Add from_owned_fd constructor to EventFd (#2563)

* add from_owned_fd to EventFd

* update changelog

* fix safety section

Author: chadaustin

changelog/2563.added.md

@@ -0,0 +1 @@
+Added `from_owned_fd` constructor to `EventFd`

src/sys/eventfd.rs

@@ -58,6 +58,15 @@ impl EventFd {
         Self::from_value_and_flags(init_val, EfdFlags::empty())
     }
 
+    /// Constructs an `EventFd` wrapping an existing `OwnedFd`.
+    ///
+    /// # Safety
+    ///
+    /// `OwnedFd` is a valid eventfd.
+    pub unsafe fn from_owned_fd(fd: OwnedFd) -> Self {
+        Self(fd)
+    }
+
     /// Enqueues `value` triggers, i.e., adds the integer value supplied in `value`
     /// to the counter.
     ///
@@ -106,4 +115,4 @@ impl From<EventFd> for OwnedFd {
     fn from(value: EventFd) -> Self {
         value.0
     }
-}
+}