src/graph.c

   1 /*
   2     graph.c -- graph algorithms
   3     Copyright (C) 2001-2009 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 "avl_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 static bool graph_changed = true;
  62
  63 /* Implementation of Kruskal's algorithm.
  64    Running time: O(EN)
  65    Please note that sorting on weight is already done by add_edge().
  66 */
  67
  68 void mst_kruskal(void)
  69 {
  70         avl_node_t *node, *next;
  71         edge_t *e;
  72         node_t *n;
  73         connection_t *c;
  74         int nodes = 0;
  75         int safe_edges = 0;
  76         bool skipped;
  77
  78         cp();
  79
  80         /* Clear MST status on connections */
  81
  82         for(node = connection_tree->head; node; node = node->next) {
  83                 c = node->data;
  84                 c->status.mst = false;
  85         }
  86
  87         /* Do we have something to do at all? */
  88
  89         if(!edge_weight_tree->head)
  90                 return;
  91
  92         ifdebug(SCARY_THINGS) logger(LOG_DEBUG, "Running Kruskal's algorithm:");
  93
  94         /* Clear visited status on nodes */
  95
  96         for(node = node_tree->head; node; node = node->next) {
  97                 n = node->data;
  98                 n->status.visited = false;
  99                 nodes++;
 100         }
 101
 102         /* Starting point */
 103
 104         for(node = edge_weight_tree->head; node; node = node->next) {
 105                 e = node->data;
 106                 if(e->from->status.reachable) {
 107                         e->from->status.visited = true;
 108                         break;
 109                 }
 110         }
 111
 112         /* Add safe edges */
 113
 114         for(skipped = false, node = edge_weight_tree->head; node; node = next) {
 115                 next = node->next;
 116                 e = node->data;
 117
 118                 if(!e->reverse || e->from->status.visited == e->to->status.visited) {
 119                         skipped = true;
 120                         continue;
 121                 }
 122
 123                 e->from->status.visited = true;
 124                 e->to->status.visited = true;
 125
 126                 if(e->connection)
 127                         e->connection->status.mst = true;
 128
 129                 if(e->reverse->connection)
 130                         e->reverse->connection->status.mst = true;
 131
 132                 safe_edges++;
 133
 134                 ifdebug(SCARY_THINGS) logger(LOG_DEBUG, " Adding edge %s - %s weight %d", e->from->name,
 135                                    e->to->name, e->weight);
 136
 137                 if(skipped) {
 138                         skipped = false;
 139                         next = edge_weight_tree->head;
 140                         continue;
 141                 }
 142         }
 143
 144         ifdebug(SCARY_THINGS) logger(LOG_DEBUG, "Done, counted %d nodes and %d safe edges.", nodes,
 145                            safe_edges);
 146 }
 147
 148 /* Implementation of a simple breadth-first search algorithm.
 149    Running time: O(E)
 150 */
 151
 152 void sssp_bfs(void)
 153 {
 154         avl_node_t *node, *next, *to;
 155         edge_t *e;
 156         node_t *n;
 157         list_t *todo_list;
 158         list_node_t *from, *todonext;
 159         bool indirect;
 160         char *name;
 161         char *address, *port;
 162         char *envp[7];
 163         int i;
 164
 165         cp();
 166
 167         todo_list = list_alloc(NULL);
 168
 169         /* Clear visited status on nodes */
 170
 171         for(node = node_tree->head; node; node = node->next) {
 172                 n = node->data;
 173                 n->status.visited = false;
 174                 n->status.indirect = true;
 175         }
 176
 177         /* Begin with myself */
 178
 179         myself->status.visited = true;
 180         myself->status.indirect = false;
 181         myself->nexthop = myself;
 182         myself->via = myself;
 183         list_insert_head(todo_list, myself);
 184
 185         /* Loop while todo_list is filled */
 186
 187         for(from = todo_list->head; from; from = todonext) {    /* "from" is the node from which we start */
 188                 n = from->data;
 189
 190                 for(to = n->edge_tree->head; to; to = to->next) {       /* "to" is the edge connected to "from" */
 191                         e = to->data;
 192
 193                         if(!e->reverse)
 194                                 continue;
 195
 196                         /* Situation:
 197
 198                                    /
 199                                   /
 200                            ----->(n)---e-->(e->to)
 201                                   \
 202                                    \
 203
 204                            Where e is an edge, (n) and (e->to) are nodes.
 205                            n->address is set to the e->address of the edge left of n to n.
 206                            We are currently examining the edge e right of n from n:
 207
 208                            - If e->reverse->address != n->address, then e->to is probably
 209                              not reachable for the nodes left of n. We do as if the indirectdata
 210                              flag is set on edge e.
 211                            - If edge e provides for better reachability of e->to, update
 212                              e->to and (re)add it to the todo_list to (re)examine the reachability
 213                              of nodes behind it.
