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

   1 /*
   2     graph.c -- graph algorithms
   3     Copyright (C) 2001-2003 Guus Sliepen <guus@sliepen.eu.org>,
   4                   2001-2003 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 1.1.2.28 2003/08/22 11:18:42 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 "system.h"
  48
  49 #include "avl_tree.h"
  50 #include "connection.h"
  51 #include "device.h"
  52 #include "edge.h"
  53 #include "logger.h"
  54 #include "netutl.h"
  55 #include "node.h"
  56 #include "process.h"
  57 #include "utils.h"
  58
  59 /* Implementation of Kruskal's algorithm.
  60    Running time: O(EN)
  61    Please note that sorting on weight is already done by add_edge().
  62 */
  63
  64 void mst_kruskal(void)
  65 {
  66         avl_node_t *node, *next;
  67         edge_t *e;
  68         node_t *n;
  69         connection_t *c;
  70         int nodes = 0;
  71         int safe_edges = 0;
  72         bool skipped;
  73
  74         cp();
  75
  76         /* Clear MST status on connections */
  77
  78         for(node = connection_tree->head; node; node = node->next) {
  79                 c = (connection_t *) node->data;
  80                 c->status.mst = false;
  81         }
  82
  83         /* Do we have something to do at all? */
  84
  85         if(!edge_weight_tree->head)
  86                 return;
  87
  88         ifdebug(SCARY_THINGS) logger(LOG_DEBUG, "Running Kruskal's algorithm:");
  89
  90         /* Clear visited status on nodes */
  91
  92         for(node = node_tree->head; node; node = node->next) {
  93                 n = (node_t *) node->data;
  94                 n->status.visited = false;
  95                 nodes++;
  96         }
  97
  98         /* Starting point */
  99
 100         ((edge_t *) edge_weight_tree->head->data)->from->status.visited = true;
 101
 102         /* Add safe edges */
 103
 104         for(skipped = false, node = edge_weight_tree->head; node; node = next) {
 105                 next = node->next;
 106                 e = (edge_t *) node->data;
 107
 108                 if(!e->reverse || e->from->status.visited == e->to->status.visited) {
 109                         skipped = true;
 110                         continue;
 111                 }
 112
 113                 e->from->status.visited = true;
 114                 e->to->status.visited = true;
 115
 116                 if(e->connection)
 117                         e->connection->status.mst = true;
 118
 119                 if(e->reverse->connection)
 120                         e->reverse->connection->status.mst = true;
 121
 122                 safe_edges++;
 123
 124                 ifdebug(SCARY_THINGS) logger(LOG_DEBUG, " Adding edge %s - %s weight %d", e->from->name,
 125                                    e->to->name, e->weight);
 126
 127                 if(skipped) {
 128                         skipped = false;
 129                         next = edge_weight_tree->head;
 130                         continue;
 131                 }
 132         }
 133
 134         ifdebug(SCARY_THINGS) logger(LOG_DEBUG, "Done, counted %d nodes and %d safe edges.", nodes,
 135                            safe_edges);
 136 }
 137
 138 /* Implementation of a simple breadth-first search algorithm.
 139    Running time: O(E)
 140 */
 141
 142 void sssp_bfs(void)
 143 {
 144         avl_node_t *node, *from, *next, *to;
 145         edge_t *e;
 146         node_t *n;
 147         avl_tree_t *todo_tree;
 148         bool indirect;
 149         char *name;
 150         char *address, *port;
 151         char *envp[7];
 152         int i;
 153
 154         cp();
 155
 156         todo_tree = avl_alloc_tree(NULL, NULL);
 157
 158         /* Clear visited status on nodes */
 159
 160         for(node = node_tree->head; node; node = node->next) {
 161                 n = (node_t *) node->data;
 162                 n->status.visited = false;
 163                 n->status.indirect = true;
 164         }
 165
 166         /* Begin with myself */
 167
 168         myself->status.visited = true;
 169         myself->status.indirect = false;
 170         myself->nexthop = myself;
 171         myself->via = myself;
 172         node = avl_alloc_node();
 173         node->data = myself;
 174         avl_insert_top(todo_tree, node);
 175
 176         /* Loop while todo_tree is filled */
 177
 178         while(todo_tree->head) {
 179                 for(from = todo_tree->head; from; from = next) {        /* "from" is the node from which we start */
 180                         next = from->next;
 181                         n = (node_t *) from->data;
 182
 183                         for(to = n->edge_tree->head; to; to = to->next) {       /* "to" is the edge connected to "from" */
 184                                 e = (edge_t *) to->data;
 185
 186                                 if(!e->reverse)
 187                                         continue;
 188
 189                                 /* Situation:
 190
 191                                     /
 192                                    /
 193                                    ------(n)-----(e->to)
 194                                    \
 195                                     \
 196
 197                                    n->address is set to the e->address of the edge left of n to n.
