Merge #1780

1780: Implement faccessat r=asomers a=nateavers

This is a re-post of #1134, which seems to have been abandoned. Includes the changes requested in [this comment](#1134 (comment)).

Co-authored-by: Zhang Miaolei <zmlcc@outlook.com>

CHANGELOG.md

@@ -6,6 +6,8 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 ## [Unreleased] - ReleaseDate
 ### Added
 
+- Added `faccessat`
+  ([#1780](https://github.com/nix-rust/nix/pull/1780))
 - Added `memfd` on Android.
   (#[1773](https://github.com/nix-rust/nix/pull/1773))
 - Added ETH_P_ALL to SockProtocol enum

src/unistd.rs

@@ -2900,6 +2900,27 @@ pub fn access<P: ?Sized + NixPath>(path: &P, amode: AccessFlags) -> Result<()> {
     })?;
     Errno::result(res).map(drop)
 }
+
+/// Checks the file named by `path` for accessibility according to the flags given by `mode`
+///
+/// If `dirfd` has a value, then `path` is relative to directory associated with the file descriptor.
+///
+/// If `dirfd` is `None`, then `path` is relative to the current working directory.
+///
+/// # References
+///
+/// [faccessat(2)](http://pubs.opengroup.org/onlinepubs/9699919799/functions/faccessat.html)
+// illumos: faccessat(2) appears to be supported, but the libc crate does not provide a binding.
+// redox: does not appear to support the *at family of syscalls.
+#[cfg(not(any(target_os = "illumos", target_os = "redox")))]
+pub fn faccessat<P: ?Sized + NixPath>(dirfd: Option<RawFd>, path: &P, mode: AccessFlags, flags: AtFlags) -> Result<()> {
+    let res = path.with_nix_path(|cstr| {
+        unsafe {
+            libc::faccessat(at_rawfd(dirfd), cstr.as_ptr(), mode.bits(), flags.bits())
+        }
+    })?;
+    Errno::result(res).map(drop)
+}
 }
 
 feature! {

test/test_unistd.rs

@@ -1308,3 +1308,71 @@ fn test_getpeereid_invalid_fd() {
     // getpeereid is not POSIX, so error codes are inconsistent between different Unices.
     getpeereid(-1).expect_err("assertion failed");
 }
+
+#[test]
+#[cfg(not(any(target_os = "illumos", target_os = "redox")))]
+fn test_faccessat_none_not_existing() {
+    use nix::fcntl::AtFlags;
+    let tempdir = tempfile::tempdir().unwrap();
+    let dir = tempdir.path().join("does_not_exist.txt");
+    assert_eq!(
+        faccessat(None, &dir, AccessFlags::F_OK, AtFlags::empty())
+            .err()
+            .unwrap(),
+        Errno::ENOENT
+    );
+}
+
+#[test]
+#[cfg(not(any(target_os = "illumos", target_os = "redox")))]
+fn test_faccessat_not_existing() {
+    use nix::fcntl::AtFlags;
+    let tempdir = tempfile::tempdir().unwrap();
+    let dirfd = open(tempdir.path(), OFlag::empty(), Mode::empty()).unwrap();
+    let not_exist_file = "does_not_exist.txt";
+    assert_eq!(
+        faccessat(
+            Some(dirfd),
+            not_exist_file,
+            AccessFlags::F_OK,
+            AtFlags::empty()
+        )
+        .err()
+        .unwrap(),
+        Errno::ENOENT
+    );
+}
+
+#[test]
+#[cfg(not(any(target_os = "illumos", target_os = "redox")))]
+fn test_faccessat_none_file_exists() {
+    use nix::fcntl::AtFlags;
+    let tempdir = tempfile::tempdir().unwrap();
+    let path = tempdir.path().join("does_exist.txt");
+    let _file = File::create(path.clone()).unwrap();
+    assert!(faccessat(
+        None,
+        &path,
+        AccessFlags::R_OK | AccessFlags::W_OK,
+        AtFlags::empty()
+    )
+    .is_ok());
+}
+
+#[test]
+#[cfg(not(any(target_os = "illumos", target_os = "redox")))]
+fn test_faccessat_file_exists() {
+    use nix::fcntl::AtFlags;
+    let tempdir = tempfile::tempdir().unwrap();
+    let dirfd = open(tempdir.path(), OFlag::empty(), Mode::empty()).unwrap();
+    let exist_file = "does_exist.txt";
+    let path = tempdir.path().join(exist_file);
+    let _file = File::create(path.clone()).unwrap();
+    assert!(faccessat(
+        Some(dirfd),
+        &path,
+        AccessFlags::R_OK | AccessFlags::W_OK,
+        AtFlags::empty()
+    )
+    .is_ok());
+}