Add a wrapper for lutimes(2)

PR #944 added wrappers for the more-modern futimens(2) and utimesat(2),
but unfortunately these APIs are not available on old-ish systems.

In particular, macOS Sierra and below don't implement them, making the
new APIs unusable.  Whether we should care about such "old" systems is
debatable, but the problem is that, at the moment, this is the only
macOS version usable on Travis to test kexts and, thus, to test FUSE
file systems.

This should have been part of PR #946, which added a wrapper for
utimes(2) following this same rationale, but missed lutimes(2) because
I simply didn't notice it existed.

CHANGELOG.md

@@ -18,7 +18,8 @@ This project adheres to [Semantic Versioning](http://semver.org/).
   ([#916](https://github.com/nix-rust/nix/pull/916))
 - Added `kmod` module that allows loading and unloading kernel modules on Linux.
   ([#930](https://github.com/nix-rust/nix/pull/930))
-- Added `futimens` and `utimesat` wrappers ([#944](https://github.com/nix-rust/nix/pull/944))
+- Added `futimens` and `utimesat` wrappers ([#944](https://github.com/nix-rust/nix/pull/944)),
+  an `lutimes` wrapper ([#967](https://github.com/nix-rust/nix/pull/967)),
   and a `utimes` wrapper ([#946](https://github.com/nix-rust/nix/pull/946)).
 - Added `AF_UNSPEC` wrapper to `AddressFamily` ([#948](https://github.com/nix-rust/nix/pull/948))
 - Added the `mode_t` public alias within `sys::stat`.

src/sys/stat.rs

@@ -199,6 +199,25 @@ pub fn utimes<P: ?Sized + NixPath>(path: &P, atime: &TimeVal, mtime: &TimeVal) -
     Errno::result(res).map(|_| ())
 }
 
+/// Change the access and modification times of a file without following symlinks.
+///
+/// `lutimes(path, times)` is identical to
+/// `utimensat(None, path, times, UtimensatFlags::NoFollowSymlink)`. The former
+/// is a deprecated API so prefer using the latter if the platforms you care
+/// about support it.
+///
+/// # References
+///
+/// [lutimes(2)](http://pubs.opengroup.org/onlinepubs/9699919799/functions/lutimes.html).
+pub fn lutimes<P: ?Sized + NixPath>(path: &P, atime: &TimeVal, mtime: &TimeVal) -> Result<()> {
+    let times: [libc::timeval; 2] = [*atime.as_ref(), *mtime.as_ref()];
+    let res = path.with_nix_path(|cstr| unsafe {
+        libc::lutimes(cstr.as_ptr(), &times[0])
+    })?;
+
+    Errno::result(res).map(|_| ())
+}
+
 /// Change the access and modification times of the file specified by a file descriptor.
 ///
 /// # References

test/test_stat.rs

@@ -6,7 +6,7 @@ use std::time::{Duration, UNIX_EPOCH};
 use libc::{S_IFMT, S_IFLNK};
 
 use nix::fcntl;
-use nix::sys::stat::{self, fchmod, fchmodat, fstat, futimens, lstat, stat, utimes, utimensat};
+use nix::sys::stat::{self, fchmod, fchmodat, fstat, futimens, lstat, lutimes, stat, utimes, utimensat};
 use nix::sys::stat::{FileStat, Mode, FchmodatFlags, UtimensatFlags};
 use nix::sys::time::{TimeSpec, TimeVal, TimeValLike};
 use nix::unistd::chdir;
@@ -178,6 +178,25 @@ fn test_utimes() {
     assert_times_eq(9990, 5550, &fs::metadata(&fullpath).unwrap());
 }
 
+#[test]
+fn test_lutimes() {
+    let tempdir = tempfile::tempdir().unwrap();
+    let target = tempdir.path().join("target");
+    let fullpath = tempdir.path().join("symlink");
+    drop(File::create(&target).unwrap());
+    symlink(&target, &fullpath).unwrap();
+
+    let exp_target_metadata = fs::symlink_metadata(&target).unwrap();
+    lutimes(&fullpath, &TimeVal::seconds(4560), &TimeVal::seconds(1230)).unwrap();
+    assert_times_eq(4560, 1230, &fs::symlink_metadata(&fullpath).unwrap());
+
+    let target_metadata = fs::symlink_metadata(&target).unwrap();
+    assert_eq!(exp_target_metadata.accessed().unwrap(), target_metadata.accessed().unwrap(),
+               "atime of symlink target was unexpectedly modified");
+    assert_eq!(exp_target_metadata.modified().unwrap(), target_metadata.modified().unwrap(),
+               "mtime of symlink target was unexpectedly modified");
+}
+
 #[test]
 fn test_futimens() {
     let tempdir = tempfile::tempdir().unwrap();