Add rename, renameat, AT_FDCWD

These syscalls are (somewhat oddly, imho) in stdio.h. I put them in
nix::fcntl because there's no nix::stdio and all their friends
(including the AT_* constants) are in nix::fcntl.

CHANGELOG.md

@@ -15,6 +15,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
   ([#1084](https://github.com/nix-rust/nix/pull/1084))
 - Add `posix_fadvise`.
   ([#1089](https://github.com/nix-rust/nix/pull/1089))
+- Added wrappers for `rename` and `renameat`.
 
 ### Changed
 - Support for `ifaddrs` now present when building for Android.

src/fcntl.rs

@@ -21,6 +21,8 @@ use sys::uio::IoVec;  // For vmsplice
           target_env = "freebsd"))]
 pub use self::posix_fadvise::*;
 
+pub const AT_FDCWD: RawFd = libc::AT_FDCWD as RawFd;
+
 libc_bitflags!{
     pub struct AtFlags: c_int {
         AT_SYMLINK_NOFOLLOW;
@@ -164,6 +166,26 @@ pub fn openat<P: ?Sized + NixPath>(dirfd: RawFd, path: &P, oflag: OFlag, mode: M
     Errno::result(fd)
 }
 
+pub fn rename<P1: ?Sized + NixPath, P2: ?Sized + NixPath>(old: &P1, new: &P2) -> Result<()> {
+    let res = try!(try!(old.with_nix_path(|old_cstr| {
+        new.with_nix_path(|new_cstr| {
+            unsafe { libc::rename(old_cstr.as_ptr(), new_cstr.as_ptr()) }
+        })
+    })));
+    Errno::result(res).map(drop)
+}
+
+pub fn renameat<P1: ?Sized + NixPath, P2: ?Sized + NixPath>(old_dirfd: RawFd, old_path: &P1,
+                                                            new_dirfd: RawFd, new_path: &P2)
+                                                            -> Result<()> {
+    let res = try!(try!(old_path.with_nix_path(|old_cstr| {
+        new_path.with_nix_path(|new_cstr| {
+            unsafe { libc::renameat(old_dirfd, old_cstr.as_ptr(), new_dirfd, new_cstr.as_ptr()) }
+        })
+    })));
+    Errno::result(res).map(drop)
+}
+
 fn wrap_readlink_result(buffer: &mut[u8], res: ssize_t) -> Result<&OsStr> {
     match Errno::result(res) {
         Err(err) => Err(err),

test/test_fcntl.rs

@@ -1,4 +1,6 @@
-use nix::fcntl::{openat, open, OFlag, readlink, readlinkat};
+use nix::Error;
+use nix::errno::*;
+use nix::fcntl::{openat, open, OFlag, readlink, readlinkat, rename, renameat};
 use nix::sys::stat::Mode;
 use nix::unistd::{close, read};
 use tempfile::{self, NamedTempFile};
@@ -27,6 +29,31 @@ fn test_openat() {
     close(dirfd).unwrap();
 }
 
+#[test]
+fn test_rename() {
+    let old_dir = tempfile::tempdir().unwrap();
+    let old_path = old_dir.path().join("old");
+    std::fs::File::create(&old_path).unwrap();
+    let new_dir = tempfile::tempdir().unwrap();
+    let new_path = new_dir.path().join("new");
+    rename(&old_path, &new_path).unwrap();
+    assert_eq!(rename(&old_path, &new_path).unwrap_err(), Error::Sys(Errno::ENOENT));
+}
+
+#[test]
+fn test_renameat() {
+    let old_dir = tempfile::tempdir().unwrap();
+    let old_dirfd = open(old_dir.path(), OFlag::empty(), Mode::empty()).unwrap();
+    std::fs::File::create(&old_dir.path().join("old")).unwrap();
+    let new_dir = tempfile::tempdir().unwrap();
+    let new_dirfd = open(new_dir.path(), OFlag::empty(), Mode::empty()).unwrap();
+    renameat(old_dirfd, "old", new_dirfd, "new").unwrap();
+    assert_eq!(renameat(old_dirfd, "old", new_dirfd, "new").unwrap_err(),
+               Error::Sys(Errno::ENOENT));
+    close(old_dirfd).unwrap();
+    close(new_dirfd).unwrap();
+}
+
 #[test]
 fn test_readlink() {
     let tempdir = tempfile::tempdir().unwrap();