}");
+                        self.fd_error_push(self.fd.as_raw_fd(), e.into())
+                            .tap_err(|e| {
+                                error!(
+                                    "Accumulated too many errors for daemon fd {:?}: {e}",
+                                    self.fd
+                                )
+                            })?;
+
+                        return Ok(());
+                    },
+                };
+
+                // Add this stream to our poll interest list.
+                // NOTE: `stream_fd` is now effectively `ManuallyDrop`.
+                let stream_fd = stream_fd.into_raw_fd();
+                let _token = self.register(stream_fd, FdKind::SockStream);
+
+                // Wait for the next poll to handle.
+            },
+            other_token => {
+                // This must be a stream fd.
+                let fd = self.fd_for_token(other_token).unwrap_or_else(|| {
+                    unreachable!("tried to get fd for non-existent token? {other_token:?}")
+                });
+                let Some(info) = self.fd_info.get(&fd) else {
+                    panic!("Received an event on an unregistered fd {fd}; IO-safety violation?");
+                };
+
+                if event.is_read_closed() {
+                    self.deregister(fd);
+                    return Ok(());
+                }
+
+                match info.kind {
+                    FdKind::Pid(pid) => {
+                        debug!("Reaping child process {pid}");
+                        // SAFETY: `fd` cannot have been closed yet, since that's what we do here.
+                        let pidfd = unsafe { BorrowedFd::borrow_raw(fd) };
+                        let status = rustix::waitid(WaitId::PidFd(pidfd), WaitIdOptions::EXITED)
+                            .unwrap_or_else(|e| {
+                                todo!("waitid() can fail? on pid {pid}: {e}");
+                            })
+                            .unwrap_or_else(|| {
+                                todo!("waitid() returned None? for pid {pid}");
+                            });
+
+                        debug!("waitid() for pid {pid} returned status: {status:?}");
+                        let is_dead = status.exited() || status.killed() || status.dumped();
+                        if !is_dead {
+                            todo!("Handle process {pid} events that aren't death: {status:?}");
+                        }
+                        let Some(exit_code) = status.exit_status() else {
+                            unreachable!("Process {pid} died with no exit code at all? {status:?}");
+                        };
+                        debug!("Child process {pid} exited with code {exit_code}");
+
+                        // Close the pidfd.
+                        self.deregister(fd);
+                    },
+                    //FdKind::ChildStdout => {
+                    //    warn!("got stdout");
+                    //    todo!();
+                    //},
+                    //FdKind::ChildStderr => {
+                    //    warn!("got stderr");
+                    //    // SAFETY: oh boy.
+                    //    let stderr = unsafe { BorrowedFd::borrow_raw(fd) };
+                    //    self.proxy_stdio(&stderr).unwrap();
+                    //},
+                    FdKind::SockStream => {
+                        // SAFETY: oh boy.
+                        let stream_fd = unsafe { BorrowedFd::borrow_raw(fd) };
+                        self.read_cmd(&stream_fd).unwrap();
+                    },
+                    kind => todo!("{kind:?}"),
+                };
+            },
+        }
+
+        Ok(())
+    }
 }
 
 impl Drop for Daemon {

src/daemon/api.rs

@@ -0,0 +1,59 @@
+use std::ops::Deref;
+
+use crate::prelude::*;
+
+use serde::{Deserialize, Serialize};
+
+mod impls;
+
+/// Unfortunately, empty-string identifiers are valid Nix...
+///
+/// This type does not provide a [`Default`] impl, however.
+#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+#[derive(Deserialize, Serialize)]
+#[serde(untagged)]
+pub enum ConvenientAttrPath {
+    Dotted(Box<str>),
+    Split(Box<[Box<str>]>),
+}
+
+impl ConvenientAttrPath {
+    pub fn clone_from_dotted(s: &str) -> Self {
+        Self::Dotted(Box::from(s))
+    }
+
+    pub fn clone_from_split(s: &[&str]) -> Self {
+        Self::from_str_iter(s.iter().map(Deref::deref))
+    }
+
+    pub fn from_str_iter<'i, I>(iter: I) -> Self
+    where
+        I: IntoIterator<Item = &'i str>,
+    {
+        let iter = iter.into_iter();
+        let boxed = iter.map(Box::from);
+        Self::Split(Box::from_iter(boxed))
+    }
+
+    pub fn to_nix_decl(&self) -> Box<str> {
+        use ConvenientAttrPath::*;
+        match self {
+            Dotted(s) => s.clone(),
+            Split(path) => {
+                // FIXME: quote if necessary
+                path.join(".").into_boxed_str()
+            },
+        }
+    }
+}
+
+#[derive(Debug, Clone, PartialEq)]
+#[derive(serde::Deserialize, serde::Serialize)]
+#[serde(tag = "action", content = "args", rename_all = "snake_case")]
+// FIXME: rename to not confuse with the clap argument type.
+pub enum DaemonCmd {
+    Append {
+        name: ConvenientAttrPath,
+        value: Box<str>,
+    },
+}

