unistd: allow linkat to take multiple path types (#2582)

Other places in the crate take independent types in use cases like this,
so bring `linkat` into line with them.

Signed-off-by: Hank Donnay <hdonnay@gmail.com>

Author: hdonnay

changelog/2582.changed.md

@@ -0,0 +1 @@
+linkat: allow distinct types for path arguments

src/unistd.rs

@@ -1577,11 +1577,11 @@ impl LinkatFlags {
 /// # References
 /// See also [linkat(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/linkat.html)
 #[cfg(not(target_os = "redox"))] // Redox does not have this yet
-pub fn linkat<Fd1: std::os::fd::AsFd, Fd2: std::os::fd::AsFd, P: ?Sized + NixPath>(
+pub fn linkat<Fd1: std::os::fd::AsFd, Fd2: std::os::fd::AsFd, P1: ?Sized + NixPath, P2: ?Sized + NixPath>(
     olddirfd: Fd1,
-    oldpath: &P,
+    oldpath: &P1,
     newdirfd: Fd2,
-    newpath: &P,
+    newpath: &P2,
     flag: AtFlags,
 ) -> Result<()> {
     use std::os::fd::AsRawFd;

test/test_unistd.rs

@@ -927,6 +927,40 @@ fn test_linkat_file() {
     assert!(newfilepath.exists());
 }
 
+#[test]
+#[cfg(not(any(target_os = "redox", target_os = "haiku")))]
+/// This test is the same as [test_linkat_file], but ensures that two different types can be used
+/// as the path arguments.
+fn test_linkat_pathtypes() {
+    use nix::fcntl::AtFlags;
+
+    let tempdir = tempdir().unwrap();
+    let oldfilename = "foo.txt";
+    let oldfilepath = tempdir.path().join(oldfilename);
+
+    let newfilename = "bar.txt";
+    let newfilepath = tempdir.path().join(newfilename);
+
+    // Create file
+    File::create(oldfilepath).unwrap();
+
+    // Get file descriptor for base directory
+    let dirfd =
+        fcntl::open(tempdir.path(), fcntl::OFlag::empty(), stat::Mode::empty())
+            .unwrap();
+
+    // Attempt hard link file at relative path
+    linkat(
+        &dirfd,
+        PathBuf::from(oldfilename).as_path(),
+        &dirfd,
+        newfilename,
+        AtFlags::AT_SYMLINK_FOLLOW,
+    )
+    .unwrap();
+    assert!(newfilepath.exists());
+}
+
 #[test]
 #[cfg(not(any(target_os = "redox", target_os = "haiku")))]
 fn test_linkat_olddirfd_none() {