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 1.1.2.30 2003/10/10 16:23:30 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 = 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->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 = 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->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 = from->data;
 182
 183                         for(to = n->edge_tree->head; to; to = to->next) {       /* "to" is the edge connected to "from" */
 184                                 e = to->data;
 185
 186                                 if(!e->reverse)
 187                                         continue;
 188
 189                                 /* Situation:
 190
 191                                            /
 192                                           /
 193                                    ----->(n)---e-->(e->to)
 194                                           \
 195                                            \
 196
 197                                    Where e is an edge, (n) and (e->to) are nodes.
 198                                    n->address is set to the e->address of the edge left of n to n.
 199                                    We are currently examining the edge e right of n from n:
 200
 201                                    - If e->reverse->address != n->address, then e->to is probably
 202                                      not reachable for the nodes left of n. We do as if the indirectdata
 203                                      flag is set on edge e.
 204                                    - If edge e provides for better reachability of e->to, update
 205                                      e->to and (re)add it to the todo_tree to (re)examine the reachability
 206                                      of nodes behind it.
 207                                  */
 208
 209                                 indirect = n->status.indirect || e->options & OPTION_INDIRECT
 210                                         || ((n != myself) && sockaddrcmp(&n->address, &e->reverse->address));
 211
 212                                 if(e->to->status.visited
 213                                    && (!e->to->status.indirect || indirect))
 214                                         continue;
 215
 216                                 e->to->status.visited = true;
 217                                 e->to->status.indirect = indirect;
 218                                 e->to->nexthop = (n->nexthop == myself) ? e->to : n->nexthop;
 219                                 e->to->via = indirect ? n->via : e->to;
 220                                 e->to->options = e->options;
 221
 222                                 if(sockaddrcmp(&e->to->address, &e->address)) {
 223                                         node = avl_unlink(node_udp_tree, e->to);
 224                                         sockaddrfree(&e->to->address);
 225                                         sockaddrcpy(&e->to->address, &e->address);
 226
 227                                         if(e->to->hostname)
 228                                                 free(e->to->hostname);
 229
 230                                         e->to->hostname = sockaddr2hostname(&e->to->address);
 231                                         avl_insert_node(node_udp_tree, node);
 232                                 }
 233
 234                                 node = avl_alloc_node();
 235                                 node->data = e->to;
 236                                 avl_insert_before(todo_tree, from, node);
 237                         }
 238
 239                         avl_delete_node(todo_tree, from);
 240                 }
 241         }
 242
 243         avl_free_tree(todo_tree);
 244
 245         /* Check reachability status. */
 246
 247         for(node = node_tree->head; node; node = next) {
 248                 next = node->next;
 249                 n = node->data;
 250
 251                 if(n->status.visited != n->status.reachable) {
 252                         n->status.reachable = !n->status.reachable;
 253
 254                         if(n->status.reachable) {
 255                                 ifdebug(TRAFFIC) logger(LOG_DEBUG, _("Node %s (%s) became reachable"),
 256                                            n->name, n->hostname);
 257                         } else {
 258                                 ifdebug(TRAFFIC) logger(LOG_DEBUG, _("Node %s (%s) became unreachable"),
 259                                            n->name, n->hostname);
 260                         }
 261
 262                         n->status.validkey = false;
 263                         n->status.waitingforkey = false;
 264
 265                         asprintf(&envp[0], "NETNAME=%s", netname ? : "");
 266                         asprintf(&envp[1], "DEVICE=%s", device ? : "");
 267                         asprintf(&envp[2], "INTERFACE=%s", iface ? : "");
 268                         asprintf(&envp[3], "NODE=%s", n->name);
 269                         sockaddr2str(&n->address, &address, &port);
 270                         asprintf(&envp[4], "REMOTEADDRESS=%s", address);
 271                         asprintf(&envp[5], "REMOTEPORT=%s", port);
 272                         envp[6] = NULL;
 273
 274                         asprintf(&name,
 275                                          n->status.reachable ? "hosts/%s-up" : "hosts/%s-down",
 276                                          n->name);
 277                         execute_script(name, envp);
 278
 279                         free(name);
 280                         free(address);
 281                         free(port);
 282
 283                         for(i = 0; i < 7; i++)
 284                                 free(envp[i]);
 285                 }
 286         }
 287 }
 288
 289 void graph(void)
 290 {
 291         mst_kruskal();
 292         sssp_bfs();
 293 }