add support for fstatat

Author: Mic92

CHANGELOG.md

@@ -6,7 +6,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 ## [Unreleased]
 
 <!--### Added-->
-- Added `openat` in `::nix::unistd`
+- Added `openat`, `fstatat` in `::nix::unistd`
   ([#497](https://github.com/nix-rust/nix/pull/551))
 
 ### Changed

Cargo.toml

@@ -22,7 +22,7 @@ preadv_pwritev = []
 signalfd = []
 
 [dependencies]
-libc = { git = "https://github.com/rust-lang/libc" }
+libc = { git = "https://github.com/Mic92/libc" }
 bitflags = "0.7"
 cfg-if = "0.1.0"
 void = "1.0.2"

src/sys/stat.rs

@@ -2,6 +2,7 @@ pub use libc::dev_t;
 pub use libc::stat as FileStat;
 
 use {Errno, Result, NixPath};
+use fcntl::AtFlags;
 use libc::{self, mode_t};
 use std::mem;
 use std::os::unix::io::RawFd;
@@ -121,3 +122,15 @@ pub fn fstat(fd: RawFd) -> Result<FileStat> {
 
     Ok(dst)
 }
+
+pub fn fstatat<P: ?Sized + NixPath>(dirfd: RawFd, pathname: &P, f: AtFlags) -> Result<FileStat> {
+    let mut dst = unsafe { mem::uninitialized() };
+    let res = try!(pathname.with_nix_path(|cstr| {
+        unsafe { libc::fstatat(dirfd, cstr.as_ptr(), &mut dst as *mut FileStat, f.bits() as libc::c_int) }
+    }));
+
+    try!(Errno::result(res));
+
+    Ok(dst)
+}
+

test/test_stat.rs

@@ -4,8 +4,8 @@ use std::os::unix::prelude::AsRawFd;
 
 use libc::{S_IFMT, S_IFLNK};
 
-use nix::sys::stat::{stat, fstat, lstat};
-
+use nix::fcntl;
+use nix::sys::stat::{self, stat, fstat, lstat};
 use nix::sys::stat::FileStat;
 use nix::Result;
 use tempdir::TempDir;
@@ -74,6 +74,21 @@ fn test_stat_and_fstat() {
     assert_stat_results(fstat_result);
 }
 
+#[test]
+fn test_fstatat() {
+    let tempdir = TempDir::new("nix-test_stat_and_fstat").unwrap();
+    let filename = tempdir.path().join("foo.txt");
+    File::create(&filename).unwrap();
+    let dirfd = fcntl::open(tempdir.path(),
+                            fcntl::OFlag::empty(),
+                            stat::Mode::empty());
+
+    let result = stat::fstatat(dirfd.unwrap(),
+                               &filename,
+                               fcntl::AtFlags::empty());
+    assert_stat_results(result);
+}
+
 #[test]
 fn test_stat_fstat_lstat() {
     let tempdir = TempDir::new("nix-test_stat_fstat_lstat").unwrap();