Adding an implementation and some basic tests for timerfd.

Removed support for timerfd on Android as it seems to have been deprecated? See https://android.googlesource.com/platform/development/+/73a5a3b/ndk/platforms/android-20/include/sys/timerfd.h or https://github.com/rust-lang/libc/issues/1589

Removed the public status of `TimerSpec`, as it should not be exposed to the user.

Implemented `FromRawFd` for `TimerFd` as it already implements `AsRawFd`.

Addressed comments from the latest code review:
  - Removed upper bound assertions on timer expirations in tests.
  - Made the main example runnable and added code to show how to wait for the timer.
  - Refactored `ClockId` to use `libc_enum`.
  - Added comments for all public parts of the module.
  - Wrapped to 80 cols.
  - Changed the size of the buffer in the tests to the minimum required.

* Ran rustfmt.
* Added a `From` implementation for `libc::timespec` -> `TimeSpec`.
* Reworked the example with the new changes and changed the timer from 5 to 1 second.
* Added a constructor for a 0-initialized `TimerSpec`.
* Added a new method to get the timer configured expiration (based on timerfd_gettime).
* Added an helper method to unset the expiration of the timer.
* Added a `wait` method to actually read from the timer.
* Renamed `settime` into just `set`.
* Refactored the tests and added a new one that tests both the `unset` and the `get` method.

Modified CHANGELOG.

2 files changed, 63 insertions, 0 deletions

diff --git a/test/sys/mod.rs b/test/sys/mod.rs
index 3dc430ee..c4391c72 100644
--- a/test/sys/mod.rs
+++ b/test/sys/mod.rs
@@ -41,3 +41,5 @@ mod test_pthread;
           target_os = "netbsd",
           target_os = "openbsd"))]
 mod test_ptrace;
+#[cfg(any(target_os = "android", target_os = "linux"))]
+mod test_timerfd;
diff --git a/test/sys/test_timerfd.rs b/test/sys/test_timerfd.rs
new file mode 100644
index 00000000..24fb2ac0
--- /dev/null
+++ b/test/sys/test_timerfd.rs
@@ -0,0 +1,61 @@
+use nix::sys::time::{TimeSpec, TimeValLike};
+use nix::sys::timerfd::{ClockId, Expiration, TimerFd, TimerFlags, TimerSetTimeFlags};
+use std::time::Instant;
+
+#[test]
+pub fn test_timerfd_oneshot() {
+    let timer = TimerFd::new(ClockId::CLOCK_MONOTONIC, TimerFlags::empty()).unwrap();
+
+    let before = Instant::now();
+
+    timer
+        .set(
+            Expiration::OneShot(TimeSpec::seconds(1)),
+            TimerSetTimeFlags::empty(),
+        )
+        .unwrap();
+
+    timer.wait().unwrap();
+
+    let millis = before.elapsed().as_millis();
+    assert!(millis > 900);
+}
+
+#[test]
+pub fn test_timerfd_interval() {
+    let timer = TimerFd::new(ClockId::CLOCK_MONOTONIC, TimerFlags::empty()).unwrap();
+
+    let before = Instant::now();
+    timer
+        .set(
+            Expiration::IntervalDelayed(TimeSpec::seconds(1), TimeSpec::seconds(2)),
+            TimerSetTimeFlags::empty(),
+        )
+        .unwrap();
+
+    timer.wait().unwrap();
+
+    let start_delay = before.elapsed().as_millis();
+    assert!(start_delay > 900);
+
+    timer.wait().unwrap();
+
+    let interval_delay = before.elapsed().as_millis();
+    assert!(interval_delay > 2900);
+}
+
+#[test]
+pub fn test_timerfd_unset() {
+    let timer = TimerFd::new(ClockId::CLOCK_MONOTONIC, TimerFlags::empty()).unwrap();
+
+    timer
+        .set(
+            Expiration::OneShot(TimeSpec::seconds(1)),
+            TimerSetTimeFlags::empty(),
+        )
+        .unwrap();
+
+    timer.unset().unwrap();
+
+    assert!(timer.get().unwrap() == None);
+}