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

@@ -28,6 +28,8 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 - Added support for `ptrace` on BSD operating systems ([#949](https://github.com/nix-rust/nix/pull/949))
 - Added `ptrace` functions for reads and writes to tracee memory and ptrace kill 
   ([#949](https://github.com/nix-rust/nix/pull/949))
+- 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

@@ -1508,6 +1508,31 @@ 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

@@ -4,12 +4,13 @@ use nix::unistd::ForkResult::*;
 use nix::sys::signal::{SaFlags, SigAction, SigHandler, SigSet, Signal, sigaction};
 use nix::sys::wait::*;
 use nix::sys::stat::{self, Mode, SFlag};
-use std::{env, iter};
+use std::{env, iter, thread, time};
 use std::ffi::CString;
-use std::fs::{self, File};
+use std::fs::{self, 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]
@@ -378,6 +379,26 @@ fn test_lseek64() {
     close(tmpfd).unwrap();
 }
 
+// Skip on FreeBSD because FreeBSD's CI environment is jailed, and jails
+// aren't allowed to use acct(2)
+#[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();
+
+    loop {
+        let len = metadata(path).unwrap().len();
+        if len > 0 { break; }
+        thread::sleep(time::Duration::from_millis(10));
+    }
+}
+
 #[test]
 fn test_fpathconf_limited() {
     let f = tempfile().unwrap();