// SPDX-License-Identifier: GPL-2.0-or-later /* * net/dccp/input.c * * An implementation of the DCCP protocol * Arnaldo Carvalho de Melo <acme@conectiva.com.br> */ #include <linux/dccp.h> #include <linux/skbuff.h> #include <linux/slab.h> #include <net/sock.h> #include "ackvec.h" #include "ccid.h" #include "dccp.h" /* rate-limit for syncs in reply to sequence-invalid packets; RFC 4340, 7.5.4 */ int sysctl_dccp_sync_ratelimit __read_mostly = HZ / 8; static void dccp_enqueue_skb(struct sock *sk, struct sk_buff *skb) { __skb_pull(skb, dccp_hdr(skb)->dccph_doff * 4); __skb_queue_tail(&sk->sk_receive_queue, skb); skb_set_owner_r(skb, sk); sk->sk_data_ready(sk); } static void dccp_fin(struct sock *sk, struct sk_buff *skb) { /* * On receiving Close/CloseReq, both RD/WR shutdown are performed. * RFC 4340, 8.3 says that we MAY send further Data/DataAcks after * receiving the closing segment, but there is no guarantee that such * data will be processed at all. */ sk->sk_shutdown = SHUTDOWN_MASK; sock_set_flag(sk, SOCK_DONE); dccp_enqueue_skb(sk, skb); } static int dccp_rcv_close(struct sock *sk, struct sk_buff *skb) { int queued = 0; switch (sk->sk_state) { /* * We ignore Close when received in one of the following states: * - CLOSED (may be a late or duplicate packet) * - PASSIVE_CLOSEREQ (the peer has sent a CloseReq earlier) * - RESPOND (already handled by dccp_check_req) */ case DCCP_CLOSING: /* * Simultaneous-close: receiving a Close after sending one. This * can happen if both client and server perform active-close and * will result in an endless ping-pong of crossing and retrans- * mitted Close packets, which only terminates when one of the * nodes times out (min. 64 seconds). Quicker convergence can be * achieved when one of the nodes acts as tie-breaker. * This is ok as both ends are done with data transfer and each * end is just waiting for the other to acknowledge termination. */ if (dccp_sk(sk)->dccps_role != DCCP_ROLE_CLIENT) break; fallthrough; case DCCP_REQUESTING: case DCCP_ACTIVE_CLOSEREQ: dccp_send_reset(sk, DCCP_RESET_CODE_CLOSED); dccp_done(sk); break; case DCCP_OPEN: case DCCP_PARTOPEN: /* Give waiting application a chance to read pending data */ queued = 1; dccp_fin(sk, skb); dccp_set_state(sk, DCCP_PASSIVE_CLOSE); fallthrough; case DCCP_PASSIVE_CLOSE: /* * Retransmitted Close: we have already enqueued the first one. */ sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_HUP); } return queued; } static int dccp_rcv_closereq(struct sock *sk, struct sk_buff *skb) { int queued = 0; /* * Step 7: Check for unexpected packet types * If (S.is_server and P.type == CloseReq) * Send Sync packet acknowledging P.seqno * Drop packet and return */ if (dccp_sk(sk)->dccps_role != DCCP_ROLE_CLIENT) { dccp_send_sync(sk, DCCP_SKB_CB(skb)->dccpd_seq, DCCP_PKT_SYNC); return queued; } /* Step 13: process relevant Client states < CLOSEREQ */ switch (sk->sk_state) { case DCCP_REQUESTING: dccp_send_close(sk, 0); dccp_set_state(sk, DCCP_CLOSING); break; case DCCP_OPEN: case DCCP_PARTOPEN: /* Give waiting application a chance to read pending data */ queued = 1; dccp_fin(sk, skb); dccp_set_state(sk, DCCP_PASSIVE_CLOSEREQ); fallthrough; case DCCP_PASSIVE_CLOSEREQ: sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_HUP); } return queued; } static u16 dccp_reset_code_convert(const u8 code) { static const u16 error_code[] = { [DCCP_RESET_CODE_CLOSED] = 