tinc-vpn.org Git - tinc/blob - src/graph.c

   1 /*
   2     graph.c -- graph algorithms
   3     Copyright (C) 2001-2012 Guus Sliepen <guus@tinc-vpn.org>,
   4                   2001-2005 Ivo Timmermans
   5
   6     This program is free software; you can redistribute it and/or modify
   7     it under the terms of the GNU General Public License as published by
   8     the Free Software Foundation; either version 2 of the License, or
   9     (at your option) any later version.
  10
  11     This program is distributed in the hope that it will be useful,
  12     but WITHOUT ANY WARRANTY; without even the implied warranty of
  13     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14     GNU General Public License for more details.
  15
  16     You should have received a copy of the GNU General Public License along
  17     with this program; if not, write to the Free Software Foundation, Inc.,
  18     51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  19 */
  20
  21 /* We need to generate two trees from the graph:
  22
  23    1. A minimum spanning tree for broadcasts,
  24    2. A single-source shortest path tree for unicasts.
  25
  26    Actually, the first one alone would suffice but would make unicast packets
  27    take longer routes than necessary.
  28
  29    For the MST algorithm we can choose from Prim's or Kruskal's. I personally
  30    favour Kruskal's, because we make an extra AVL tree of edges sorted on
  31    weights (metric). That tree only has to be updated when an edge is added or
  32    removed, and during the MST algorithm we just have go linearly through that
  33    tree, adding safe edges until #edges = #nodes - 1. The implementation here
  34    however is not so fast, because I tried to avoid having to make a forest and
  35    merge trees.
  36
  37    For the SSSP algorithm Dijkstra's seems to be a nice choice. Currently a
  38    simple breadth-first search is presented here.
  39
  40    The SSSP algorithm will also be used to determine whether nodes are directly,
  41    indirectly or not reachable from the source. It will also set the correct
  42    destination address and port of a node if possible.
  43 */
  44
  45 #include "system.h"
  46
  47 #include "config.h"
  48 #include "connection.h"
  49 #include "device.h"
  50 #include "edge.h"
  51 #include "graph.h"
  52 #include "list.h"
  53 #include "logger.h"
  54 #include "netutl.h"
  55 #include "node.h"
  56 #include "process.h"
  57 #include "protocol.h"
  58 #include "subnet.h"
  59 #include "utils.h"
  60 #include "xalloc.h"
  61 #include "graph.h"
  62
  63 /* Implementation of Kruskal's algorithm.
  64    Running time: O(E)
  65    Please note that sorting on weight is already done by add_edge().
  66 */
  67
  68 static void mst_kruskal(void) {
  69         /* Clear MST status on connections */
  70
  71         for list_each(connection_t, c, connection_list)
  72                 c->status.mst = false;
  73
  74         logger(DEBUG_SCARY_THINGS, LOG_DEBUG, "Running Kruskal's algorithm:");
  75
  76         /* Clear visited status on nodes */
  77
  78         for splay_each(node_t, n, node_tree)
  79                 n->status.visited = false;
  80
  81         /* Add safe edges */
  82
  83         for splay_each(edge_t, e, edge_weight_tree) {
  84                 if(!e->reverse || (e->from->status.visited && e->to->status.visited))
  85                         continue;
  86
  87                 e->from->status.visited = true;
  88                 e->to->status.visited = true;
  89
  90                 if(e->connection)
  91                         e->connection->status.mst = true;
  92
  93                 if(e->reverse->connection)
  94                         e->reverse->connection->status.mst = true;
  95
  96                 logger(DEBUG_SCARY_THINGS, LOG_DEBUG, " Adding edge %s - %s weight %d", e->from->name,
  97                                    e->to->name, e->weight);
  98         }
  99 }
 100
 101 /* Implementation of a simple breadth-first search algorithm.
 102    Running time: O(E)
 103 */
 104
 105 static void sssp_bfs(void) {
 106         list_t *todo_list = list_alloc(NULL);
 107
 108         /* Clear visited status on nodes */
 109
 110         for splay_each(node_t, n, node_tree) {
 111                 n->status.visited = false;
 112                 n->status.indirect = true;
 113                 n->distance = -1;
 114         }
 115
 116         /* Begin with myself */
 117
 118         myself->status.visited = true;
 119         myself->status.indirect = false;
 120         myself->nexthop = myself;
 121         myself->prevedge = NULL;
 122         myself->via = myself;
 123         myself->distance = 0;
 124         list_insert_head(todo_list, myself);
 125
 126         /* Loop while todo_list is filled */
 127
 128         for list_each(node_t, n, todo_list) {                   /* "n" is the node from which we start */
 129                 logger(DEBUG_SCARY_THINGS, LOG_DEBUG, " Examining edges from %s", n->name);
 130
 131                 if(n->distance < 0)
 132                         abort();
 133
 134                 for splay_each(edge_t, e, n->edge_tree) {       /* "e" is the edge connected to "from" */
 135                         if(!e->reverse)
 136                                 continue;
 137
 138                         /* Situation:
 139
 140                                    /
 141                                   /
 142                            ----->(n)---e-->(e->to)
 143                                   \
 144                                    \
 145
 146                            Where e is an edge, (n) and (e->to) are nodes.
 147                            n->address is set to the e->address of the edge left of n to n.
