Add AsyncFd::try_clone

Duplicates the underlying file descriptor.

src/lib.rs

@@ -1267,6 +1267,17 @@ impl AsyncFd {
         AsyncFd::new(OwnedFd::from_raw_fd(fd), sq)
     }
 
+    /// Creates a new independently owned `AsyncFd` that shares the same
+    /// underlying file descriptor as the existing `AsyncFd`.
+    #[doc(alias = "dup")]
+    #[doc(alias = "dup2")]
+    #[doc(alias = "F_DUPFD")]
+    #[doc(alias = "F_DUPFD_CLOEXEC")]
+    pub fn try_clone(&self) -> io::Result<AsyncFd> {
+        let fd = self.fd.try_clone()?;
+        Ok(AsyncFd::new(fd, self.sq.clone()))
+    }
+
     /// Returns the `RawFd` of this `AsyncFd`.
     fn fd(&self) -> RawFd {
         self.fd.as_raw_fd()

tests/async_fd/io.rs

@@ -24,6 +24,25 @@ use crate::util::{
 const BUF_SIZE: usize = 4096;
 const NO_OFFSET: u64 = u64::MAX;
 
+#[test]
+fn try_clone() {
+    let sq = test_queue();
+    let waker = Waker::new();
+
+    let (r, w) = pipe2(sq).expect("failed to create pipe");
+    let w2 = w.try_clone().expect("failed to clone fd");
+
+    const DATA: &[u8] = b"hello world";
+    waker.block_on(w.write(&DATA[..5])).unwrap();
+    waker.block_on(w2.write(&DATA[5..])).unwrap();
+
+    let buf = BadReadBuf {
+        data: Vec::with_capacity(30),
+    };
+    let buf = waker.block_on(r.read_n(buf, DATA.len())).unwrap();
+    assert_eq!(&buf.data, DATA);
+}
+
 #[test]
 fn read_read_buf_pool() {
     require_kernel!(5, 19);