src/daemon/api/impls.rs

@@ -0,0 +1,27 @@
+use super::ConvenientAttrPath;
+
+impl<'i> FromIterator<&'i str> for ConvenientAttrPath {
+    fn from_iter<I>(iter: I) -> Self
+    where
+        I: IntoIterator<Item = &'i str>,
+    {
+        Self::from_str_iter(iter)
+    }
+}
+impl FromIterator<Box<str>> for ConvenientAttrPath {
+    fn from_iter<I>(iter: I) -> Self
+    where
+        I: IntoIterator<Item = Box<str>>,
+    {
+        Self::Split(Box::from_iter(iter))
+    }
+}
+impl FromIterator<String> for ConvenientAttrPath {
+    fn from_iter<I>(iter: I) -> Self
+    where
+        I: IntoIterator<Item = String>,
+    {
+        let iter = iter.into_iter();
+        Self::Split(Box::from_iter(iter.map(String::into_boxed_str)))
+    }
+}

src/daemon_tokfd.rs

@@ -3,6 +3,7 @@ use std::{os::fd::RawFd, sync::OnceLock};
 use circular_buffer::CircularBuffer;
 use iddqd::{BiHashItem, IdOrdItem};
 use mio::Token;
+use rustix::process::Pid;
 
 use crate::prelude::*;
 
@@ -76,11 +77,11 @@ impl FdInfo {
 impl IdOrdItem for FdInfo {
     type Key<'a> = &'a RawFd;
 
+    iddqd::id_upcast!();
+
     fn key(&self) -> &RawFd {
         &self.fd
     }
-
-    iddqd::id_upcast!();
 }
 
 #[derive(Debug)]
@@ -105,13 +106,16 @@ impl<'a> Display for FdInfoDisplay<'a> {
 }
 
 #[derive(Copy)]
-#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Default)]
+#[derive(Debug, Clone, PartialEq, Eq, Hash, Default)]
 #[non_exhaustive]
 pub enum FdKind {
     File,
     Socket,
     SockStream,
     Poller,
+    ChildStdout,
+    ChildStderr,
+    Pid(Pid),
     #[default]
     Unknown,
 }
@@ -124,6 +128,9 @@ impl FdKind {
             Socket => "socket",
             SockStream => "socket stream",
             Poller => "poller",
+            ChildStdout => "child stdout",
+            ChildStderr => "child stderr",
+            Pid(_) => "pidfd",
             Unknown => "«unknown»",
         }
     }
@@ -140,6 +147,8 @@ impl BiHashItem for TokenFd {
     type K1<'a> = Token;
     type K2<'a> = RawFd;
 
+    iddqd::bi_upcast!();
+
     fn key1(&self) -> Token {
         self.token
     }
@@ -147,8 +156,6 @@ impl BiHashItem for TokenFd {
     fn key2(&self) -> RawFd {
         self.fd
     }
-
-    iddqd::bi_upcast!();
 }
 
 impl From<TokenFd> for (Token, RawFd) {

src/lib.rs

@@ -55,6 +55,7 @@ mod color;
 pub use color::{_CLI_ENABLE_COLOR, SHOULD_COLOR};
 mod daemon;
 pub use daemon::Daemon;
+pub use daemon::api as daemon_api;
 mod daemon_io;
 pub use daemon_io::OwnedFdWithFlags;
 mod daemon_tokfd;
@@ -98,6 +99,22 @@ static MK_OVERRIDE_RE: LazyLock<Regex> = LazyLock::new(|| {
     Regex::new(r"(?-u)\bmkOverride\s+\((?<priority>[\d-]+)\)").unwrap()
 });
 
