read and write never return -1 now: error return is through the error variable only

R=rsc
DELTA=13  (9 added, 0 deleted, 4 changed)
OCL=19538
CL=19570

src/lib/os/os_file.go

@@ -55,35 +55,44 @@ func (fd *FD) Close() *Error {
 
 func (fd *FD) Read(b *[]byte) (ret int, err *Error) {
 	if fd == nil {
-		return -1, EINVAL
+		return 0, EINVAL
 	}
 	var r, e int64;
 	if len(b) > 0 {  // because we access b[0]
 		r, e = syscall.read(fd.fd, &b[0], int64(len(b)));
+		if r < 0 {
+			r = 0
+		}
 	}
 	return int(r), ErrnoToError(e)
 }
 
 func (fd *FD) Write(b *[]byte) (ret int, err *Error) {
 	if fd == nil {
-		return -1, EINVAL
+		return 0, EINVAL
 	}
 	var r, e int64;
 	if len(b) > 0 {  // because we access b[0]
 		r, e = syscall.write(fd.fd, &b[0], int64(len(b)));
+		if r < 0 {
+			r = 0
+		}
 	}
 	return int(r), ErrnoToError(e)
 }
 
 func (fd *FD) WriteString(s string) (ret int, err *Error) {
 	if fd == nil {
-		return -1, EINVAL
+		return 0, EINVAL
 	}
 	b := new([]byte, len(s)+1);
 	if !syscall.StringToBytes(b, s) {
-		return -1, EINVAL
+		return 0, EINVAL
 	}
 	r, e := syscall.write(fd.fd, &b[0], int64(len(s)));
+	if r < 0 {
+		r = 0
+	}
 	return int(r), ErrnoToError(e)
 }