[release-branch.go1.20] os: if descriptor is non-blocking, retain that in Fd method

For #58408
For #60211
Fixes #60217

Change-Id: I30f5678b46e15121865b19d1c0f82698493fad4e
Reviewed-on: https://go-review.googlesource.com/c/go/+/495079
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>
(cherry picked from commit f777726ff073f8066c017649b572bd8c40940a42)
Reviewed-on: https://go-review.googlesource.com/c/go/+/496015
Reviewed-by: Heschi Kreinick <heschi@google.com>
Auto-Submit: Heschi Kreinick <heschi@google.com>

5 files changed, 71 insertions, 2 deletions

diff --git a/src/internal/syscall/unix/nonblocking.go b/src/internal/syscall/unix/nonblocking.go
index a0becd1e01..6c6f0674d6 100644
--- a/src/internal/syscall/unix/nonblocking.go
+++ b/src/internal/syscall/unix/nonblocking.go
@@ -19,3 +19,7 @@ func IsNonblock(fd int) (nonblocking bool, err error) {
 	}
 	return flag&syscall.O_NONBLOCK != 0, nil
 }
+
+func HasNonblockFlag(flag int) bool {
+	return flag&syscall.O_NONBLOCK != 0
+}
diff --git a/src/internal/syscall/unix/nonblocking_js.go b/src/internal/syscall/unix/nonblocking_js.go
index 8ed40f3f91..cfe78c58d8 100644
--- a/src/internal/syscall/unix/nonblocking_js.go
+++ b/src/internal/syscall/unix/nonblocking_js.go
@@ -9,3 +9,7 @@ package unix
 func IsNonblock(fd int) (nonblocking bool, err error) {
 	return false, nil
 }
+
+func HasNonblockFlag(flag int) bool {
+	return false
+}
diff --git a/src/internal/syscall/unix/nonblocking_libc.go b/src/internal/syscall/unix/nonblocking_libc.go
index bff6684962..1310dbf8ce 100644
--- a/src/internal/syscall/unix/nonblocking_libc.go
+++ b/src/internal/syscall/unix/nonblocking_libc.go
@@ -19,6 +19,10 @@ func IsNonblock(fd int) (nonblocking bool, err error) {
 	return flag&syscall.O_NONBLOCK != 0, nil
 }
 
+func HasNonblockFlag(flag int) bool {
+	return flag&syscall.O_NONBLOCK != 0
+}
+
 // Implemented in the syscall package.
 //
 //go:linkname fcntl syscall.fcntl
diff --git a/src/os/fifo_test.go b/src/os/fifo_test.go
index de70927961..ca68e82f05 100644
--- a/src/os/fifo_test.go
+++ b/src/os/fifo_test.go
@@ -10,6 +10,7 @@ import (
 	"bufio"
 	"bytes"
 	"fmt"
+	"internal/syscall/unix"
 	"io"
 	"os"
 	"path/filepath"
@@ -101,3 +102,52 @@ func TestFifoEOF(t *testing.T) {
 		r.Close()
 	}
 }
+
+// Issue 60211.
+func TestOpenFileNonBlocking(t *testing.T) {
+	exe, err := os.Executable()
+	if err != nil {
+		t.Skipf("can't find executable: %v", err)
+	}
+	f, err := os.OpenFile(exe, os.O_RDONLY|syscall.O_NONBLOCK, 0666)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer f.Close()
+	nonblock, err := unix.IsNonblock(int(f.Fd()))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !nonblock {
+		t.Errorf("file opened with O_NONBLOCK but in blocking mode")
+	}
+}
+
+func TestNewFileNonBlocking(t *testing.T) {
+	var p [2]int
+	if err := syscall.Pipe(p[:]); err != nil {
+		t.Fatal(err)
+	}
+	if err := syscall.SetNonblock(p[0], true); err != nil {
+		t.Fatal(err)
+	}
+	f := os.NewFile(uintptr(p[0]), "pipe")
+	nonblock, err := unix.IsNonblock(p[0])
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !nonblock {
+		t.Error("pipe blocking after NewFile")
+	}
+	fd := f.Fd()
+	if fd != uintptr(p[0]) {
+		t.Errorf("Fd returned %d, want %d", fd, p[0])
+	}
+	nonblock, err = unix.IsNonblock(p[0])
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !nonblock {
+		t.Error("pipe blocking after Fd")
+	}
+}
diff --git a/src/os/file_unix.go b/src/os/file_unix.go
index 1833c26531..8f531d9a10 100644
--- a/src/os/file_unix.go
+++ b/src/os/file_unix.go
@@ -171,7 +171,9 @@ func newFile(fd uintptr, name string, kind newFileKind) *File {
 	clearNonBlock := false
 	if pollable {
 		if kind == kindNonBlock {
-			f.nonblock = true
+			// The descriptor is already in non-blocking mode.
+			// We only set f.nonblock if we put the file into
+			// non-blocking mode.
 		} else if err := syscall.SetNonblock(fdi, true); err == nil {
 			f.nonblock = true
 			clearNonBlock = true
@@ -247,7 +249,12 @@ func openFileNolog(name string, flag int, perm FileMode) (*File, error) {
 		syscall.CloseOnExec(r)
 	}
 
-	return newFile(uintptr(r), name, kindOpenFile), nil
+	kind := kindOpenFile
+	if unix.HasNonblockFlag(flag) {
+		kind = kindNonBlock
+	}
+
+	return newFile(uintptr(r), name, kind), nil
 }
 
 func (file *file) close() error {