Add missing kqueue event filters on FreeBSD

CHANGELOG.md

@@ -13,6 +13,8 @@ This project adheres to [Semantic Versioning](http://semver.org/).
   ([#853](https://github.com/nix-rust/nix/pull/853))
 - Added `statvfs` module to all MacOS and Linux architectures.
   ([#832](https://github.com/nix-rust/nix/pull/832))
+- Added `EVFILT_EMPTY`, `EVFILT_PROCDESC` and `EVFILT_SENDFILE` on FreeBSD.
+  ([#825](https://github.com/nix-rust/nix/pull/825))
 
 ### Changed
 - Display and Debug for SysControlAddr now includes all fields.

src/sys/event.rs

@@ -40,6 +40,9 @@ libc_enum! {
     #[cfg_attr(not(target_os = "netbsd"), repr(i16))]
     pub enum EventFilter {
         EVFILT_AIO,
+        /// Returns whenever there is no remaining data in the write buffer
+        #[cfg(target_os = "freebsd")]
+        EVFILT_EMPTY,
         #[cfg(target_os = "dragonfly")]
         EVFILT_EXCEPT,
         #[cfg(any(target_os = "dragonfly",
@@ -52,7 +55,16 @@ libc_enum! {
         #[cfg(any(target_os = "ios", target_os = "macos"))]
         EVFILT_MACHPORT,
         EVFILT_PROC,
+        /// Returns events associated with the process referenced by a given
+        /// process descriptor, created by `pdfork()`. The events to monitor are:
+        ///
+        /// - NOTE_EXIT: the process has exited. The exit status will be stored in data.
+        #[cfg(target_os = "freebsd")]
+        EVFILT_PROCDESC,
         EVFILT_READ,
+        /// Returns whenever an asynchronous `sendfile()` call completes.
+        #[cfg(target_os = "freebsd")]
+        EVFILT_SENDFILE,
         EVFILT_SIGNAL,
         EVFILT_TIMER,
         #[cfg(any(target_os = "dragonfly",