/*
 *  net/dccp/output.c
 *
 *  An implementation of the DCCP protocol
 *  Arnaldo Carvalho de Melo <acme@conectiva.com.br>
 *
 *      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.
 */

#include <linux/dccp.h>
#include <linux/kernel.h>
#include <linux/skbuff.h>

#include <net/inet_sock.h>
#include <net/sock.h>

#include "ackvec.h"
#include "ccid.h"
#include "dccp.h"

static inline void dccp_event_ack_sent(struct sock *sk)
{
        inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK);
}

static void dccp_skb_entail(struct sock *sk, struct sk_buff *skb)
{
        skb_set_owner_w(skb, sk);
        WARN_ON(sk->sk_send_head);
        sk->sk_send_head = skb;
}

/*
 * All SKB's seen here are completely headerless. It is our
 * job to build the DCCP header, and pass the packet down to
 * IP so it can do the same plus pass the packet off to the
 * device.
 */
static int dccp_transmit_skb(struct sock *sk, struct sk_buff *skb)
{
        if (likely(skb != NULL)) {
                const struct inet_sock *inet = inet_sk(sk);
                const struct inet_connection_sock *icsk = inet_csk(sk);
                struct dccp_sock *dp = dccp_sk(sk);
                struct dccp_skb_cb *dcb = DCCP_SKB_CB(skb);
                struct dccp_hdr *dh;
                /* XXX For now we're using only 48 bits sequence numbers */
                const u32 dccp_header_size = sizeof(*dh) +
                                             sizeof(struct dccp_hdr_ext) +
                                          dccp_packet_hdr_len(dcb->dccpd_type);
                int err, set_ack = 1;
                u64 ackno = dp->dccps_gsr;

                dccp_inc_seqno(&dp->dccps_gss);

                switch (dcb->dccpd_type) {
                case DCCP_PKT_DATA:
                        set_ack = 0;
                        /* fall through */
                case DCCP_PKT_DATAACK:
                case DCCP_PKT_RESET:
                        break;

                case DCCP_PKT_REQUEST:
                        set_ack = 0;
                        /* fall through */

                case DCCP_PKT_SYNC:
                case DCCP_PKT_SYNCACK:
                        ackno = dcb->dccpd_ack_seq;
                        /* fall through */
                default:
                        /*
                         * Set owner/destructor: some skbs are allocated via
                         * alloc_skb (e.g. when retransmission may happen).
                         * Only Data, DataAck, and Reset packets should come
                         * through here with skb->sk set.
                         */
                        WARN_ON(skb->sk);
                        skb_set_owner_w(skb, sk);
                        break;
                }

                dcb->dccpd_seq = dp->dccps_gss;

                if (dccp_insert_options(sk, skb)) {
                        kfree_skb(skb);
                        return -EPROTO;
                }


                /* Build DCCP header and checksum it. */
                dh = dccp_zeroed_hdr(skb, dccp_header_size);
                dh->dccph_type  = dcb->dccpd_type;
                dh->dccph_sport = inet->sport;
                dh->dccph_dport = inet->dport;
                dh->dccph_doff  = (dccp_header_size + dcb->dccpd_opt_len) / 4;
                dh->dccph_ccval = dcb->dccpd_ccval;
                dh->dccph_cscov = dp->dccps_pcslen;
                /* XXX For now we're using only 48 bits sequence numbers */
                dh->dccph_x     = 1;

                dp->dccps_awh = dp->dccps_gss;
                dccp_hdr_set_seq(dh, dp->dccps_gss);
                if (set_ack)
                        dccp_hdr_set_ack(dccp_hdr_ack_bits(skb), ackno);

                switch (dcb->dccpd_type) {
                case DCCP_PKT_REQUEST:
                        dccp_hdr_request(skb)->dccph_req_service =
                                                        dp->dccps_service;
                        break;
                case DCCP_PKT_RESET:
                        dccp_hdr_reset(skb)->dccph_reset_code =
                                                        dcb->dccpd_reset_code;
                        break;
                }

                icsk->icsk_af_ops->send_check(sk, 0, skb);

                if (set_ack)
                        dccp_event_ack_sent(sk);

