drbg_max_request_bytes
if (buflen > (drbg_max_request_bytes(drbg))) {
slice = ((buflen - len) / drbg_max_request_bytes(drbg));
chunk = slice ? drbg_max_request_bytes(drbg) : (buflen - len);
max_request_bytes = drbg_max_request_bytes(drbg);