Accept -listenfd and pass on to Xwayland

src/lib.rs

@@ -8,7 +8,7 @@ use log::{error, info};
 use rustix::event::{poll, PollFd, PollFlags};
 use smithay_client_toolkit::data_device_manager::WritePipe;
 use std::io::{BufRead, BufReader, Read, Write};
-use std::os::fd::{AsFd, AsRawFd, BorrowedFd};
+use std::os::fd::{AsFd, AsRawFd, BorrowedFd, OwnedFd};
 use std::os::unix::net::UnixStream;
 use std::process::{Command, ExitStatus, Stdio};
 use wayland_server::{Display, ListeningSocket};
@@ -35,6 +35,7 @@ type RealServerState = ServerState<RealConnection>;
 
 pub trait RunData {
     fn display(&self) -> Option<&str>;
+    fn listenfds(&mut self) -> Vec<OwnedFd>;
     fn server(&self) -> Option<UnixStream> {
         None
     }
@@ -46,7 +47,7 @@ pub trait RunData {
     fn xwayland_ready(&self, _display: String, _pid: u32) {}
 }
 
-pub fn main(data: impl RunData) -> Option<()> {
+pub fn main(mut data: impl RunData) -> Option<()> {
     let mut version = env!("VERGEN_GIT_DESCRIBE");
     if version == "VERGEN_IDEMPOTENT_OUTPUT" {
         version = env!("CARGO_PKG_VERSION");
@@ -70,6 +71,12 @@ pub fn main(data: impl RunData) -> Option<()> {
     if let Some(display) = data.display() {
         xwayland.arg(display);
     }
+
+    let fds = data.listenfds();
+    for fd in &fds {
+        xwayland.args(["-listenfd", &fd.as_raw_fd().to_string()]);
+    }
+
     let mut xwayland = xwayland
         .args([
             "-rootless",
@@ -84,6 +91,9 @@ pub fn main(data: impl RunData) -> Option<()> {
         .spawn()
         .unwrap();
 
+    // Now that Xwayland spawned and got the listenfds, we can close them here.
+    drop(fds);
+
     let xwl_pid = xwayland.id();
 
     let (mut finish_tx, mut finish_rx) = UnixStream::pair().unwrap();

src/main.rs

@@ -1,24 +1,63 @@
+use std::os::fd::{FromRawFd, OwnedFd, RawFd};
+
 fn main() {
     pretty_env_logger::formatted_timed_builder()
         .filter_level(log::LevelFilter::Info)
         .parse_default_env()
         .init();
-    xwayland_satellite::main(RealData(get_display()));
+    xwayland_satellite::main(parse_args());
 }
 
-#[repr(transparent)]
-struct RealData(Option<String>);
+struct RealData {
+    display: Option<String>,
+    listenfds: Vec<OwnedFd>,
+}
 impl xwayland_satellite::RunData for RealData {
     fn display(&self) -> Option<&str> {
-        self.0.as_deref()
+        self.display.as_deref()
+    }
+
+    fn listenfds(&mut self) -> Vec<OwnedFd> {
+        std::mem::take(&mut self.listenfds)
     }
 }
 
-fn get_display() -> Option<String> {
+fn parse_args() -> RealData {
+    let mut data = RealData {
+        display: None,
+        listenfds: Vec::new(),
+    };
+
     let mut args: Vec<_> = std::env::args().collect();
-    if args.len() > 2 {
-        panic!("Unexpected arguments: {:?}", &args[2..]);
+    if args.len() < 2 {
+        return data;
     }
 
-    (args.len() == 2).then(|| args.swap_remove(1))
+    // Argument at index 1 is our display name. The rest can be -listenfd.
+    let mut i = 2;
+    while i < args.len() {
+        let arg = &args[i];
+        if arg == "-listenfd" {
+            let next = i + 1;
+            if next == args.len() {
+                // Matches the Xwayland error message.
+                panic!("Required argument to -listenfd not specified");
+            }
+
+            let fd: RawFd = args[next].parse().expect("Error parsing -listenfd number");
+            // SAFETY:
+            // - whoever runs the binary must ensure this fd is open and valid.
+            // - parse_args() must only be called once to avoid double closing.
+            let fd = unsafe { OwnedFd::from_raw_fd(fd) };
+
+            data.listenfds.push(fd);
+            i += 2;
+        } else {
+            panic!("Unrecognized argument: {arg}");
+        }
+    }
+
+    data.display = Some(args.swap_remove(1));
+
+    data
 }