From 34c982ae5208aff5efd9ece0248743dbca84eec9 Mon Sep 17 00:00:00 2001
From: Folkert de Vries <folkert@tweedegolf.com>
Date: Fri, 17 Nov 2023 15:28:34 +0100
Subject: [PATCH] use the new error interest in tokio to detect the timestamp
 being available

---
 Cargo.toml                |  2 +-
 ntp-udp/src/raw_socket.rs | 60 ---------------------------------------
 ntp-udp/src/socket.rs     | 42 ++++++---------------------
 3 files changed, 10 insertions(+), 94 deletions(-)

diff --git a/Cargo.toml b/Cargo.toml
index e1e1f1e45..8b39a1fb1 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -49,7 +49,7 @@ rand = "0.8.0"
 arbitrary = { version = "1.0" }
 thiserror = "1.0.10"
 libc = "0.2.145"
-tokio = "1.28"
+tokio = "1.32"
 toml = ">=0.5.0,<0.8.0"
 async-trait = "0.1.22"
 
diff --git a/ntp-udp/src/raw_socket.rs b/ntp-udp/src/raw_socket.rs
index 02be6ba54..5732c03ec 100644
--- a/ntp-udp/src/raw_socket.rs
+++ b/ntp-udp/src/raw_socket.rs
@@ -528,66 +528,6 @@ pub(crate) mod timestamping_config {
     }
 }
 
-#[cfg(target_os = "linux")]
-pub(crate) mod err_queue_waiter {
-
-    use std::os::unix::prelude::{AsRawFd, RawFd};
-
-    use tokio::io::{unix::AsyncFd, Interest};
-
-    use crate::raw_socket::cerr;
-
-    pub struct ErrQueueWaiter {
-        epoll_fd: AsyncFd<RawFd>,
-    }
-
-    fn create_error(inner: std::io::Error) -> std::io::Error {
-        std::io::Error::new(
-            std::io::ErrorKind::Other,
-            format!("could not create error queue waiter epoll socket: {inner:?}"),
-        )
-    }
-
-    impl ErrQueueWaiter {
-        pub fn new(source: &impl AsRawFd) -> std::io::Result<Self> {
-            // Safety: safe to call with
-            let epoll = cerr(unsafe { libc::epoll_create(1) }).map_err(create_error)?;
-
-            let mut ev = libc::epoll_event {
-                events: libc::EPOLLERR as _,
-                u64: 0,
-            };
-
-            cerr(unsafe {
-                libc::epoll_ctl(
-                    epoll,
-                    libc::EPOLL_CTL_ADD,
-                    source.as_raw_fd(),
-                    &mut ev as *mut _,
-                )
-            })
-            .map_err(create_error)?;
-
-            Ok(Self {
-                epoll_fd: AsyncFd::new(epoll)?,
-            })
-        }
-
-        pub async fn wait(&self) -> std::io::Result<()> {
-            self.epoll_fd
-                .async_io(Interest::READABLE, |fd| {
-                    let mut ev = libc::epoll_event { events: 0, u64: 0 };
-
-                    match unsafe { libc::epoll_wait(*fd, &mut ev as *mut _, 1, 0) } {
-                        0 => Err(std::io::ErrorKind::WouldBlock.into()),
-                        _ => Ok(()),
-                    }
-                })
-                .await
-        }
-    }
-}
-
 pub(crate) mod interface_iterator {
     use crate::interface::{sockaddr_to_socket_addr, InterfaceData, InterfaceName};
     use std::str::FromStr;
diff --git a/ntp-udp/src/socket.rs b/ntp-udp/src/socket.rs
index 02d34ee03..63d9b2ec8 100644
--- a/ntp-udp/src/socket.rs
+++ b/ntp-udp/src/socket.rs
@@ -15,13 +15,8 @@ use crate::{
     EnableTimestamps,
 };
 
-#[cfg(target_os = "linux")]
-use crate::raw_socket::err_queue_waiter::ErrQueueWaiter;
-
 pub struct UdpSocket {
     io: AsyncFd<std::net::UdpSocket>,
-    #[cfg(target_os = "linux")]
-    err_queue_waiter: ErrQueueWaiter,
     send_counter: u32,
     timestamping: EnableTimestamps,
 }
@@ -92,8 +87,6 @@ impl UdpSocket {
         set_timestamping_options(&socket, method, timestamping)?;
 
         Ok(UdpSocket {
-            #[cfg(target_os = "linux")]
-            err_queue_waiter: ErrQueueWaiter::new(&socket)?,
             io: AsyncFd::new(socket)?,
             send_counter: 0,
             timestamping,
@@ -132,8 +125,6 @@ impl UdpSocket {
         set_timestamping_options(&socket, DEFAULT_TIMESTAMP_METHOD, timestamping)?;
 
         Ok(UdpSocket {
-            #[cfg(target_os = "linux")]
-            err_queue_waiter: ErrQueueWaiter::new(&socket)?,
             io: AsyncFd::new(socket)?,
             send_counter: 0,
             timestamping,
@@ -202,31 +193,16 @@ impl UdpSocket {
         let msg = "waiting for timestamp socket to become readable to fetch a send timestamp";
         tracing::trace!(msg);
 
-        // Send timestamps are sent to the udp socket's error queue. Sadly, tokio does not
-        // currently support awaiting whether there is something in the error queue
-        // see https://github.com/tokio-rs/tokio/issues/4885.
-        //
-        // Therefore, we manually configure an extra file descriptor to listen for POLLPRI on
-        // the main udp socket. This `exceptional_condition` file descriptor becomes readable
-        // when there is something in the error queue.
+        let try_read = |udp_socket: &std::net::UdpSocket| {
+            fetch_send_timestamp_help(udp_socket, expected_counter)
+        };
+
         loop {
-            // Send timestamps are sent to the udp socket's error queue. Sadly, tokio does not
-            // currently support awaiting whether there is something in the error queue
-            // see https://github.com/tokio-rs/tokio/issues/4885.
-            self.err_queue_waiter.wait().await?;
-
-            match fetch_send_timestamp_help(self.io.get_ref(), expected_counter) {
-                Ok(Some(send_timestamp)) => {
-                    return Ok(send_timestamp);
-                }
-                Ok(None) => {
-                    continue;
-                }
-                Err(e) => {
-                    tracing::warn!(error = ?&e, "Error fetching timestamp");
-                    return Err(e);
-                }
-            }
+            // the timestamp being available triggers the error interest
+            match self.io.async_io(Interest::ERROR, try_read).await? {
+                Some(timestamp) => return Ok(timestamp),
+                None => continue,
+            };
         }
     }