/* 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)
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version
 * 2 of the License, or (at your option) any later version.
 */

#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.
 */
static void rxrpc_propose_ping(struct rxrpc_call *call,
                               bool immediate, bool background)
{
        if (immediate) {
                if (background &&
                    !test_and_set_bit(RXRPC_CALL_EV_PING, &call->events))
                        rxrpc_queue_call(call);
        } else {
                unsigned long now = jiffies;
                unsigned long ping_at = now + rxrpc_idle_ack_delay;

                if (time_before(ping_at, call->ping_at)) {
                        WRITE_ONCE(call->ping_at, ping_at);
                        rxrpc_reduce_call_timer(call, ping_at, now,
                                                rxrpc_timer_set_for_ping);
                }
        }
}

/*
 * propose an ACK be sent
 */
static void __rxrpc_propose_ACK(struct rxrpc_call *call, u8 ack_reason,
                                u16 skew, u32 serial, bool immediate,
                                bool background,
                                enum rxrpc_propose_ack_trace why)
{
        enum rxrpc_propose_ack_outcome outcome = rxrpc_propose_ack_use;
        unsigned long expiry = rxrpc_soft_ack_delay;
        s8 prior = rxrpc_ack_priority[ack_reason];

        /* Pings are handled specially because we don't want to accidentally
         * lose a ping response by subsuming it into a ping.
         */
        if (ack_reason == RXRPC_ACK_PING) {
                rxrpc_propose_ping(call, immediate, background);
                goto trace;
        }

        /* Update DELAY, IDLE, REQUESTED and PING_RESPONSE ACK serial
         * numbers, but we don't alter the timeout.
         */
        _debug("prior %u %u vs %u %u",
               ack_reason, prior,
               call->ackr_reason, rxrpc_ack_priority[call->ackr_reason]);
        if (ack_reason == call->ackr_reason) {
                if (RXRPC_ACK_UPDATEABLE & (1 << ack_reason)) {
                        outcome = rxrpc_propose_ack_update;
                        call->ackr_serial = serial;
                        call->ackr_skew = skew;
                }
                if (!immediate)
                        goto trace;
        } else if (prior > rxrpc_ack_priority[call->ackr_reason]) {
                call->ackr_reason = ack_reason;
                call->ackr_serial = serial;
                call->ackr_skew = skew;
        } else {
                outcome = rxrpc_propose_ack_subsume;
        }

        switch (ack_reason) {
        case RXRPC_ACK_REQUESTED:
                if (rxrpc_requested_ack_delay < expiry)
                        expiry = rxrpc_requested_ack_delay;
                if (serial == 1)
                        immediate = false;
                break;

        case RXRPC_ACK_DELAY:
                if (rxrpc_soft_ack_delay < expiry)
                        expiry = rxrpc_soft_ack_delay;
                break;

        case RXRPC_ACK_IDLE:
                if (rxrpc_idle_ack_delay < expiry)
                        expiry = rxrpc_idle_ack_delay;
                break;

        default:
                immediate = true;
                break;
        }

        if (test_bit(RXRPC_CALL_EV_ACK, &call->events)) {
                _debug("already scheduled");
        } else if (immediate || expiry == 0) {
                _debug("immediate ACK %lx", call->events);
                if (!test_and_set_bit(RXRPC_CALL_EV_ACK, &call->events) &&
                    background)
                        rxrpc_queue_call(call);
        } else {
                unsigned long now = jiffies, ack_at;

                if (call->peer->rtt_usage > 0)
                        ack_at = nsecs_to_jiffies(call->peer->rtt);
                else
                        ack_at = expiry;

                ack_at += now;
                if (time_before(ack_at, call->ack_at)) {
                        WRITE_ONCE(call->ack_at, ack_at);
                        rxrpc_reduce_call_timer(call, ack_at, now,
                                                rxrpc_timer_set_for_ack);
                }
        }

trace:
        trace_rxrpc_propose_ack(call, why, ack_reason, serial, immediate,
                                background, outcome);
}

