+
+ /* We always get an MSS option. The option bytes which will be seen in
+ * normal data packets should timestamps be used, must be in the MSS
+ * advertised. But we subtract them from tp->mss_cache so that
+ * calculations in tcp_sendmsg are simpler etc. So account for this
+ * fact here if necessary. If we don't do this correctly, as a
+ * receiver we won't recognize data packets as being full sized when we
+ * should, and thus we won't abide by the delayed ACK rules correctly.
+ * SACKs don't matter, we never delay an ACK when we have any of those
+ * going out. */
+ opts->mss = tcp_advertise_mss(sk);
+ size += TCPOLEN_MSS_ALIGNED;
+
+ if (likely(sysctl_tcp_timestamps && *md5 == NULL)) {
+ opts->options |= OPTION_TS;
+ opts->tsval = TCP_SKB_CB(skb)->when;
+ opts->tsecr = tp->rx_opt.ts_recent;
+ size += TCPOLEN_TSTAMP_ALIGNED;
+ }
+ if (likely(sysctl_tcp_window_scaling)) {
+ opts->ws = tp->rx_opt.rcv_wscale;
+ if (likely(opts->ws))
+ size += TCPOLEN_WSCALE_ALIGNED;
+ }
+ if (likely(sysctl_tcp_sack)) {
+ opts->options |= OPTION_SACK_ADVERTISE;
+ if (unlikely(!(OPTION_TS & opts->options)))
+ size += TCPOLEN_SACKPERM_ALIGNED;
+ }
+
+ return size;
+}
+
+static unsigned tcp_synack_options(struct sock *sk,
+ struct request_sock *req,
+ unsigned mss, struct sk_buff *skb,
+ struct tcp_out_options *opts,
+ struct tcp_md5sig_key **md5) {
+ unsigned size = 0;
+ struct inet_request_sock *ireq = inet_rsk(req);
+ char doing_ts;
+
+#ifdef CONFIG_TCP_MD5SIG
+ *md5 = tcp_rsk(req)->af_specific->md5_lookup(sk, req);
+ if (*md5) {
+ opts->options |= OPTION_MD5;
+ size += TCPOLEN_MD5SIG_ALIGNED;
+ }
+#else
+ *md5 = NULL;
+#endif
+
+ /* we can't fit any SACK blocks in a packet with MD5 + TS
+ options. There was discussion about disabling SACK rather than TS in
+ order to fit in better with old, buggy kernels, but that was deemed
+ to be unnecessary. */
+ doing_ts = ireq->tstamp_ok && !(*md5 && ireq->sack_ok);
+
+ opts->mss = mss;
+ size += TCPOLEN_MSS_ALIGNED;
+
+ if (likely(ireq->wscale_ok)) {
+ opts->ws = ireq->rcv_wscale;
+ if (likely(opts->ws))
+ size += TCPOLEN_WSCALE_ALIGNED;
+ }
+ if (likely(doing_ts)) {
+ opts->options |= OPTION_TS;
+ opts->tsval = TCP_SKB_CB(skb)->when;
+ opts->tsecr = req->ts_recent;
+ size += TCPOLEN_TSTAMP_ALIGNED;
+ }
+ if (likely(ireq->sack_ok)) {
+ opts->options |= OPTION_SACK_ADVERTISE;
+ if (unlikely(!doing_ts))
+ size += TCPOLEN_SACKPERM_ALIGNED;
+ }
+
+ return size;
+}
+
+static unsigned tcp_established_options(struct sock *sk, struct sk_buff *skb,
+ struct tcp_out_options *opts,
+ struct tcp_md5sig_key **md5) {
+ struct tcp_skb_cb *tcb = skb ? TCP_SKB_CB(skb) : NULL;
+ struct tcp_sock *tp = tcp_sk(sk);
+ unsigned size = 0;
+
+#ifdef CONFIG_TCP_MD5SIG
+ *md5 = tp->af_specific->md5_lookup(sk, sk);
+ if (unlikely(*md5)) {
+ opts->options |= OPTION_MD5;
+ size += TCPOLEN_MD5SIG_ALIGNED;
+ }
+#else
+ *md5 = NULL;
+#endif
+
+ if (likely(tp->rx_opt.tstamp_ok)) {
+ opts->options |= OPTION_TS;
+ opts->tsval = tcb ? tcb->when : 0;
+ opts->tsecr = tp->rx_opt.ts_recent;
+ size += TCPOLEN_TSTAMP_ALIGNED;
+ }
+
+ if (unlikely(tp->rx_opt.eff_sacks)) {
+ const unsigned remaining = MAX_TCP_OPTION_SPACE - size;
+ opts->num_sack_blocks =
+ min_t(unsigned, tp->rx_opt.eff_sacks,
+ (remaining - TCPOLEN_SACK_BASE_ALIGNED) /
+ TCPOLEN_SACK_PERBLOCK);
+ size += TCPOLEN_SACK_BASE_ALIGNED +
+ opts->num_sack_blocks * TCPOLEN_SACK_PERBLOCK;
+ }
+
+ return size;