text: /*
   * 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;
  }
  