/*
 * propose an ACK be sent, locking the call structure
 */
void rxrpc_propose_ACK(struct rxrpc_call *call, u8 ack_reason,
                       u16 skew, u32 serial, bool immediate, bool background,
                       enum rxrpc_propose_ack_trace why)
{
        spin_lock_bh(&call->lock);
        __rxrpc_propose_ACK(call, ack_reason, skew, serial,
                            immediate, background, why);
        spin_unlock_bh(&call->lock);
}

/*
 * Handle congestion being detected by the retransmit timeout.
 */
static void rxrpc_congestion_timeout(struct rxrpc_call *call)
{
        set_bit(RXRPC_CALL_RETRANS_TIMEOUT, &call->flags);
}

/*
 * Perform retransmission of NAK'd and unack'd packets.
 */
static void rxrpc_resend(struct rxrpc_call *call, unsigned long now_j)
{
        struct rxrpc_skb_priv *sp;
        struct sk_buff *skb;
        unsigned long resend_at;
        rxrpc_seq_t cursor, seq, top;
        ktime_t now, max_age, oldest, ack_ts, timeout, min_timeo;
        int ix;
        u8 annotation, anno_type, retrans = 0, unacked = 0;

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

        if (call->peer->rtt_usage > 1)
                timeout = ns_to_ktime(call->peer->rtt * 3 / 2);
        else
                timeout = ms_to_ktime(rxrpc_resend_timeout);
        min_timeo = ns_to_ktime((1000000000 / HZ) * 4);
        if (ktime_before(timeout, min_timeo))
                timeout = min_timeo;

        now = ktime_get_real();
        max_age = ktime_sub(now, timeout);

        spin_lock_bh(&call->lock);

        cursor = call->tx_hard_ack;
        top = call->tx_top;
        ASSERT(before_eq(cursor, top));
        if (cursor == top)
                goto out_unlock;

        /* Scan the packet list without dropping the lock and decide which of
         * the packets in the Tx buffer we're going to resend and what the new
         * resend timeout will be.
         */
        trace_rxrpc_resend(call, (cursor + 1) & RXRPC_RXTX_BUFF_MASK);
        oldest = now;
        for (seq = cursor + 1; before_eq(seq, top); seq++) {
                ix = seq & RXRPC_RXTX_BUFF_MASK;
                annotation = call->rxtx_annotations[ix];
                anno_type = annotation & RXRPC_TX_ANNO_MASK;
                annotation &= ~RXRPC_TX_ANNO_MASK;
                if (anno_type == RXRPC_TX_ANNO_ACK)
                        continue;

                skb = call->rxtx_buffer[ix];
                rxrpc_see_skb(skb, rxrpc_skb_tx_seen);
                sp = rxrpc_skb(skb);

                if (anno_type == RXRPC_TX_ANNO_UNACK) {
                        if (ktime_after(skb->tstamp, max_age)) {
                                if (ktime_before(skb->tstamp, oldest))
                                        oldest = skb->tstamp;
                                continue;
                        }
                        if (!(annotation & RXRPC_TX_ANNO_RESENT))
                                unacked++;
                }

                /* Okay, we need to retransmit a packet. */
                call->rxtx_annotations[ix] = RXRPC_TX_ANNO_RETRANS | annotation;
                retrans++;
                trace_rxrpc_retransmit(call, seq, annotation | anno_type,
                                       ktime_to_ns(ktime_sub(skb->tstamp, max_age)));
        }

        resend_at = nsecs_to_jiffies(ktime_to_ns(ktime_sub(now, oldest)));
        resend_at += jiffies + rxrpc_resend_timeout;
        WRITE_ONCE(call->resend_at, resend_at);

        if (unacked)
                rxrpc_congestion_timeout(call);

        /* If there was nothing that needed retransmission then it's likely
         * that an ACK got lost somewhere.  Send a ping to find out instead of
         * retransmitting data.
         */
        if (!retrans) {
                rxrpc_reduce_call_timer(call, resend_at, now_j,
                                        rxrpc_timer_set_for_resend);
                spin_unlock_bh(&call->lock);
                ack_ts = ktime_sub(now, call->acks_latest_ts);
                if (ktime_to_ns(ack_ts) < call->peer->rtt)
                        goto out;
                rxrpc_propose_ACK(call, RXRPC_ACK_PING, 0, 0, true, false,
                                  rxrpc_propose_ack_ping_for_lost_ack);
                rxrpc_send_ack_packet(call, true, NULL);
                goto out;
        }

