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 along
  17     with this program; if not, write to the Free Software Foundation, Inc.,
  18     51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  19 */
  20
  21 /* We need to generate two trees from the graph:
  22
  23    1. A minimum spanning tree for broadcasts,
  24    2. A single-source shortest path tree for unicasts.
  25
  26    Actually, the first one alone would suffice but would make unicast packets
  27    take longer routes than necessary.
  28
  29    For the MST algorithm we can choose from Prim's or Kruskal's. I personally
  30    favour Kruskal's, because we make an extra AVL tree of edges sorted on
  31    weights (metric). That tree only has to be updated when an edge is added or
  32    removed, and during the MST algorithm we just have go linearly through that
  33    tree, adding safe edges until #edges = #nodes - 1. The implementation here
  34    however is not so fast, because I tried to avoid having to make a forest and
  35    merge trees.
  36
  37    For the SSSP algorithm Dijkstra's seems to be a nice choice. Currently a
  38    simple breadth-first search is presented here.
  39
  40    The SSSP algorithm will also be used to determine whether nodes are directly,
  41    indirectly or not reachable from the source. It will also set the correct
  42    destination address and port of a node if possible.
  43 */
  44
  45 #include "system.h"
  46
  47 #include "avl_tree.h"
  48 #include "config.h"
  49 #include "connection.h"
  50 #include "device.h"
  51 #include "edge.h"
  52 #include "logger.h"
  53 #include "netutl.h"
  54 #include "node.h"
  55 #include "process.h"
  56 #include "subnet.h"
  57 #include "utils.h"
  58 #include "xalloc.h"
  59
  60 static bool graph_changed = true;
  61
  62 /* Implementation of Kruskal's algorithm.
  63    Running time: O(EN)
  64    Please note that sorting on weight is already done by add_edge().
  65 */
  66
  67 void mst_kruskal(void) {
  68         avl_node_t *node, *next;
  69         edge_t *e;
  70         node_t *n;
  71         connection_t *c;
  72         int nodes = 0;
  73         int safe_edges = 0;
  74         bool skipped;
  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         for(node = edge_weight_tree->head; node; node = node->next) {
 101                 e = node->data;
 102                 if(e->from->status.reachable) {
 103                         e->from->status.visited = true;
 104                         break;
 105                 }
 106         }
 107
 108         /* Add safe edges */
 109
 110         for(skipped = false, node = edge_weight_tree->head; node; node = next) {
 111                 next = node->next;
 112                 e = node->data;
 113
 114                 if(!e->reverse || e->from->status.visited == e->to->status.visited) {
 115                         skipped = true;
 116                         continue;
 117                 }
 118
 119                 e->from->status.visited = true;
 120                 e->to->status.visited = true;
 121
 122                 if(e->connection)
 123                         e->connection->status.mst = true;
 124
 125                 if(e->reverse->connection)
 126                         e->reverse->connection->status.mst = true;
 127
 128                 safe_edges++;
 129
 130                 ifdebug(SCARY_THINGS) logger(LOG_DEBUG, " Adding edge %s - %s weight %d", e->from->name,
 131                                    e->to->name, e->weight);
 132
 133                 if(skipped) {
 134                         skipped = false;
 135                         next = edge_weight_tree->head;
 136                         continue;
 137                 }
 138         }
 139
 140         ifdebug(SCARY_THINGS) logger(LOG_DEBUG, "Done, counted %d nodes and %d safe edges.", nodes,
 141                            safe_edges);
 142 }
 143
 144 /* Implementation of a simple breadth-first search algorithm.
