os: use syscall.Pipe2 on Linux

Update #2656

R=golang-dev, iant, minux.ma, bradfitz
CC=golang-dev
https://golang.org/cl/7065063

src/pkg/os/file_unix.go

@@ -274,25 +274,6 @@ func basename(name string) string {
 	return name
 }
 
-// Pipe returns a connected pair of Files; reads from r return bytes written to w.
-// It returns the files and an error, if any.
-func Pipe() (r *File, w *File, err error) {
-	var p [2]int
-
-	// See ../syscall/exec.go for description of lock.
-	syscall.ForkLock.RLock()
-	e := syscall.Pipe(p[0:])
-	if e != nil {
-		syscall.ForkLock.RUnlock()
-		return nil, nil, NewSyscallError("pipe", e)
-	}
-	syscall.CloseOnExec(p[0])
-	syscall.CloseOnExec(p[1])
-	syscall.ForkLock.RUnlock()
-
-	return NewFile(uintptr(p[0]), "|0"), NewFile(uintptr(p[1]), "|1"), nil
-}
-
 // TempDir returns the default directory to use for temporary files.
 func TempDir() string {
 	dir := Getenv("TMPDIR")

src/pkg/os/pipe_bsd.go

+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build darwin freebsd netbsd openbsd
+
+package os
+
+import "syscall"
+
+// Pipe returns a connected pair of Files; reads from r return bytes written to w.
+// It returns the files and an error, if any.
+func Pipe() (r *File, w *File, err error) {
+	var p [2]int
+
+	// See ../syscall/exec.go for description of lock.
+	syscall.ForkLock.RLock()
+	e := syscall.Pipe(p[0:])
+	if e != nil {
+		syscall.ForkLock.RUnlock()
+		return nil, nil, NewSyscallError("pipe", e)
+	}
+	syscall.CloseOnExec(p[0])
+	syscall.CloseOnExec(p[1])
+	syscall.ForkLock.RUnlock()
+
+	return NewFile(uintptr(p[0]), "|0"), NewFile(uintptr(p[1]), "|1"), nil
+}

src/pkg/os/pipe_linux.go

+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package os
+
+import "syscall"
+
+// Pipe returns a connected pair of Files; reads from r return bytes written to w.
+// It returns the files and an error, if any.
+func Pipe() (r *File, w *File, err error) {
+	var p [2]int
+
+	e := syscall.Pipe2(p[0:], syscall.O_CLOEXEC)
+	// pipe2 was added in 2.6.27 and our minimum requirement is 2.6.23, so it
+	// might not be implemented.
+	if e == syscall.ENOSYS {
+		// See ../syscall/exec.go for description of lock.
+		syscall.ForkLock.RLock()
+		e = syscall.Pipe(p[0:])
+		if e != nil {
+			syscall.ForkLock.RUnlock()
+			return nil, nil, NewSyscallError("pipe", e)
+		}
+		syscall.CloseOnExec(p[0])
+		syscall.CloseOnExec(p[1])
+		syscall.ForkLock.RUnlock()
+	} else if e != nil {
+		return nil, nil, NewSyscallError("pipe2", e)
+	}
+
+	return NewFile(uintptr(p[0]), "|0"), NewFile(uintptr(p[1]), "|1"), nil
+}