// SPDX-License-Identifier: GPL-2.0-or-later
/* Management of Tx window, Tx resend, ACKs and out-of-sequence reception
 *
 * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/module.h>
#include <linux/circ_buf.h>
#include <linux/net.h>
#include <linux/skbuff.h>
#include <linux/slab.h>
#include <linux/udp.h>
#include <net/sock.h>
#include <net/af_rxrpc.h>
#include "ar-internal.h"

/*
 * Propose a PING ACK be sent.
 */
void rxrpc_propose_ping(struct rxrpc_call *call, u32 serial,
                        enum rxrpc_propose_ack_trace why)
{
        ktime_t delay = ms_to_ktime(READ_ONCE(rxrpc_idle_ack_delay));
        ktime_t now = ktime_get_real();
        ktime_t ping_at = ktime_add(now, delay);

        trace_rxrpc_propose_ack(call, why, RXRPC_ACK_PING, serial);
        if (ktime_before(ping_at, call->ping_at)) {
                call->ping_at = ping_at;
                trace_rxrpc_timer_set(call, delay, rxrpc_timer_trace_ping);
        }
}

/*
 * Propose a DELAY ACK be sent in the future.
 */
void rxrpc_propose_delay_ACK(struct rxrpc_call *call, rxrpc_serial_t serial,
                             enum rxrpc_propose_ack_trace why)
{
        ktime_t now = ktime_get_real(), delay;

        trace_rxrpc_propose_ack(call, why, RXRPC_ACK_DELAY, serial);

        if (call->srtt_us)
                delay = (call->srtt_us >> 3) * NSEC_PER_USEC;
        else
                delay = ms_to_ktime(READ_ONCE(rxrpc_soft_ack_delay));
        ktime_add_ms(delay, call->tx_backoff);

        call->delay_ack_at = ktime_add(now, delay);
        trace_rxrpc_timer_set(call, delay, rxrpc_timer_trace_delayed_ack);
}

/*
 * Retransmit one or more packets.
 */
static bool rxrpc_retransmit_data(struct rxrpc_call *call,
                                  struct rxrpc_send_data_req *req)
{
        struct rxrpc_txqueue *tq = req->tq;
        unsigned int ix = req->seq & RXRPC_TXQ_MASK;
        struct rxrpc_txbuf *txb = tq->bufs[ix];

        _enter("%x,%x,%x,%x", tq->qbase, req->seq, ix, txb->debug_id);

        req->retrans = true;
        trace_rxrpc_retransmit(call, req, txb);

        txb->flags |= RXRPC_TXBUF_RESENT;
        rxrpc_send_data_packet(call, req);
        rxrpc_inc_stat(call->rxnet, stat_tx_data_retrans);

        req->tq         = NULL;
        req->n          = 0;
        req->did_send   = true;
        req->now        = ktime_get_real();
        return true;
}

/*
 * Perform retransmission of NAK'd and unack'd packets.
 */
static void rxrpc_resend(struct rxrpc_call *call)
{
        struct rxrpc_send_data_req req = {
                .now    = ktime_get_real(),
                .trace  = rxrpc_txdata_retransmit,
        };
        struct rxrpc_txqueue *tq;

        _enter("{%d,%d}", call->tx_bottom, call->tx_top);

        trace_rxrpc_resend(call, call->acks_highest_serial);

        /* Scan the transmission queue, looking for lost packets. */
        for (tq = call->tx_queue; tq; tq = tq->next) {
                unsigned long lost = tq->segment_lost;

                if (after(tq->qbase, call->tx_transmitted))
                        break;

                _debug("retr %16lx %u c=%08x [%x]",
                       tq->segment_acked, tq->nr_reported_acks, call->debug_id, tq->qbase);
                _debug("lost %16lx", lost);

                trace_rxrpc_resend_lost(call, tq, lost);
                while (lost) {
                        unsigned int ix = __ffs(lost);
                        struct rxrpc_txbuf *txb = tq->bufs[ix];

                        __clear_bit(ix, &lost);
                        rxrpc_see_txbuf(txb, rxrpc_txbuf_see_lost);

                        req.tq  = tq;
                        req.seq = tq->qbase + ix;
                        req.n   = 1;
                        rxrpc_retransmit_data(call, &req);
                }
        }

        rxrpc_get_rto_backoff(call, req.did_send);
        _leave("");
}

/*
 * Resend the highest-seq DATA packet so far transmitted for RACK-TLP [RFC8985 7.3].
 */
void rxrpc_resend_tlp(struct rxrpc_call *call)
{
        struct rxrpc_send_data_req req = {
                .now            = ktime_get_real(),
                .seq            = call->tx_transmitted,
                .n              = 1,
                .tlp_probe      = true,
                .trace          = rxrpc_txdata_tlp_retransmit,
        };