0, /* normal termination */ [DCCP_RESET_CODE_UNSPECIFIED] = 0, /* nothing known */ [DCCP_RESET_CODE_ABORTED] = ECONNRESET, [DCCP_RESET_CODE_NO_CONNECTION] = ECONNREFUSED, [DCCP_RESET_CODE_CONNECTION_REFUSED] = ECONNREFUSED, [DCCP_RESET_CODE_TOO_BUSY] = EUSERS, [DCCP_RESET_CODE_AGGRESSION_PENALTY] = EDQUOT, [DCCP_RESET_CODE_PACKET_ERROR] = ENOMSG, [DCCP_RESET_CODE_BAD_INIT_COOKIE] = EBADR, [DCCP_RESET_CODE_BAD_SERVICE_CODE] = EBADRQC, [DCCP_RESET_CODE_OPTION_ERROR] = EILSEQ, [DCCP_RESET_CODE_MANDATORY_ERROR] = EOPNOTSUPP, }; return code >= DCCP_MAX_RESET_CODES ? 0 : error_code[code]; } static void dccp_rcv_reset(struct sock *sk, struct sk_buff *skb) { u16 err = dccp_reset_code_convert(dccp_hdr_reset(skb)->dccph_reset_code); sk->sk_err = err; /* Queue the equivalent of TCP fin so that dccp_recvmsg exits the loop */ dccp_fin(sk, skb); if (err && !sock_flag(sk, SOCK_DEAD)) sk_wake_async(sk, SOCK_WAKE_IO, POLL_ERR); dccp_time_wait(sk, DCCP_TIME_WAIT, 0); } static void dccp_handle_ackvec_processing(struct sock *sk, struct sk_buff *skb) { struct dccp_ackvec *av = dccp_sk(sk)->dccps_hc_rx_ackvec; if (av == NULL) return; if (DCCP_SKB_CB(skb)->dccpd_ack_seq != DCCP_PKT_WITHOUT_ACK_SEQ) dccp_ackvec_clear_state(av, DCCP_SKB_CB(skb)->dccpd_ack_seq); dccp_ackvec_input(av, skb); } static void dccp_deliver_input_to_ccids(struct sock *sk, struct sk_buff *skb) { const struct dccp_sock *dp = dccp_sk(sk); /* Don't deliver to RX CCID when node has shut down read end. */ if (!(sk->sk_shutdown & RCV_SHUTDOWN)) ccid_hc_rx_packet_recv(dp->dccps_hc_rx_ccid, sk, skb); /* * Until the TX queue has been drained, we can not honour SHUT_WR, since * we need received feedback as input to adjust congestion control. */ if (sk->sk_write_queue.qlen > 0 || !(sk->sk_shutdown & SEND_SHUTDOWN)) ccid_hc_tx_packet_recv(dp->dccps_hc_tx_ccid, sk, skb); } static int dccp_check_seqno(struct sock *sk, struct sk_buff *skb) { const struct dccp_hdr *dh = dccp_hdr(skb); struct dccp_sock *dp = dccp_sk(sk); u64 lswl, lawl, seqno = DCCP_SKB_CB(skb)->dccpd_seq, ackno = DCCP_SKB_CB(skb)->dccpd_ack_seq; /* * Step 5: Prepare sequence numbers for Sync * If P.type == Sync or P.type == SyncAck, * If S.AWL <= P.ackno <= S.AWH and P.seqno >= S.SWL, * / * P is valid, so update sequence number variables * accordingly. After this update, P will pass the tests * in Step 6. A SyncAck is generated if necessary in * Step 15 * / * Update S.GSR, S.SWL, S.SWH * Otherwise, * Drop packet and return */ if (dh->dccph_type == DCCP_PKT_SYNC || dh->dccph_type == DCCP_PKT_SYNCACK) { if (between48(ackno, dp->dccps_awl, dp->dccps_awh) && dccp_delta_seqno(dp->dccps_swl, seqno) >= 0) dccp_update_gsr(sk, seqno); else return -1; } /* * Step 6: Check sequence numbers * Let LSWL = S.SWL and LAWL = S.AWL * If P.type == CloseReq or P.type == Close or P.type == Reset, * LSWL := S.GSR + 1, LAWL := S.GAR * If LSWL <= P.seqno <= S.SWH * and (P.ackno does not exist or LAWL <= P.ackno <= S.AWH), * Update S.GSR, S.SWL, S.SWH * If P.type != Sync, * Update S.GAR */ lswl = dp->dccps_swl; lawl = dp->dccps_awl; if (dh->dccph_type == DCCP_PKT_CLOSEREQ || dh->dccph_type == DCCP_PKT_CLOSE || dh->dccph_type == DCCP_PKT_RESET) { lswl = ADD48(dp->dccps_gsr, 1); lawl = dp->dccps_gar; } if (between48(seqno, lswl, dp->dccps_swh) && (ackno == DCCP_PKT_WITHOUT_ACK_SEQ || between48(ackno, lawl, dp->dccps_awh))) { dccp_update_gsr(sk, seqno); if (dh->dccph_type != DCCP_PKT_SYNC && ackno != DCCP_PKT_WITHOUT_ACK_SEQ && after48(ackno, dp->dccps_gar)) dp->dccps_gar = ackno; } else { unsigned long now = jiffies; /* * Step 6: Check sequence numbers * Otherwise, * If P.type == Reset, * Send Sync packet acknowledging S.GSR * Otherwise, * Send Sync packet acknowledging P.seqno * Drop packet and return * * These Syncs are rate-limited as per RFC 4340, 7.5.4: * at most 1 / (dccp_sync_rate_limit * HZ) Syncs per second. */ if (time_before(now, (dp->dccps_rate_last + sysctl_dccp_sync_ratelimit))) return -1; DCCP_WARN("Step 6 failed for %s packet, " "(LSWL(%llu) <= P.seqno(%llu) <= S.SWH(%llu)) and " "(P.ackno %s or LAWL(%llu) <= P.ackno(%llu) <= S.AWH(%llu), " "sending SYNC...\n", dccp_packet_name(dh->dccph_type), (unsigned long long) lswl, (unsigned long long) seqno, (unsigned long long) dp->dccps_swh, (ackno == DCCP_PKT_WITHOUT_ACK_SEQ) ? "doesn't exist" : "exists", (unsigned long long) lawl, (unsigned long long) ackno, (unsigned long long) dp->dccps_awh); dp->dccps_rate_last = now; if (dh->dccph_type == DCCP_PKT_RESET) seqno = dp->dccps_gsr; dccp_send_sync(sk, seqno, DCCP_PKT_SYNC); return -1; } return 0; } static int __dccp_rcv_established(struct sock *sk, struct sk_buff *skb, const struct dccp_hdr *dh, const unsigned int len) { struct dccp_sock *dp = dccp_sk(sk); switch (dccp_hdr(skb)->dccph_type) { case DCCP_PKT_DATAACK: case DCCP_PKT_DATA: /* * FIXME: schedule DATA_DROPPED (RFC 4340, 11.7.2) if and when * - sk_shutdown == RCV_SHUTDOWN, use Code 1, "Not Listening" * - sk_receive_queue is full, use Code 2, "Receive Buffer" */ dccp_enqueue_skb(sk, skb); return 0; case DCCP_PKT_ACK: goto discard; case DCCP_PKT_RESET: /* * Step 9: Process Reset * If P.type == Reset, * Tear down connection * S.state := TIMEWAIT * Set TIMEWAIT timer * Drop packet and return */ dccp_rcv_reset(sk, skb); return 0; case DCCP_PKT_CLOSEREQ: if (dccp_rcv_closereq(sk, skb)) return 0; goto discard; case DCCP_PKT_CLOSE: if (dccp_rcv_close(sk, skb)) return 0; goto discard; case DCCP_PKT_REQUEST: /* Step 7 * or (S.is_server and P.type == Response) * or (S.is_client and P.type == Request) * or (S.state >= OPEN and P.type == Request * and P.seqno >= S.OSR) * or (S.state >= OPEN and P.type == Response * and P.seqno >= S.OSR) * or (S.state == RESPOND and P.type == Data), * Send Sync packet acknowledging P.seqno * Drop packet and return */ if (dp->dccps_role != DCCP_ROLE_LISTEN) goto send_sync; goto check_seq; case DCCP_PKT_RESPONSE: if (dp->dccps_role != DCCP_ROLE_CLIENT) goto send_sync; check_seq: if (dccp_delta_seqno(dp->dccps_osr, DCCP_SKB_CB(skb)->dccpd_seq) >= 0) { send_sync: dccp_send_sync(sk, DCCP_SKB_CB(skb)->dccpd_seq, DCCP_PKT_SYNC); } break; case DCCP_PKT_SYNC: dccp_send_sync(sk, DCCP_SKB_CB(skb)->dccpd_seq, DCCP_PKT_SYNCACK); /* * From RFC 4340, sec. 5.7 * * As with DCCP-Ack packets, DCCP-Sync and DCCP-SyncAck packets * MAY have non-zero-length application data areas, whose * contents receivers MUST ignore. */ goto discard; } DCCP_INC_STATS(DCCP_MIB_INERRS); discard: __kfree_skb(skb); return 0; } int dccp_rcv_established(struct sock *sk, struct sk_buff *skb, const struct dccp_hdr *dh, const unsigned int len) { if (dccp_check_seqno(sk, skb)) goto discard; if (dccp_parse_options(sk, NULL, skb)) return 1; dccp_handle_ackvec_processing(sk, skb); dccp_deliver_input_to_ccids(sk, skb); return __dccp_rcv_established(sk, skb, dh, len); discard: __kfree_skb(skb); return 0; } EXPORT_SYMBOL_GPL(dccp_rcv_established); static int dccp_rcv_request_sent_state_process(struct sock *sk, struct sk_buff *skb, const struct dccp_hdr *dh, const unsigned int len) { /* * Step 4: Prepare sequence numbers in REQUEST * If S.state == REQUEST, * If (P.type == Response or P.type == Reset) * and S.AWL <= P.ackno <= S.AWH, * / * Set sequence number variables corresponding to the * other endpoint, so P will pass the tests in Step 6 * / * Set S.GSR, S.ISR, S.SWL, S.SWH * / * Response processing continues in Step 10; Reset * processing continues in Step 9 * / */ if (dh->dccph_type == DCCP_PKT_RESPONSE) { const struct inet_connection_sock *icsk = inet_csk(sk); struct dccp_sock *dp = dccp_sk(sk); long tstamp = dccp_timestamp(); if (!between48(DCCP_SKB_CB(skb)->dccpd_ack_seq, dp->dccps_awl, dp->dccps_awh)) { dccp_pr_debug("invalid ackno: S.AWL=%llu, " "P.ackno=%llu, S.AWH=%llu\n", (unsigned long long)dp->dccps_awl, (unsigned long long)DCCP_SKB_CB(skb)->dccpd_ack_seq, (unsigned long long)dp->dccps_awh); goto out_invalid_packet; } /* * If option processing (Step 8) failed, return 1 here so that * dccp_v4_do_rcv() sends a Reset. The Reset code depends on * the option type and is set in dccp_parse_options(). */ if (dccp_parse_options(sk, NULL, skb)) return 1; /* Obtain usec RTT sample from SYN exchange (used by TFRC). */ if (likely(dp->dccps_options_received.dccpor_timestamp_echo)) dp->dccps_syn_rtt = dccp_sample_rtt(sk, 10 * (tstamp - dp->dccps_options_received.dccpor_timestamp_echo)); /* Stop the REQUEST timer */ inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS); WARN_ON(sk->sk_send_head == NULL); kfree_skb(sk->sk_send_head); sk->sk_send_head = NULL; /* * Set ISR, GSR from packet. ISS was set in dccp_v{4,6}_connect * and GSS in dccp_transmit_skb(). Setting AWL/AWH and SWL/SWH * is done as part of activating the feature values below, since * these settings depend on the local/remote Sequence Window * features, which were undefined or not confirmed until now. */ dp->dccps_gsr = dp->dccps_isr = DCCP_SKB_CB(skb)->dccpd_seq; dccp_sync_mss(sk, icsk->icsk_pmtu_cookie); /* * Step 10: Process REQUEST state (second part) * If S.state == REQUEST, * / * If we get here, P is a valid Response from the * server (see Step 4), and we should move to * PARTOPEN state. PARTOPEN means send an Ack, * don't send Data packets, retransmit Acks * periodically, and always include any Init Cookie * from the Response * / * S.state := PARTOPEN * Set PARTOPEN timer * Continue with S.state == PARTOPEN * / * Step 12 will send the Ack completing the * three-way handshake * / */ dccp_set_state(sk, DCCP_PARTOPEN); /* * If feature negotiation was successful, activate features now; * an activation failure means that this host could not activate * one ore more features (e.g. insufficient memory), which would * leave at least one feature in an undefined state. */ if (dccp_feat_activate_values(sk, &dp->dccps_featneg)) goto unable_to_proceed; /* Make sure socket is routed, for correct metrics. */ icsk->icsk_af_ops->rebuild_header(sk); if (!sock_flag(sk, SOCK_DEAD)) { sk->sk_state_change(sk); sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT); } if (sk->sk_write_pending || inet_csk_in_pingpong_mode(sk) || icsk->icsk_accept_queue.rskq_defer_accept) { /* Save one ACK. Data will be ready after * several ticks, if write_pending is set. * * It