                DCCP_INC_STATS(DCCP_MIB_OUTSEGS);

                memset(&(IPCB(skb)->opt), 0, sizeof(IPCB(skb)->opt));
                err = icsk->icsk_af_ops->queue_xmit(skb, 0);
                return net_xmit_eval(err);
        }
        return -ENOBUFS;
}

unsigned int dccp_sync_mss(struct sock *sk, u32 pmtu)
{
        struct inet_connection_sock *icsk = inet_csk(sk);
        struct dccp_sock *dp = dccp_sk(sk);
        int mss_now = (pmtu - icsk->icsk_af_ops->net_header_len -
                       sizeof(struct dccp_hdr) - sizeof(struct dccp_hdr_ext));

        /* Now subtract optional transport overhead */
        mss_now -= icsk->icsk_ext_hdr_len;

        /*
         * FIXME: this should come from the CCID infrastructure, where, say,
         * TFRC will say it wants TIMESTAMPS, ELAPSED time, etc, for now lets
         * put a rough estimate for NDP + TIMESTAMP + TIMESTAMP_ECHO + ELAPSED
         * TIME + TFRC_OPT_LOSS_EVENT_RATE + TFRC_OPT_RECEIVE_RATE + padding to
         * make it a multiple of 4
         */

        mss_now -= ((5 + 6 + 10 + 6 + 6 + 6 + 3) / 4) * 4;

        /* And store cached results */
        icsk->icsk_pmtu_cookie = pmtu;
        dp->dccps_mss_cache = mss_now;

        return mss_now;
}

EXPORT_SYMBOL_GPL(dccp_sync_mss);

void dccp_write_space(struct sock *sk)
{
        read_lock(&sk->sk_callback_lock);

        if (sk->sk_sleep && waitqueue_active(sk->sk_sleep))
                wake_up_interruptible(sk->sk_sleep);
        /* Should agree with poll, otherwise some programs break */
        if (sock_writeable(sk))
                sk_wake_async(sk, 2, POLL_OUT);

        read_unlock(&sk->sk_callback_lock);
}

/**
 * dccp_wait_for_ccid - Wait for ccid to tell us we can send a packet
 * @sk:    socket to wait for
 * @skb:   current skb to pass on for waiting
 * @delay: sleep timeout in milliseconds (> 0)
 * This function is called by default when the socket is closed, and
 * when a non-zero linger time is set on the socket. For consistency
 */
static int dccp_wait_for_ccid(struct sock *sk, struct sk_buff *skb, int delay)
{
        struct dccp_sock *dp = dccp_sk(sk);
        DEFINE_WAIT(wait);
        unsigned long jiffdelay;
        int rc;

        do {
                dccp_pr_debug("delayed send by %d msec\n", delay);
                jiffdelay = msecs_to_jiffies(delay);

                prepare_to_wait(sk->sk_sleep, &wait, TASK_INTERRUPTIBLE);

                sk->sk_write_pending++;
                release_sock(sk);
                schedule_timeout(jiffdelay);
                lock_sock(sk);
                sk->sk_write_pending--;

                if (sk->sk_err)
                        goto do_error;
                if (signal_pending(current))
                        goto do_interrupted;

                rc = ccid_hc_tx_send_packet(dp->dccps_hc_tx_ccid, sk, skb);
        } while ((delay = rc) > 0);
out:
        finish_wait(sk->sk_sleep, &wait);
        return rc;

do_error:
        rc = -EPIPE;
        goto out;
do_interrupted:
        rc = -EINTR;
        goto out;
}

void dccp_write_xmit(struct sock *sk, int block)
{
        struct dccp_sock *dp = dccp_sk(sk);
        struct sk_buff *skb;

        while ((skb = skb_peek(&sk->sk_write_queue))) {
                int err = ccid_hc_tx_send_packet(dp->dccps_hc_tx_ccid, sk, skb);

                if (err > 0) {
                        if (!block) {
                                sk_reset_timer(sk, &dp->dccps_xmit_timer,
                                                msecs_to_jiffies(err)+jiffies);
                                break;
                        } else
                                err = dccp_wait_for_ccid(sk, skb, err);
                        if (err && err != -EINTR)
                                DCCP_BUG("err=%d after dccp_wait_for_ccid", err);
                }

                skb_dequeue(&sk->sk_write_queue);
                if (err == 0) {
                        struct dccp_skb_cb *dcb = DCCP_SKB_CB(skb);
                        const int len = skb->len;