 148                            We are currently examining the edge e right of n from n:
 149
 150                            - If edge e provides for better reachability of e->to, update
 151                              e->to and (re)add it to the todo_list to (re)examine the reachability
 152                              of nodes behind it.
 153                          */
 154
 155                         bool indirect = n->status.indirect || e->options & OPTION_INDIRECT;
 156
 157                         if(e->to->status.visited
 158                            && (!e->to->status.indirect || indirect)
 159                            && (e->to->distance != n->distance + 1 || e->weight >= e->to->prevedge->weight))
 160                                 continue;
 161
 162                         e->to->status.visited = true;
 163                         e->to->status.indirect = indirect;
 164                         e->to->nexthop = (n->nexthop == myself) ? e->to : n->nexthop;
 165                         e->to->prevedge = e;
 166                         e->to->via = indirect ? n->via : e->to;
 167                         e->to->options = e->options;
 168                         e->to->distance = n->distance + 1;
 169
 170                         if(!e->to->status.reachable || (e->to->address.sa.sa_family == AF_UNSPEC && e->address.sa.sa_family != AF_UNKNOWN))
 171                                 update_node_udp(e->to, &e->address);
 172
 173                         list_insert_tail(todo_list, e->to);
 174                 }
 175
 176                 next = node->next; /* Because the list_insert_tail() above could have added something extra for us! */
 177                 list_delete_node(todo_list, node);
 178         }
 179
 180         list_free(todo_list);
 181 }
 182
 183 static void check_reachability(void) {
 184         /* Check reachability status. */
 185
 186         for splay_each(node_t, n, node_tree) {
 187                 if(n->status.visited != n->status.reachable) {
 188                         n->status.reachable = !n->status.reachable;
 189                         n->last_state_change = time(NULL);
 190
 191                         if(n->status.reachable) {
 192                                 logger(DEBUG_TRAFFIC, LOG_DEBUG, "Node %s (%s) became reachable",
 193                                            n->name, n->hostname);
 194                         } else {
 195                                 logger(DEBUG_TRAFFIC, LOG_DEBUG, "Node %s (%s) became unreachable",
 196                                            n->name, n->hostname);
 197                         }
 198
 199                         if(experimental && OPTION_VERSION(n->options) >= 2)
 200                                 n->status.sptps = true;
 201
 202                         /* TODO: only clear status.validkey if node is unreachable? */
 203
 204                         n->status.validkey = false;
 205                         if(n->status.sptps) {
 206                                 sptps_stop(&n->sptps);
 207                                 n->status.waitingforkey = false;
 208                         }
 209                         n->last_req_key = 0;
 210
 211                         n->status.udp_confirmed = false;
 212                         n->maxmtu = MTU;
 213                         n->minmtu = 0;
 214                         n->mtuprobes = 0;
 215
 216                         timeout_del(&n->mtutimeout);
 217
 218                         char *name;
 219                         char *address;
 220                         char *port;
 221                         char *envp[7];
 222
 223                         xasprintf(&envp[0], "NETNAME=%s", netname ? : "");
 224                         xasprintf(&envp[1], "DEVICE=%s", device ? : "");
 225                         xasprintf(&envp[2], "INTERFACE=%s", iface ? : "");
 226                         xasprintf(&envp[3], "NODE=%s", n->name);
 227                         sockaddr2str(&n->address, &address, &port);
 228                         xasprintf(&envp[4], "REMOTEADDRESS=%s", address);
 229                         xasprintf(&envp[5], "REMOTEPORT=%s", port);
 230                         envp[6] = NULL;
 231
 232                         execute_script(n->status.reachable ? "host-up" : "host-down", envp);
 233
 234                         xasprintf(&name, n->status.reachable ? "hosts/%s-up" : "hosts/%s-down", n->name);
 235                         execute_script(name, envp);
 236
 237                         free(name);
 238                         free(address);
 239                         free(port);
 240
 241                         for(int i = 0; i < 6; i++)
 242                                 free(envp[i]);
 243
 244                         subnet_update(n, NULL, n->status.reachable);
 245
 246                         if(!n->status.reachable) {
 247                                 update_node_udp(n, NULL);
 248                                 memset(&n->status, 0, sizeof n->status);
 249                                 n->options = 0;
 250                         } else if(n->connection) {
 251                                 if(n->status.sptps) {
 252                                         if(n->connection->outgoing)
 253                                                 send_req_key(n);
 254                                 } else {
 255                                         send_ans_key(n);
 256                                 }
 257                         }
 258                 }
 259         }
 260 }
 261
 262 void graph(void) {
 263         subnet_cache_flush();
 264         sssp_bfs();
 265         check_reachability();
 266         mst_kruskal();
 267 }