signal: add SignalKind::info on illumos

illumos has supported SIGINFO for a long time; see illumos/illumos-gate@19d32b9.

tokio/src/signal/unix.rs

@@ -23,13 +23,25 @@ pub(crate) type OsStorage = Box<[SignalInfo]>;
 impl Init for OsStorage {
     fn init() -> Self {
         // There are reliable signals ranging from 1 to 33 available on every Unix platform.
-        #[cfg(not(target_os = "linux"))]
+        #[cfg(not(any(target_os = "linux", target_os = "illumos")))]
         let possible = 0..=33;
 
         // On Linux, there are additional real-time signals available.
         #[cfg(target_os = "linux")]
         let possible = 0..=libc::SIGRTMAX();
 
+        // On illumos, signal numbers go up to 41 (SIGINFO). The list of signals
+        // hasn't changed since 2013. See
+        // https://github.com/illumos/illumos-gate/blob/master/usr/src/uts/common/sys/iso/signal_iso.h.
+        //
+        // illumos also has real-time signals, but (a) the number of real-time
+        // signals is actually configurable at runtime and (b) this capability
+        // isn't exposed by libc as of 0.2.167, so we don't support them at the
+        // moment. If support for real-time signals on illumos is desired, this
+        // code would have to be changed to accommodate that.
+        #[cfg(target_os = "illumos")]
+        let possible = 0..=41;
+
         possible.map(|_| SignalInfo::default()).collect()
     }
 }
@@ -130,7 +142,8 @@ impl SignalKind {
         target_os = "freebsd",
         target_os = "macos",
         target_os = "netbsd",
-        target_os = "openbsd"
+        target_os = "openbsd",
+        target_os = "illumos"
     ))]
     pub const fn info() -> Self {
         Self(libc::SIGINFO)

tokio/tests/signal_info.rs

@@ -0,0 +1,38 @@
+#![warn(rust_2018_idioms)]
+#![cfg(feature = "full")]
+#![cfg(any(
+    target_os = "dragonfly",
+    target_os = "freebsd",
+    target_os = "macos",
+    target_os = "netbsd",
+    target_os = "openbsd",
+    target_os = "illumos"
+))]
+#![cfg(not(miri))] // No `sigaction` on Miri
+
+mod support {
+    pub mod signal;
+}
+use support::signal::send_signal;
+
+use tokio::signal;
+use tokio::signal::unix::SignalKind;
+use tokio::sync::oneshot;
+
+#[tokio::test]
+async fn siginfo() {
+    let mut sig = signal::unix::signal(SignalKind::info()).expect("installed signal handler");
+
+    let (fire, wait) = oneshot::channel();
+
+    // NB: simulate a signal coming in by exercising our signal handler
+    // to avoid complications with sending SIGINFO to the test process
+    tokio::spawn(async {
+        wait.await.expect("wait failed");
+        send_signal(libc::SIGINFO);
+    });
+
+    let _ = fire.send(());
+
+    sig.recv().await.expect("received SIGINFO signal");
+}