        /* There's a chance it'll be on the tail segment of the queue. */
        req.tq = READ_ONCE(call->tx_qtail);
        if (req.tq &&
            before(call->tx_transmitted, req.tq->qbase + RXRPC_NR_TXQUEUE)) {
                rxrpc_retransmit_data(call, &req);
                return;
        }

        for (req.tq = call->tx_queue; req.tq; req.tq = req.tq->next) {
                if (after_eq(call->tx_transmitted, req.tq->qbase) &&
                    before(call->tx_transmitted, req.tq->qbase + RXRPC_NR_TXQUEUE)) {
                        rxrpc_retransmit_data(call, &req);
                        return;
                }
        }
}

/*
 * Start transmitting the reply to a service.  This cancels the need to ACK the
 * request if we haven't yet done so.
 */
static void rxrpc_begin_service_reply(struct rxrpc_call *call)
{
        rxrpc_set_call_state(call, RXRPC_CALL_SERVER_SEND_REPLY);
        if (call->ackr_reason == RXRPC_ACK_DELAY)
                call->ackr_reason = 0;
        call->delay_ack_at = KTIME_MAX;
        trace_rxrpc_timer_can(call, rxrpc_timer_trace_delayed_ack);
}

/*
 * Close the transmission phase.  After this point there is no more data to be
 * transmitted in the call.
 */
static void rxrpc_close_tx_phase(struct rxrpc_call *call)
{
        _debug("________awaiting reply/ACK__________");

        switch (__rxrpc_call_state(call)) {
        case RXRPC_CALL_CLIENT_SEND_REQUEST:
                rxrpc_set_call_state(call, RXRPC_CALL_CLIENT_AWAIT_REPLY);
                break;
        case RXRPC_CALL_SERVER_SEND_REPLY:
                rxrpc_set_call_state(call, RXRPC_CALL_SERVER_AWAIT_ACK);
                break;
        default:
                break;
        }
}

/*
 * Transmit some as-yet untransmitted data, to a maximum of the supplied limit.
 */
static void rxrpc_transmit_fresh_data(struct rxrpc_call *call, unsigned int limit,
                                      enum rxrpc_txdata_trace trace)
{
        int space = rxrpc_tx_window_space(call);

        if (!test_bit(RXRPC_CALL_EXPOSED, &call->flags)) {
                if (call->send_top == call->tx_top)
                        return;
                rxrpc_expose_client_call(call);
        }

        while (space > 0) {
                struct rxrpc_send_data_req req = {
                        .now    = ktime_get_real(),
                        .seq    = call->tx_transmitted + 1,
                        .n      = 0,
                        .trace  = trace,
                };
                struct rxrpc_txqueue *tq;
                struct rxrpc_txbuf *txb;
                rxrpc_seq_t send_top, seq;
                int limit = min(space, max(call->peer->pmtud_jumbo, 1));

                /* Order send_top before the contents of the new txbufs and
                 * txqueue pointers
                 */
                send_top = smp_load_acquire(&call->send_top);
                if (call->tx_top == send_top)
                        break;

                trace_rxrpc_transmit(call, send_top, space);

                tq = call->tx_qtail;
                seq = call->tx_top;
                trace_rxrpc_tq(call, tq, seq, rxrpc_tq_decant);

                do {
                        int ix;

                        seq++;
                        ix = seq & RXRPC_TXQ_MASK;
                        if (!ix) {
                                tq = tq->next;
                                trace_rxrpc_tq(call, tq, seq, rxrpc_tq_decant_advance);
                        }
                        if (!req.tq)
                                req.tq = tq;
                        txb = tq->bufs[ix];
                        req.n++;
                        if (!txb->jumboable)
                                break;
                } while (req.n < limit && before(seq, send_top));

                if (txb->flags & RXRPC_LAST_PACKET) {
                        rxrpc_close_tx_phase(call);
                        tq = NULL;
                }
                call->tx_qtail = tq;
                call->tx_top = seq;

                space -= req.n;
                rxrpc_send_data_packet(call, &req);
        }
}

void rxrpc_transmit_some_data(struct rxrpc_call *call, unsigned int limit,
                              enum rxrpc_txdata_trace trace)
{
        switch (__rxrpc_call_state(call)) {
        case RXRPC_CALL_SERVER_ACK_REQUEST:
                if (call->tx_bottom == READ_ONCE(call->send_top))
                        return;
                rxrpc_begin_service_reply(call);
                fallthrough;

        case RXRPC_CALL_SERVER_SEND_REPLY:
        case RXRPC_CALL_CLIENT_SEND_REQUEST:
                if (!rxrpc_tx_window_space(call))
                        return;
                if (call->tx_bottom == READ_ONCE(call->send_top)) {
                        rxrpc_inc_stat(call->rxnet, stat_tx_data_underflow);
                        return;
                }
                rxrpc_transmit_fresh_data(call, limit, trace);
                break;
        default:
                return;
        }
}