 145    Running time: O(E)
 146 */
 147
 148 void sssp_bfs(void) {
 149         avl_node_t *node, *next, *to;
 150         edge_t *e;
 151         node_t *n;
 152         list_t *todo_list;
 153         list_node_t *from, *todonext;
 154         bool indirect;
 155         char *name;
 156         char *address, *port;
 157         char *envp[7];
 158         int i;
 159
 160         todo_list = list_alloc(NULL);
 161
 162         /* Clear visited status on nodes */
 163
 164         for(node = node_tree->head; node; node = node->next) {
 165                 n = node->data;
 166                 n->status.visited = false;
 167                 n->status.indirect = true;
 168         }
 169
 170         /* Begin with myself */
 171
 172         myself->status.visited = true;
 173         myself->status.indirect = false;
 174         myself->nexthop = myself;
 175         myself->via = myself;
 176         list_insert_head(todo_list, myself);
 177
 178         /* Loop while todo_list is filled */
 179
 180         for(from = todo_list->head; from; from = todonext) {    /* "from" is the node from which we start */
 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_list 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(e->to->address.sa.sa_family == AF_UNSPEC && e->address.sa.sa_family != AF_UNKNOWN)
 223                                 update_node_udp(e->to, &e->address);
 224
 225                         list_insert_tail(todo_list, e->to);
 226                 }
 227
 228                 todonext = from->next;
 229                 list_delete_node(todo_list, from);
 230         }
 231
 232         list_free(todo_list);
 233
 234         /* Check reachability status. */
 235
 236         for(node = node_tree->head; node; node = next) {
 237                 next = node->next;
 238                 n = node->data;
 239
 240                 if(n->status.visited != n->status.reachable) {
 241                         n->status.reachable = !n->status.reachable;
 242
 243                         if(n->status.reachable) {
 244                                 ifdebug(TRAFFIC) logger(LOG_DEBUG, "Node %s (%s) became reachable",
 245                                            n->name, n->hostname);
 246                         } else {
 247                                 ifdebug(TRAFFIC) logger(LOG_DEBUG, "Node %s (%s) became unreachable",
 248                                            n->name, n->hostname);
 249                         }
 250
 251                         /* TODO: only clear status.validkey if node is unreachable? */
 252
 253                         n->status.validkey = false;
 254                         n->status.waitingforkey = false;
 255
 256                         n->maxmtu = MTU;
 257                         n->minmtu = 0;
 258                         n->mtuprobes = 0;
 259
 260                         if(n->mtuevent) {
 261                                 event_del(n->mtuevent);
 262                                 n->mtuevent = NULL;
 263                         }
 264
 265                         xasprintf(&envp[0], "NETNAME=%s", netname ? : "");
 266                         xasprintf(&envp[1], "DEVICE=%s", device ? : "");
 267                         xasprintf(&envp[2], "INTERFACE=%s", iface ? : "");
 268                         xasprintf(&envp[3], "NODE=%s", n->name);
 269                         sockaddr2str(&n->address, &address, &port);
 270                         xasprintf(&envp[4], "REMOTEADDRESS=%s", address);
 271                         xasprintf(&envp[5], "REMOTEPORT=%s", port);
 272                         envp[6] = NULL;
 273
 274                         execute_script(n->status.reachable ? "host-up" : "host-down", envp);
 275
 276                         xasprintf(&name,
 277                                          n->status.reachable ? "hosts/%s-up" : "hosts/%s-down",
 278                                          n->name);
 279                         execute_script(name, envp);
 280
 281                         free(name);
 282                         free(address);
 283                         free(port);
 284
 285                         for(i = 0; i < 6; i++)
 286                                 free(envp[i]);
 287
 288                         subnet_update(n, NULL, n->status.reachable);
 289                 }
 290         }
 291 }
 292
 293 void graph(void) {
 294         subnet_cache_flush();
 295         sssp_bfs();
 296         mst_kruskal();
 297         graph_changed = true;
 298 }
 299
 300
 301
 302 /* Dump nodes and edges to a graphviz file.
 303
 304    The file can be converted to an image with
 305    dot -Tpng graph_filename -o image_filename.png -Gconcentrate=true
 306 */
 307
 308 void dump_graph(void) {
 309         avl_node_t *node;
 310         node_t *n;
 311         edge_t *e;
 312         char *filename = NULL, *tmpname = NULL;
 313         FILE *file;
 314
 315         if(!graph_changed || !get_config_string(lookup_config(config_tree, "GraphDumpFile"), &filename))
 316                 return;
 317
 318         graph_changed = false;
 319
 320         ifdebug(PROTOCOL) logger(LOG_NOTICE, "Dumping graph");
 321
 322         if(filename[0] == '|') {
 323                 file = popen(filename + 1, "w");
 324         } else {
 325                 xasprintf(&tmpname, "%s.new", filename);
 326                 file = fopen(tmpname, "w");
 327         }
 328
 329         if(!file) {
 330                 logger(LOG_ERR, "Unable to open graph dump file %s: %s", filename, strerror(errno));
 331                 free(tmpname);
 332                 return;
 333         }
 334
 335         fprintf(file, "digraph {\n");
 336
 337         /* dump all nodes first */
 338         for(node = node_tree->head; node; node = node->next) {
 339                 n = node->data;
 340                 fprintf(file, " %s [label = \"%s\"];\n", n->name, n->name);
 341         }
 342
 343         /* now dump all edges */
 344         for(node = edge_weight_tree->head; node; node = node->next) {
 345                 e = node->data;
 346                 fprintf(file, " %s -> %s;\n", e->from->name, e->to->name);
 347         }
 348
 349         fprintf(file, "}\n");
 350
 351         if(filename[0] == '|') {
 352                 pclose(file);
 353         } else {
 354                 fclose(file);
 355 #ifdef HAVE_MINGW
 356                 unlink(filename);
 357 #endif
 358                 rename(tmpname, filename);
 359                 free(tmpname);
 360         }
 361 }