Merge #851

851: Added `getsid` in `::nix::unistd` r=asomers a=ggriffiniii

Resolves Issue #850 

3 files changed, 21 insertions, 0 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index dda99f98..2571a71e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,8 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 ## [Unreleased]
 
 ### Added
+- Added `getsid` in `::nix::unistd`
+  ([#850](https://github.com/nix-rust/nix/pull/850))
 
 - Added `alarm`. ([#830](https://github.com/nix-rust/nix/pull/830))
 
diff --git a/src/unistd.rs b/src/unistd.rs
index 5f3a3806..8022aa0b 100644
--- a/src/unistd.rs
+++ b/src/unistd.rs
@@ -264,6 +264,17 @@ pub fn setsid() -> Result<Pid> {
     Errno::result(unsafe { libc::setsid() }).map(Pid)
 }
 
+/// Get the process group ID of a session leader
+/// [getsid(2)](http://pubs.opengroup.org/onlinepubs/9699919799/functions/getsid.html).
+///
+/// Obtain the process group ID of the process that is the session leader of the process specified
+/// by pid. If pid is zero, it specifies the calling process.
+#[inline]
+pub fn getsid(pid: Option<Pid>) -> Result<Pid> {
+    let res = unsafe { libc::getsid(pid.unwrap_or(Pid(0)).into()) };
+    Errno::result(res).map(Pid)
+}
+
 
 /// Get the terminal foreground process group (see
 /// [tcgetpgrp(3)](http://pubs.opengroup.org/onlinepubs/9699919799/functions/tcgetpgrp.html)).
diff --git a/test/test_unistd.rs b/test/test_unistd.rs
index d78b6ba8..fe33b1d0 100644
--- a/test/test_unistd.rs
+++ b/test/test_unistd.rs
@@ -108,6 +108,14 @@ fn test_getpid() {
     assert!(ppid > 0);
 }
 
+#[test]
+fn test_getsid() {
+    let none_sid: ::libc::pid_t = getsid(None).unwrap().into();
+    let pid_sid: ::libc::pid_t = getsid(Some(getpid())).unwrap().into();
+    assert!(none_sid > 0);
+    assert!(none_sid == pid_sid);
+}
+
 #[cfg(any(target_os = "linux", target_os = "android"))]
 mod linux_android {
     use nix::unistd::gettid;