Use the real pipe2(2) on all BSD targets.

All supported non-Apple platforms now use the native syscall.  Only ios
and macos lack it.  Deprecate pipe2 on those platforms, because it's
impossible to guarantee atomicity with a userland implementation.  It
was added in:
* DragonflyBSD 4.2
* FreeBSD 10.0
* NetBSD 6.0
* OpenBSD 5.7

CHANGELOG.md

@@ -47,6 +47,8 @@ This project adheres to [Semantic Versioning](http://semver.org/).
   ([#800](https://github.com/nix-rust/nix/pull/800))
 
 ### Changed
+- Use native `pipe` on all BSD targets.  Users should notice no difference.
+  ([#777](https://github.com/nix-rust/nix/pull/777))
 - Renamed existing `ptrace` wrappers to encourage namespacing ([#692](https://github.com/nix-rust/nix/pull/692))
 - Marked `sys::ptrace::ptrace` as `unsafe`.
 - Changed function signature of `socket()` and `socketpair()`. The `protocol` argument

src/unistd.rs

@@ -876,10 +876,22 @@ pub fn pipe() -> Result<(RawFd, RawFd)> {
     }
 }
 
-// libc only defines `pipe2` in `libc::notbsd`.
-#[cfg(any(target_os = "linux",
-          target_os = "android",
-          target_os = "emscripten"))]
+/// Like `pipe`, but allows setting certain file descriptor flags.
+///
+/// The following flags are supported, and will be set atomically as the pipe is
+/// created:
+///
+/// `O_CLOEXEC`:    Set the close-on-exec flag for the new file descriptors.
+/// `O_NONBLOCK`:   Set the non-blocking flag for the ends of the pipe.
+///
+/// See also [pipe(2)](http://man7.org/linux/man-pages/man2/pipe.2.html)
+#[cfg(any(target_os = "android",
+          target_os = "dragonfly",
+          target_os = "emscripten",
+          target_os = "freebsd",
+          target_os = "linux",
+          target_os = "netbsd",
+          target_os = "openbsd"))]
 pub fn pipe2(flags: OFlag) -> Result<(RawFd, RawFd)> {
     let mut fds: [c_int; 2] = unsafe { mem::uninitialized() };
 
@@ -890,9 +902,19 @@ pub fn pipe2(flags: OFlag) -> Result<(RawFd, RawFd)> {
     Ok((fds[0], fds[1]))
 }
 
-#[cfg(not(any(target_os = "linux",
-              target_os = "android",
-              target_os = "emscripten")))]
+/// Like `pipe`, but allows setting certain file descriptor flags.
+///
+/// The following flags are supported, and will be set after the pipe is
+/// created:
+///
+/// `O_CLOEXEC`:    Set the close-on-exec flag for the new file descriptors.
+/// `O_NONBLOCK`:   Set the non-blocking flag for the ends of the pipe.
+#[cfg(any(target_os = "ios",
+          target_os = "macos"))]
+#[deprecated(
+    since="0.10.0",
+    note="pipe2(2) is not actually atomic on these platforms.  Use pipe(2) and fcntl(2) instead"
+)]
 pub fn pipe2(flags: OFlag) -> Result<(RawFd, RawFd)> {
     let mut fds: [c_int; 2] = unsafe { mem::uninitialized() };
 
@@ -905,9 +927,8 @@ pub fn pipe2(flags: OFlag) -> Result<(RawFd, RawFd)> {
     Ok((fds[0], fds[1]))
 }
 
-#[cfg(not(any(target_os = "linux",
-              target_os = "android",
-              target_os = "emscripten")))]
+#[cfg(any(target_os = "ios",
+          target_os = "macos"))]
 fn pipe2_setflags(fd1: RawFd, fd2: RawFd, flags: OFlag) -> Result<()> {
     use fcntl::O_NONBLOCK;
     use fcntl::FcntlArg::F_SETFL;

test/test_unistd.rs

@@ -379,3 +379,26 @@ fn test_sysconf_unsupported() {
     let open_max = sysconf(SysconfVar::_XOPEN_CRYPT);
     assert!(open_max.expect("sysconf failed").is_none())
 }
+
+// Test that we can create a pair of pipes.  No need to verify that they pass
+// data; that's the domain of the OS, not nix.
+#[test]
+fn test_pipe() {
+    let (fd0, fd1) = pipe().unwrap();
+    let m0 = stat::SFlag::from_bits_truncate(stat::fstat(fd0).unwrap().st_mode);
+    // S_IFIFO means it's a pipe
+    assert_eq!(m0, stat::S_IFIFO);
+    let m1 = stat::SFlag::from_bits_truncate(stat::fstat(fd1).unwrap().st_mode);
+    assert_eq!(m1, stat::S_IFIFO);
+}
+
+// pipe2(2) is the same as pipe(2), except it allows setting some flags.  Check
+// that we can set a flag.
+#[test]
+fn test_pipe2() {
+    let (fd0, fd1) = pipe2(fcntl::O_CLOEXEC).unwrap();
+    let f0 = fcntl::FdFlag::from_bits_truncate(fcntl::fcntl(fd0, fcntl::F_GETFD).unwrap());
+    assert!(f0.contains(fcntl::FD_CLOEXEC));
+    let f1 = fcntl::FdFlag::from_bits_truncate(fcntl::fcntl(fd1, fcntl::F_GETFD).unwrap());
+    assert!(f1.contains(fcntl::FD_CLOEXEC));
+}