h2g_has_room
bool h2g = h2g_has_room(ct, h2g_dw);
if (unlikely(!h2g_has_room(ct, len + GUC_CTB_HDR_LEN) ||
if (!h2g_has_room(ct, len + GUC_CTB_HDR_LEN)) {
if (!g2h_has_room(ct, g2h_len) || !h2g_has_room(ct, cmd_len))