Support nullable timeout in ppoll

src/poll.rs

@@ -133,13 +133,17 @@ pub fn poll(fds: &mut [PollFd], timeout: libc::c_int) -> Result<libc::c_int> {
 /// with the `sigmask` argument.
 ///
 #[cfg(any(target_os = "android", target_os = "dragonfly", target_os = "freebsd", target_os = "linux"))]
-pub fn ppoll(fds: &mut [PollFd], timeout: TimeSpec, sigmask: SigSet) -> Result<libc::c_int> {
-
+pub fn ppoll(fds: &mut [PollFd], timeout: Option<TimeSpec>, sigmask: SigSet) -> Result<libc::c_int> {
+    let timeout = &timeout;
+    let timeout = match timeout {
+        Some(t) => t.as_ref(),
+        None => core::ptr::null()
+    };
 
     let res = unsafe {
         libc::ppoll(fds.as_mut_ptr() as *mut libc::pollfd,
                     fds.len() as libc::nfds_t,
-                    timeout.as_ref(),
+                    timeout,
                     sigmask.as_ref())
     };
     Errno::result(res)