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 "qemu/osdep.h"
   9 #include <slirp.h>
  10 #include "qemu/timer.h"
  11
  12 static void
  13 ifs_insque(struct mbuf *ifm, struct mbuf *ifmhead)
  14 {
  15         ifm->ifs_next = ifmhead->ifs_next;
  16         ifmhead->ifs_next = ifm;
  17         ifm->ifs_prev = ifmhead;
  18         ifm->ifs_next->ifs_prev = ifm;
  19 }
  20
  21 static void
  22 ifs_remque(struct mbuf *ifm)
  23 {
  24         ifm->ifs_prev->ifs_next = ifm->ifs_next;
  25         ifm->ifs_next->ifs_prev = ifm->ifs_prev;
  26 }
  27
  28 void
  29 if_init(Slirp *slirp)
  30 {
  31     slirp->if_fastq.ifq_next = slirp->if_fastq.ifq_prev = &slirp->if_fastq;
  32     slirp->if_batchq.ifq_next = slirp->if_batchq.ifq_prev = &slirp->if_batchq;
  33     slirp->next_m = &slirp->if_batchq;
  34 }
  35
  36 /*
  37  * if_output: Queue packet into an output queue.
  38  * There are 2 output queue's, if_fastq and if_batchq.
  39  * Each output queue is a doubly linked list of double linked lists
  40  * of mbufs, each list belonging to one "session" (socket).  This
  41  * way, we can output packets fairly by sending one packet from each
  42  * session, instead of all the packets from one session, then all packets
  43  * from the next session, etc.  Packets on the if_fastq get absolute
  44  * priority, but if one session hogs the link, it gets "downgraded"
  45  * to the batchq until it runs out of packets, then it'll return
  46  * to the fastq (eg. if the user does an ls -alR in a telnet session,
  47  * it'll temporarily get downgraded to the batchq)
  48  */
  49 void
  50 if_output(struct socket *so, struct mbuf *ifm)
  51 {
  52         Slirp *slirp = ifm->slirp;
  53         struct mbuf *ifq;
  54         int on_fastq = 1;
  55
  56         DEBUG_CALL("if_output");
  57         DEBUG_ARG("so = %p", so);
  58         DEBUG_ARG("ifm = %p", ifm);
  59
  60         /*
  61          * First remove the mbuf from m_usedlist,
  62          * since we're gonna use m_next and m_prev ourselves
  63          * XXX Shouldn't need this, gotta change dtom() etc.
  64          */
  65         if (ifm->m_flags & M_USEDLIST) {
  66                 remque(ifm);
  67                 ifm->m_flags &= ~M_USEDLIST;
  68         }
  69
  70         /*
  71          * See if there's already a batchq list for this session.
  72          * This can include an interactive session, which should go on fastq,
  73          * but gets too greedy... hence it'll be downgraded from fastq to batchq.
  74          * We mustn't put this packet back on the fastq (or we'll send it out of order)
  75          * XXX add cache here?
  76          */
  77         for (ifq = slirp->if_batchq.ifq_prev; ifq != &slirp->if_batchq;
  78              ifq = ifq->ifq_prev) {
  79                 if (so == ifq->ifq_so) {
  80                         /* A match! */
  81                         ifm->ifq_so = so;
  82                         ifs_insque(ifm, ifq->ifs_prev);
  83                         goto diddit;
  84                 }
  85         }
  86
  87         /* No match, check which queue to put it on */
  88         if (so && (so->so_iptos & IPTOS_LOWDELAY)) {
  89                 ifq = slirp->if_fastq.ifq_prev;
  90                 on_fastq = 1;
  91                 /*
  92                  * Check if this packet is a part of the last
  93                  * packet's session
  94                  */
  95                 if (ifq->ifq_so == so) {
  96                         ifm->ifq_so = so;
  97                         ifs_insque(ifm, ifq->ifs_prev);
  98                         goto diddit;
  99                 }
 100         } else {
 101                 ifq = slirp->if_batchq.ifq_prev;
 102                 /* Set next_m if the queue was empty so far */
 103                 if (slirp->next_m == &slirp->if_batchq) {
 104                     slirp->next_m = ifm;
 105                 }
 106         }
 107
 108         /* Create a new doubly linked list for this session */
 109         ifm->ifq_so = so;
 110         ifs_init(ifm);
 111         insque(ifm, ifq);
 112
 113 diddit:
 114         if (so) {
 115                 /* Update *_queued */
 116                 so->so_queued++;
 117                 so->so_nqueued++;
 118                 /*
 119                  * Check if the interactive session should be downgraded to
 120                  * the batchq.  A session is downgraded if it has queued 6
 121                  * packets without pausing, and at least 3 of those packets
 122                  * have been sent over the link
 123                  * (XXX These are arbitrary numbers, probably not optimal..)