may be deleted, but with this feature tcpdumps * look so _wonderfully_ clever, that I was not able * to stand against the temptation 8) --ANK */ /* * OK, in DCCP we can as well do a similar trick, its * even in the draft, but there is no need for us to * schedule an ack here, as dccp_sendmsg does this for * us, also stated in the draft. -acme */ __kfree_skb(skb); return 0; } dccp_send_ack(sk); return -1; } out_invalid_packet: /* dccp_v4_do_rcv will send a reset */ DCCP_SKB_CB(skb)->dccpd_reset_code = DCCP_RESET_CODE_PACKET_ERROR; return 1; unable_to_proceed: DCCP_SKB_CB(skb)->dccpd_reset_code = DCCP_RESET_CODE_ABORTED; /* * We mark this socket as no longer usable, so that the loop in * dccp_sendmsg() terminates and the application gets notified. */ dccp_set_state(sk, DCCP_CLOSED); sk->sk_err = ECOMM; return 1; } static int dccp_rcv_respond_partopen_state_process(struct sock *sk, struct sk_buff *skb, const struct dccp_hdr *dh, const unsigned int len) { struct dccp_sock *dp = dccp_sk(sk); u32 sample = dp->dccps_options_received.dccpor_timestamp_echo; int queued = 0; switch (dh->dccph_type) { case DCCP_PKT_RESET: inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK); break; case DCCP_PKT_DATA: if (sk->sk_state == DCCP_RESPOND) break; fallthrough; case DCCP_PKT_DATAACK: case DCCP_PKT_ACK: /* * FIXME: we should be resetting the PARTOPEN (DELACK) timer * here but only if we haven't used the DELACK timer for * something else, like sending a delayed ack for a TIMESTAMP * echo, etc, for now were not clearing it, sending an extra * ACK when there is nothing else to do in DELACK is not a big * deal after all. */ /* Stop the PARTOPEN timer */ if (sk->sk_state == DCCP_PARTOPEN) inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK); /* Obtain usec RTT sample from SYN exchange (used by TFRC). */ if (likely(sample)) { long delta = dccp_timestamp() - sample; dp->dccps_syn_rtt = dccp_sample_rtt(sk, 10 * delta); } dp->dccps_osr = DCCP_SKB_CB(skb)->dccpd_seq; dccp_set_state(sk, DCCP_OPEN); if (dh->dccph_type == DCCP_PKT_DATAACK || dh->dccph_type == DCCP_PKT_DATA) { __dccp_rcv_established(sk, skb, dh, len); queued = 1; /* packet was queued (by __dccp_rcv_established) */ } break; } return queued; } int dccp_rcv_state_process(struct sock *sk, struct sk_buff *skb, struct dccp_hdr *dh, unsigned int len) { struct dccp_sock *dp = dccp_sk(sk); struct dccp_skb_cb *dcb = DCCP_SKB_CB(skb); const int old_state = sk->sk_state; bool acceptable; int queued = 0; /* * Step 3: Process LISTEN state * * If S.state == LISTEN, * If P.type == Request or P contains a valid Init Cookie option, * (* Must scan the packet's options to check for Init * Cookies. Only Init Cookies are processed here, * however; other options are processed in Step 8. This * scan need only be performed if the endpoint uses Init * Cookies *) * (* Generate a new socket and switch to that socket *) * Set S := new socket for this port pair * S.state = RESPOND * Choose S.ISS (initial seqno) or set from Init Cookies * Initialize S.GAR := S.ISS * Set S.ISR, S.GSR, S.SWL, S.SWH from packet or Init * Cookies Continue with S.state == RESPOND * (* A Response packet will be generated in Step 11 *) * Otherwise, * Generate Reset(No Connection) unless P.type == Reset * Drop packet and return */ if (sk->sk_state == DCCP_LISTEN) { if (dh->dccph_type == DCCP_PKT_REQUEST) { /* It is possible that we process SYN packets