Added support for renameat2 on linux

CHANGELOG.md

@@ -12,6 +12,8 @@ This project adheres to [Semantic Versioning](https://semver.org/).
   (#[1456](https://github.com/nix-rust/nix/pull/1456))
 - Added `TcpUserTimeout` socket option (sockopt) on Linux and Fuchsia.
   (#[1457](https://github.com/nix-rust/nix/pull/1457))
+- Added `renameat2` for Linux
+  (#[1458](https://github.com/nix-rust/nix/pull/1458))
 
 ### Changed
 - `ptsname_r` now returns a lossily-converted string in the event of bad UTF,

src/fcntl.rs

@@ -210,6 +210,43 @@ pub fn renameat<P1: ?Sized + NixPath, P2: ?Sized + NixPath>(
     Errno::result(res).map(drop)
 }
 
+#[cfg(all(
+    target_os = "linux",
+    target_env = "gnu",
+))]
+libc_bitflags! {
+    pub struct RenameFlags: u32 {
+        RENAME_EXCHANGE;
+        RENAME_NOREPLACE;
+        RENAME_WHITEOUT;
+    }
+}
+
+#[cfg(all(
+    target_os = "linux",
+    target_env = "gnu",
+))]
+pub fn renameat2<P1: ?Sized + NixPath, P2: ?Sized + NixPath>(
+    old_dirfd: Option<RawFd>,
+    old_path: &P1,
+    new_dirfd: Option<RawFd>,
+    new_path: &P2,
+    flags: RenameFlags,
+) -> Result<()> {
+    let res = old_path.with_nix_path(|old_cstr| {
+        new_path.with_nix_path(|new_cstr| unsafe {
+            libc::renameat2(
+                at_rawfd(old_dirfd),
+                old_cstr.as_ptr(),
+                at_rawfd(new_dirfd),
+                new_cstr.as_ptr(),
+                flags.bits(),
+            )
+        })
+    })??;
+    Errno::result(res).map(drop)
+}
+
 fn wrap_readlink_result(mut v: Vec<u8>, len: ssize_t) -> Result<OsString> {
     unsafe { v.set_len(len as usize) }
     v.shrink_to_fit();

test/test_fcntl.rs

@@ -4,6 +4,17 @@ use nix::errno::*;
 use nix::fcntl::{open, OFlag, readlink};
 #[cfg(not(target_os = "redox"))]
 use nix::fcntl::{openat, readlinkat, renameat};
+#[cfg(all(
+    target_os = "linux",
+    target_env = "gnu",
+    any(
+        target_arch = "x86_64",
+        target_arch = "x32",
+        target_arch = "powerpc",
+        target_arch = "s390x"
+    )
+))]
+use nix::fcntl::{RenameFlags, renameat2};
 #[cfg(not(target_os = "redox"))]
 use nix::sys::stat::Mode;
 #[cfg(not(target_os = "redox"))]
@@ -59,6 +70,132 @@ fn test_renameat() {
     assert!(new_dir.path().join("new").exists());
 }
 
+#[test]
+#[cfg(all(
+    target_os = "linux",
+    target_env = "gnu",
+    any(
+        target_arch = "x86_64",
+        target_arch = "x32",
+        target_arch = "powerpc",
+        target_arch = "s390x"
+    )
+))]
+fn test_renameat2_behaves_like_renameat_with_no_flags() {
+    let old_dir = tempfile::tempdir().unwrap();
+    let old_dirfd = open(old_dir.path(), OFlag::empty(), Mode::empty()).unwrap();
+    let old_path = old_dir.path().join("old");
+    File::create(&old_path).unwrap();
+    let new_dir = tempfile::tempdir().unwrap();
+    let new_dirfd = open(new_dir.path(), OFlag::empty(), Mode::empty()).unwrap();
+    renameat2(
+        Some(old_dirfd),
+        "old",
+        Some(new_dirfd),
+        "new",
+        RenameFlags::empty(),
+    )
+    .unwrap();
+    assert_eq!(
+        renameat2(
+            Some(old_dirfd),
+            "old",
+            Some(new_dirfd),
+            "new",
+            RenameFlags::empty()
+        )
+        .unwrap_err(),
+        Errno::ENOENT
+    );
+    close(old_dirfd).unwrap();
+    close(new_dirfd).unwrap();
+    assert!(new_dir.path().join("new").exists());
+}
+
+#[test]
+#[cfg(all(
+    target_os = "linux",
+    target_env = "gnu",
+    any(
+        target_arch = "x86_64",
+        target_arch = "x32",
+        target_arch = "powerpc",
+        target_arch = "s390x"
+    )
+))]
+fn test_renameat2_exchange() {
+    let old_dir = tempfile::tempdir().unwrap();
+    let old_dirfd = open(old_dir.path(), OFlag::empty(), Mode::empty()).unwrap();
+    let old_path = old_dir.path().join("old");
+    {
+        let mut old_f = File::create(&old_path).unwrap();
+        old_f.write(b"old").unwrap();
+    }
+    let new_dir = tempfile::tempdir().unwrap();
+    let new_dirfd = open(new_dir.path(), OFlag::empty(), Mode::empty()).unwrap();
+    let new_path = new_dir.path().join("new");
+    {
+        let mut new_f = File::create(&new_path).unwrap();
+        new_f.write(b"new").unwrap();
+    }
+    renameat2(
+        Some(old_dirfd),
+        "old",
+        Some(new_dirfd),
+        "new",
+        RenameFlags::RENAME_EXCHANGE,
+    )
+    .unwrap();
+    let mut buf = String::new();
+    let mut new_f = File::open(&new_path).unwrap();
+    new_f.read_to_string(&mut buf).unwrap();
+    assert_eq!(buf, "old");
+    buf = "".to_string();
+    let mut old_f = File::open(&old_path).unwrap();
+    old_f.read_to_string(&mut buf).unwrap();
+    assert_eq!(buf, "new");
+    close(old_dirfd).unwrap();
+    close(new_dirfd).unwrap();
+}
+
+#[test]
+#[cfg(all(
+    target_os = "linux",
+    target_env = "gnu",
+    any(
+        target_arch = "x86_64",
+        target_arch = "x32",
+        target_arch = "powerpc",
+        target_arch = "s390x"
+    )
+))]
+fn test_renameat2_noreplace() {
+    let old_dir = tempfile::tempdir().unwrap();
+    let old_dirfd = open(old_dir.path(), OFlag::empty(), Mode::empty()).unwrap();
+    let old_path = old_dir.path().join("old");
+    File::create(&old_path).unwrap();
+    let new_dir = tempfile::tempdir().unwrap();
+    let new_dirfd = open(new_dir.path(), OFlag::empty(), Mode::empty()).unwrap();
+    let new_path = new_dir.path().join("new");
+    File::create(&new_path).unwrap();
+    assert_eq!(
+        renameat2(
+            Some(old_dirfd),
+            "old",
+            Some(new_dirfd),
+            "new",
+            RenameFlags::RENAME_NOREPLACE
+        )
+        .unwrap_err(),
+        Errno::EEXIST
+    );
+    close(old_dirfd).unwrap();
+    close(new_dirfd).unwrap();
+    assert!(new_dir.path().join("new").exists());
+    assert!(old_dir.path().join("old").exists());
+}
+
+
 #[test]
 #[cfg(not(target_os = "redox"))]
 fn test_readlink() {