select: add pselect syscall

This is a straight port of @abbradar's work in #276, with
two (somewhat weak) tests and a bit of documentation.

src/sys/select.rs

@@ -1,10 +1,11 @@
 use std::mem;
 use std::os::unix::io::RawFd;
-use std::ptr::null_mut;
+use std::ptr::{null, null_mut};
 use libc::{self, c_int};
 use Result;
 use errno::Errno;
-use sys::time::TimeVal;
+use sys::signal::SigSet;
+use sys::time::{TimeSpec, TimeVal};
 
 pub use libc::FD_SETSIZE;
 
@@ -131,6 +132,78 @@ where
     Errno::result(res)
 }
 
+/// Monitors file descriptors for readiness with an altered signal mask.
+///
+/// Returns the total number of ready file descriptors in all sets. The sets are changed so that all
+/// file descriptors that are ready for the given operation are set.
+///
+/// When this function returns, the original signal mask is restored.
+///
+/// Unlike [`select`](#fn.select), `pselect` does not mutate the `timeout` value.
+///
+/// # Parameters
+///
+/// * `nfds`: The highest file descriptor set in any of the passed `FdSet`s, plus 1. If `None`, this
+///   is calculated automatically by calling [`FdSet::highest`] on all descriptor sets and adding 1
+///   to the maximum of that.
+/// * `readfds`: File descriptors to check for being ready to read.
+/// * `writefds`: File descriptors to check for being ready to write.
+/// * `errorfds`: File descriptors to check for pending error conditions.
+/// * `timeout`: Maximum time to wait for descriptors to become ready (`None` to block
+///   indefinitely).
+/// * `sigmask`: Signal mask to activate while waiting for file descriptors to turn
+///    ready (`None` to set no alternative signal mask).
+///
+/// # References
+///
+/// [pselect(2)](http://pubs.opengroup.org/onlinepubs/9699919799/functions/pselect.html)
+///
+/// [The new pselect() system call](https://lwn.net/Articles/176911/)
+///
+/// [`FdSet::highest`]: struct.FdSet.html#method.highest
+pub fn pselect<'a, N, R, W, E, T, S>(nfds: N,
+                                     readfds: R,
+                                     writefds: W,
+                                     errorfds: E,
+                                     timeout: T,
+                                     sigmask: S) -> Result<c_int>
+where
+    N: Into<Option<c_int>>,
+    R: Into<Option<&'a mut FdSet>>,
+    W: Into<Option<&'a mut FdSet>>,
+    E: Into<Option<&'a mut FdSet>>,
+    T: Into<Option<&'a TimeSpec>>,
+    S: Into<Option<&'a SigSet>>,
+{
+    let mut readfds = readfds.into();
+    let mut writefds = writefds.into();
+    let mut errorfds = errorfds.into();
+    let sigmask = sigmask.into();
+    let timeout = timeout.into();
+
+    let nfds = nfds.into().unwrap_or_else(|| {
+        readfds.iter_mut()
+            .chain(writefds.iter_mut())
+            .chain(errorfds.iter_mut())
+            .map(|set| set.highest().unwrap_or(-1))
+            .max()
+            .unwrap_or(-1) + 1
+    });
+
+    let readfds = readfds.map(|set| set as *mut _ as *mut libc::fd_set).unwrap_or(null_mut());
+    let writefds = writefds.map(|set| set as *mut _ as *mut libc::fd_set).unwrap_or(null_mut());
+    let errorfds = errorfds.map(|set| set as *mut _ as *mut libc::fd_set).unwrap_or(null_mut());
+    let timeout = timeout.map(|ts| ts.as_ref() as *const libc::timespec).unwrap_or(null());
+    let sigmask = sigmask.map(|sm| sm.as_ref() as *const libc::sigset_t).unwrap_or(null());
+
+    let res = unsafe {
+        libc::pselect(nfds, readfds, writefds, errorfds, timeout, sigmask)
+    };
+
+    Errno::result(res)
+}
+
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -227,6 +300,29 @@ mod tests {
         assert!(!fd_set.contains(r2));
     }
 
+    #[test]
+    #[cfg_attr(any(target_arch = "powerpc", target_arch = "mips"), ignore)]
+    fn test_pselect() {
+        let (r1, w1) = pipe().unwrap();
+        write(w1, b"hi!").unwrap();
+        let (r2, _w2) = pipe().unwrap();
+
+        let mut fd_set = FdSet::new();
+        fd_set.insert(r1);
+        fd_set.insert(r2);
+
+        let timeout = TimeSpec::seconds(10);
+        let sigmask = SigSet::empty();
+        assert_eq!(1, pselect(None,
+                              &mut fd_set,
+                              None,
+                              None,
+                              &timeout,
+                              &sigmask).unwrap());
+        assert!(fd_set.contains(r1));
+        assert!(!fd_set.contains(r2));
+    }
+
     #[test]
     #[cfg_attr(any(target_arch = "powerpc", target_arch = "mips"), ignore)]
     fn test_select_nfds() {
@@ -268,4 +364,26 @@ mod tests {
         assert!(fd_set.contains(r1));
         assert!(!fd_set.contains(r2));
     }
+
+    #[test]
+    #[cfg_attr(any(target_arch = "powerpc", target_arch = "mips"), ignore)]
+    fn test_pselect_nfds2() {
+        let (r1, w1) = pipe().unwrap();
+        write(w1, b"hi!").unwrap();
+        let (r2, _w2) = pipe().unwrap();
+
+        let mut fd_set = FdSet::new();
+        fd_set.insert(r1);
+        fd_set.insert(r2);
+
+        let timeout = TimeSpec::seconds(10);
+        assert_eq!(1, pselect(::std::cmp::max(r1, r2) + 1,
+                              &mut fd_set,
+                              None,
+                              None,
+                              &timeout,
+                              None).unwrap());
+        assert!(fd_set.contains(r1));
+        assert!(!fd_set.contains(r2));
+    }
 }