From 7e2fe10021459005e43840c34fb43bd7277453cd Mon Sep 17 00:00:00 2001
From: Alice Ryhl <aliceryhl@google.com>
Date: Sun, 30 Jun 2024 13:40:16 +0200
Subject: [PATCH 1/2] io: hardcode platform list in short-read optimization

---
 tokio/src/io/poll_evented.rs | 34 +++++++++++++++++++++++++++++-----
 1 file changed, 29 insertions(+), 5 deletions(-)

diff --git a/tokio/src/io/poll_evented.rs b/tokio/src/io/poll_evented.rs
index 3952a31e783..fb829748138 100644
--- a/tokio/src/io/poll_evented.rs
+++ b/tokio/src/io/poll_evented.rs
@@ -183,11 +183,35 @@ feature! {
 
                 match self.io.as_ref().unwrap().read(b) {
                     Ok(n) => {
-                        // if we read a partially full buffer, this is sufficient on unix to show
-                        // that the socket buffer has been drained.  Unfortunately this assumption
-                        // fails for level-triggered selectors (like on Windows or poll even for
-                        // UNIX): https://github.com/tokio-rs/tokio/issues/5866
-                        if n > 0 && (!cfg!(windows) && !cfg!(mio_unsupported_force_poll_poll) && n < len) {
+                        // When mio is using the epoll or kqueue selector, reading a partially full
+                        // buffer is sufficient to show that the socket buffer has been drained.
+                        //
+                        // This optimization does not work for level-triggered selectors such as
+                        // windows or when poll is used.
+                        //
+                        // Read more:
+                        // https://github.com/tokio-rs/tokio/issues/5866
+                        #[cfg(all(
+                            not(mio_unsupported_force_poll_poll),
+                            any(
+                                // epoll
+                                target_os = "android",
+                                target_os = "illumos",
+                                target_os = "linux",
+                                target_os = "redox",
+                                // kqueue
+                                target_os = "dragonfly",
+                                target_os = "freebsd",
+                                target_os = "ios",
+                                target_os = "macos",
+                                target_os = "netbsd",
+                                target_os = "openbsd",
+                                target_os = "tvos",
+                                target_os = "visionos",
+                                target_os = "watchos",
+                            )
+                        ))]
+                        if 0 < n && n < len {
                             self.registration.clear_readiness(evt);
                         }
 

From d03ba27cd78d83333e9bb948f5cc8a97cf95cffa Mon Sep 17 00:00:00 2001
From: Alice Ryhl <aliceryhl@google.com>
Date: Tue, 2 Jul 2024 22:16:55 +0200
Subject: [PATCH 2/2] Fix unused vars warning

---
 tokio/src/io/poll_evented.rs | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/tokio/src/io/poll_evented.rs b/tokio/src/io/poll_evented.rs
index fb829748138..73cb8e5809e 100644
--- a/tokio/src/io/poll_evented.rs
+++ b/tokio/src/io/poll_evented.rs
@@ -179,6 +179,9 @@ feature! {
                 let evt = ready!(self.registration.poll_read_ready(cx))?;
 
                 let b = &mut *(buf.unfilled_mut() as *mut [std::mem::MaybeUninit<u8>] as *mut [u8]);
+
+                // used only when the cfgs below apply
+                #[allow(unused_variables)]
                 let len = b.len();
 
                 match self.io.as_ref().unwrap().read(b) {