daemon: drop cmd before readiness wait so early child exit yields EOF (fix hwd/acpid spawn deadlock)

daemon/src/lib.rs

@@ -72,19 +72,28 @@ impl Daemon {
 
         unsafe { pass_fd(&mut cmd, "INIT_NOTIFY", write_pipe.into()) };
 
+        let desc = format!("{cmd:?}");
         if let Err(err) = cmd.spawn() {
-            eprintln!("daemon: failed to execute {cmd:?}: {err}");
+            eprintln!("daemon: failed to execute {desc}: {err}");
             return;
         }
 
+        // Release this process's copy of the INIT_NOTIFY write end. pass_fd
+        // moved it into cmd's pre_exec closure, so while cmd is alive the
+        // parent keeps the write end open and read_exact below never sees EOF
+        // if the child exits without notifying readiness — a deadlock (e.g.
+        // hwd spawning a duplicate acpid that exits early on EEXIST). Dropping
+        // cmd closes the parent's copy so a child exit yields EOF.
+        drop(cmd);
+
         let mut data = [0];
         match read_pipe.read_exact(&mut data) {
             Ok(()) => {}
             Err(err) if err.kind() == io::ErrorKind::UnexpectedEof => {
-                eprintln!("daemon: {cmd:?} exited without notifying readiness");
+                eprintln!("daemon: {desc} exited without notifying readiness");
             }
             Err(err) => {
-                eprintln!("daemon: failed to wait for {cmd:?}: {err}");
+                eprintln!("daemon: failed to wait for {desc}: {err}");
             }
         }
     }

drivers/hwd/src/backend/acpi.rs

@@ -27,7 +27,13 @@ impl Backend for AcpiBackend {
         // no acpid init unit.
         // TODO: rather than put it in the namespace, have init pass the acpi
         // handle to hwd, and then pass it to acpid?
-        if Fd::open("/scheme/acpi", libredox::flag::O_CLOEXEC, 0).is_err() {
+        if Fd::open(
+            "/scheme/acpi/symbols",
+            libredox::flag::O_DIRECTORY | libredox::flag::O_CLOEXEC,
+            0,
+        )
+        .is_err()
+        {
             #[allow(deprecated, reason = "we can't yet move this to init")]
             daemon::Daemon::spawn(Command::new("acpid"));
         }