From a9b377e9e10eb5194c0bdff32136c11b17253bfd Mon Sep 17 00:00:00 2001
From: "Jason A. Donenfeld" <Jason@zx2c4.com>
Date: Thu, 20 May 2021 17:42:34 +0200
Subject: [PATCH] rwcancel: use poll instead of select

Suggested-by: Lennart Poettering <lennart@poettering.net>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 rwcancel/fdset.go          | 24 ------------------------
 rwcancel/rwcancel.go       | 33 ++++++++++++---------------------
 rwcancel/select_default.go | 15 ---------------
 rwcancel/select_linux.go   | 13 -------------
 4 files changed, 12 insertions(+), 73 deletions(-)
 delete mode 100644 rwcancel/fdset.go
 delete mode 100644 rwcancel/select_default.go
 delete mode 100644 rwcancel/select_linux.go

diff --git a/rwcancel/fdset.go b/rwcancel/fdset.go
deleted file mode 100644
index 2c5ca9e..0000000
--- a/rwcancel/fdset.go
+++ /dev/null
@@ -1,24 +0,0 @@
-// +build !windows
-
-/* SPDX-License-Identifier: MIT
- *
- * Copyright (C) 2017-2021 WireGuard LLC. All Rights Reserved.
- */
-
-package rwcancel
-
-import "golang.org/x/sys/unix"
-
-type fdSet struct {
-	unix.FdSet
-}
-
-func (fdset *fdSet) set(i int) {
-	bits := 32 << (^uint(0) >> 63)
-	fdset.Bits[i/bits] |= 1 << uint(i%bits)
-}
-
-func (fdset *fdSet) check(i int) bool {
-	bits := 32 << (^uint(0) >> 63)
-	return (fdset.Bits[i/bits] & (1 << uint(i%bits))) != 0
-}
diff --git a/rwcancel/rwcancel.go b/rwcancel/rwcancel.go
index 70eb4ca..05484e1 100644
--- a/rwcancel/rwcancel.go
+++ b/rwcancel/rwcancel.go
@@ -17,13 +17,6 @@ import (
 	"golang.org/x/sys/unix"
 )
 
-func max(a, b int) int {
-	if a > b {
-		return a
-	}
-	return b
-}
-
 type RWCancel struct {
 	fd            int
 	closingReader *os.File
@@ -50,13 +43,12 @@ func RetryAfterError(err error) bool {
 }
 
 func (rw *RWCancel) ReadyRead() bool {
-	closeFd := int(rw.closingReader.Fd())
-	fdset := fdSet{}
-	fdset.set(rw.fd)
-	fdset.set(closeFd)
+	closeFd := int32(rw.closingReader.Fd())
+
+	pollFds := []unix.PollFd{{Fd: int32(rw.fd), Events: unix.POLLIN}, {Fd: closeFd, Events: unix.POLLIN}}
 	var err error
 	for {
-		err = unixSelect(max(rw.fd, closeFd)+1, &fdset.FdSet, nil, nil, nil)
+		_, err = unix.Poll(pollFds, -1)
 		if err == nil || !RetryAfterError(err) {
 			break
 		}
@@ -64,20 +56,18 @@ func (rw *RWCancel) ReadyRead() bool {
 	if err != nil {
 		return false
 	}
-	if fdset.check(closeFd) {
+	if pollFds[1].Revents != 0 {
 		return false
 	}
-	return fdset.check(rw.fd)
+	return pollFds[0].Revents != 0
 }
 
 func (rw *RWCancel) ReadyWrite() bool {
-	closeFd := int(rw.closingReader.Fd())
-	fdset := fdSet{}
-	fdset.set(rw.fd)
-	fdset.set(closeFd)
+	closeFd := int32(rw.closingReader.Fd())
+	pollFds := []unix.PollFd{{Fd: int32(rw.fd), Events: unix.POLLOUT}, {Fd: closeFd, Events: unix.POLLOUT}}
 	var err error
 	for {
-		err = unixSelect(max(rw.fd, closeFd)+1, nil, &fdset.FdSet, nil, nil)
+		_, err = unix.Poll(pollFds, -1)
 		if err == nil || !RetryAfterError(err) {
 			break
 		}
@@ -85,10 +75,11 @@ func (rw *RWCancel) ReadyWrite() bool {
 	if err != nil {
 		return false
 	}
-	if fdset.check(closeFd) {
+
+	if pollFds[1].Revents != 0 {
 		return false
 	}
-	return fdset.check(rw.fd)
+	return pollFds[0].Revents != 0
 }
 
 func (rw *RWCancel) Read(p []byte) (n int, err error) {
diff --git a/rwcancel/select_default.go b/rwcancel/select_default.go
deleted file mode 100644
index 990de83..0000000
--- a/rwcancel/select_default.go
+++ /dev/null
@@ -1,15 +0,0 @@
-// +build !linux,!windows
-
-/* SPDX-License-Identifier: MIT
- *
- * Copyright (C) 2017-2021 WireGuard LLC. All Rights Reserved.
- */
-
-package rwcancel
-
-import "golang.org/x/sys/unix"
-
-func unixSelect(nfd int, r *unix.FdSet, w *unix.FdSet, e *unix.FdSet, timeout *unix.Timeval) error {
-	_, err := unix.Select(nfd, r, w, e, timeout)
-	return err
-}
diff --git a/rwcancel/select_linux.go b/rwcancel/select_linux.go
deleted file mode 100644
index ac941fd..0000000
--- a/rwcancel/select_linux.go
+++ /dev/null
@@ -1,13 +0,0 @@
-/* SPDX-License-Identifier: MIT
- *
- * Copyright (C) 2017-2021 WireGuard LLC. All Rights Reserved.
- */
-
-package rwcancel
-
-import "golang.org/x/sys/unix"
-
-func unixSelect(nfd int, r *unix.FdSet, w *unix.FdSet, e *unix.FdSet, timeout *unix.Timeval) (err error) {
-	_, err = unix.Select(nfd, r, w, e, timeout)
-	return
-}