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 #include "qemu/timer.h"
  10
  11 static void
  12 ifs_insque(struct mbuf *ifm, struct mbuf *ifmhead)
  13 {
  14         ifm->ifs_next = ifmhead->ifs_next;
  15         ifmhead->ifs_next = ifm;
  16         ifm->ifs_prev = ifmhead;
  17         ifm->ifs_next->ifs_prev = ifm;
  18 }
  19
  20 static void
  21 ifs_remque(struct mbuf *ifm)
  22 {
  23         ifm->ifs_prev->ifs_next = ifm->ifs_next;
  24         ifm->ifs_next->ifs_prev = ifm->ifs_prev;
  25 }
  26
  27 void
  28 if_init(Slirp *slirp)
  29 {
  30     slirp->if_fastq.ifq_next = slirp->if_fastq.ifq_prev = &slirp->if_fastq;
  31     slirp->if_batchq.ifq_next = slirp->if_batchq.ifq_prev = &slirp->if_batchq;
  32     slirp->next_m = &slirp->if_batchq;
  33 }
  34
  35 /*
  36  * if_output: Queue packet into an output queue.
  37  * There are 2 output queue's, if_fastq and if_batchq.
  38  * Each output queue is a doubly linked list of double linked lists
  39  * of mbufs, each list belonging to one "session" (socket).  This
  40  * way, we can output packets fairly by sending one packet from each
  41  * session, instead of all the packets from one session, then all packets
  42  * from the next session, etc.  Packets on the if_fastq get absolute
  43  * priority, but if one session hogs the link, it gets "downgraded"
  44  * to the batchq until it runs out of packets, then it'll return
  45  * to the fastq (eg. if the user does an ls -alR in a telnet session,
  46  * it'll temporarily get downgraded to the batchq)
  47  */
  48 void
  49 if_output(struct socket *so, struct mbuf *ifm)
  50 {
  51         Slirp *slirp = ifm->slirp;
  52         struct mbuf *ifq;
  53         int on_fastq = 1;
  54
  55         DEBUG_CALL("if_output");
  56         DEBUG_ARG("so = %p", so);
  57         DEBUG_ARG("ifm = %p", ifm);
  58
  59         /*
  60          * First remove the mbuf from m_usedlist,
  61          * since we're gonna use m_next and m_prev ourselves
  62          * XXX Shouldn't need this, gotta change dtom() etc.
  63          */
  64         if (ifm->m_flags & M_USEDLIST) {
  65                 remque(ifm);
  66                 ifm->m_flags &= ~M_USEDLIST;
  67         }
  68
  69         /*
  70          * See if there's already a batchq list for this session.
  71          * This can include an interactive session, which should go on fastq,
  72          * but gets too greedy... hence it'll be downgraded from fastq to batchq.
  73          * We mustn't put this packet back on the fastq (or we'll send it out of order)
  74          * XXX add cache here?
  75          */
  76         for (ifq = slirp->if_batchq.ifq_prev; ifq != &slirp->if_batchq;
  77              ifq = ifq->ifq_prev) {
  78                 if (so == ifq->ifq_so) {
  79                         /* A match! */
  80                         ifm->ifq_so = so;
  81                         ifs_insque(ifm, ifq->ifs_prev);
  82                         goto diddit;
  83                 }
  84         }
  85
  86         /* No match, check which queue to put it on */
  87         if (so && (so->so_iptos & IPTOS_LOWDELAY)) {
  88                 ifq = slirp->if_fastq.ifq_prev;
  89                 on_fastq = 1;
  90                 /*
  91                  * Check if this packet is a part of the last
  92                  * packet's session
  93                  */
  94                 if (ifq->ifq_so == so) {
  95                         ifm->ifq_so = so;
  96                         ifs_insque(ifm, ifq->ifs_prev);
  97                         goto diddit;
  98                 }
  99         } else {
 100                 ifq = slirp->if_batchq.ifq_prev;
 101                 /* Set next_m if the queue was empty so far */
 102                 if (slirp->next_m == &slirp->if_batchq) {
 103                     slirp->next_m = ifm;
 104                 }
 105         }
 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 (so) {
 114                 /* Update *_queued */
 115                 so->so_queued++;
 116                 so->so_nqueued++;
 117                 /*
 118                  * Check if the interactive session should be downgraded to
 119                  * the batchq.  A session is downgraded if it has queued 6
 120                  * packets without pausing, and at least 3 of those packets
 121                  * have been sent over the link
 122                  * (XXX These are arbitrary numbers, probably not optimal..)
