timerfd: Add TFD_TIMER_CANCEL_ON_SET flag

Author: apohrebniak

CHANGELOG.md

@@ -16,6 +16,8 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 - Added `mq_timedreceive` to `::nix::mqueue`.
   ([#1966])(https://github.com/nix-rust/nix/pull/1966)
 - Added `LocalPeerPid` to `nix::sys::socket::sockopt` for macOS. ([#1967](https://github.com/nix-rust/nix/pull/1967))
+- Added `TFD_TIMER_CANCEL_ON_SET` to `::nix::sys::time::TimerSetTimeFlags` on Linux and Android.
+  ([#2040](https://github.com/nix-rust/nix/pull/2040))
 
 ### Changed
 

src/sys/time.rs

@@ -93,6 +93,7 @@ pub(crate) mod timer {
         /// Flags that are used for arming the timer.
         pub struct TimerSetTimeFlags: libc::c_int {
             const TFD_TIMER_ABSTIME = libc::TFD_TIMER_ABSTIME;
+            const TFD_TIMER_CANCEL_ON_SET = libc::TFD_TIMER_CANCEL_ON_SET;
         }
     }
     #[cfg(any(

src/sys/timerfd.rs

@@ -135,6 +135,13 @@ impl TimerFd {
     /// Then the one shot TimeSpec and the delay TimeSpec of the delayed
     /// interval are going to be interpreted as absolute.
     ///
+    /// # Cancel on a clock change
+    ///
+    /// If you set a `TFD_TIMER_CANCEL_ON_SET` alongside `TFD_TIMER_ABSTIME`
+    /// and the clock for this timer is `CLOCK_REALTIME` or `CLOCK_REALTIME_ALARM`,
+    /// then this timer is marked as cancelable if the real-time clock undergoes
+    /// a discontinuous change.
+    ///
     /// # Disabling alarms
     ///
     /// Note: Only one alarm can be set for any given timer. Setting a new alarm
@@ -202,6 +209,9 @@ impl TimerFd {
     /// Note: If the alarm is unset, then you will wait forever.
     pub fn wait(&self) -> Result<()> {
         while let Err(e) = read(self.fd.as_fd().as_raw_fd(), &mut [0u8; 8]) {
+            if e == Errno::ECANCELED {
+                break;
+            }
             if e != Errno::EINTR {
                 return Err(e);
             }