syscallcompat: don't retry Close()

After Close() returns, the fd is dead, even if we
received EINTR. Don't retry, we could shoot down
an unrelated fd that received the same fd number.

internal/fusefrontend/file.go

@@ -391,9 +391,9 @@ func (f *File) Release(ctx context.Context) syscall.Errno {
 	}
 	f.released = true
 	openfiletable.Unregister(f.qIno)
-	f.fd.Close()
+	err := f.fd.Close()
 	f.fdLock.Unlock()
-	return 0
+	return fs.ToErrno(err)
 }
 
 // Flush - FUSE call
@@ -401,15 +401,7 @@ func (f *File) Flush(ctx context.Context) syscall.Errno {
 	f.fdLock.RLock()
 	defer f.fdLock.RUnlock()
 
-	// Since Flush() may be called for each dup'd fd, we don't
-	// want to really close the file, we just want to flush. This
-	// is achieved by closing a dup'd fd.
-	newFd, err := syscall.Dup(f.intFd())
-
-	if err != nil {
-		return fs.ToErrno(err)
-	}
-	err = syscallcompat.Close(newFd)
+	err := syscallcompat.Flush(f.intFd())
 	return fs.ToErrno(err)
 }
 

internal/syscallcompat/eintr.go

@@ -11,6 +11,9 @@ import (
 //
 // This is needed because CIFS throws lots of EINTR errors:
 // https://github.com/rfjakob/gocryptfs/issues/483
+//
+// Don't use retryEINTR() with syscall.Close()!
+// See https://code.google.com/p/chromium/issues/detail?id=269623 .
 func retryEINTR(op func() error) error {
 	for {
 		err := op()
@@ -40,9 +43,25 @@ func Open(path string, mode int, perm uint32) (fd int, err error) {
 	return fd, err
 }
 
-// Close wraps syscall.Close.
+// Flush is a helper for the FUSE command FLUSH.
 // Retries on EINTR.
-func Close(fd int) (err error) {
-	err = retryEINTR(func() error { return syscall.Close(fd) })
+func Flush(fd int) error {
+	for {
+		// Flushing is achieved by closing a dup'd fd.
+		newFd, err := syscall.Dup(fd)
+		if err == syscall.EINTR {
+			continue
+		}
+		if err != nil {
 			return err
+		}
+		err = syscall.Close(newFd)
+		// Even if we get EINTR here, newFd is dead - see
+		// https://code.google.com/p/chromium/issues/detail?id=269623 .
+		// We have to make a new one with Dup(), so continue at the top.
+		if err == syscall.EINTR {
+			continue
+		}
+		return err
+	}
 }