        /* Now go through the Tx window and perform the retransmissions.  We
         * have to drop the lock for each send.  If an ACK comes in whilst the
         * lock is dropped, it may clear some of the retransmission markers for
         * packets that it soft-ACKs.
         */
        for (seq = cursor + 1; before_eq(seq, top); seq++) {
                ix = seq & RXRPC_RXTX_BUFF_MASK;
                annotation = call->rxtx_annotations[ix];
                anno_type = annotation & RXRPC_TX_ANNO_MASK;
                if (anno_type != RXRPC_TX_ANNO_RETRANS)
                        continue;

                skb = call->rxtx_buffer[ix];
                rxrpc_get_skb(skb, rxrpc_skb_tx_got);
                spin_unlock_bh(&call->lock);

                if (rxrpc_send_data_packet(call, skb, true) < 0) {
                        rxrpc_free_skb(skb, rxrpc_skb_tx_freed);
                        return;
                }

                if (rxrpc_is_client_call(call))
                        rxrpc_expose_client_call(call);

                rxrpc_free_skb(skb, rxrpc_skb_tx_freed);
                spin_lock_bh(&call->lock);

                /* We need to clear the retransmit state, but there are two
                 * things we need to be aware of: A new ACK/NAK might have been
                 * received and the packet might have been hard-ACK'd (in which
                 * case it will no longer be in the buffer).
                 */
                if (after(seq, call->tx_hard_ack)) {
                        annotation = call->rxtx_annotations[ix];
                        anno_type = annotation & RXRPC_TX_ANNO_MASK;
                        if (anno_type == RXRPC_TX_ANNO_RETRANS ||
                            anno_type == RXRPC_TX_ANNO_NAK) {
                                annotation &= ~RXRPC_TX_ANNO_MASK;
                                annotation |= RXRPC_TX_ANNO_UNACK;
                        }
                        annotation |= RXRPC_TX_ANNO_RESENT;
                        call->rxtx_annotations[ix] = annotation;
                }

                if (after(call->tx_hard_ack, seq))
                        seq = call->tx_hard_ack;
        }

out_unlock:
        spin_unlock_bh(&call->lock);
out:
        _leave("");
}

/*
 * Handle retransmission and deferred ACK/abort generation.
 */
void rxrpc_process_call(struct work_struct *work)
{
        struct rxrpc_call *call =
                container_of(work, struct rxrpc_call, processor);
        rxrpc_serial_t *send_ack;
        unsigned long now, next, t;

        rxrpc_see_call(call);

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

recheck_state:
        if (test_and_clear_bit(RXRPC_CALL_EV_ABORT, &call->events)) {
                rxrpc_send_abort_packet(call);
                goto recheck_state;
        }

        if (call->state == RXRPC_CALL_COMPLETE) {
                del_timer_sync(&call->timer);
                rxrpc_notify_socket(call);
                goto out_put;
        }

        /* Work out if any timeouts tripped */
        now = jiffies;
        t = READ_ONCE(call->expect_rx_by);
        if (time_after_eq(now, t)) {
                trace_rxrpc_timer(call, rxrpc_timer_exp_normal, now);
                set_bit(RXRPC_CALL_EV_EXPIRED, &call->events);
        }

        t = READ_ONCE(call->expect_req_by);
        if (call->state == RXRPC_CALL_SERVER_RECV_REQUEST &&
            time_after_eq(now, t)) {
                trace_rxrpc_timer(call, rxrpc_timer_exp_idle, now);
                set_bit(RXRPC_CALL_EV_EXPIRED, &call->events);
        }

        t = READ_ONCE(call->expect_term_by);
        if (time_after_eq(now, t)) {
                trace_rxrpc_timer(call, rxrpc_timer_exp_hard, now);
                set_bit(RXRPC_CALL_EV_EXPIRED, &call->events);
        }

