feat: I/O safety for 'sys/signal' (#1936)

* refactor: I/O safety for sys/signal.rs

* chore: changelog entry

changelog/1936.changed.md

@@ -0,0 +1 @@
+Module sys/signal now adopts I/O safety

changelog/1936.removed.md

@@ -0,0 +1 @@
+Type `SigevNotify` is no longer `PartialEq`, `Eq` and `Hash` due to the use of `BorrowedFd`

src/sys/signal.rs

@@ -1,6 +1,3 @@
-// Portions of this file are Copyright 2014 The Rust Project Developers.
-// See https://www.rust-lang.org/policies/licenses.
-
 //! Operating system signals.
 
 use crate::errno::Errno;
@@ -10,8 +7,6 @@ use std::fmt;
 use std::hash::{Hash, Hasher};
 use std::mem;
 use std::ops::BitOr;
-#[cfg(freebsdlike)]
-use std::os::unix::io::RawFd;
 use std::ptr;
 use std::str::FromStr;
 
@@ -1114,8 +1109,8 @@ pub type type_of_thread_id = libc::pid_t;
 // as a pointer, because neither libc nor the kernel ever dereference it.  nix
 // therefore presents it as an intptr_t, which is how kevent uses it.
 #[cfg(not(any(target_os = "fuchsia", target_os = "hurd", target_os = "openbsd", target_os = "redox")))]
-#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
-pub enum SigevNotify {
+#[derive(Clone, Copy, Debug)]
+pub enum SigevNotify<'fd> {
     /// No notification will be delivered
     SigevNone,
     /// Notify by delivering a signal to the process.
@@ -1131,7 +1126,7 @@ pub enum SigevNotify {
     #[cfg(freebsdlike)]
     SigevKevent {
         /// File descriptor of the kqueue to notify.
-        kq: RawFd,
+        kq: std::os::fd::BorrowedFd<'fd>,
         /// Will be contained in the kevent's `udata` field.
         udata: libc::intptr_t
     },
@@ -1140,7 +1135,7 @@ pub enum SigevNotify {
     #[cfg(feature = "event")]
     SigevKeventFlags {
         /// File descriptor of the kqueue to notify.
-        kq: RawFd,
+        kq: std::os::fd::BorrowedFd<'fd>,
         /// Will be contained in the kevent's `udata` field.
         udata: libc::intptr_t,
         /// Flags that will be set on the delivered event.  See `kevent(2)`.
@@ -1161,6 +1156,14 @@ pub enum SigevNotify {
         /// structure of the queued signal.
         si_value: libc::intptr_t
     },
+    /// A helper variant to resolve the unused parameter (`'fd`) problem on
+    /// platforms other than FreeBSD and DragonFlyBSD.
+    ///
+    /// This variant can never be constructed due to the usage of an enum with 0
+    /// variants.
+    #[doc(hidden)]
+    #[cfg(not(freebsdlike))]
+    _Unreachable(&'fd std::convert::Infallible),
 }
 }
 
@@ -1337,15 +1340,19 @@ mod sigevent {
                 },
                 #[cfg(freebsdlike)]
                 SigevNotify::SigevKevent{kq, udata} => {
+                    use std::os::fd::AsRawFd;
+
                     sev.sigev_notify = libc::SIGEV_KEVENT;
-                    sev.sigev_signo = kq;
+                    sev.sigev_signo = kq.as_raw_fd();
                     sev.sigev_value.sival_ptr = udata as *mut libc::c_void;
                 },
                 #[cfg(target_os = "freebsd")]
                 #[cfg(feature = "event")]
                 SigevNotify::SigevKeventFlags{kq, udata, flags} => {
+                    use std::os::fd::AsRawFd;
+
                     sev.sigev_notify = libc::SIGEV_KEVENT;
-                    sev.sigev_signo = kq;
+                    sev.sigev_signo = kq.as_raw_fd();
                     sev.sigev_value.sival_ptr = udata as *mut libc::c_void;
                     sev._sigev_un._kevent_flags = flags.bits();
                 },
@@ -1363,6 +1370,8 @@ mod sigevent {
                     sev.sigev_value.sival_ptr = si_value as *mut libc::c_void;
                     sev.sigev_notify_thread_id = thread_id;
                 }
+                #[cfg(not(freebsdlike))]
+                SigevNotify::_Unreachable(_) => unreachable!("This variant could never be constructed")
             }
             SigEvent{sigevent: sev}
         }