REQ_HDR_LEN
#define LEN_MAX (BUF_LEN - REQ_HDR_LEN) /* Max payload size */
if ((write && (req->data_len > BUF_LEN - REQ_HDR_LEN)) ||
wlen = REQ_HDR_LEN;
memcpy(&state->buf[REQ_HDR_LEN], req->data, req->data_len);
if (req->wlen > (BUF_LEN - REQ_HDR_LEN - CHECKSUM_LEN) ||
state->buf[0] = REQ_HDR_LEN + req->wlen + CHECKSUM_LEN - 1;
memcpy(&state->buf[REQ_HDR_LEN], req->wbuf, req->wlen);
wlen = REQ_HDR_LEN + req->wlen + CHECKSUM_LEN;