Merge #1381

1381: Close file descriptor on drop in TimerFd r=asomers a=crdumoul

This change closes the TimerFd file descriptor on drop. Note that the TimerFd will no longer be `Clone` or `Copy`. Since it has a destructor it can't be `Copy`, and if it were `Clone` you could end up trying to use a closed TimerFd, or double-closing the file descriptor.

Addresses #1379.

Co-authored-by: Christopher Dumoulin <cdumouli@akamai.com>
Co-authored-by: Alan Somers <asomers@gmail.com>

CHANGELOG.md

@@ -16,6 +16,8 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 ### Changed
 
 ### Fixed
+- `TimerFd` now closes the underlying fd on drop.
+  ([#1381](https://github.com/nix-rust/nix/pull/1381))
 - Define `*_MAGIC` filesystem constants on Linux s390x
   (#[1372](https://github.com/nix-rust/nix/pull/1372))
 - mqueue, sysinfo, timespec, statfs, test_ptrace_syscall() on x32
@@ -39,6 +41,8 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 
 - Removed `SockLevel`, which hasn't been used for a few years
   (#[1362](https://github.com/nix-rust/nix/pull/1362))
+- Removed both `Copy` and `Clone` from `TimerFd`.
+  ([#1381](https://github.com/nix-rust/nix/pull/1381))
 
 ## [0.19.1] - 28 November 2020
 ### Fixed

src/sys/timerfd.rs

@@ -37,7 +37,7 @@ use std::os::unix::io::{AsRawFd, FromRawFd, RawFd};
 
 /// A timerfd instance. This is also a file descriptor, you can feed it to
 /// other interfaces consuming file descriptors, epoll for example.
-#[derive(Debug, Clone, Copy)]
+#[derive(Debug)]
 pub struct TimerFd {
     fd: RawFd,
 }
@@ -166,7 +166,7 @@ pub enum Expiration {
 impl TimerFd {
     /// Creates a new timer based on the clock defined by `clockid`. The
     /// underlying fd can be assigned specific flags with `flags` (CLOEXEC,
-    /// NONBLOCK).
+    /// NONBLOCK). The underlying fd will be closed on drop.
     pub fn new(clockid: ClockId, flags: TimerFlags) -> Result<Self> {
         Errno::result(unsafe { libc::timerfd_create(clockid as i32, flags.bits()) })
             .map(|fd| Self { fd })
@@ -270,3 +270,16 @@ impl TimerFd {
         Ok(())
     }
 }
+
+impl Drop for TimerFd {
+    fn drop(&mut self) {
+        if !std::thread::panicking() {
+            let result = Errno::result(unsafe {
+                libc::close(self.fd)
+            });
+            if let Err(Error::Sys(Errno::EBADF)) = result {
+                panic!("close of TimerFd encountered EBADF");
+            }
+        }
+    }
+}