/*
 * Ping the other end to fill our RTT cache and to retrieve the rwind
 * and MTU parameters.
 */
static void rxrpc_send_initial_ping(struct rxrpc_call *call)
{
        if (call->rtt_count < 3 ||
            ktime_before(ktime_add_ms(call->rtt_last_req, 1000),
                         ktime_get_real()))
                rxrpc_send_ACK(call, RXRPC_ACK_PING, 0,
                               rxrpc_propose_ack_ping_for_params);
}

/*
 * Handle retransmission and deferred ACK/abort generation.
 */
bool rxrpc_input_call_event(struct rxrpc_call *call)
{
        struct sk_buff *skb;
        ktime_t now, t;
        bool did_receive = false, saw_ack = false;
        s32 abort_code;

        rxrpc_see_call(call, rxrpc_call_see_input);

        //printk("\n--------------------\n");
        _enter("{%d,%s,%lx}",
               call->debug_id, rxrpc_call_states[__rxrpc_call_state(call)],
               call->events);

        /* Handle abort request locklessly, vs rxrpc_propose_abort(). */
        abort_code = smp_load_acquire(&call->send_abort);
        if (abort_code) {
                rxrpc_abort_call(call, 0, call->send_abort, call->send_abort_err,
                                 call->send_abort_why);
                goto out;
        }

        do {
                skb = __skb_dequeue(&call->rx_queue);
                if (skb) {
                        struct rxrpc_skb_priv *sp = rxrpc_skb(skb);

                        if (__rxrpc_call_is_complete(call) ||
                            skb->mark == RXRPC_SKB_MARK_ERROR) {
                                rxrpc_free_skb(skb, rxrpc_skb_put_call_rx);
                                goto out;
                        }

                        saw_ack |= sp->hdr.type == RXRPC_PACKET_TYPE_ACK;

                        rxrpc_input_call_packet(call, skb);
                        rxrpc_free_skb(skb, rxrpc_skb_put_call_rx);
                        did_receive = true;
                }

                t = ktime_sub(call->rack_timo_at, ktime_get_real());
                if (t <= 0) {
                        trace_rxrpc_timer_exp(call, t,
                                              rxrpc_timer_trace_rack_off + call->rack_timer_mode);
                        call->rack_timo_at = KTIME_MAX;
                        rxrpc_rack_timer_expired(call, t);
                }

        } while (!skb_queue_empty(&call->rx_queue));

        /* If we see our async-event poke, check for timeout trippage. */
        now = ktime_get_real();
        t = ktime_sub(call->expect_rx_by, now);
        if (t <= 0) {
                trace_rxrpc_timer_exp(call, t, rxrpc_timer_trace_expect_rx);
                goto expired;
        }

        t = ktime_sub(call->expect_req_by, now);
        if (t <= 0) {
                call->expect_req_by = KTIME_MAX;
                if (__rxrpc_call_state(call) == RXRPC_CALL_SERVER_RECV_REQUEST) {
                        trace_rxrpc_timer_exp(call, t, rxrpc_timer_trace_idle);
                        goto expired;
                }
        }

        t = ktime_sub(READ_ONCE(call->expect_term_by), now);
        if (t <= 0) {
                trace_rxrpc_timer_exp(call, t, rxrpc_timer_trace_hard);
                goto expired;
        }

        t = ktime_sub(call->delay_ack_at, now);
        if (t <= 0) {
                trace_rxrpc_timer_exp(call, t, rxrpc_timer_trace_delayed_ack);
                call->delay_ack_at = KTIME_MAX;
                rxrpc_send_ACK(call, RXRPC_ACK_DELAY, 0,
                               rxrpc_propose_ack_delayed_ack);
        }

        t = ktime_sub(call->ping_at, now);
        if (t <= 0) {
                trace_rxrpc_timer_exp(call, t, rxrpc_timer_trace_ping);
                call->ping_at = KTIME_MAX;
                rxrpc_send_ACK(call, RXRPC_ACK_PING, 0,
                               rxrpc_propose_ack_ping_for_keepalive);
        }

