slirp/if.c

   1 /*
   2  * Copyright (c) 1995 Danny Gasparovski.
   3  *
   4  * Please read the file COPYRIGHT for the
   5  * terms and conditions of the copyright.
   6  */
   7
   8 #include <slirp.h>
   9
  10 int     if_queued = 0;                  /* Number of packets queued so far */
  11
  12 struct  mbuf if_fastq;                  /* fast queue (for interactive data) */
  13 struct  mbuf if_batchq;                 /* queue for non-interactive data */
  14 struct  mbuf *next_m;                   /* Pointer to next mbuf to output */
  15
  16 #define ifs_init(ifm) ((ifm)->ifs_next = (ifm)->ifs_prev = (ifm))
  17
  18 static void
  19 ifs_insque(struct mbuf *ifm, struct mbuf *ifmhead)
  20 {
  21         ifm->ifs_next = ifmhead->ifs_next;
  22         ifmhead->ifs_next = ifm;
  23         ifm->ifs_prev = ifmhead;
  24         ifm->ifs_next->ifs_prev = ifm;
  25 }
  26
  27 static void
  28 ifs_remque(struct mbuf *ifm)
  29 {
  30         ifm->ifs_prev->ifs_next = ifm->ifs_next;
  31         ifm->ifs_next->ifs_prev = ifm->ifs_prev;
  32 }
  33
  34 void
  35 if_init(void)
  36 {
  37         if_fastq.ifq_next = if_fastq.ifq_prev = &if_fastq;
  38         if_batchq.ifq_next = if_batchq.ifq_prev = &if_batchq;
  39         next_m = &if_batchq;
  40 }
  41
  42 /*
  43  * if_output: Queue packet into an output queue.
  44  * There are 2 output queue's, if_fastq and if_batchq.
  45  * Each output queue is a doubly linked list of double linked lists
  46  * of mbufs, each list belonging to one "session" (socket).  This
  47  * way, we can output packets fairly by sending one packet from each
  48  * session, instead of all the packets from one session, then all packets
  49  * from the next session, etc.  Packets on the if_fastq get absolute
  50  * priority, but if one session hogs the link, it gets "downgraded"
  51  * to the batchq until it runs out of packets, then it'll return
  52  * to the fastq (eg. if the user does an ls -alR in a telnet session,
  53  * it'll temporarily get downgraded to the batchq)
  54  */
  55 void
  56 if_output(struct socket *so, struct mbuf *ifm)
  57 {
  58         struct mbuf *ifq;
  59         int on_fastq = 1;
  60
  61         DEBUG_CALL("if_output");
  62         DEBUG_ARG("so = %lx", (long)so);
  63         DEBUG_ARG("ifm = %lx", (long)ifm);
  64
  65         /*
  66          * First remove the mbuf from m_usedlist,
  67          * since we're gonna use m_next and m_prev ourselves
  68          * XXX Shouldn't need this, gotta change dtom() etc.
  69          */
  70         if (ifm->m_flags & M_USEDLIST) {
  71                 remque(ifm);
  72                 ifm->m_flags &= ~M_USEDLIST;
  73         }
  74
  75         /*
  76          * See if there's already a batchq list for this session.
  77          * This can include an interactive session, which should go on fastq,
  78          * but gets too greedy... hence it'll be downgraded from fastq to batchq.
  79          * We mustn't put this packet back on the fastq (or we'll send it out of order)
  80          * XXX add cache here?
