os: Null device

R=rsc, cw
CC=golang-dev
https://golang.org/cl/1854042

src/pkg/exec/exec.go

@@ -39,7 +39,7 @@ func modeToFiles(mode, fd int) (*os.File, *os.File, os.Error) {
 		if fd == 0 {
 			rw = os.O_RDONLY
 		}
-		f, err := os.Open("/dev/null", rw, 0)
+		f, err := os.Open(os.DevNull, rw, 0)
 		return f, nil, err
 	case PassThrough:
 		switch fd {

src/pkg/os/file_unix.go

@@ -18,6 +18,10 @@ type dirInfo struct {
 	bufp int    // location of next record in buf.
 }
 
+// DevNull is the name of the operating system's ``null device.''
+// On Unix-like systems, it is "/dev/null"; on Windows, "NUL".
+const DevNull = "/dev/null"
+
 // Open opens the named file with specified flag (O_RDONLY etc.) and perm, (0666 etc.)
 // if applicable.  If successful, methods on the returned File can be used for I/O.
 // It returns the File and an Error, if any.

src/pkg/os/file_windows.go

@@ -17,6 +17,8 @@ type dirInfo struct {
 	usefirststat bool
 }
 
+const DevNull = "NUL"
+
 func (file *File) isdir() bool { return file != nil && file.dirinfo != nil }
 
 func openFile(name string, flag int, perm int) (file *File, err Error) {