add support for mknodat

Author: Mic92

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 mknodat
+  ([#747](https://github.com/nix-rust/nix/pull/747))
 
 ### Changed
 - Renamed existing `ptrace` wrappers to encourage namespacing ([#692](https://github.com/nix-rust/nix/pull/692))

src/sys/stat.rs

@@ -50,6 +50,19 @@ pub fn mknod<P: ?Sized + NixPath>(path: &P, kind: SFlag, perm: Mode, dev: dev_t)
     Errno::result(res).map(drop)
 }
 
+/// Create a special or ordinary file
+/// ([posix specification](http://pubs.opengroup.org/onlinepubs/9699919799/functions/mknod.html)).
+#[cfg(not(any(target_os = "ios", target_os = "macos")))]
+pub fn mknodat<P: ?Sized + NixPath>(dirfd: &RawFd, path: &P, kind: SFlag, perm: Mode, dev: dev_t) -> Result<()> {
+    let res = try!(path.with_nix_path(|cstr| {
+        unsafe {
+            libc::mknodat(*dirfd, cstr.as_ptr(), kind.bits | perm.bits() as mode_t, dev)
+        }
+    }));
+
+    Errno::result(res).map(drop)
+}
+
 #[cfg(target_os = "linux")]
 pub fn major(dev: dev_t) -> u64 {
     ((dev >> 32) & 0xfffff000) |