+pub(crate) fn open_source_file(path: Arc<Path>) -> Result<SourceFile, IoError> {
+    let mut opts = File::options();
+    opts.read(true)
+        .write(true)
+        .create(false)
+        .custom_flags(libc::O_CLOEXEC);
+
+    SourceFile::open_from(Arc::clone(&path), opts)
+        .tap_err(|e| error!("couldn't open source file at {}: {e}", path.display()))
+}
+
+pub(crate) fn get_line_to_insert() -> SourceLine {
+    //
+    todo!();
+}
+
 #[tracing::instrument(level = "debug")]
 pub fn do_append(args: Arc<Args>, append_args: AppendCmd) -> Result<(), BoxDynError> {
     let filepath = Path::new(&args.file);
@@ -109,22 +126,16 @@ pub fn do_append(args: Arc<Args>, append_args: AppendCmd) -> Result<(), BoxDynEr
         filepath.to_path_buf()
     };
 
-    let mut opts = File::options();
-    opts.read(true)
-        .write(true)
-        .create(false)
-        .custom_flags(libc::O_CLOEXEC);
-
-    let source_file = SourceFile::open_from(Arc::from(filepath), opts)?;
+    let source_file = open_source_file(Arc::from(filepath))?;
     let pri = get_where(source_file.clone())?;
 
     let new_pri = pri - 1;
 
     let new_pri_line = get_next_prio_line(
         source_file.clone(),
-        append_args.name,
+        &append_args.name,
         new_pri,
-        append_args.value,
+        &append_args.value,
     )?;
 
     debug!("new_pri_line={new_pri_line}");
@@ -209,9 +220,9 @@ pub fn get_where(dynamic_nix: SourceFile) -> Result<i64, BoxDynError> {
 
 pub fn get_next_prio_line(
     source: SourceFile,
-    option_name: Arc<str>,
+    option_name: &str,
     new_prio: i64,
-    new_value: Arc<str>,
+    new_value: &str,
 ) -> Result<SourceLine, BoxDynError> {
     let source_lines = source.lines()?;
     let penultimate = source_lines.get(source_lines.len() - 2);

src/source.rs

@@ -6,6 +6,7 @@ use std::{
     cell::{Ref, RefCell},
     hash::Hash,
     io::{BufRead, BufReader, BufWriter},
+    mem::{self, MaybeUninit},
     ops::Deref,
     ptr,
     sync::{Arc, Mutex, OnceLock},
@@ -103,6 +104,28 @@ pub struct SourceFile {
     lines: Arc<OnceLock<RefCell<Vec<SourceLine>>>>,
 }
 
+#[derive(Debug)]
+#[repr(transparent)]
+pub struct OpaqueDerefSourceLines<'s>(Ref<'s, [SourceLine]>);
+impl<'s> Deref for OpaqueDerefSourceLines<'s> {
+    type Target = [SourceLine];
+
+    fn deref(&self) -> &[SourceLine] {
+        &*self.0
+    }
+}
+
+#[derive(Debug)]
+#[repr(transparent)]
+pub struct OpaqueDerefSourceLine<'s>(Ref<'s, SourceLine>);
+impl<'s> Deref for OpaqueDerefSourceLine<'s> {
+    type Target = SourceLine;
+
+    fn deref(&self) -> &SourceLine {
+        &*self.0
+    }
+}
+
 impl SourceFile {
     /// Panics if `path` is a directory path instead of a file path.
     pub fn open_from(path: Arc<Path>, options: OpenOptions) -> Result<Self, IoError> {
@@ -159,15 +182,17 @@ impl SourceFile {
         Ok(self._lines_slice())
     }
 
-    pub fn lines(&self) -> Result<impl Deref<Target = [SourceLine]> + '_, IoError> {
-        self._lines()
+    pub fn lines(&self) -> Result<OpaqueDerefSourceLines<'_>, IoError> {
+        let lines = self._lines()?;
+
+        Ok(OpaqueDerefSourceLines(lines))
     }
 
-    pub fn line(&self, line: Line) -> Result<impl Deref<Target = SourceLine> + '_, IoError> {
+    pub fn line(&self, line: Line) -> Result<OpaqueDerefSourceLine<'_>, IoError> {
         let lines_lock = self._lines()?;
         let line = Ref::map(lines_lock, |lines| &lines[line.index() as usize]);
 
-        Ok(line)
+        Ok(OpaqueDerefSourceLine(line))
     }
 
     /// `lines` but already be initialized.

tests/harmonia/test-script.py

@@ -80,6 +80,7 @@ machine.wait_for_unit("install-dynix.service")
 dynix_out = machine.succeed("dynix --version")
 assert "dynix" in dynix_out, f"dynix not in {dynix_out=}"
 
+
 # Config should have our initial values.
 config_toml = get_config_file()
 assert int(config_toml['workers']) == 4, f"{config_toml['workers']=} != 4"