 123                  */
 124                 if (on_fastq && ((so->so_nqueued >= 6) &&
 125                                  (so->so_nqueued - so->so_queued) >= 3)) {
 126
 127                         /* Remove from current queue... */
 128                         remque(ifm->ifs_next);
 129
 130                         /* ...And insert in the new.  That'll teach ya! */
 131                         insque(ifm->ifs_next, &slirp->if_batchq);
 132                 }
 133         }
 134
 135 #ifndef FULL_BOLT
 136         /*
 137          * This prevents us from malloc()ing too many mbufs
 138          */
 139         if_start(ifm->slirp);
 140 #endif
 141 }
 142
 143 /*
 144  * Send a packet
 145  * We choose a packet based on its position in the output queues;
 146  * If there are packets on the fastq, they are sent FIFO, before
 147  * everything else.  Otherwise we choose the first packet from the
 148  * batchq and send it.  the next packet chosen will be from the session
 149  * after this one, then the session after that one, and so on..  So,
 150  * for example, if there are 3 ftp session's fighting for bandwidth,
 151  * one packet will be sent from the first session, then one packet
 152  * from the second session, then one packet from the third, then back
 153  * to the first, etc. etc.
 154  */
 155 void if_start(Slirp *slirp)
 156 {
 157     uint64_t now = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
 158     bool from_batchq, next_from_batchq;
 159     struct mbuf *ifm, *ifm_next, *ifqt;
 160
 161     DEBUG_CALL("if_start");
 162
 163     if (slirp->if_start_busy) {
 164         return;
 165     }
 166     slirp->if_start_busy = true;
 167
 168     if (slirp->if_fastq.ifq_next != &slirp->if_fastq) {
 169         ifm_next = slirp->if_fastq.ifq_next;
 170         next_from_batchq = false;
 171     } else if (slirp->next_m != &slirp->if_batchq) {
 172         /* Nothing on fastq, pick up from batchq via next_m */
 173         ifm_next = slirp->next_m;
 174         next_from_batchq = true;
 175     } else {
 176         ifm_next = NULL;
 177     }
 178
 179     while (ifm_next) {
 180         ifm = ifm_next;
 181         from_batchq = next_from_batchq;
 182
 183         ifm_next = ifm->ifq_next;
 184         if (ifm_next == &slirp->if_fastq) {
 185             /* No more packets in fastq, switch to batchq */
 186             ifm_next = slirp->next_m;
 187             next_from_batchq = true;
 188         }
 189         if (ifm_next == &slirp->if_batchq) {
 190             /* end of batchq */
 191             ifm_next = NULL;
 192         }
 193
 194         /* Try to send packet unless it already expired */
 195         if (ifm->expiration_date >= now && !if_encap(slirp, ifm)) {
 196             /* Packet is delayed due to pending ARP resolution */
 197             continue;
 198         }
 199
 200         if (ifm == slirp->next_m) {
 201             /* Set which packet to send on next iteration */
 202             slirp->next_m = ifm->ifq_next;
 203         }
 204
 205         /* Remove it from the queue */
 206         ifqt = ifm->ifq_prev;
 207         remque(ifm);
 208
 209         /* If there are more packets for this session, re-queue them */
 210         if (ifm->ifs_next != ifm) {
 211             struct mbuf *next = ifm->ifs_next;
 212
 213             insque(next, ifqt);
 214             ifs_remque(ifm);
 215
 216             if (!from_batchq) {
 217                 /* Next packet in fastq is from the same session */
 218                 ifm_next = next;
 219                 next_from_batchq = false;
 220             } else if (slirp->next_m == &slirp->if_batchq) {
 221                 /* Set next_m and ifm_next if the session packet is now the
 222                  * only one on batchq */
 223                 slirp->next_m = ifm_next = next;
 224             }
 225         }
 226
 227         /* Update so_queued */
 228         if (ifm->ifq_so && --ifm->ifq_so->so_queued == 0) {
 229             /* If there's no more queued, reset nqueued */
 230             ifm->ifq_so->so_nqueued = 0;
 231         }
 232
 233         m_free(ifm);
 234     }
 235
 236     slirp->if_start_busy = false;
 237 }