os: add ErrClosed, return for use of closed File

This is clearer than syscall.EBADF.

Fixes #17320.

Change-Id: I14c6a362f9a6044c9b07cd7965499f4a83d2a860
Reviewed-on: https://go-review.googlesource.com/30614
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

1 files changed, 4 insertions, 4 deletions

diff --git a/src/os/file_plan9.go b/src/os/file_plan9.go
index 880d56a16f..704e95b1e6 100644
--- a/src/os/file_plan9.go
+++ b/src/os/file_plan9.go
@@ -130,21 +130,21 @@ func OpenFile(name string, flag int, perm FileMode) (*File, error) {
 // Close closes the File, rendering it unusable for I/O.
 // It returns an error, if any.
 func (f *File) Close() error {
-	if f == nil {
-		return ErrInvalid
+	if err := f.checkValid("close"); err != nil {
+		return err
 	}
 	return f.file.close()
 }
 
 func (file *file) close() error {
-	if file == nil || file.fd < 0 {
+	if file == nil || file.fd == badFd {
 		return ErrInvalid
 	}
 	var err error
 	if e := syscall.Close(file.fd); e != nil {
 		err = &PathError{"close", file.name, e}
 	}
-	file.fd = -1 // so it can't be closed again
+	file.fd = badFd // so it can't be closed again
 
 	// no need for a finalizer anymore
 	runtime.SetFinalizer(file, nil)