signalfd optional file descriptor

CHANGELOG.md

@@ -6,6 +6,8 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 ## [Unreleased] - ReleaseDate
 ### Added
 
+- The `fd` argument to `sys::signalfd::signalfd` is now of type `Option<BorrowedFd>`.
+  ([#1874](https://github.com/nix-rust/nix/pull/1874))
 - Add `MntFlags` and `unmount` on all of the BSDs.
   ([#1849](https://github.com/nix-rust/nix/pull/1849))
 - Added a 'Statfs::flags' method.

src/sys/signalfd.rs

@@ -22,7 +22,8 @@ use crate::Result;
 pub use libc::signalfd_siginfo as siginfo;
 
 use std::mem;
-use std::os::unix::io::{AsRawFd, RawFd};
+use std::os::unix::io::{AsRawFd, RawFd, BorrowedFd, FromRawFd, OwnedFd, AsFd};
+use std::mem::ManuallyDrop;
 
 libc_bitflags! {
     pub struct SfdFlags: libc::c_int {
@@ -31,7 +32,6 @@ libc_bitflags! {
     }
 }
 
-pub const SIGNALFD_NEW: RawFd = -1;
 #[deprecated(since = "0.23.0", note = "use mem::size_of::<siginfo>() instead")]
 pub const SIGNALFD_SIGINFO_SIZE: usize = mem::size_of::<siginfo>();
 
@@ -46,13 +46,14 @@ pub const SIGNALFD_SIGINFO_SIZE: usize = mem::size_of::<siginfo>();
 /// signalfd (the default handler will be invoked instead).
 ///
 /// See [the signalfd man page for more information](https://man7.org/linux/man-pages/man2/signalfd.2.html)
-pub fn signalfd(fd: RawFd, mask: &SigSet, flags: SfdFlags) -> Result<RawFd> {
+pub fn signalfd(fd: Option<BorrowedFd>, mask: &SigSet, flags: SfdFlags) -> Result<OwnedFd> {
+    let raw_fd = fd.as_ref().map_or(-1,AsRawFd::as_raw_fd);
     unsafe {
         Errno::result(libc::signalfd(
-            fd as libc::c_int,
+            raw_fd,
             mask.as_ref(),
             flags.bits(),
-        ))
+        )).map(|raw_fd|FromRawFd::from_raw_fd(raw_fd))
     }
 }
 
@@ -82,30 +83,30 @@ pub fn signalfd(fd: RawFd, mask: &SigSet, flags: SfdFlags) -> Result<RawFd> {
 ///     Err(err) => (), // some error happend
 /// }
 /// ```
-#[derive(Debug, Eq, Hash, PartialEq)]
-pub struct SignalFd(RawFd);
+#[derive(Debug)]
+pub struct SignalFd(ManuallyDrop<OwnedFd>);
 
 impl SignalFd {
     pub fn new(mask: &SigSet) -> Result<SignalFd> {
         Self::with_flags(mask, SfdFlags::empty())
     }
 
     pub fn with_flags(mask: &SigSet, flags: SfdFlags) -> Result<SignalFd> {
-        let fd = signalfd(SIGNALFD_NEW, mask, flags)?;
+        let fd = signalfd(None, mask, flags)?;
 
-        Ok(SignalFd(fd))
+        Ok(SignalFd(ManuallyDrop::new(fd)))
     }
 
     pub fn set_mask(&mut self, mask: &SigSet) -> Result<()> {
-        signalfd(self.0, mask, SfdFlags::empty()).map(drop)
+        signalfd(Some(self.0.as_fd()), mask, SfdFlags::empty()).map(drop)
     }
 
     pub fn read_signal(&mut self) -> Result<Option<siginfo>> {
         let mut buffer = mem::MaybeUninit::<siginfo>::uninit();
 
         let size = mem::size_of_val(&buffer);
         let res = Errno::result(unsafe {
-            libc::read(self.0, buffer.as_mut_ptr() as *mut libc::c_void, size)
+            libc::read(self.0.as_raw_fd(), buffer.as_mut_ptr() as *mut libc::c_void, size)
         })
         .map(|r| r as usize);
         match res {
@@ -119,7 +120,7 @@ impl SignalFd {
 
 impl Drop for SignalFd {
     fn drop(&mut self) {
-        let e = unistd::close(self.0);
+        let e = unistd::close(self.0.as_raw_fd());
         if !std::thread::panicking() && e == Err(Errno::EBADF) {
             panic!("Closing an invalid file descriptor!");
         };
@@ -128,7 +129,7 @@ impl Drop for SignalFd {
 
 impl AsRawFd for SignalFd {
     fn as_raw_fd(&self) -> RawFd {
-        self.0
+        self.0.as_raw_fd()
     }
 }
 

src/unistd.rs

@@ -34,7 +34,7 @@ use std::ffi::{CString, OsStr};
 #[cfg(not(target_os = "redox"))]
 use std::os::unix::ffi::OsStrExt;
 use std::os::unix::ffi::OsStringExt;
-use std::os::unix::io::RawFd;
+use std::os::unix::io::{IntoRawFd, RawFd};
 use std::path::PathBuf;
 use std::{fmt, mem, ptr};
 
@@ -1060,8 +1060,8 @@ pub fn gethostname() -> Result<OsString> {
 /// let f = tempfile::tempfile().unwrap();
 /// close(f.into_raw_fd()).unwrap(); // Good.  into_raw_fd consumes f
 /// ```
-pub fn close(fd: RawFd) -> Result<()> {
-    let res = unsafe { libc::close(fd) };
+pub fn close<F: IntoRawFd>(fd: F) -> Result<()> {
+    let res = unsafe { libc::close(fd.into_raw_fd()) };
     Errno::result(res).map(drop)
 }