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

   1 /*
   2     graph.c -- graph algorithms
   3     Copyright (C) 2001-2006 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
  17     along with this program; if not, write to the Free Software
  18     Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  19
  20     $Id$
  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 "splay_tree.h"
  50 #include "config.h"
  51 #include "connection.h"
  52 #include "device.h"
  53 #include "edge.h"
  54 #include "logger.h"
  55 #include "netutl.h"
  56 #include "node.h"
  57 #include "process.h"
  58 #include "subnet.h"
  59 #include "utils.h"
  60
  61 /* Implementation of Kruskal's algorithm.
  62    Running time: O(EN)
  63    Please note that sorting on weight is already done by add_edge().
  64 */
  65
  66 void mst_kruskal(void) {
  67         splay_node_t *node, *next;
  68         edge_t *e;
  69         node_t *n;
  70         connection_t *c;
  71         int nodes = 0;
  72         int safe_edges = 0;
  73         bool skipped;
  74
  75         cp();
  76
  77         /* Clear MST status on connections */
  78
  79         for(node = connection_tree->head; node; node = node->next) {
  80                 c = node->data;
  81                 c->status.mst = false;
  82         }
  83
  84         /* Do we have something to do at all? */
  85
  86         if(!edge_weight_tree->head)
  87                 return;
  88
  89         ifdebug(SCARY_THINGS) logger(LOG_DEBUG, "Running Kruskal's algorithm:");
  90
  91         /* Clear visited status on nodes */
  92
  93         for(node = node_tree->head; node; node = node->next) {
  94                 n = node->data;
  95                 n->status.visited = false;
  96                 nodes++;
  97         }
  98
  99         /* Starting point */
 100
 101         for(node = edge_weight_tree->head; node; node = node->next) {
 102                 e = node->data;
 103                 if(e->from->status.reachable) {
 104                         e->from->status.visited = true;
 105                         break;
 106                 }
 107         }
 108
 109         /* Add safe edges */
 110
 111         for(skipped = false, node = edge_weight_tree->head; node; node = next) {
 112                 next = node->next;
 113                 e = node->data;
 114
 115                 if(!e->reverse || e->from->status.visited == e->to->status.visited) {
 116                         skipped = true;
 117                         continue;
 118                 }
 119
 120                 e->from->status.visited = true;
 121                 e->to->status.visited = true;
 122
 123                 if(e->connection)
 124                         e->connection->status.mst = true;
 125
 126                 if(e->reverse->connection)
 127                         e->reverse->connection->status.mst = true;
 128
 129                 safe_edges++;
 130
 131                 ifdebug(SCARY_THINGS) logger(LOG_DEBUG, " Adding edge %s - %s weight %d", e->from->name,
 132                                    e->to->name, e->weight);
 133
 134                 if(skipped) {
 135                         skipped = false;
 136                         next = edge_weight_tree->head;
 137                         continue;
 138                 }
 139         }
 140
 141         ifdebug(SCARY_THINGS) logger(LOG_DEBUG, "Done, counted %d nodes and %d safe edges.", nodes,
 142                            safe_edges);
 143 }
 144
 145 /* Implementation of a simple breadth-first search algorithm.
 146    Running time: O(E)
 147 */
 148
 149 void sssp_bfs(void) {
 150         splay_node_t *node, *next, *to;
 151         edge_t *e;
 152         node_t *n;
 153         list_t *todo_list;
 154         list_node_t *from, *todonext;
 155         bool indirect;
 156         char *name;
 157         char *address, *port;
 158         char *envp[7];
 159         int i;
 160
 161         cp();
 162
 163         todo_list = list_alloc(NULL);
 164
 165         /* Clear visited status on nodes */
 166
 167         for(node = node_tree->head; node; node = node->next) {
 168                 n = node->data;
 169                 n->status.visited = false;
 170                 n->status.indirect = true;
 171         }
 172
 173         /* Begin with myself */
 174
 175         myself->status.visited = true;
 176         myself->status.indirect = false;
 177         myself->nexthop = myself;
 178         myself->via = myself;
 179         list_insert_head(todo_list, myself);
 180
 181         /* Loop while todo_list is filled */
 182
 183         for(from = todo_list->head; from; from = todonext) {    /* "from" is the node from which we start */
 184                 n = from->data;
 185
 186                 for(to = n->edge_tree->head; to; to = to->next) {       /* "to" is the edge connected to "from" */
 187                         e = to->data;
 188
 189                         if(!e->reverse)
 190                                 continue;
 191
 192                         /* Situation:
 193
 194                                    /
 195                                   /
 196                            ----->(n)---e-->(e->to)
 197                                   \
 198                                    \
 199
 200                            Where e is an edge, (n) and (e->to) are nodes.
 201                            n->address is set to the e->address of the edge left of n to n.
 202                            We are currently examining the edge e right of n from n:
 203
 204                            - If e->reverse->address != n->address, then e->to is probably
 205                              not reachable for the nodes left of n. We do as if the indirectdata
 206                              flag is set on edge e.
 207                            - If edge e provides for better reachability of e->to, update
 208                              e->to and (re)add it to the todo_list to (re)examine the reachability
 209                              of nodes behind it.
