if.c

/*
 * Copyright (c) 1995 Danny Gasparovski.
 *
 * Please read the file COPYRIGHT for the
 * terms and conditions of the copyright.
 */

#include <slirp.h>

#define ifs_init(ifm) ((ifm)->ifs_next = (ifm)->ifs_prev = (ifm))

static void ifs_insque(struct mbuf *ifm, struct mbuf *ifmhead)
{
    ifm->ifs_next = ifmhead->ifs_next;
    ifmhead->ifs_next = ifm;
    ifm->ifs_prev = ifmhead;
    ifm->ifs_next->ifs_prev = ifm;
}

static void ifs_remque(struct mbuf *ifm)
{
    ifm->ifs_prev->ifs_next = ifm->ifs_next;
    ifm->ifs_next->ifs_prev = ifm->ifs_prev;
}

void if_init(Slirp *slirp)
{
    slirp->if_fastq.ifq_next = slirp->if_fastq.ifq_prev = &slirp->if_fastq;
    slirp->if_batchq.ifq_next = slirp->if_batchq.ifq_prev = &slirp->if_batchq;
    slirp->next_m = &slirp->if_batchq;
}

/*
 * if_output: Queue packet into an output queue.
 * There are 2 output queue's, if_fastq and if_batchq.
 * Each output queue is a doubly linked list of double linked lists
 * of mbufs, each list belonging to one "session" (socket).  This
 * way, we can output packets fairly by sending one packet from each
 * session, instead of all the packets from one session, then all packets
 * from the next session, etc.  Packets on the if_fastq get absolute
 * priority, but if one session hogs the link, it gets "downgraded"
 * to the batchq until it runs out of packets, then it'll return
 * to the fastq (eg. if the user does an ls -alR in a telnet session,
 * it'll temporarily get downgraded to the batchq)
 */
void if_output(struct socket *so, struct mbuf *ifm)
{
    Slirp *slirp = ifm->slirp;
    struct mbuf *ifq;
    int on_fastq = 1;

    DEBUG_CALL("if_output");
    DEBUG_ARG("so = %lx", (long)so);
    DEBUG_ARG("ifm = %lx", (long)ifm);

    /*
     * First remove the mbuf from m_usedlist,
     * since we're gonna use m_next and m_prev ourselves
     * XXX Shouldn't need this, gotta change dtom() etc.
     */
    if (ifm->m_flags & M_USEDLIST) {
        remque(ifm);
        ifm->m_flags &= ~M_USEDLIST;
    }

    /*
     * See if there's already a batchq list for this session.
     * This can include an interactive session, which should go on fastq,
     * but gets too greedy... hence it'll be downgraded from fastq to batchq.
     * We mustn't put this packet back on the fastq (or we'll send it out of
     * order)
     * XXX add cache here?
     */
    for (ifq = slirp->if_batchq.ifq_prev; ifq != &slirp->if_batchq;
         ifq = ifq->ifq_prev) {
        if (so == ifq->ifq_so) {
            /* A match! */
            ifm->ifq_so = so;
            ifs_insque(ifm, ifq->ifs_prev);
            goto diddit;
        }
    }

    /* No match, check which queue to put it on */
    if (so && (so->so_iptos & IPTOS_LOWDELAY)) {
        ifq = slirp->if_fastq.ifq_prev;
        on_fastq = 1;
        /*
         * Check if this packet is a part of the last
         * packet's session
         */
        if (ifq->ifq_so == so) {
            ifm->ifq_so = so;
            ifs_insque(ifm, ifq->ifs_prev);
            goto diddit;
        }
    } else
        ifq = slirp->if_batchq.ifq_prev;

    /* Create a new doubly linked list for this session */
    ifm->ifq_so = so;
    ifs_init(ifm);
    insque(ifm, ifq);

diddit:
    slirp->if_queued++;

    if (so) {
        /* Update *_queued */
        so->so_queued++;
        so->so_nqueued++;
        /*
         * Check if the interactive session should be downgraded to
         * the batchq.  A session is downgraded if it has queued 6
         * packets without pausing, and at least 3 of those packets
         * have been sent over the link
         * (XXX These are arbitrary numbers, probably not optimal..)
         */
        if (on_fastq &&
            ((so->so_nqueued >= 6) && (so->so_nqueued - so->so_queued) >= 3)) {
            /* Remove from current queue... */
            remque(ifm->ifs_next);

            /* ...And insert in the new.  That'll teach ya! */
            insque(ifm->ifs_next, &slirp->if_batchq);
        }
    }

#ifndef FULL_BOLT
    /*
     * This prevents us from malloc()ing too many mbufs
     */
    if_start(ifm->slirp);
#endif
}

/*
 * Send a packet
 * We choose a packet based on it's position in the output queues;
 * If there are packets on the fastq, they are sent FIFO, before
 * everything else.  Otherwise we choose the first packet from the
 * batchq and send it.  the next packet chosen will be from the session
 * after this one, then the session after that one, and so on..  So,
 * for example, if there are 3 ftp session's fighting for bandwidth,
 * one packet will be sent from the first session, then one packet
 * from the second session, then one packet from the third, then back
 * to the first, etc. etc.
 */
void if_start(Slirp *slirp)
{
    struct mbuf *ifm, *ifqt;

    DEBUG_CALL("if_start");

    if (slirp->if_queued == 0)
        return; /* Nothing to do */

again:
    /* check if we can really output */
    if (!slirp_can_output(slirp->opaque))
        return;

    /*
     * See which queue to get next packet from
     * If there's something in the fastq, select it immediately
     */
    if (slirp->if_fastq.ifq_next != &slirp->if_fastq) {
        ifm = slirp->if_fastq.ifq_next;
    } else {
        /* Nothing on fastq, see if next_m is valid */
        if (slirp->next_m != &slirp->if_batchq)
            ifm = slirp->next_m;
        else
            ifm = slirp->if_batchq.ifq_next;

        /* Set which packet to send on next iteration */
        slirp->next_m = ifm->ifq_next;
    }
    /* Remove it from the queue */
    ifqt = ifm->ifq_prev;
    remque(ifm);
    slirp->if_queued--;

    /* If there are more packets for this session, re-queue them */
    if (ifm->ifs_next != /* ifm->ifs_prev != */ ifm) {
        insque(ifm->ifs_next, ifqt);
        ifs_remque(ifm);
    }

    /* Update so_queued */
    if (ifm->ifq_so) {
        if (--ifm->ifq_so->so_queued == 0)
            /* If there's no more queued, reset nqueued */
            ifm->ifq_so->so_nqueued = 0;
    }

    /* Encapsulate the packet for sending */
    if_encap(slirp, (uint8_t *)ifm->m_data, ifm->m_len);

    m_free(ifm);

    if (slirp->if_queued)
        goto again;
}