Re: NFS4 mount problem

[David Howells <dhowells@redhat.com>]

Trond Myklebust <trond.myklebust@fys.uio.no> wrote:

> > We've come across an interesting problem with NFS4 mount on a PPC64 box. If
> > the mount program is compiled as PPC32, then the mount() syscall is returned
> > EFAULT.
>
> So, why is this not a case of "Doctor it hurts..."?

Because:

 (1) The kernel is returning EFAULT to the 32-bit userspace; this implies that
     userspace is handing over a bad address. It isn't, the kernel is
     malfunctioning as it stands.

 (2) The kernel API does not prohibit 32-bit userspace calling mount() under a
     64-bit kernel. All other filesystems cope with it (AFAIK), so NFS4 must
     too.

Either the kernel should return ENOSYS for any 32-bit mount on a 64-bit kernel
or it must support it fully. I think the latter is the right thing to do;
despite what you'd prefer, there are other callers of the mount syscall out
there.

> There should therefore be exactly ONE instance of usage, and that is in
> the "mount" program itself.

Exactly. That should then be the ppc32 mount; which should work equally well
with a ppc32 or a ppc64 kernel.

David