+ (unless (and (member (stream-element-type stream) '(character base-char))
+ ;; give up if it's not a file stream, or it's an
+ ;; fd-stream but it's either not bivalent or not
+ ;; seekable (doesn't really have a file)
+ (or (not (typep stream 'file-stream))
+ (and (typep stream 'fd-stream)
+ (or (not (sb!impl::fd-stream-bivalent-p stream))
+ (not (sb!impl::fd-stream-file stream))))))