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

   1 /*
   2     graph.c -- graph algorithms
   3     Copyright (C) 2001-2002 Guus Sliepen <guus@sliepen.eu.org>,
   4                   2001-2002 Ivo Timmermans <ivo@o2w.nl>
   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
  17     along with this program; if not, write to the Free Software
  18     Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  19
  20     $Id: graph.c,v 1.1.2.22 2003/01/17 00:37:17 guus Exp $
  21 */
  22
  23 /* We need to generate two trees from the graph:
  24
  25    1. A minimum spanning tree for broadcasts,
  26    2. A single-source shortest path tree for unicasts.
  27
  28    Actually, the first one alone would suffice but would make unicast packets
  29    take longer routes than necessary.
  30
  31    For the MST algorithm we can choose from Prim's or Kruskal's. I personally
  32    favour Kruskal's, because we make an extra AVL tree of edges sorted on
  33    weights (metric). That tree only has to be updated when an edge is added or
  34    removed, and during the MST algorithm we just have go linearly through that
  35    tree, adding safe edges until #edges = #nodes - 1. The implementation here
  36    however is not so fast, because I tried to avoid having to make a forest and
  37    merge trees.
  38
  39    For the SSSP algorithm Dijkstra's seems to be a nice choice. Currently a
  40    simple breadth-first search is presented here.
  41
  42    The SSSP algorithm will also be used to determine whether nodes are directly,
  43    indirectly or not reachable from the source. It will also set the correct
  44    destination address and port of a node if possible.
  45 */
  46
  47 #include "config.h"
  48
  49 #include <stdio.h>
  50 #include <syslog.h>
  51 #include <string.h>
  52 #ifdef HAVE_SYS_PARAM_H
  53 #include <sys/param.h>
  54 #endif
  55 #include <netinet/in.h>
  56
  57 #include <avl_tree.h>
  58 #include <utils.h>
  59
  60 #include "netutl.h"
  61 #include "node.h"
  62 #include "edge.h"
  63 #include "connection.h"
  64 #include "process.h"
  65 #include "device.h"
  66
  67 #include "system.h"
  68
  69 /* Implementation of Kruskal's algorithm.
  70    Running time: O(EN)
  71    Please note that sorting on weight is already done by add_edge().
  72 */
  73
  74 void mst_kruskal(void)
  75 {
  76         avl_node_t *node, *next;
  77         edge_t *e;
  78         node_t *n;
  79         connection_t *c;
  80         int nodes = 0;
  81         int safe_edges = 0;
  82         int skipped;
  83
  84         cp();
  85
  86         /* Clear MST status on connections */
  87
  88         for(node = connection_tree->head; node; node = node->next) {
  89                 c = (connection_t *) node->data;
  90                 c->status.mst = 0;
  91         }
  92
  93         /* Do we have something to do at all? */
  94
  95         if(!edge_weight_tree->head)
  96                 return;
  97
  98         if(debug_lvl >= DEBUG_SCARY_THINGS)
  99                 syslog(LOG_DEBUG, "Running Kruskal's algorithm:");
 100
 101         /* Clear visited status on nodes */
 102
 103         for(node = node_tree->head; node; node = node->next) {
 104                 n = (node_t *) node->data;
 105                 n->status.visited = 0;
 106                 nodes++;
 107         }
 108
 109         /* Starting point */
 110
 111         ((edge_t *) edge_weight_tree->head->data)->from->status.visited = 1;
 112
 113         /* Add safe edges */
 114
 115         for(skipped = 0, node = edge_weight_tree->head; node; node = next) {
 116                 next = node->next;
 117                 e = (edge_t *) node->data;
 118
 119                 if(!e->reverse || e->from->status.visited == e->to->status.visited) {
 120                         skipped = 1;
 121                         continue;
 122                 }
 123
 124                 e->from->status.visited = 1;
 125                 e->to->status.visited = 1;
 126
 127                 if(e->connection)
 128                         e->connection->status.mst = 1;
 129
 130                 if(e->reverse->connection)
 131                         e->reverse->connection->status.mst = 1;
 132
 133                 safe_edges++;
 134
 135                 if(debug_lvl >= DEBUG_SCARY_THINGS)
 136                         syslog(LOG_DEBUG, " Adding edge %s - %s weight %d", e->from->name,
 137                                    e->to->name, e->weight);
 138
 139                 if(skipped) {
 140                         skipped = 0;
 141                         next = edge_weight_tree->head;
 142                         continue;
 143                 }
 144         }
 145
 146         if(debug_lvl >= DEBUG_SCARY_THINGS)
 147                 syslog(LOG_DEBUG, "Done, counted %d nodes and %d safe edges.", nodes,
 148                            safe_edges);
 149 }
 150
 151 /* Implementation of a simple breadth-first search algorithm.
