Auto merge of #491 - zethra:master, r=fiveop

Added getpgrp

CHANGELOG.md

@@ -22,6 +22,8 @@ This project adheres to [Semantic Versioning](http://semver.org/).
   ([#451](https://github.com/nix-rust/nix/pull/451))
 - Added `CLONE_NEWCGROUP` in `::nix::sched`
   ([#457](https://github.com/nix-rust/nix/pull/457))
+- Added `getpgrp` in `::nix::unistd`
+  ([#491](https://github.com/nix-rust/nix/pull/491))
 
 ### Changed
 - Changed `TimeVal` into an opaque Newtype

src/unistd.rs

@@ -151,6 +151,17 @@ pub fn tcsetpgrp(fd: c_int, pgrp: pid_t) -> Result<()> {
     Errno::result(res).map(drop)
 }
 
+
+/// Get the group id of the calling process (see
+///[getpgrp(3)](http://man7.org/linux/man-pages/man3/getpgrp.3p.html)).
+///
+/// Get the process group id (PGID) of the calling process.
+/// According to the man page it is always successful.
+#[inline]
+pub fn getpgrp() -> pid_t {
+    unsafe { libc::getpgrp() }
+}
+
 /// Get the caller's thread ID (see
 /// [gettid(2)](http://man7.org/linux/man-pages/man2/gettid.2.html).
 ///