src/graph.c

   1 /*
   2     graph.c -- graph algorithms
   3     Copyright (C) 2001-2010 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 "protocol.h"
  57 #include "subnet.h"
  58 #include "utils.h"
  59 #include "xalloc.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         avl_node_t *node, *next;
  70         edge_t *e;
  71         node_t *n;
  72         connection_t *c;
  73         int nodes = 0;
  74         int safe_edges = 0;
  75         bool skipped;
  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         avl_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         todo_list = list_alloc(NULL);
 162
 163         /* Clear visited status on nodes */
 164
 165         for(node = node_tree->head; node; node = node->next) {
 166                 n = node->data;
 167                 n->status.visited = false;
 168                 n->status.indirect = true;
 169         }
 170
 171         /* Begin with myself */
 172
 173         myself->status.visited = true;
 174         myself->status.indirect = false;
 175         myself->nexthop = myself;
 176         myself->via = myself;
 177         list_insert_head(todo_list, myself);
 178
 179         /* Loop while todo_list is filled */
 180
 181         for(from = todo_list->head; from; from = todonext) {    /* "from" is the node from which we start */
 182                 n = from->data;
 183
 184                 for(to = n->edge_tree->head; to; to = to->next) {       /* "to" is the edge connected to "from" */
 185                         e = to->data;
 186
 187                         if(!e->reverse)
 188                                 continue;
 189
 190                         /* Situation:
 191
 192                                    /
 193                                   /
 194                            ----->(n)---e-->(e->to)
 195                                   \
 196                                    \
 197
 198                            Where e is an edge, (n) and (e->to) are nodes.
 199                            n->address is set to the e->address of the edge left of n to n.
 200                            We are currently examining the edge e right of n from n:
 201
 202                            - If e->reverse->address != n->address, then e->to is probably
 203                              not reachable for the nodes left of n. We do as if the indirectdata
 204                              flag is set on edge e.
 205                            - If edge e provides for better reachability of e->to, update
 206                              e->to and (re)add it to the todo_list to (re)examine the reachability
 207                              of nodes behind it.
 208                          */
 209
 210                         indirect = n->status.indirect || e->options & OPTION_INDIRECT
 211                                 || ((n != myself) && sockaddrcmp(&n->address, &e->reverse->address));
 212
 213                         if(e->to->status.visited
 214                            && (!e->to->status.indirect || indirect))
 215                                 continue;
 216
 217                         e->to->status.visited = true;
 218                         e->to->status.indirect = indirect;
 219                         e->to->nexthop = (n->nexthop == myself) ? e->to : n->nexthop;
 220                         e->to->via = indirect ? n->via : e->to;
 221                         e->to->options = e->options;
 222
 223                         if(e->to->address.sa.sa_family == AF_UNSPEC && e->address.sa.sa_family != AF_UNKNOWN)
 224                                 update_node_udp(e->to, &e->address);
 225
 226                         list_insert_tail(todo_list, e->to);
 227                 }
 228
 229                 todonext = from->next;
 230                 list_delete_node(todo_list, from);
 231         }
 232
 233         list_free(todo_list);
 234
 235         /* Check reachability status. */
 236
 237         for(node = node_tree->head; node; node = next) {
 238                 next = node->next;
 239                 n = node->data;
 240
 241                 if(n->status.visited != n->status.reachable) {
 242                         n->status.reachable = !n->status.reachable;
 243
 244                         if(n->status.reachable) {
 245                                 ifdebug(TRAFFIC) logger(LOG_DEBUG, "Node %s (%s) became reachable",
 246                                            n->name, n->hostname);
