Add wrapper for acct(2)

This PR aims to add a nix wrapper for acct(2).

src/unistd.rs

@@ -1439,6 +1439,18 @@ pub fn sleep(seconds: c_uint) -> c_uint {
     unsafe { libc::sleep(seconds) }
 }
 
+/// Switch process accounting on or off
+///
+/// See also [acct(2)](https://linux.die.net/man/2/acct)
+#[cfg(any(target_os = "linux", target_os = "android"))]
+pub fn acct(filename: &CString) -> Result<Void> {
+    unsafe {
+        libc::acct(filename.as_ptr())
+    };
+
+    Err(Error::Sys(Errno::last()))
+}
+
 /// 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 +336,18 @@ fn test_lseek64() {
     close(tmpfd).unwrap();
 }
 
+#[cfg(any(target_os = "linux", target_os = "android"))]
+#[test]
+fn test_acct() {
+    skip_if_not_root!("test_acct");
+    let file = NamedTempFile::new().unwrap();
+    let path = file.path().to_str().unwrap();
+    acct(&CString::new(path).unwrap()).unwrap();
+    Command::new("echo").arg("Hello world");
+    let md = metadata(path).unwrap();
+    assert!(md.len() > 0);
+}
+
 #[test]
 fn test_fpathconf_limited() {
     let f = tempfile().unwrap();