 152    Running time: O(E)
 153 */
 154
 155 void sssp_bfs(void)
 156 {
 157         avl_node_t *node, *from, *next, *to;
 158         edge_t *e;
 159         node_t *n;
 160         avl_tree_t *todo_tree;
 161         int indirect;
 162         char *name;
 163         char *address, *port;
 164         char *envp[7];
 165         int i;
 166
 167         cp();
 168
 169         todo_tree = avl_alloc_tree(NULL, NULL);
 170
 171         /* Clear visited status on nodes */
 172
 173         for(node = node_tree->head; node; node = node->next) {
 174                 n = (node_t *) node->data;
 175                 n->status.visited = 0;
 176                 n->status.indirect = 1;
 177         }
 178
 179         /* Begin with myself */
 180
 181         myself->status.visited = 1;
 182         myself->status.indirect = 0;
 183         myself->nexthop = myself;
 184         myself->via = myself;
 185         node = avl_alloc_node();
 186         node->data = myself;
 187         avl_insert_top(todo_tree, node);
 188
 189         /* Loop while todo_tree is filled */
 190
 191         while(todo_tree->head) {
 192                 for(from = todo_tree->head; from; from = next) {        /* "from" is the node from which we start */
 193                         next = from->next;
 194                         n = (node_t *) from->data;
 195
 196                         for(to = n->edge_tree->head; to; to = to->next) {       /* "to" is the edge connected to "from" */
 197                                 e = (edge_t *) to->data;
 198
 199                                 if(!e->reverse)
 200                                         continue;
 201
 202                                 /* Situation:
 203
 204                                     /
 205                                    /
 206                                    ------(n)-----(e->to)
 207                                    \
 208                                     \
 209
 210                                    n->address is set to the e->address of the edge left of n to n.
 211                                    We are currently examining the edge e right of n from n:
 212
 213                                    - If e->reverse->address != n->address, then e->to is probably
 214                                      not reachable for the nodes left of n. We do as if the indirectdata
 215                                      flag is set on edge e.
 216                                    - If edge e provides for better reachability of e->to, update
 217                                      e->to and (re)add it to the todo_tree to (re)examine the reachability
 218                                      of nodes behind it.
 219                                  */
 220
 221                                 indirect = n->status.indirect || e->options & OPTION_INDIRECT
 222                                         || ((n != myself) && sockaddrcmp(&n->address, &e->reverse->address));
 223
 224                                 if(e->to->status.visited
 225                                    && (!e->to->status.indirect || indirect))
 226                                         continue;
 227
 228                                 e->to->status.visited = 1;
 229                                 e->to->status.indirect = indirect;
 230                                 e->to->nexthop = (n->nexthop == myself) ? e->to : n->nexthop;
 231                                 e->to->via = indirect ? n->via : e->to;
 232                                 e->to->options = e->options;
 233
 234                                 if(sockaddrcmp(&e->to->address, &e->address)) {
 235                                         node = avl_unlink(node_udp_tree, e->to);
 236                                         e->to->address = e->address;
 237
 238                                         if(e->to->hostname)
 239                                                 free(e->to->hostname);
 240
 241                                         e->to->hostname = sockaddr2hostname(&e->to->address);
 242                                         avl_insert_node(node_udp_tree, node);
 243                                 }
 244
 245                                 node = avl_alloc_node();
 246                                 node->data = e->to;
 247                                 avl_insert_before(todo_tree, from, node);
 248                         }
 249
 250                         avl_delete_node(todo_tree, from);
 251                 }
 252         }
 253
 254         avl_free_tree(todo_tree);
 255
 256         /* Check reachability status. */
 257
 258         for(node = node_tree->head; node; node = next) {
 259                 next = node->next;
 260                 n = (node_t *) node->data;
 261
 262                 if(n->status.visited != n->status.reachable) {
 263                         n->status.reachable = !n->status.reachable;
 264
 265                         if(debug_lvl >= DEBUG_TRAFFIC) {
 266                                 if(n->status.reachable)
 267                                         syslog(LOG_DEBUG, _("Node %s (%s) became reachable"),
 268                                                    n->name, n->hostname);
 269                                 else
 270                                         syslog(LOG_DEBUG, _("Node %s (%s) became unreachable"),
 271                                                    n->name, n->hostname);
 272                         }
 273
 274                         n->status.validkey = 0;
 275                         n->status.waitingforkey = 0;
 276
 277                         asprintf(&envp[0], "NETNAME=%s", netname ? : "");
 278                         asprintf(&envp[1], "DEVICE=%s", device ? : "");
 279                         asprintf(&envp[2], "INTERFACE=%s", interface ? : "");
 280                         asprintf(&envp[3], "NODE=%s", n->name);
 281                         sockaddr2str(&n->address, &address, &port);
 282                         asprintf(&envp[4], "REMOTEADDRESS=%s", address);
 283                         asprintf(&envp[5], "REMOTEPORT=%s", port);
 284                         envp[6] = NULL;
 285
 286                         asprintf(&name,
 287                                          n->status.reachable ? "hosts/%s-up" : "hosts/%s-down",
 288                                          n->name);
 289                         execute_script(name, envp);
 290
 291                         free(name);
 292                         free(address);
 293                         free(port);
 294
 295                         for(i = 0; i < 7; i++)
 296                                 free(envp[i]);
 297                 }
 298         }
 299 }
 300
 301 void graph(void)
 302 {
 303         mst_kruskal();
 304         sssp_bfs();
 305 }