> It's been years now and that hasn't happened, even with more recent flag additions. I think it's safe to say it won't, and such a fallback upon error won't put us back into a bogus pre-close_range situation where we're needlessly close()ing a bunch of closed fds.

Yes, I also find it unlikely that close_range() will start reporting an error if it fails to close some fd, especially if not given some new flag. Such error reporting doesn't seem very useful to userspace because there is no way to associate the error with the fd.

But even if such change happens, it will be just a performance regression, not a potential correctness/security issue.