Re: nfs-utils: v3 mounts broken due to statx() returning EINVAL

["J. Bruce Fields" <bfields@redhat.com>]

On Tue, Nov 26, 2019 at 02:22:40AM -0500, Doug Nazar wrote:
> On Fri, Oct 11, 2019 at 17:07:09PM +0000, Bruce Fields wrote:
> >On Tue, Oct 08, 2019 at 10:23:56PM +0200, Thomas Deutschmann wrote:
> >> Hi,
> >>
> >> we have some user reporting that NFS v3 mounts are broken
> >> when using glibc-2.29 and linux-4.9.x (4.9.128) because
> >> statx() with mask=STATX_BASIC_STATS returns EINVAL.
> >>
> >> Looks like this isn't happening with <nfs-utils-2.4.1 or
> >> newer kernels.
> >>
> >> The following workaround was confirmed to be working:
> >>
> >> --- a/support/misc/xstat.c    2019-06-24 21:31:55.260371592 +0200
> >> +++ b/support/misc/xstat.c    2019-06-24 21:32:29.098777436 +0200
> >> @@ -47,6 +47,8 @@
> >>              statx_copy(statbuf, &stxbuf);
> >>              return 0;
> >>          }
> >> +        if (errno == EINVAL)
> >> +            errno = ENOSYS;
> >>          if (errno == ENOSYS)
> >>              statx_supported = 0;
> >>      } else
> >>
> >>
> >> Bug: https://bugs.gentoo.org/688644
> >>
> >> At the moment I have no clue whether this is kernel/glibc or
> >> nfs-utils related; if the patch is safe to apply...
> >
> >Well, sounds like nfs-utils started using statx in 2.4.1.  And just the
> >fact that varying the kernel version makes it sound like there was a
> >kernel bug causing an EINVAL return in this case, and that bug got
> >fixed.
> >
> >One way to confirm might be running mount under strace and looking for
> >that EINVAL return.
> 
> Just to provide an update on this issue, it was tracked down to glibc's
> statx emulation not supporting AT_STATX_DONT_SYNC and returning EINVAL.
> 
> So on a kernel without statx support, but a new glibc with statx support,
> nfs-utils will always fail to stat any paths.
> 
> Either this or a similar fix is required to support older kernels.

OK.  So maybe your patch is the best we can do.  I'd just add a comment
there documenting the situation.

--b.