un               1643 http/ngx_http_upstream.c     ngx_http_upstream_next_t  *un;
un               1647 http/ngx_http_upstream.c     for (un = ngx_http_upstream_next_errors; un->status; un++) {
un               1649 http/ngx_http_upstream.c         if (status != un->status) {
un               1653 http/ngx_http_upstream.c         if (u->peer.tries > 1 && (u->conf->next_upstream & un->mask)) {
un               1654 http/ngx_http_upstream.c             ngx_http_upstream_next(r, u, un->mask);
un               1661 http/ngx_http_upstream.c             && (u->conf->cache_use_stale & un->mask))