        t = READ_ONCE(call->ack_at);
        if (time_after_eq(now, t)) {
                trace_rxrpc_timer(call, rxrpc_timer_exp_ack, now);
                cmpxchg(&call->ack_at, t, now + MAX_JIFFY_OFFSET);
                set_bit(RXRPC_CALL_EV_ACK, &call->events);
        }

        t = READ_ONCE(call->ack_lost_at);
        if (time_after_eq(now, t)) {
                trace_rxrpc_timer(call, rxrpc_timer_exp_lost_ack, now);
                cmpxchg(&call->ack_lost_at, t, now + MAX_JIFFY_OFFSET);
                set_bit(RXRPC_CALL_EV_ACK_LOST, &call->events);
        }

        t = READ_ONCE(call->keepalive_at);
        if (time_after_eq(now, t)) {
                trace_rxrpc_timer(call, rxrpc_timer_exp_keepalive, now);
                cmpxchg(&call->keepalive_at, t, now + MAX_JIFFY_OFFSET);
                rxrpc_propose_ACK(call, RXRPC_ACK_PING, 0, 0, true, true,
                                  rxrpc_propose_ack_ping_for_keepalive);
                set_bit(RXRPC_CALL_EV_PING, &call->events);
        }

        t = READ_ONCE(call->ping_at);
        if (time_after_eq(now, t)) {
                trace_rxrpc_timer(call, rxrpc_timer_exp_ping, now);
                cmpxchg(&call->ping_at, t, now + MAX_JIFFY_OFFSET);
                set_bit(RXRPC_CALL_EV_PING, &call->events);
        }

        t = READ_ONCE(call->resend_at);
        if (time_after_eq(now, t)) {
                trace_rxrpc_timer(call, rxrpc_timer_exp_resend, now);
                cmpxchg(&call->resend_at, t, now + MAX_JIFFY_OFFSET);
                set_bit(RXRPC_CALL_EV_RESEND, &call->events);
        }

        /* Process events */
        if (test_and_clear_bit(RXRPC_CALL_EV_EXPIRED, &call->events)) {
                rxrpc_abort_call("EXP", call, 0, RX_USER_ABORT, -ETIME);
                set_bit(RXRPC_CALL_EV_ABORT, &call->events);
                goto recheck_state;
        }

        send_ack = NULL;
        if (test_and_clear_bit(RXRPC_CALL_EV_ACK_LOST, &call->events)) {
                call->acks_lost_top = call->tx_top;
                rxrpc_propose_ACK(call, RXRPC_ACK_PING, 0, 0, true, false,
                                  rxrpc_propose_ack_ping_for_lost_ack);
                send_ack = &call->acks_lost_ping;
        }

        if (test_and_clear_bit(RXRPC_CALL_EV_ACK, &call->events) ||
            send_ack) {
                if (call->ackr_reason) {
                        rxrpc_send_ack_packet(call, false, send_ack);
                        goto recheck_state;
                }
        }

        if (test_and_clear_bit(RXRPC_CALL_EV_PING, &call->events)) {
                rxrpc_send_ack_packet(call, true, NULL);
                goto recheck_state;
        }

        if (test_and_clear_bit(RXRPC_CALL_EV_RESEND, &call->events)) {
                rxrpc_resend(call, now);
                goto recheck_state;
        }

        /* Make sure the timer is restarted */
        next = call->expect_rx_by;

#define set(T) { t = READ_ONCE(T); if (time_before(t, next)) next = t; }

        set(call->expect_req_by);
        set(call->expect_term_by);
        set(call->ack_at);
        set(call->ack_lost_at);
        set(call->resend_at);
        set(call->keepalive_at);
        set(call->ping_at);

        now = jiffies;
        if (time_after_eq(now, next))
                goto recheck_state;

        rxrpc_reduce_call_timer(call, next, now, rxrpc_timer_restart);

        /* other events may have been raised since we started checking */
        if (call->events && call->state < RXRPC_CALL_COMPLETE) {
                __rxrpc_queue_call(call);
                goto out;
        }

out_put:
        rxrpc_put_call(call, rxrpc_call_put);
out:
        _leave("");
}