[WIP] add support for mkdirat

CHANGELOG.md

@@ -24,6 +24,8 @@ This project adheres to [Semantic Versioning](http://semver.org/).
   ([#739](https://github.com/nix-rust/nix/pull/739))
 - Added nix::sys::ptrace::detach. 
   ([#749](https://github.com/nix-rust/nix/pull/749))
+- Added `nix::unistd::mkdirat`
+  ([#754](https://github.com/nix-rust/nix/pull/754))
 
 ### Changed
 - Renamed existing `ptrace` wrappers to encourage namespacing ([#692](https://github.com/nix-rust/nix/pull/692))

src/unistd.rs

@@ -441,6 +441,16 @@ pub fn mkdir<P: ?Sized + NixPath>(path: &P, mode: Mode) -> Result<()> {
     Errno::result(res).map(drop)
 }
 
+/// Create a directory
+/// ([posix specification)](http://pubs.opengroup.org/onlinepubs/9699919799/functions/mkdirat.html)).
+pub fn mkdirat<P: ?Sized + NixPath>(dirfd: RawFd, pathname: &P, mode: Mode) -> Result<()> {
+    let res = try!(pathname.with_nix_path(|cstr| {
+        unsafe { libc::mkdirat(dirfd, cstr.as_ptr(), mode.bits() as mode_t) }
+    }));
+
+    Errno::result(res).map(drop)
+}
+
 /// Returns the current directory as a PathBuf
 ///
 /// Err is returned if the current user doesn't have the permission to read or search a component

test/test_unistd.rs

@@ -1,5 +1,6 @@
 extern crate tempdir;
 
+use nix::fcntl;
 use nix::unistd::*;
 use nix::unistd::ForkResult::*;
 use nix::sys::wait::*;
@@ -104,6 +105,22 @@ mod linux_android {
     }
 }
 
+#[test]
+fn test_mkdirat() {
+    let tempdir = TempDir::new("nix-test_mkdirat").unwrap();
+    let path = tempdir.path().join("test_path");
+
+    let dirfd = fcntl::open(tempdir.path(),
+                            fcntl::OFlag::empty(),
+                            stat::Mode::empty());
+
+    mkdirat(dirfd.unwrap(),
+            &path.file_name(),
+            stat::Mode::empty()).unwrap();
+
+    assert!(path.exists());
+}
+
 macro_rules! execve_test_factory(
     ($test_name:ident, $syscall:ident, $exe: expr) => (
     #[test]