Take BorrowedFd as the argument for PollFd::new

&AsFd didn't work because there are 'static types, like std::fs::File,
which implement AsFd.  The created BorrowedFd type within the
PollFd::new method would have a very brief lifetime, but the PhantomData
would capture the lifetime of the std::fs::File.  Taking BorrowFd<'fd>
argument makes the lifetime explicit.

Author: asomers

CHANGELOG.md

@@ -5,9 +5,10 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 
 ## [Unreleased] - ReleaseDate
 
-### Fixed
+### Changed
 
-- Relaxed lifetime requirements for `PollFd::new`.
+- `PollFd::new` now takes a `BorrowedFd` argument, with relaxed lifetime
+  requirements relative to the previous version.
   ([#2134](https://github.com/nix-rust/nix/pull/2134))
 
 ## [0.27.1] - 2023-08-28

src/poll.rs

@@ -32,30 +32,27 @@ impl<'fd> PollFd<'fd> {
     /// # };
     /// let (r, w) = pipe().unwrap();
     /// let r = unsafe { OwnedFd::from_raw_fd(r) };
-    /// let pfd = PollFd::new(&r.as_fd(), PollFlags::POLLIN);
+    /// let pfd = PollFd::new(r.as_fd(), PollFlags::POLLIN);
     /// let mut fds = [pfd];
     /// poll(&mut fds, -1).unwrap();
     /// let mut buf = [0u8; 80];
     /// read(r.as_raw_fd(), &mut buf[..]);
     /// ```
-    // Unlike I/O functions, constructors like this must take `AsFd` by
-    // reference.  Otherwise, an `OwnedFd` argument would be dropped at the end
-    // of the method, leaving the structure referencing a closed file
-    // descriptor.
-    // Different from other I/O-safe interfaces, here, we have to take `AsFd`
-    // by reference to prevent the case where the `fd` is closed but it is
-    // still in use. For example:
+    // Unlike I/O functions, constructors like this must take `BorrowedFd` 
+    // instead of AsFd or &AsFd.  Otherwise, an `OwnedFd` argument would be
+    // dropped at the end of the method, leaving the structure referencing a
+    // closed file descriptor.  For example:
     //
     // ```rust
     // let (r, _) = pipe().unwrap();
     // let reader: OwnedFd = unsafe { OwnedFd::from_raw_fd(r) };
     // let pollfd = PollFd::new(reader, flag);  // Drops the OwnedFd
     // // Do something with `pollfd`, which uses the CLOSED fd.
     // ```
-    pub fn new<Fd: AsFd + 'fd>(fd: &Fd, events: PollFlags) -> PollFd<'fd> {
+    pub fn new(fd: BorrowedFd<'fd>, events: PollFlags) -> PollFd<'fd> {
         PollFd {
             pollfd: libc::pollfd {
-                fd: fd.as_fd().as_raw_fd(),
+                fd: fd.as_raw_fd(),
                 events: events.bits(),
                 revents: PollFlags::empty().bits(),
             },

test/test_poll.rs

@@ -3,7 +3,10 @@ use nix::{
     poll::{poll, PollFd, PollFlags},
     unistd::{close, pipe, write},
 };
-use std::os::unix::io::{BorrowedFd, FromRawFd, OwnedFd};
+use std::os::{
+    fd::AsFd,
+    unix::io::{BorrowedFd, FromRawFd, OwnedFd}
+};
 
 macro_rules! loop_while_eintr {
     ($poll_expr: expr) => {
@@ -21,7 +24,7 @@ macro_rules! loop_while_eintr {
 fn test_poll() {
     let (r, w) = pipe().unwrap();
     let r = unsafe { OwnedFd::from_raw_fd(r) };
-    let mut fds = [PollFd::new(&r, PollFlags::POLLIN)];
+    let mut fds = [PollFd::new(r.as_fd(), PollFlags::POLLIN)];
 
     // Poll an idle pipe.  Should timeout
     let nfds = loop_while_eintr!(poll(&mut fds, 100));
@@ -55,7 +58,7 @@ fn test_ppoll() {
     let timeout = TimeSpec::milliseconds(1);
     let (r, w) = pipe().unwrap();
     let r = unsafe { OwnedFd::from_raw_fd(r) };
-    let mut fds = [PollFd::new(&r, PollFlags::POLLIN)];
+    let mut fds = [PollFd::new(r.as_fd(), PollFlags::POLLIN)];
 
     // Poll an idle pipe.  Should timeout
     let sigset = SigSet::empty();
@@ -75,7 +78,7 @@ fn test_ppoll() {
 #[test]
 fn test_pollfd_events() {
     let fd_zero = unsafe { BorrowedFd::borrow_raw(0) };
-    let mut pfd = PollFd::new(&fd_zero, PollFlags::POLLIN);
+    let mut pfd = PollFd::new(fd_zero.as_fd(), PollFlags::POLLIN);
     assert_eq!(pfd.events(), PollFlags::POLLIN);
     pfd.set_events(PollFlags::POLLOUT);
     assert_eq!(pfd.events(), PollFlags::POLLOUT);