Add sync (fix #959)

Author: r-darwish

CHANGELOG.md

@@ -6,6 +6,8 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 ## [Unreleased]
 
 ### Added
+- Added a `sync` wrapper.
+  ([#961](https://github.com/nix-rust/nix/pull/961))
 - Added a `sysinfo` wrapper.
   ([#922](https://github.com/nix-rust/nix/pull/922))
 - Support the `SO_PEERCRED` socket option and the `UnixCredentials` type on all Linux and Android targets.

src/unistd.rs

@@ -1101,6 +1101,20 @@ pub fn chroot<P: ?Sized + NixPath>(path: &P) -> Result<()> {
     Errno::result(res).map(drop)
 }
 
+/// Commit filesystem caches to disk
+///
+/// See also [sync(2)](http://pubs.opengroup.org/onlinepubs/9699919799/functions/sync.html)
+#[cfg(any(
+    target_os = "dragonfly",
+    target_os = "freebsd",
+    target_os = "linux",
+    target_os = "netbsd",
+    target_os = "openbsd"
+))]
+pub fn sync() -> () {
+    unsafe { libc::sync() };
+}
+
 /// Synchronize changes to a file
 ///
 /// See also [fsync(2)](http://pubs.opengroup.org/onlinepubs/9699919799/functions/fsync.html)