Add acct(2) wrapper API

This patch adds a wrapper for the acct(2) syscall, with two functions
for enabling and disabling process accounting.

CHANGELOG.md

@@ -18,6 +18,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
   ([#930](https://github.com/nix-rust/nix/pull/930))
 - Added `futimens` and `utimesat` wrappers ([#944](https://github.com/nix-rust/nix/pull/944))
   and a `utimes` wrapper ([#946](https://github.com/nix-rust/nix/pull/946)).
+- Added a `acct` wrapper module for enabling and disabling process accounting ([#952](https://github.com/nix-rust/nix/pull/952))
 
 ### Changed
 - Increased required Rust version to 1.22.1/

src/unistd.rs

@@ -1439,6 +1439,31 @@ pub fn sleep(seconds: c_uint) -> c_uint {
     unsafe { libc::sleep(seconds) }
 }
 
+pub mod acct {
+    use libc;
+    use {Result, NixPath};
+    use errno::Errno;
+    use std::ptr;
+
+    /// Enable process accounting
+    ///
+    /// See also [acct(2)](https://linux.die.net/man/2/acct)
+    pub fn enable<P: ?Sized + NixPath>(filename: &P) -> Result<()> {
+        let res = try!(filename.with_nix_path(|cstr| {
+            unsafe { libc::acct(cstr.as_ptr()) }
+        }));
+
+        Errno::result(res).map(drop)
+    }
+
+    /// Disable process accounting
+    pub fn disable() -> Result<()> {
+        let res = unsafe { libc::acct(ptr::null()) };
+
+        Errno::result(res).map(drop)
+    }
+}
+
 /// Creates a regular file which persists even after process termination
 ///
 /// * `template`: a path whose 6 rightmost characters must be X, e.g. `/tmp/tmpfile_XXXXXX`

test/test_unistd.rs

@@ -6,10 +6,11 @@ use nix::sys::wait::*;
 use nix::sys::stat::{self, Mode, SFlag};
 use std::{env, iter};
 use std::ffi::CString;
-use std::fs::File;
+use std::fs::{File, metadata};
 use std::io::Write;
 use std::os::unix::prelude::*;
-use tempfile::{self, tempfile};
+use std::process::Command;
+use tempfile::{self, tempfile, NamedTempFile};
 use libc::{self, _exit, off_t};
 
 #[test]
@@ -335,6 +336,21 @@ fn test_lseek64() {
     close(tmpfd).unwrap();
 }
 
+#[cfg(not(target_os = "freebsd"))]
+#[test]
+fn test_acct() {
+    skip_if_not_root!("test_acct");
+    let file = NamedTempFile::new().unwrap();
+    let path = file.path().to_str().unwrap();
+
+    acct::enable(path).unwrap();
+    Command::new("echo").arg("Hello world");
+    acct::disable().unwrap();
+
+    let md = metadata(path).unwrap();
+    assert!(md.len() > 0);
+}
+
 #[test]
 fn test_fpathconf_limited() {
     let f = tempfile().unwrap();