Future-proof the kevent ABI

FreeBSD 12 adds some new private fields to struct kevent, and it changes
the type of "data" from intptr_t to i64.  For now libc only binds the
11-compat ABI, but that will change some day.  Adjust mio's structure
definitions for compatibility with either ABI.

This should work on all 32 and 64 bit platforms.

src/sys/unix/selector/kqueue.rs

@@ -1,6 +1,6 @@
 use crate::{Interest, Token};
 use log::error;
-use std::mem::MaybeUninit;
+use std::mem::{self, MaybeUninit};
 use std::ops::{Deref, DerefMut};
 use std::os::unix::io::{AsRawFd, RawFd};
 #[cfg(debug_assertions)]
@@ -34,17 +34,6 @@ type Flags = u16;
 #[cfg(target_os = "netbsd")]
 type Flags = u32;
 
-// Type of the `data` field in the `kevent` structure.
-#[cfg(any(
- target_os = "dragonfly",
- target_os = "freebsd",
- target_os = "ios",
- target_os = "macos"
-))]
-type Data = libc::intptr_t;
-#[cfg(any(target_os = "netbsd", target_os = "openbsd"))]
-type Data = i64;
-
 // Type of the `udata` field in the `kevent` structure.
 #[cfg(not(target_os = "netbsd"))]
 type UData = *mut libc::c_void;
@@ -60,6 +49,7 @@ macro_rules! kevent {
  fflags: 0,
  data: 0,
  udata: $data as UData,
+ ..unsafe { mem::zeroed() }
  }
  };
 }
@@ -163,7 +153,7 @@ impl Selector {
  // the array.
  slice::from_raw_parts_mut(changes[0].as_mut_ptr(), n_changes)
  };
- kevent_register(self.kq, changes, &[libc::EPIPE as Data])
+ kevent_register(self.kq, changes, &[libc::EPIPE as i64])
  }
 
  pub fn reregister(&self, fd: RawFd, token: Token, interests: Interest) -> io::Result<()> {
@@ -195,7 +185,7 @@ impl Selector {
  kevent_register(
  self.kq,
  &mut changes,
- &[libc::ENOENT as Data, libc::EPIPE as Data],
+ &[libc::ENOENT as i64, libc::EPIPE as i64],
  )
  }
 
@@ -211,7 +201,7 @@ impl Selector {
  // the ENOENT error when it comes up. The ENOENT error informs us that
  // the filter wasn't there in first place, but we don't really care
  // about that since our goal is to remove it.
- kevent_register(self.kq, &mut changes, &[libc::ENOENT as Data])
+ kevent_register(self.kq, &mut changes, &[libc::ENOENT as i64])
  }
 
  #[cfg(debug_assertions)]
@@ -264,7 +254,7 @@ impl Selector {
 fn kevent_register(
  kq: RawFd,
  changes: &mut [libc::kevent],
- ignored_errors: &[Data],
+ ignored_errors: &[i64],
 ) -> io::Result<()> {
  syscall!(kevent(
  kq,
@@ -289,11 +279,11 @@ fn kevent_register(
 }
 
 /// Check all events for possible errors, it returns the first error found.
-fn check_errors(events: &[libc::kevent], ignored_errors: &[Data]) -> io::Result<()> {
+fn check_errors(events: &[libc::kevent], ignored_errors: &[i64]) -> io::Result<()> {
  for event in events {
  // We can't use references to packed structures (in checking the ignored
  // errors), so we need copy the data out before use.
- let data = event.data;
+ let data = event.data as _;
  // Check for the error flag, the actual error will be in the `data`
  // field.
  if (event.flags & libc::EV_ERROR != 0) && data != 0 && !ignored_errors.contains(&data) {