                        if (sk->sk_state == DCCP_PARTOPEN) {
                                /* See 8.1.5.  Handshake Completion */
                                inet_csk_schedule_ack(sk);
                                inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
                                                  inet_csk(sk)->icsk_rto,
                                                  DCCP_RTO_MAX);
                                dcb->dccpd_type = DCCP_PKT_DATAACK;
                        } else if (dccp_ack_pending(sk))
                                dcb->dccpd_type = DCCP_PKT_DATAACK;
                        else
                                dcb->dccpd_type = DCCP_PKT_DATA;

                        err = dccp_transmit_skb(sk, skb);
                        ccid_hc_tx_packet_sent(dp->dccps_hc_tx_ccid, sk, 0, len);
                        if (err)
                                DCCP_BUG("err=%d after ccid_hc_tx_packet_sent",
                                         err);
                } else {
                        dccp_pr_debug("packet discarded due to err=%d\n", err);
                        kfree_skb(skb);
                }
        }
}

int dccp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
{
        if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk) != 0)
                return -EHOSTUNREACH; /* Routing failure or similar. */

        return dccp_transmit_skb(sk, (skb_cloned(skb) ?
                                      pskb_copy(skb, GFP_ATOMIC):
                                      skb_clone(skb, GFP_ATOMIC)));
}

struct sk_buff *dccp_make_response(struct sock *sk, struct dst_entry *dst,
                                   struct request_sock *req)
{
        struct dccp_hdr *dh;
        struct dccp_request_sock *dreq;
        const u32 dccp_header_size = sizeof(struct dccp_hdr) +
                                     sizeof(struct dccp_hdr_ext) +
                                     sizeof(struct dccp_hdr_response);
        struct sk_buff *skb = sock_wmalloc(sk, sk->sk_prot->max_header, 1,
                                           GFP_ATOMIC);
        if (skb == NULL)
                return NULL;

        /* Reserve space for headers. */
        skb_reserve(skb, sk->sk_prot->max_header);

        skb->dst = dst_clone(dst);

        dreq = dccp_rsk(req);
        if (inet_rsk(req)->acked)       /* increase ISS upon retransmission */
                dccp_inc_seqno(&dreq->dreq_iss);
        DCCP_SKB_CB(skb)->dccpd_type = DCCP_PKT_RESPONSE;
        DCCP_SKB_CB(skb)->dccpd_seq  = dreq->dreq_iss;

        if (dccp_insert_options(sk, skb)) {
                kfree_skb(skb);
                return NULL;
        }

        /* Build and checksum header */
        dh = dccp_zeroed_hdr(skb, dccp_header_size);

        dh->dccph_sport = inet_sk(sk)->sport;
        dh->dccph_dport = inet_rsk(req)->rmt_port;
        dh->dccph_doff  = (dccp_header_size +
                           DCCP_SKB_CB(skb)->dccpd_opt_len) / 4;
        dh->dccph_type  = DCCP_PKT_RESPONSE;
        dh->dccph_x     = 1;
        dccp_hdr_set_seq(dh, dreq->dreq_iss);
        dccp_hdr_set_ack(dccp_hdr_ack_bits(skb), dreq->dreq_isr);
        dccp_hdr_response(skb)->dccph_resp_service = dreq->dreq_service;

        dccp_csum_outgoing(skb);

        /* We use `acked' to remember that a Response was already sent. */
        inet_rsk(req)->acked = 1;
        DCCP_INC_STATS(DCCP_MIB_OUTSEGS);
        return skb;
}

EXPORT_SYMBOL_GPL(dccp_make_response);

/* answer offending packet in @rcv_skb with Reset from control socket @ctl */
struct sk_buff *dccp_ctl_make_reset(struct socket *ctl, struct sk_buff *rcv_skb)
{
        struct dccp_hdr *rxdh = dccp_hdr(rcv_skb), *dh;
        struct dccp_skb_cb *dcb = DCCP_SKB_CB(rcv_skb);
        const u32 dccp_hdr_reset_len = sizeof(struct dccp_hdr) +
                                       sizeof(struct dccp_hdr_ext) +
                                       sizeof(struct dccp_hdr_reset);
        struct dccp_hdr_reset *dhr;
        struct sk_buff *skb;

        skb = alloc_skb(ctl->sk->sk_prot->max_header, GFP_ATOMIC);
        if (skb == NULL)
                return NULL;

        skb_reserve(skb, ctl->sk->sk_prot->max_header);

