On Fri, Jul 29, 2016 at 03:03:36PM +1000, NeilBrown wrote:
> If an export point should be mounted ("mountpoint" option set) but
> isn't, then an attempt to mount using the MOUNT protocol for NFSv3
> will fail and an attempt to access the filesystem using a pre-existing
> filehandle will block because nfsd_fh wont tell the kernel about it.
>
> However a lookup from the parent, as happens with an NFSv4 mount
> request, will pass the name to nfsd_export(), and it doesn't check the
> mointpoint option, and so exports the underlying (typically "/")
> filesystem.
>
> So change nfsd_export() to refused to export that exportpoint, but
> instead to explictly say that it isn't exported.
> This will cause an 'ls' in the parent pseudo-root directory to not show
> the name and will cause a "mount" attempt which walks down through the
> pseudo root to fail in the same way that it does with NFSv3.
>
> An access from a pre-existing NFSv4 mount will still hang until the
> filesystem is mounted, just like it does with NFSv3.
>
> In order to be a bit more responsive to the filesystem getting mounted,
> just a short timeout (1 minutes) on exports of missing "mountpoint"
> exportpoints.
OK, I'm still haven't learned to love "mountpoint", but, I agree, it
looks like this fixes the complaint about the v4 case with minimal risk
of disruption to existing users.
ACK.--b.
>
> Signed-off-by: NeilBrown <neilb@xxxxxxxx>
> ---
> utils/mountd/cache.c | 18 +++++++++++++++++-
> 1 file changed, 17 insertions(+), 1 deletion(-)
>
> diff --git a/utils/mountd/cache.c b/utils/mountd/cache.c
> index 9cc270690d90..ca6c84f4d93d 100644
> --- a/utils/mountd/cache.c
> +++ b/utils/mountd/cache.c
> @@ -1334,7 +1334,23 @@ static void nfsd_export(int f)
> found = lookup_export(dom, path, ai);
>
> if (found) {
> - if (dump_to_cache(f, buf, sizeof(buf), dom, path, &found->m_export, 0) < 0) {
> + char *mp = found->m_export.e_mountpoint;
> +
> + if (mp && !*mp)
> + mp = found->m_export.e_path;
> + if (mp && !is_mountpoint(mp))
> + /* Exportpoint is not mounted, so tell kernel it is
> + * not available.
> + * This will cause it not to appear in the V4 Pseudo-root
> + * and so a "mount" of this path will fail, just like with
> + * V3.
> + * And filehandle for this mountpoint from an earlier
> + * mount will block in nfsd.fh lookup.
> + */
> + dump_to_cache(f, buf, sizeof(buf), dom, path,
> + NULL, 60);
> + else if (dump_to_cache(f, buf, sizeof(buf), dom, path,
> + &found->m_export, 0) < 0) {
> xlog(L_WARNING,
> "Cannot export %s, possibly unsupported filesystem"
> " or fsid= required", path);
>
--
To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