 124                  */
 125                 if (on_fastq && ((so->so_nqueued >= 6) &&
 126                                  (so->so_nqueued - so->so_queued) >= 3)) {
 127
 128                         /* Remove from current queue... */
 129                         remque(ifm->ifs_next);
 130
 131                         /* ...And insert in the new.  That'll teach ya! */
 132                         insque(ifm->ifs_next, &slirp->if_batchq);
 133                 }
 134         }
 135
 136 #ifndef FULL_BOLT
 137         /*
 138          * This prevents us from malloc()ing too many mbufs
 139          */
 140         if_start(ifm->slirp);
 141 #endif
 142 }
 143
 144 /*
 145  * Send a packet
 146  * We choose a packet based on its position in the output queues;
 147  * If there are packets on the fastq, they are sent FIFO, before
 148  * everything else.  Otherwise we choose the first packet from the
 149  * batchq and send it.  the next packet chosen will be from the session
 150  * after this one, then the session after that one, and so on..  So,
 151  * for example, if there are 3 ftp session's fighting for bandwidth,
 152  * one packet will be sent from the first session, then one packet
 153  * from the second session, then one packet from the third, then back
 154  * to the first, etc. etc.
 155  */
 156 void if_start(Slirp *slirp)
 157 {
 158     uint64_t now = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
 159     bool from_batchq, next_from_batchq;
 160     struct mbuf *ifm, *ifm_next, *ifqt;
 161
 162     DEBUG_CALL("if_start");
 163
 164     if (slirp->if_start_busy) {
 165         return;
 166     }
 167     slirp->if_start_busy = true;
 168
 169     if (slirp->if_fastq.ifq_next != &slirp->if_fastq) {
 170         ifm_next = slirp->if_fastq.ifq_next;
 171         next_from_batchq = false;
 172     } else if (slirp->next_m != &slirp->if_batchq) {
 173         /* Nothing on fastq, pick up from batchq via next_m */
 174         ifm_next = slirp->next_m;
 175         next_from_batchq = true;
 176     } else {
 177         ifm_next = NULL;
 178     }
 179
 180     while (ifm_next) {
 181         ifm = ifm_next;
 182         from_batchq = next_from_batchq;
 183
 184         ifm_next = ifm->ifq_next;
 185         if (ifm_next == &slirp->if_fastq) {
 186             /* No more packets in fastq, switch to batchq */
 187             ifm_next = slirp->next_m;
 188             next_from_batchq = true;
 189         }
 190         if (ifm_next == &slirp->if_batchq) {
 191             /* end of batchq */
 192             ifm_next = NULL;
 193         }
 194
 195         /* Try to send packet unless it already expired */
 196         if (ifm->expiration_date >= now && !if_encap(slirp, ifm)) {
 197             /* Packet is delayed due to pending ARP resolution */
 198             continue;
 199         }
 200
 201         if (ifm == slirp->next_m) {
 202             /* Set which packet to send on next iteration */
 203             slirp->next_m = ifm->ifq_next;
 204         }
 205
 206         /* Remove it from the queue */
 207         ifqt = ifm->ifq_prev;
 208         remque(ifm);
 209
 210         /* If there are more packets for this session, re-queue them */
 211         if (ifm->ifs_next != ifm) {
 212             struct mbuf *next = ifm->ifs_next;
 213
 214             insque(next, ifqt);
 215             ifs_remque(ifm);
 216
 217             if (!from_batchq) {
 218                 /* Next packet in fastq is from the same session */
 219                 ifm_next = next;
 220                 next_from_batchq = false;
 221             } else if (slirp->next_m == &slirp->if_batchq) {
 222                 /* Set next_m and ifm_next if the session packet is now the
 223                  * only one on batchq */
 224                 slirp->next_m = ifm_next = next;
 225             }
 226         }
 227
 228         /* Update so_queued */
 229         if (ifm->ifq_so && --ifm->ifq_so->so_queued == 0) {
 230             /* If there's no more queued, reset nqueued */
 231             ifm->ifq_so->so_nqueued = 0;
 232         }
 233
 234         m_free(ifm);
 235     }
 236
 237     slirp->if_start_busy = false;
 238 }