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   1 /*
   2     graph.c -- graph algorithms
   3     Copyright (C) 2001-2011 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 "splay_tree.h"
  48 #include "config.h"
  49 #include "connection.h"
  50 #include "device.h"
  51 #include "edge.h"
  52 #include "graph.h"
  53 #include "logger.h"
  54 #include "netutl.h"
  55 #include "node.h"
  56 #include "process.h"
  57 #include "protocol.h"
  58 #include "subnet.h"
  59 #include "utils.h"
  60 #include "xalloc.h"
  61 #include "graph.h"
  62
  63 /* Implementation of Kruskal's algorithm.
  64    Running time: O(E)
  65    Please note that sorting on weight is already done by add_edge().
  66 */
  67
  68 void mst_kruskal(void) {
  69         splay_node_t *node, *next;
  70         edge_t *e;
  71         node_t *n;
  72         connection_t *c;
  73
  74         /* Clear MST status on connections */
  75
  76         for(node = connection_tree->head; node; node = node->next) {
  77                 c = node->data;
  78                 c->status.mst = false;
  79         }
  80
  81         ifdebug(SCARY_THINGS) logger(LOG_DEBUG, "Running Kruskal's algorithm:");
  82
  83         /* Clear visited status on nodes */
  84
  85         for(node = node_tree->head; node; node = node->next) {
  86                 n = node->data;
  87                 n->status.visited = false;
  88         }
  89
  90         /* Add safe edges */
  91
  92         for(node = edge_weight_tree->head; node; node = next) {
  93                 next = node->next;
  94                 e = node->data;
  95
  96                 if(!e->reverse || (e->from->status.visited && e->to->status.visited))
  97                         continue;
  98
  99                 e->from->status.visited = true;
 100                 e->to->status.visited = true;
 101
 102                 if(e->connection)
 103                         e->connection->status.mst = true;
 104
 105                 if(e->reverse->connection)
 106                         e->reverse->connection->status.mst = true;
 107
 108                 ifdebug(SCARY_THINGS) logger(LOG_DEBUG, " Adding edge %s - %s weight %d", e->from->name,
 109                                    e->to->name, e->weight);
 110         }
 111 }
 112
 113 /* Implementation of Dijkstra's algorithm.
 114    Running time: O(N^2)
 115 */
 116
 117 static void sssp_dijkstra(void) {
 118         splay_node_t *node, *to;
 119         edge_t *e;
 120         node_t *n, *m;
 121         list_t *todo_list;
 122         list_node_t *lnode, *nnode;
 123         bool indirect;
 124
 125         todo_list = list_alloc(NULL);
 126
 127         ifdebug(SCARY_THINGS) logger(LOG_DEBUG, "Running Dijkstra's algorithm:");
 128
 129         /* Clear visited status on nodes */
 130
 131         for(node = node_tree->head; node; node = node->next) {
 132                 n = node->data;
 133                 n->status.visited = false;
 134                 n->status.indirect = true;
 135                 n->distance = -1;
 136         }
 137
 138         /* Begin with myself */
 139
 140         myself->status.indirect = false;
 141         myself->nexthop = myself;
 142         myself->via = myself;
 143         myself->distance = 0;
 144         list_insert_head(todo_list, myself);
 145
 146         /* Loop while todo_list is filled */
 147
 148         while(todo_list->head) {
 149                 n = NULL;
 150                 nnode = NULL;
 151
 152                 /* Select node from todo_list with smallest distance */
 153
 154                 for(lnode = todo_list->head; lnode; lnode = lnode->next) {
 155                         m = lnode->data;
 156                         if(!n || m->status.indirect < n->status.indirect || m->distance < n->distance) {
 157                                 n = m;
 158                                 nnode = lnode;
 159                         }
 160                 }
 161
 162                 /* Mark this node as visited and remove it from the todo_list */
 163
 164                 n->status.visited = true;
 165                 list_unlink_node(todo_list, nnode);
 166
 167                 /* Update distance of neighbours and add them to the todo_list */
 168
 169                 for(to = n->edge_tree->head; to; to = to->next) {       /* "to" is the edge connected to "from" */
 170                         e = to->data;
 171
 172                         if(e->to->status.visited || !e->reverse)
 173                                 continue;
 174
 175                         /* Situation:
 176
 177                                    /
 178                                   /
 179                            ----->(n)---e-->(e->to)
 180                                   \
 181                                    \
 182
 183                            Where e is an edge, (n) and (e->to) are nodes.
 184                            n->address is set to the e->address of the edge left of n to n.
 185                            We are currently examining the edge e right of n from n:
 186
 187                            - If edge e provides for better reachability of e->to, update e->to.
