readdir and ENOENT error or EOF?

[Mark Olesen]

I apologize for what I posted in libc-alpha. I did not realize the
post actually made it on the list. I reposted it in libc-help.
However, thanks for your answer.

Should ENOENT be handled as an error or is it indeed an EOF condition?



On Thu, Jun 17, 2021 at 1:07 AM Florian Weimer <fweimer@redhat.com> wrote:
>
> * Mark Olesen via Libc-alpha:
>
> > There appears to be ambiguity in user documentation for readdir when
> > it returns NULL and errno is set to ENOENT.
> >
> > Is this an EOF condition or an actual error that should be handled?
> >
> > ...
> > /* On some systems getdents fails with ENOENT when the
> > open directory has been rmdir'd already. POSIX.1
> > requires that we treat this condition like normal EOF. */
> > if (bytes < 0 && errno == ENOENT)
> > bytes = 0;
> > ...
> > https://code.woboq.org/userspace/glibc/sysdeps/posix/readdir.c.htmlin
>
> Note that the Linux implementation is in
> sysdeps/unix/sysv/linux/readdir.c, but it has this quirk as well.
>
> I believe this has been copied over from historic times.  In general,
> Linux handles this corner case differently.  However, the Linux VFS
> layer will pass through ENOENT from file system implementations, so if a
> file system implementation generates ENOENT in its readdir
> implementation, we might still see ENOENT in userspace.  That's why it's
> difficult to remove the check from glibc's readdir implementation.
>
> Thanks,
> Florian
>