 198                                    We are currently examining the edge e right of n from n:
 199
 200                                    - If e->reverse->address != n->address, then e->to is probably
 201                                      not reachable for the nodes left of n. We do as if the indirectdata
 202                                      flag is set on edge e.
 203                                    - If edge e provides for better reachability of e->to, update
 204                                      e->to and (re)add it to the todo_tree to (re)examine the reachability
 205                                      of nodes behind it.
 206                                  */
 207
 208                                 indirect = n->status.indirect || e->options & OPTION_INDIRECT
 209                                         || ((n != myself) && sockaddrcmp(&n->address, &e->reverse->address));
 210
 211                                 if(e->to->status.visited
 212                                    && (!e->to->status.indirect || indirect))
 213                                         continue;
 214
 215                                 e->to->status.visited = true;
 216                                 e->to->status.indirect = indirect;
 217                                 e->to->nexthop = (n->nexthop == myself) ? e->to : n->nexthop;
 218                                 e->to->via = indirect ? n->via : e->to;
 219                                 e->to->options = e->options;
 220
 221                                 if(sockaddrcmp(&e->to->address, &e->address)) {
 222                                         node = avl_unlink(node_udp_tree, e->to);
 223                                         sockaddrfree(&e->to->address);
 224                                         sockaddrcpy(&e->to->address, &e->address);
 225
 226                                         if(e->to->hostname)
 227                                                 free(e->to->hostname);
 228
 229                                         e->to->hostname = sockaddr2hostname(&e->to->address);
 230                                         avl_insert_node(node_udp_tree, node);
 231                                 }
 232
 233                                 node = avl_alloc_node();
 234                                 node->data = e->to;
 235                                 avl_insert_before(todo_tree, from, node);
 236                         }
 237
 238                         avl_delete_node(todo_tree, from);
 239                 }
 240         }
 241
 242         avl_free_tree(todo_tree);
 243
 244         /* Check reachability status. */
 245
 246         for(node = node_tree->head; node; node = next) {
 247                 next = node->next;
 248                 n = (node_t *) node->data;
 249
 250                 if(n->status.visited != n->status.reachable) {
 251                         n->status.reachable = !n->status.reachable;
 252
 253                         if(n->status.reachable) {
 254                                 ifdebug(TRAFFIC) logger(LOG_DEBUG, _("Node %s (%s) became reachable"),
 255                                            n->name, n->hostname);
 256                         } else {
 257                                 ifdebug(TRAFFIC) logger(LOG_DEBUG, _("Node %s (%s) became unreachable"),
 258                                            n->name, n->hostname);
 259                         }
 260
 261                         n->status.validkey = false;
 262                         n->status.waitingforkey = false;
 263
 264                         asprintf(&envp[0], "NETNAME=%s", netname ? : "");
 265                         asprintf(&envp[1], "DEVICE=%s", device ? : "");
 266                         asprintf(&envp[2], "INTERFACE=%s", iface ? : "");
 267                         asprintf(&envp[3], "NODE=%s", n->name);
 268                         sockaddr2str(&n->address, &address, &port);
 269                         asprintf(&envp[4], "REMOTEADDRESS=%s", address);
 270                         asprintf(&envp[5], "REMOTEPORT=%s", port);
 271                         envp[6] = NULL;
 272
 273                         asprintf(&name,
 274                                          n->status.reachable ? "hosts/%s-up" : "hosts/%s-down",
 275                                          n->name);
 276                         execute_script(name, envp);
 277
 278                         free(name);
 279                         free(address);
 280                         free(port);
 281
 282                         for(i = 0; i < 7; i++)
 283                                 free(envp[i]);
 284                 }
 285         }
 286 }
 287
 288 void graph(void)
 289 {
 290         mst_kruskal();
 291         sssp_bfs();
 292 }