 210                          */
 211
 212                         indirect = n->status.indirect || e->options & OPTION_INDIRECT
 213                                 || ((n != myself) && sockaddrcmp(&n->address, &e->reverse->address));
 214
 215                         if(e->to->status.visited
 216                            && (!e->to->status.indirect || indirect))
 217                                 continue;
 218
 219                         e->to->status.visited = true;
 220                         e->to->status.indirect = indirect;
 221                         e->to->nexthop = (n->nexthop == myself) ? e->to : n->nexthop;
 222                         e->to->via = indirect ? n->via : e->to;
 223                         e->to->options = e->options;
 224
 225                         if(sockaddrcmp(&e->to->address, &e->address)) {
 226                                 node = splay_unlink(node_udp_tree, e->to);
 227                                 sockaddrfree(&e->to->address);
 228                                 sockaddrcpy(&e->to->address, &e->address);
 229
 230                                 if(e->to->hostname)
 231                                         free(e->to->hostname);
 232
 233                                 e->to->hostname = sockaddr2hostname(&e->to->address);
 234
 235                                 if(node)
 236                                         splay_insert_node(node_udp_tree, node);
 237
 238                                 if(e->to->options & OPTION_PMTU_DISCOVERY) {
 239                                         e->to->mtuprobes = 0;
 240                                         e->to->minmtu = 0;
 241                                         e->to->maxmtu = MTU;
 242                                         if(e->to->status.validkey)
 243                                                 send_mtu_probe(e->to);
 244                                 }
 245                         }
 246
 247                         list_insert_tail(todo_list, e->to);
 248                 }
 249
 250                 todonext = from->next;
 251                 list_delete_node(todo_list, from);
 252         }
 253
 254         list_free(todo_list);
 255
 256         /* Check reachability status. */
 257
 258         for(node = node_tree->head; node; node = next) {
 259                 next = node->next;
 260                 n = node->data;
 261
 262                 if(n->status.visited != n->status.reachable) {
 263                         n->status.reachable = !n->status.reachable;
 264
 265                         if(n->status.reachable) {
 266                                 ifdebug(TRAFFIC) logger(LOG_DEBUG, _("Node %s (%s) became reachable"),
 267                                            n->name, n->hostname);
 268                                 splay_insert(node_udp_tree, n);
 269                         } else {
 270                                 ifdebug(TRAFFIC) logger(LOG_DEBUG, _("Node %s (%s) became unreachable"),
 271                                            n->name, n->hostname);
 272                                 splay_delete(node_udp_tree, n);
 273                         }
 274
 275                         n->status.validkey = false;
 276                         n->status.waitingforkey = false;
 277
 278                         n->maxmtu = MTU;
 279                         n->minmtu = 0;
 280                         n->mtuprobes = 0;
 281
 282                         asprintf(&envp[0], "NETNAME=%s", netname ? : "");
 283                         asprintf(&envp[1], "DEVICE=%s", device ? : "");
 284                         asprintf(&envp[2], "INTERFACE=%s", iface ? : "");
 285                         asprintf(&envp[3], "NODE=%s", n->name);
 286                         sockaddr2str(&n->address, &address, &port);
 287                         asprintf(&envp[4], "REMOTEADDRESS=%s", address);
 288                         asprintf(&envp[5], "REMOTEPORT=%s", port);
 289                         envp[6] = NULL;
 290
 291                         execute_script(n->status.reachable ? "host-up" : "host-down", envp);
 292
 293                         asprintf(&name,
 294                                          n->status.reachable ? "hosts/%s-up" : "hosts/%s-down",
 295                                          n->name);
 296                         execute_script(name, envp);
 297
 298                         free(name);
 299                         free(address);
 300                         free(port);
 301
 302                         for(i = 0; i < 6; i++)
 303                                 free(envp[i]);
 304
 305                         subnet_update(n, NULL, n->status.reachable);
 306                 }
 307         }
 308 }
 309
 310 /* Dump nodes and edges to a graphviz file.
 311
 312    The file can be converted to an image with
 313    dot -Tpng graph_filename -o image_filename.png -Gconcentrate=true
 314 */
 315
 316 int dump_graph(struct evbuffer *out) {
 317         splay_node_t *node;
 318         node_t *n;
 319         edge_t *e;
 320
 321         if(evbuffer_add_printf(out, "digraph {\n") == -1)
 322                 return errno;
 323
 324         /* dump all nodes first */
 325         for(node = node_tree->head; node; node = node->next) {
 326                 n = node->data;
 327                 if(evbuffer_add_printf(out, "   %s [label = \"%s\"];\n",
 328                                                            n->name, n->name) == -1)
 329                         return errno;
 330         }
 331
 332         /* now dump all edges */
 333         for(node = edge_weight_tree->head; node; node = node->next) {
 334                 e = node->data;
 335                 if(evbuffer_add_printf(out, "   %s -> %s;\n",
 336                                                            e->from->name, e->to->name) == -1)
 337                         return errno;
 338         }
 339
 340         if(evbuffer_add_printf(out, "}\n") == -1)
 341                 return errno;
 342
 343         return 0;
 344 }
 345
 346 void graph(void) {
 347         sssp_bfs();
 348         mst_kruskal();
 349 }