        /* Swap the send and the receive. */
        dh = dccp_zeroed_hdr(skb, dccp_hdr_reset_len);
        dh->dccph_type  = DCCP_PKT_RESET;
        dh->dccph_sport = rxdh->dccph_dport;
        dh->dccph_dport = rxdh->dccph_sport;
        dh->dccph_doff  = dccp_hdr_reset_len / 4;
        dh->dccph_x     = 1;

        dhr = dccp_hdr_reset(skb);
        dhr->dccph_reset_code = dcb->dccpd_reset_code;

        switch (dcb->dccpd_reset_code) {
        case DCCP_RESET_CODE_PACKET_ERROR:
                dhr->dccph_reset_data[0] = rxdh->dccph_type;
                break;
        case DCCP_RESET_CODE_OPTION_ERROR:      /* fall through */
        case DCCP_RESET_CODE_MANDATORY_ERROR:
                memcpy(dhr->dccph_reset_data, dcb->dccpd_reset_data, 3);
                break;
        }
        /*
         * From RFC 4340, 8.3.1:
         *   If P.ackno exists, set R.seqno := P.ackno + 1.
         *   Else set R.seqno := 0.
         */
        if (dcb->dccpd_ack_seq != DCCP_PKT_WITHOUT_ACK_SEQ)
                dccp_hdr_set_seq(dh, ADD48(dcb->dccpd_ack_seq, 1));
        dccp_hdr_set_ack(dccp_hdr_ack_bits(skb), dcb->dccpd_seq);

        dccp_csum_outgoing(skb);
        return skb;
}

EXPORT_SYMBOL_GPL(dccp_ctl_make_reset);

/* send Reset on established socket, to close or abort the connection */
int dccp_send_reset(struct sock *sk, enum dccp_reset_codes code)
{
        struct sk_buff *skb;
        /*
         * FIXME: what if rebuild_header fails?
         * Should we be doing a rebuild_header here?
         */
        int err = inet_sk_rebuild_header(sk);

        if (err != 0)
                return err;

        skb = sock_wmalloc(sk, sk->sk_prot->max_header, 1, GFP_ATOMIC);
        if (skb == NULL)
                return -ENOBUFS;

        /* Reserve space for headers and prepare control bits. */
        skb_reserve(skb, sk->sk_prot->max_header);
        DCCP_SKB_CB(skb)->dccpd_type       = DCCP_PKT_RESET;
        DCCP_SKB_CB(skb)->dccpd_reset_code = code;

        return dccp_transmit_skb(sk, skb);
}

/*
 * Do all connect socket setups that can be done AF independent.
 */
static inline void dccp_connect_init(struct sock *sk)
{
        struct dccp_sock *dp = dccp_sk(sk);
        struct dst_entry *dst = __sk_dst_get(sk);
        struct inet_connection_sock *icsk = inet_csk(sk);

        sk->sk_err = 0;
        sock_reset_flag(sk, SOCK_DONE);

        dccp_sync_mss(sk, dst_mtu(dst));

        /*
         * SWL and AWL are initially adjusted so that they are not less than
         * the initial Sequence Numbers received and sent, respectively:
         *      SWL := max(GSR + 1 - floor(W/4), ISR),
         *      AWL := max(GSS - W' + 1, ISS).
         * These adjustments MUST be applied only at the beginning of the
         * connection.
         */
        dccp_update_gss(sk, dp->dccps_iss);
        dccp_set_seqno(&dp->dccps_awl, max48(dp->dccps_awl, dp->dccps_iss));

        /* S.GAR - greatest valid acknowledgement number received on a non-Sync;
         *         initialized to S.ISS (sec. 8.5)                            */
        dp->dccps_gar = dp->dccps_iss;

        icsk->icsk_retransmits = 0;
}

int dccp_connect(struct sock *sk)
{
        struct sk_buff *skb;
        struct inet_connection_sock *icsk = inet_csk(sk);

        dccp_connect_init(sk);

        skb = alloc_skb(sk->sk_prot->max_header, sk->sk_allocation);
        if (unlikely(skb == NULL))
                return -ENOBUFS;

        /* Reserve space for headers. */
        skb_reserve(skb, sk->sk_prot->max_header);

        DCCP_SKB_CB(skb)->dccpd_type = DCCP_PKT_REQUEST;

        dccp_skb_entail(sk, skb);
        dccp_transmit_skb(sk, skb_clone(skb, GFP_KERNEL));
        DCCP_INC_STATS(DCCP_MIB_ACTIVEOPENS);

