circ_space_to_end
n = min(len, circ_space_to_end(crc));
n = min_t(size_t, len, circ_space_to_end(crc));
n = min(sz, circ_space_to_end(&rd->fifo));
len = circ_space_to_end(crc);
len = circ_space_to_end(crc);
len = circ_space_to_end(crc);