* 1st subvol is up
* nfs xlator is loaded on top of distribute
* ls does not show anything on nfs mount point
* nfs does not send openddir
* nfs does readdir on ls on an older already opened fd (the same fd everytime)
* dht_readdir_cbk is called with op_ret=-1 op_errno=77 from 1st subvol because it had previously got error when 1st subvol was down. so client_readdirp returns errno 77
* dht returns op_ret=0 to NFS as it filters out all directories read from the 2nd subvol :

                if (check_is_linkfile (NULL, (&orig_entry->d_stat), NULL)
                    || (check_is_dir (NULL, (&orig_entry->d_stat), NULL)
                        && (prev->this != dht_first_up_subvol (this)))) {
                        continue;
                }

* this behavior is not seen without nfs xlator as opendir would be sent before readdir.