Added direct support for fchown and dup3

CHANGELOG.md

@@ -25,10 +25,16 @@ This project adheres to [Semantic Versioning](http://semver.org/).
   ([#956](https://github.com/nix-rust/nix/pull/956))
 - Added a `fchownat` wrapper.
   ([#955](https://github.com/nix-rust/nix/pull/955))
+- Added a `fchown` wrapper.
+  ([#957](https://github.com/nix-rust/nix/pull/957))
 
 ### Changed
 - Increased required Rust version to 1.22.1/
   ([#900](https://github.com/nix-rust/nix/pull/900))
+- Changed the `dup3` wrapper to perform a direct call to the system call `dup3` instead of emulating
+  it via `dup2` and `fcntl` which could cause a race condition. The `dup3` system call is supported
+  on the following platforms: Fuchsia, Emscripten, FreeBSD, Linux, Solaris, NetBSD, OpenBSD.
+  ([#957](https://github.com/nix-rust/nix/pull/957))
 
 ### Fixed
 - Made `preadv` take immutable slice of IoVec.
@@ -37,6 +43,9 @@ This project adheres to [Semantic Versioning](http://semver.org/).
   ([#918](https://github.com/nix-rust/nix/pull/918))
 
 ### Removed
+- Removed the `dup3` wrapper on OSX, which was emulated via `dup2` and `fcntl`, which could cause
+  a race condition. The `dup3` system call is not supported on OSX.
+  ([#957](https://github.com/nix-rust/nix/pull/957))
 
 ## [0.11.0] 2018-06-01
 

src/unistd.rs

@@ -2,8 +2,7 @@
 
 use errno::{self, Errno};
 use {Error, Result, NixPath};
-use fcntl::{AtFlags, at_rawfd, fcntl, FdFlag, OFlag};
-use fcntl::FcntlArg::F_SETFD;
+use fcntl::{AtFlags, at_rawfd, OFlag};
 use libc::{self, c_char, c_void, c_int, c_long, c_uint, size_t, pid_t, off_t,
            uid_t, gid_t, mode_t};
 use std::{fmt, mem, ptr};
@@ -374,26 +373,17 @@ pub fn dup2(oldfd: RawFd, newfd: RawFd) -> Result<RawFd> {
 ///
 /// This function behaves similar to `dup2()` but allows for flags to be
 /// specified.
+#[cfg(any(target_os = "emscripten",
+          target_os = "freebsd",
+          target_os = "fuchsia",
+          target_os = "linux",
+          target_os = "netbsd",
+          target_os = "openbsd",
+          target_os = "solaris"))]
 pub fn dup3(oldfd: RawFd, newfd: RawFd, flags: OFlag) -> Result<RawFd> {
-    dup3_polyfill(oldfd, newfd, flags)
-}
+    let res = unsafe { libc::dup3(oldfd, newfd, flags.bits()) };
 
-#[inline]
-fn dup3_polyfill(oldfd: RawFd, newfd: RawFd, flags: OFlag) -> Result<RawFd> {
-    if oldfd == newfd {
-        return Err(Error::Sys(Errno::EINVAL));
-    }
-
-    let fd = try!(dup2(oldfd, newfd));
-
-    if flags.contains(OFlag::O_CLOEXEC) {
-        if let Err(e) = fcntl(fd, F_SETFD(FdFlag::FD_CLOEXEC)) {
-            let _ = close(fd);
-            return Err(e);
-        }
-    }
-
-    Ok(fd)
+    Errno::result(res)
 }
 
 /// Change the current working directory of the calling process (see
@@ -633,6 +623,20 @@ pub fn fchownat<P: ?Sized + NixPath>(
     Errno::result(res).map(|_| ())
 }
 
+/// Change the ownership of the file specified by the file descriptor `fd` to be owned by the
+/// specified `owner` (user) and `group` (see
+/// [fchown(2)](http://pubs.opengroup.org/onlinepubs/9699919799/functions/fchown.html)).
+///
+/// The owner/group for the provided path name will not be modified if `None` is
+/// provided for that argument.  Ownership change will be attempted for the path
+/// only if `Some` owner/group is provided.
+pub fn fchown(fd: RawFd, owner: Option<Uid>, group: Option<Gid>) -> Result<()> {
+    let (uid, gid) = chown_raw_ids(owner, group);
+    let res = unsafe { libc::fchown(fd, uid, gid) };
+
+    Errno::result(res).map(drop)
+}
+
 fn to_exec_array(args: &[CString]) -> Vec<*const c_char> {
     let mut args_p: Vec<*const c_char> = args.iter().map(|s| s.as_ptr()).collect();
     args_p.push(ptr::null());