        now = ktime_get_real();
        t = ktime_sub(call->keepalive_at, now);
        if (t <= 0) {
                trace_rxrpc_timer_exp(call, t, rxrpc_timer_trace_keepalive);
                call->keepalive_at = KTIME_MAX;
                rxrpc_send_ACK(call, RXRPC_ACK_PING, 0,
                               rxrpc_propose_ack_ping_for_keepalive);
        }

        if (test_and_clear_bit(RXRPC_CALL_EV_INITIAL_PING, &call->events))
                rxrpc_send_initial_ping(call);

        rxrpc_transmit_some_data(call, UINT_MAX, rxrpc_txdata_new_data);

        if (saw_ack)
                rxrpc_congestion_degrade(call);

        if (did_receive &&
            (__rxrpc_call_state(call) == RXRPC_CALL_CLIENT_SEND_REQUEST ||
             __rxrpc_call_state(call) == RXRPC_CALL_SERVER_SEND_REPLY)) {
                t = ktime_sub(call->rack_timo_at, ktime_get_real());
                trace_rxrpc_rack(call, t);
        }

        /* Process events */
        if (test_and_clear_bit(RXRPC_CALL_EV_ACK_LOST, &call->events))
                rxrpc_send_ACK(call, RXRPC_ACK_PING, 0,
                               rxrpc_propose_ack_ping_for_lost_ack);

        if (call->tx_nr_lost > 0 &&
            __rxrpc_call_state(call) != RXRPC_CALL_CLIENT_RECV_REPLY &&
            !test_bit(RXRPC_CALL_TX_ALL_ACKED, &call->flags))
                rxrpc_resend(call);

        if (test_and_clear_bit(RXRPC_CALL_RX_IS_IDLE, &call->flags))
                rxrpc_send_ACK(call, RXRPC_ACK_IDLE, 0,
                               rxrpc_propose_ack_rx_idle);

        if (call->ackr_nr_unacked > 2) {
                if (call->rtt_count < 3)
                        rxrpc_send_ACK(call, RXRPC_ACK_PING, 0,
                                       rxrpc_propose_ack_ping_for_rtt);
                else if (ktime_before(ktime_add_ms(call->rtt_last_req, 1000),
                                      ktime_get_real()))
                        rxrpc_send_ACK(call, RXRPC_ACK_PING, 0,
                                       rxrpc_propose_ack_ping_for_old_rtt);
                else
                        rxrpc_send_ACK(call, RXRPC_ACK_IDLE, 0,
                                       rxrpc_propose_ack_input_data);
        }

        /* Make sure the timer is restarted */
        if (!__rxrpc_call_is_complete(call)) {
                ktime_t next = READ_ONCE(call->expect_term_by), delay;

#define set(T) { ktime_t _t = (T); if (ktime_before(_t, next)) next = _t; }

                set(call->expect_req_by);
                set(call->expect_rx_by);
                set(call->delay_ack_at);
                set(call->rack_timo_at);
                set(call->keepalive_at);
                set(call->ping_at);

                now = ktime_get_real();
                delay = ktime_sub(next, now);
                if (delay <= 0) {
                        rxrpc_poke_call(call, rxrpc_call_poke_timer_now);
                } else {
                        unsigned long nowj = jiffies, delayj, nextj;

                        delayj = umax(nsecs_to_jiffies(delay), 1);
                        nextj = nowj + delayj;
                        if (time_before(nextj, call->timer.expires) ||
                            !timer_pending(&call->timer)) {
                                trace_rxrpc_timer_restart(call, delay, delayj);
                                timer_reduce(&call->timer, nextj);
                        }
                }
        }

out:
        if (__rxrpc_call_is_complete(call)) {
                timer_delete_sync(&call->timer);
                if (!test_bit(RXRPC_CALL_DISCONNECTED, &call->flags))
                        rxrpc_disconnect_call(call);
                if (call->security)
                        call->security->free_call_crypto(call);
        } else {
                if (did_receive &&
                    call->peer->ackr_adv_pmtud &&
                    call->peer->pmtud_pending)
                        rxrpc_send_probe_for_pmtud(call);
        }
        _leave("");
        return true;

expired:
        if (test_bit(RXRPC_CALL_RX_HEARD, &call->flags) &&
            (int)call->conn->hi_serial - (int)call->rx_serial > 0) {
                trace_rxrpc_call_reset(call);
                rxrpc_abort_call(call, 0, RX_CALL_DEAD, -ECONNRESET,
                                 rxrpc_abort_call_reset);
        } else {
                rxrpc_abort_call(call, 0, RX_CALL_TIMEOUT, -ETIME,
                                 rxrpc_abort_call_timeout);
        }
        goto out;
}