feat: AT_EMPTY_PATH for fchownat on Linux/Android/FreeBSD/Hurd (#2267)

Author: SteveLauC

changelog/2267.added.md

@@ -0,0 +1 @@
+Enable the `AT_EMPTY_PATH` flag for the `fchownat()` function

changelog/2267.removed.md

@@ -0,0 +1 @@
+The `FchownatFlags` type has been deprecated, please use `AtFlags` instead.

src/fcntl.rs

@@ -43,7 +43,7 @@ use crate::{sys::stat::Mode, NixPath, Result};
 pub use self::posix_fadvise::{posix_fadvise, PosixFadviseAdvice};
 
 #[cfg(not(target_os = "redox"))]
-#[cfg(any(feature = "fs", feature = "process"))]
+#[cfg(any(feature = "fs", feature = "process", feature = "user"))]
 libc_bitflags! {
     #[cfg_attr(docsrs, doc(cfg(any(feature = "fs", feature = "process"))))]
     pub struct AtFlags: c_int {

src/unistd.rs

@@ -737,11 +737,17 @@ pub fn fchown(fd: RawFd, owner: Option<Uid>, group: Option<Gid>) -> Result<()> {
     Errno::result(res).map(drop)
 }
 
-/// Flags for `fchownat` function.
-#[derive(Clone, Copy, Debug)]
-pub enum FchownatFlags {
-    FollowSymlink,
-    NoFollowSymlink,
+// Just a wrapper around `AtFlags` so that we can help our users migrate.
+#[cfg(not(target_os = "redox"))]
+pub type FchownatFlags = AtFlags;
+#[cfg(not(target_os = "redox"))]
+impl FchownatFlags {
+    #[deprecated(since = "0.28.0", note = "The variant is deprecated, please use `AtFlags` instead")]
+    #[allow(non_upper_case_globals)]
+    pub const FollowSymlink: FchownatFlags = FchownatFlags::empty();
+    #[deprecated(since = "0.28.0", note = "The variant is deprecated, please use `AtFlags` instead")]
+    #[allow(non_upper_case_globals)]
+    pub const NoFollowSymlink: FchownatFlags = FchownatFlags::AT_SYMLINK_NOFOLLOW;
 }
 
 /// Change the ownership of the file at `path` to be owned by the specified
@@ -755,10 +761,10 @@ pub enum FchownatFlags {
 /// with the file descriptor `dirfd` or the current working directory
 /// if `dirfd` is `None`.
 ///
-/// If `flag` is `FchownatFlags::NoFollowSymlink` and `path` names a symbolic link,
+/// If `flag` is `AtFlags::AT_SYMLINK_NOFOLLOW` and `path` names a symbolic link,
 /// then the mode of the symbolic link is changed.
 ///
-/// `fchownat(None, path, owner, group, FchownatFlags::NoFollowSymlink)` is identical to
+/// `fchownat(None, path, owner, group, AtFlags::AT_SYMLINK_NOFOLLOW)` is identical to
 /// a call `libc::lchown(path, owner, group)`.  That's why `lchown` is unimplemented in
 /// the `nix` crate.
 ///
@@ -771,20 +777,16 @@ pub fn fchownat<P: ?Sized + NixPath>(
     path: &P,
     owner: Option<Uid>,
     group: Option<Gid>,
-    flag: FchownatFlags,
+    flag: AtFlags,
 ) -> Result<()> {
-    let atflag = match flag {
-        FchownatFlags::FollowSymlink => AtFlags::empty(),
-        FchownatFlags::NoFollowSymlink => AtFlags::AT_SYMLINK_NOFOLLOW,
-    };
     let res = path.with_nix_path(|cstr| unsafe {
         let (uid, gid) = chown_raw_ids(owner, group);
         libc::fchownat(
             at_rawfd(dirfd),
             cstr.as_ptr(),
             uid,
             gid,
-            atflag.bits() as libc::c_int,
+            flag.bits()
         )
     })?;
 

test/test_unistd.rs

@@ -551,6 +551,8 @@ fn test_fchown() {
 #[test]
 #[cfg(not(target_os = "redox"))]
 fn test_fchownat() {
+    use nix::fcntl::AtFlags;
+
     let _dr = crate::DirRestore::new();
     // Testing for anything other than our own UID/GID is hard.
     let uid = Some(getuid());
@@ -564,14 +566,13 @@ fn test_fchownat() {
 
     let dirfd = open(tempdir.path(), OFlag::empty(), Mode::empty()).unwrap();
 
-    fchownat(Some(dirfd), "file", uid, gid, FchownatFlags::FollowSymlink)
-        .unwrap();
+    fchownat(Some(dirfd), "file", uid, gid, AtFlags::empty()).unwrap();
 
     chdir(tempdir.path()).unwrap();
-    fchownat(None, "file", uid, gid, FchownatFlags::FollowSymlink).unwrap();
+    fchownat(None, "file", uid, gid, AtFlags::empty()).unwrap();
 
     fs::remove_file(&path).unwrap();
-    fchownat(None, "file", uid, gid, FchownatFlags::FollowSymlink).unwrap_err();
+    fchownat(None, "file", uid, gid, AtFlags::empty()).unwrap_err();
 }
 
 #[test]