 247                         } else {
 248                                 ifdebug(TRAFFIC) logger(LOG_DEBUG, "Node %s (%s) became unreachable",
 249                                            n->name, n->hostname);
 250                         }
 251
 252                         /* TODO: only clear status.validkey if node is unreachable? */
 253
 254                         n->status.validkey = false;
 255                         n->last_req_key = 0;
 256
 257                         n->maxmtu = MTU;
 258                         n->minmtu = 0;
 259                         n->mtuprobes = 0;
 260
 261                         if(n->mtuevent) {
 262                                 event_del(n->mtuevent);
 263                                 n->mtuevent = NULL;
 264                         }
 265
 266                         xasprintf(&envp[0], "NETNAME=%s", netname ? : "");
 267                         xasprintf(&envp[1], "DEVICE=%s", device ? : "");
 268                         xasprintf(&envp[2], "INTERFACE=%s", iface ? : "");
 269                         xasprintf(&envp[3], "NODE=%s", n->name);
 270                         sockaddr2str(&n->address, &address, &port);
 271                         xasprintf(&envp[4], "REMOTEADDRESS=%s", address);
 272                         xasprintf(&envp[5], "REMOTEPORT=%s", port);
 273                         envp[6] = NULL;
 274
 275                         execute_script(n->status.reachable ? "host-up" : "host-down", envp);
 276
 277                         xasprintf(&name,
 278                                          n->status.reachable ? "hosts/%s-up" : "hosts/%s-down",
 279                                          n->name);
 280                         execute_script(name, envp);
 281
 282                         free(name);
 283                         free(address);
 284                         free(port);
 285
 286                         for(i = 0; i < 6; i++)
 287                                 free(envp[i]);
 288
 289                         subnet_update(n, NULL, n->status.reachable);
 290
 291                         if(!n->status.reachable)
 292                                 update_node_udp(n, NULL);
 293                         else if(n->connection)
 294                                 send_ans_key(n);
 295                 }
 296         }
 297 }
 298
 299 void graph(void) {
 300         subnet_cache_flush();
 301         sssp_bfs();
 302         mst_kruskal();
 303         graph_changed = true;
 304 }
 305
 306
 307
 308 /* Dump nodes and edges to a graphviz file.
 309
 310    The file can be converted to an image with
 311    dot -Tpng graph_filename -o image_filename.png -Gconcentrate=true
 312 */
 313
 314 void dump_graph(void) {
 315         avl_node_t *node;
 316         node_t *n;
 317         edge_t *e;
 318         char *filename = NULL, *tmpname = NULL;
 319         FILE *file;
 320
 321         if(!graph_changed || !get_config_string(lookup_config(config_tree, "GraphDumpFile"), &filename))
 322                 return;
 323
 324         graph_changed = false;
 325
 326         ifdebug(PROTOCOL) logger(LOG_NOTICE, "Dumping graph");
 327
 328         if(filename[0] == '|') {
 329                 file = popen(filename + 1, "w");
 330         } else {
 331                 xasprintf(&tmpname, "%s.new", filename);
 332                 file = fopen(tmpname, "w");
 333         }
 334
 335         if(!file) {
 336                 logger(LOG_ERR, "Unable to open graph dump file %s: %s", filename, strerror(errno));
 337                 free(tmpname);
 338                 return;
 339         }
 340
 341         fprintf(file, "digraph {\n");
 342
 343         /* dump all nodes first */
 344         for(node = node_tree->head; node; node = node->next) {
 345                 n = node->data;
 346                 fprintf(file, " %s [label = \"%s\"];\n", n->name, n->name);
 347         }
 348
 349         /* now dump all edges */
 350         for(node = edge_weight_tree->head; node; node = node->next) {
 351                 e = node->data;
 352                 fprintf(file, " %s -> %s;\n", e->from->name, e->to->name);
 353         }
 354
 355         fprintf(file, "}\n");
 356
 357         if(filename[0] == '|') {
 358                 pclose(file);
 359         } else {
 360                 fclose(file);
 361 #ifdef HAVE_MINGW
 362                 unlink(filename);
 363 #endif
 364                 rename(tmpname, filename);
 365                 free(tmpname);
 366         }
 367 }