        /* Timer for repeating the REQUEST until an answer. */
        inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
                                  icsk->icsk_rto, DCCP_RTO_MAX);
        return 0;
}

EXPORT_SYMBOL_GPL(dccp_connect);

void dccp_send_ack(struct sock *sk)
{
        /* If we have been reset, we may not send again. */
        if (sk->sk_state != DCCP_CLOSED) {
                struct sk_buff *skb = alloc_skb(sk->sk_prot->max_header,
                                                GFP_ATOMIC);

                if (skb == NULL) {
                        inet_csk_schedule_ack(sk);
                        inet_csk(sk)->icsk_ack.ato = TCP_ATO_MIN;
                        inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
                                                  TCP_DELACK_MAX,
                                                  DCCP_RTO_MAX);
                        return;
                }

                /* Reserve space for headers */
                skb_reserve(skb, sk->sk_prot->max_header);
                DCCP_SKB_CB(skb)->dccpd_type = DCCP_PKT_ACK;
                dccp_transmit_skb(sk, skb);
        }
}

EXPORT_SYMBOL_GPL(dccp_send_ack);

/* FIXME: Is this still necessary (11.3) - currently nowhere used by DCCP. */
void dccp_send_delayed_ack(struct sock *sk)
{
        struct inet_connection_sock *icsk = inet_csk(sk);
        /*
         * FIXME: tune this timer. elapsed time fixes the skew, so no problem
         * with using 2s, and active senders also piggyback the ACK into a
         * DATAACK packet, so this is really for quiescent senders.
         */
        unsigned long timeout = jiffies + 2 * HZ;

        /* Use new timeout only if there wasn't a older one earlier. */
        if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) {
                /* If delack timer was blocked or is about to expire,
                 * send ACK now.
                 *
                 * FIXME: check the "about to expire" part
                 */
                if (icsk->icsk_ack.blocked) {
                        dccp_send_ack(sk);
                        return;
                }

                if (!time_before(timeout, icsk->icsk_ack.timeout))
                        timeout = icsk->icsk_ack.timeout;
        }
        icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER;
        icsk->icsk_ack.timeout = timeout;
        sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout);
}

void dccp_send_sync(struct sock *sk, const u64 ackno,
                    const enum dccp_pkt_type pkt_type)
{
        /*
         * We are not putting this on the write queue, so
         * dccp_transmit_skb() will set the ownership to this
         * sock.
         */
        struct sk_buff *skb = alloc_skb(sk->sk_prot->max_header, GFP_ATOMIC);

        if (skb == NULL) {
                /* FIXME: how to make sure the sync is sent? */
                DCCP_CRIT("could not send %s", dccp_packet_name(pkt_type));
                return;
        }

        /* Reserve space for headers and prepare control bits. */
        skb_reserve(skb, sk->sk_prot->max_header);
        DCCP_SKB_CB(skb)->dccpd_type = pkt_type;
        DCCP_SKB_CB(skb)->dccpd_ack_seq = ackno;

        dccp_transmit_skb(sk, skb);
}

EXPORT_SYMBOL_GPL(dccp_send_sync);

/*
 * Send a DCCP_PKT_CLOSE/CLOSEREQ. The caller locks the socket for us. This
 * cannot be allowed to fail queueing a DCCP_PKT_CLOSE/CLOSEREQ frame under
 * any circumstances.
 */
void dccp_send_close(struct sock *sk, const int active)
{
        struct dccp_sock *dp = dccp_sk(sk);
        struct sk_buff *skb;
        const gfp_t prio = active ? GFP_KERNEL : GFP_ATOMIC;

        skb = alloc_skb(sk->sk_prot->max_header, prio);
        if (skb == NULL)
                return;

        /* Reserve space for headers and prepare control bits. */
        skb_reserve(skb, sk->sk_prot->max_header);
        DCCP_SKB_CB(skb)->dccpd_type = dp->dccps_role == DCCP_ROLE_CLIENT ?
                                        DCCP_PKT_CLOSE : DCCP_PKT_CLOSEREQ;

        if (active) {
                dccp_write_xmit(sk, 1);
                dccp_skb_entail(sk, skb);
                dccp_transmit_skb(sk, skb_clone(skb, prio));
                /* FIXME do we need a retransmit timer here? */
        } else
                dccp_transmit_skb(sk, skb);
}