  81          */
  82         for (ifq = if_batchq.ifq_prev; ifq != &if_batchq; ifq = ifq->ifq_prev) {
  83                 if (so == ifq->ifq_so) {
  84                         /* A match! */
  85                         ifm->ifq_so = so;
  86                         ifs_insque(ifm, ifq->ifs_prev);
  87                         goto diddit;
  88                 }
  89         }
  90
  91         /* No match, check which queue to put it on */
  92         if (so && (so->so_iptos & IPTOS_LOWDELAY)) {
  93                 ifq = if_fastq.ifq_prev;
  94                 on_fastq = 1;
  95                 /*
  96                  * Check if this packet is a part of the last
  97                  * packet's session
  98                  */
  99                 if (ifq->ifq_so == so) {
 100                         ifm->ifq_so = so;
 101                         ifs_insque(ifm, ifq->ifs_prev);
 102                         goto diddit;
 103                 }
 104         } else
 105                 ifq = if_batchq.ifq_prev;
 106
 107         /* Create a new doubly linked list for this session */
 108         ifm->ifq_so = so;
 109         ifs_init(ifm);
 110         insque(ifm, ifq);
 111
 112 diddit:
 113         ++if_queued;
 114
 115         if (so) {
 116                 /* Update *_queued */
 117                 so->so_queued++;
 118                 so->so_nqueued++;
 119                 /*
 120                  * Check if the interactive session should be downgraded to
 121                  * the batchq.  A session is downgraded if it has queued 6
 122                  * packets without pausing, and at least 3 of those packets
 123                  * have been sent over the link
 124                  * (XXX These are arbitrary numbers, probably not optimal..)
 125                  */
 126                 if (on_fastq && ((so->so_nqueued >= 6) &&
 127                                  (so->so_nqueued - so->so_queued) >= 3)) {
 128
 129                         /* Remove from current queue... */
 130                         remque(ifm->ifs_next);
 131
 132                         /* ...And insert in the new.  That'll teach ya! */
 133                         insque(ifm->ifs_next, &if_batchq);
 134                 }
 135         }
 136
 137 #ifndef FULL_BOLT
 138         /*
 139          * This prevents us from malloc()ing too many mbufs
 140          */
 141         if_start();
 142 #endif
 143 }
 144
 145 /*
 146  * Send a packet
 147  * We choose a packet based on it's position in the output queues;
 148  * If there are packets on the fastq, they are sent FIFO, before
 149  * everything else.  Otherwise we choose the first packet from the
 150  * batchq and send it.  the next packet chosen will be from the session
 151  * after this one, then the session after that one, and so on..  So,
 152  * for example, if there are 3 ftp session's fighting for bandwidth,
 153  * one packet will be sent from the first session, then one packet
 154  * from the second session, then one packet from the third, then back
 155  * to the first, etc. etc.
 156  */
 157 void
 158 if_start(void)
 159 {
 160         struct mbuf *ifm, *ifqt;
 161
 162         DEBUG_CALL("if_start");
 163
 164         if (if_queued == 0)
 165            return; /* Nothing to do */
 166
 167  again:
 168         /* check if we can really output */
 169         if (!slirp_can_output())
 170             return;
 171
 172         /*
 173          * See which queue to get next packet from
 174          * If there's something in the fastq, select it immediately
 175          */
 176         if (if_fastq.ifq_next != &if_fastq) {
 177                 ifm = if_fastq.ifq_next;
 178         } else {
 179                 /* Nothing on fastq, see if next_m is valid */
 180                 if (next_m != &if_batchq)
 181                    ifm = next_m;
 182                 else
 183                    ifm = if_batchq.ifq_next;
 184
 185                 /* Set which packet to send on next iteration */
 186                 next_m = ifm->ifq_next;
 187         }
 188         /* Remove it from the queue */
 189         ifqt = ifm->ifq_prev;
 190         remque(ifm);
 191         --if_queued;
 192
 193         /* If there are more packets for this session, re-queue them */
 194         if (ifm->ifs_next != /* ifm->ifs_prev != */ ifm) {
 195                 insque(ifm->ifs_next, ifqt);
 196                 ifs_remque(ifm);
 197         }
 198
 199         /* Update so_queued */
 200         if (ifm->ifq_so) {
 201                 if (--ifm->ifq_so->so_queued == 0)
 202                    /* If there's no more queued, reset nqueued */
 203                    ifm->ifq_so->so_nqueued = 0;
 204         }
 205
 206         /* Encapsulate the packet for sending */
 207         if_encap((uint8_t *)ifm->m_data, ifm->m_len);
 208
 209         m_free(ifm);
 210
 211         if (if_queued)
 212            goto again;
 213 }