tools: add Fd helper

stores a raw file descriptor with a drop handler for
safekeeping in closures

Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>

src/tools.rs

@@ -14,8 +14,7 @@ use std::io::Read;
 use std::io::ErrorKind;
 use std::time::Duration;
 
-use std::os::unix::io::RawFd;
-use std::os::unix::io::AsRawFd;
+use std::os::unix::io::{AsRawFd, FromRawFd, IntoRawFd, RawFd};
 
 use std::collections::HashMap;
 
@@ -641,3 +640,38 @@ pub fn fail_on_shutdown() -> Result<(), Error> {
     }
     Ok(())
 }
+
+/// Guard a raw file descriptor with a drop handler. This is mostly useful when access to an owned
+/// `RawFd` is required without the corresponding handler object (such as when only the file
+/// descriptor number is required in a closure which may be dropped instead of being executed).
+pub struct Fd(pub RawFd);
+
+impl Drop for Fd {
+    fn drop(&mut self) {
+        if self.0 != -1 {
+            unsafe {
+                libc::close(self.0);
+            }
+        }
+    }
+}
+
+impl AsRawFd for Fd {
+    fn as_raw_fd(&self) -> RawFd {
+        self.0
+    }
+}
+
+impl IntoRawFd for Fd {
+    fn into_raw_fd(mut self) -> RawFd {
+        let fd = self.0;
+        self.0 = -1;
+        fd
+    }
+}
+
+impl FromRawFd for Fd {
+    unsafe fn from_raw_fd(fd: RawFd) -> Self {
+        Self(fd)
+    }
+}