from backlog, * so we need to make sure to disable BH and RCU right there. */ rcu_read_lock(); local_bh_disable(); acceptable = inet_csk(sk)->icsk_af_ops->conn_request(sk, skb) >= 0; local_bh_enable(); rcu_read_unlock(); if (!acceptable) return 1; consume_skb(skb); return 0; } if (dh->dccph_type == DCCP_PKT_RESET) goto discard; /* Caller (dccp_v4_do_rcv) will send Reset */ dcb->dccpd_reset_code = DCCP_RESET_CODE_NO_CONNECTION; return 1; } else if (sk->sk_state == DCCP_CLOSED) { dcb->dccpd_reset_code = DCCP_RESET_CODE_NO_CONNECTION; return 1; } /* Step 6: Check sequence numbers (omitted in LISTEN/REQUEST state) */ if (sk->sk_state != DCCP_REQUESTING && dccp_check_seqno(sk, skb)) goto discard; /* * Step 7: Check for unexpected packet types * If (S.is_server and P.type == Response) * or (S.is_client and P.type == Request) * or (S.state == RESPOND and P.type == Data), * Send Sync packet acknowledging P.seqno * Drop packet and return */ if ((dp->dccps_role != DCCP_ROLE_CLIENT && dh->dccph_type == DCCP_PKT_RESPONSE) || (dp->dccps_role == DCCP_ROLE_CLIENT && dh->dccph_type == DCCP_PKT_REQUEST) || (sk->sk_state == DCCP_RESPOND && dh->dccph_type == DCCP_PKT_DATA)) { dccp_send_sync(sk, dcb->dccpd_seq, DCCP_PKT_SYNC); goto discard; } /* Step 8: Process options */ if (dccp_parse_options(sk, NULL, skb)) return 1; /* * Step 9: Process Reset * If P.type == Reset, * Tear down connection * S.state := TIMEWAIT * Set TIMEWAIT timer * Drop packet and return */ if (dh->dccph_type == DCCP_PKT_RESET) { dccp_rcv_reset(sk, skb); return 0; } else if (dh->dccph_type == DCCP_PKT_CLOSEREQ) { /* Step 13 */ if (dccp_rcv_closereq(sk, skb)) return 0; goto discard; } else if (dh->dccph_type == DCCP_PKT_CLOSE) { /* Step 14 */ if (dccp_rcv_close(sk, skb)) return 0; goto discard; } switch (sk->sk_state) { case DCCP_REQUESTING: queued = dccp_rcv_request_sent_state_process(sk, skb, dh, len); if (queued >= 0) return queued; __kfree_skb(skb); return 0; case DCCP_PARTOPEN: /* Step 8: if using Ack Vectors, mark packet acknowledgeable */ dccp_handle_ackvec_processing(sk, skb); dccp_deliver_input_to_ccids(sk, skb); fallthrough; case DCCP_RESPOND: queued = dccp_rcv_respond_partopen_state_process(sk, skb, dh, len); break; } if (dh->dccph_type == DCCP_PKT_ACK || dh->dccph_type == DCCP_PKT_DATAACK) { switch (old_state) { case DCCP_PARTOPEN: sk->sk_state_change(sk); sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT); break; } } else if (unlikely(dh->dccph_type == DCCP_PKT_SYNC)) { dccp_send_sync(sk, dcb->dccpd_seq, DCCP_PKT_SYNCACK); goto discard; } if (!queued) { discard: __kfree_skb(skb); } return 0; } EXPORT_SYMBOL_GPL(dccp_rcv_state_process); /** * dccp_sample_rtt - Validate and finalise computation of RTT sample * @sk: socket structure * @delta: number of microseconds between packet and acknowledgment * * The routine is kept generic to work in different contexts. It should be * called immediately when the ACK used for the RTT sample arrives. */ u32 dccp_sample_rtt(struct sock *sk, long delta) { /* dccpor_elapsed_time is either zeroed out or set and > 0 */ delta -= dccp_sk(sk)->dccps_options_received.dccpor_elapsed_time * 10; if (unlikely(delta <= 0)) { DCCP_WARN("unusable RTT sample %ld, using min\n", delta); return DCCP_SANE_RTT_MIN; } if (unlikely(delta > DCCP_SANE_RTT_MAX)) { DCCP_WARN("RTT sample %ld too large, using max\n", delta); return DCCP_SANE_RTT_MAX; } return delta; }