 214                          */
 215
 216                         indirect = n->status.indirect || e->options & OPTION_INDIRECT
 217                                 || ((n != myself) && sockaddrcmp(&n->address, &e->reverse->address));
 218
 219                         if(e->to->status.visited
 220                            && (!e->to->status.indirect || indirect))
 221                                 continue;
 222
 223                         e->to->status.visited = true;
 224                         e->to->status.indirect = indirect;
 225                         e->to->nexthop = (n->nexthop == myself) ? e->to : n->nexthop;
 226                         e->to->via = indirect ? n->via : e->to;
 227                         e->to->options = e->options;
 228
 229                         if(e->to->address.sa.sa_family == AF_UNSPEC && e->address.sa.sa_family != AF_UNKNOWN)
 230                                 update_node_udp(e->to, &e->address);
 231
 232                         list_insert_tail(todo_list, e->to);
 233                 }
 234
 235                 todonext = from->next;
 236                 list_delete_node(todo_list, from);
 237         }
 238
 239         list_free(todo_list);
 240
 241         /* Check reachability status. */
 242
 243         for(node = node_tree->head; node; node = next) {
 244                 next = node->next;
 245                 n = node->data;
 246
 247                 if(n->status.visited != n->status.reachable) {
 248                         n->status.reachable = !n->status.reachable;
 249
 250                         if(n->status.reachable) {
 251                                 ifdebug(TRAFFIC) logger(LOG_DEBUG, _("Node %s (%s) became reachable"),
 252                                            n->name, n->hostname);
 253                         } else {
 254                                 ifdebug(TRAFFIC) logger(LOG_DEBUG, _("Node %s (%s) became unreachable"),
 255                                            n->name, n->hostname);
 256                         }
 257
 258                         /* TODO: only clear status.validkey if node is unreachable? */
 259
 260                         n->status.validkey = false;
 261                         n->status.waitingforkey = false;
 262
 263                         n->maxmtu = MTU;
 264                         n->minmtu = 0;
 265                         n->mtuprobes = 0;
 266
 267                         asprintf(&envp[0], "NETNAME=%s", netname ? : "");
 268                         asprintf(&envp[1], "DEVICE=%s", device ? : "");
 269                         asprintf(&envp[2], "INTERFACE=%s", iface ? : "");
 270                         asprintf(&envp[3], "NODE=%s", n->name);
 271                         sockaddr2str(&n->address, &address, &port);
 272                         asprintf(&envp[4], "REMOTEADDRESS=%s", address);
 273                         asprintf(&envp[5], "REMOTEPORT=%s", port);
 274                         envp[6] = NULL;
 275
 276                         execute_script(n->status.reachable ? "host-up" : "host-down", envp);
 277
 278                         asprintf(&name,
 279                                          n->status.reachable ? "hosts/%s-up" : "hosts/%s-down",
 280                                          n->name);
 281                         execute_script(name, envp);
 282
 283                         free(name);
 284                         free(address);
 285                         free(port);
 286
 287                         for(i = 0; i < 6; i++)
 288                                 free(envp[i]);
 289
 290                         subnet_update(n, NULL, n->status.reachable);
 291                 }
 292         }
 293 }
 294
 295 void graph(void)
 296 {
 297         subnet_cache_flush();
 298         sssp_bfs();
 299         mst_kruskal();
 300         graph_changed = true;
 301 }
 302
 303
 304
 305 /* Dump nodes and edges to a graphviz file.
 306
 307    The file can be converted to an image with
 308    dot -Tpng graph_filename -o image_filename.png -Gconcentrate=true
 309 */
 310
 311 void dump_graph(void)
 312 {
 313         avl_node_t *node;
 314         node_t *n;
 315         edge_t *e;
 316         char *filename = NULL, *tmpname = NULL;
 317         FILE *file;
 318
 319         if(!graph_changed || !get_config_string(lookup_config(config_tree, "GraphDumpFile"), &filename))
 320                 return;
 321
 322         graph_changed = false;
 323
 324         ifdebug(PROTOCOL) logger(LOG_NOTICE, "Dumping graph");
 325
 326         if(filename[0] == '|') {
 327                 file = popen(filename + 1, "w");
 328         } else {
 329                 asprintf(&tmpname, "%s.new", filename);
 330                 file = fopen(tmpname, "w");
 331         }
 332
 333         if(!file) {
 334                 logger(LOG_ERR, "Unable to open graph dump file %s: %s", filename, strerror(errno));
 335                 free(tmpname);
 336                 return;
 337         }
 338
 339         fprintf(file, "digraph {\n");
 340
 341         /* dump all nodes first */
 342         for(node = node_tree->head; node; node = node->next) {
 343                 n = node->data;
 344                 fprintf(file, " %s [label = \"%s\"];\n", n->name, n->name);
 345         }
 346
 347         /* now dump all edges */
 348         for(node = edge_weight_tree->head; node; node = node->next) {
 349                 e = node->data;
 350                 fprintf(file, " %s -> %s;\n", e->from->name, e->to->name);
 351         }
 352
 353         fprintf(file, "}\n");
 354
 355         if(filename[0] == '|') {
 356                 pclose(file);
 357         } else {
 358                 fclose(file);
 359 #ifdef HAVE_MINGW
 360                 unlink(filename);
 361 #endif
 362                 rename(tmpname, filename);
 363                 free(tmpname);
 364         }
 365 }