 188                          */
 189
 190                         if(e->to->distance < 0)
 191                                 list_insert_tail(todo_list, e->to);
 192
 193                         indirect = n->status.indirect || e->options & OPTION_INDIRECT || ((n != myself) && sockaddrcmp(&n->address, &e->reverse->address));
 194
 195                         if(e->to->distance >= 0 && (!e->to->status.indirect || indirect) && e->to->distance <= n->distance + e->weight)
 196                                 continue;
 197
 198                         e->to->distance = n->distance + e->weight;
 199                         e->to->status.indirect = indirect;
 200                         e->to->nexthop = (n->nexthop == myself) ? e->to : n->nexthop;
 201                         e->to->via = indirect ? n->via : e->to;
 202                         e->to->options = e->options;
 203
 204                         if(e->to->address.sa.sa_family == AF_UNSPEC && e->address.sa.sa_family != AF_UNKNOWN)
 205                                 update_node_udp(e->to, &e->address);
 206
 207                         ifdebug(SCARY_THINGS) logger(LOG_DEBUG, " Updating edge %s - %s weight %d distance %d", e->from->name,
 208                                            e->to->name, e->weight, e->to->distance);
 209                 }
 210         }
 211
 212         list_free(todo_list);
 213 }
 214
 215 /* Implementation of a simple breadth-first search algorithm.
 216    Running time: O(E)
 217 */
 218
 219 void sssp_bfs(void) {
 220         splay_node_t *node, *to;
 221         edge_t *e;
 222         node_t *n;
 223         list_t *todo_list;
 224         list_node_t *from, *todonext;
 225         bool indirect;
 226
 227         todo_list = list_alloc(NULL);
 228
 229         /* Clear visited status on nodes */
 230
 231         for(node = node_tree->head; node; node = node->next) {
 232                 n = node->data;
 233                 n->status.visited = false;
 234                 n->status.indirect = true;
 235         }
 236
 237         /* Begin with myself */
 238
 239         myself->status.visited = true;
 240         myself->status.indirect = false;
 241         myself->nexthop = myself;
 242         myself->via = myself;
 243         list_insert_head(todo_list, myself);
 244
 245         /* Loop while todo_list is filled */
 246
 247         for(from = todo_list->head; from; from = todonext) {    /* "from" is the node from which we start */
 248                 n = from->data;
 249
 250                 for(to = n->edge_tree->head; to; to = to->next) {       /* "to" is the edge connected to "from" */
 251                         e = to->data;
 252
 253                         if(!e->reverse)
 254                                 continue;
 255
 256                         /* Situation:
 257
 258                                    /
 259                                   /
 260                            ----->(n)---e-->(e->to)
 261                                   \
 262                                    \
 263
 264                            Where e is an edge, (n) and (e->to) are nodes.
 265                            n->address is set to the e->address of the edge left of n to n.
 266                            We are currently examining the edge e right of n from n:
 267
 268                            - If edge e provides for better reachability of e->to, update
 269                              e->to and (re)add it to the todo_list to (re)examine the reachability
 270                              of nodes behind it.
 271                          */
 272
 273                         indirect = n->status.indirect || e->options & OPTION_INDIRECT;
 274
 275                         if(e->to->status.visited
 276                            && (!e->to->status.indirect || indirect))
 277                                 continue;
 278
 279                         e->to->status.visited = true;
 280                         e->to->status.indirect = indirect;
 281                         e->to->nexthop = (n->nexthop == myself) ? e->to : n->nexthop;
 282                         e->to->via = indirect ? n->via : e->to;
 283                         e->to->options = e->options;
 284
 285                         if(e->to->address.sa.sa_family == AF_UNSPEC && e->address.sa.sa_family != AF_UNKNOWN)
 286                                 update_node_udp(e->to, &e->address);
 287
 288                         list_insert_tail(todo_list, e->to);
 289                 }
 290
 291                 todonext = from->next;
 292                 list_delete_node(todo_list, from);
 293         }
 294
 295         list_free(todo_list);
 296 }
 297
 298 static void check_reachability(void) {
 299         splay_node_t *node, *next;
 300         node_t *n;
 301         char *name;
 302         char *address, *port;
 303         char *envp[7];
 304         int i;
 305
 306         /* Check reachability status. */
 307
 308         for(node = node_tree->head; node; node = next) {
 309                 next = node->next;
 310                 n = node->data;
 311
 312                 if(n->status.visited != n->status.reachable) {
 313                         n->status.reachable = !n->status.reachable;
 314
 315                         if(n->status.reachable) {
 316                                 ifdebug(TRAFFIC) logger(LOG_DEBUG, "Node %s (%s) became reachable",
 317                                            n->name, n->hostname);
 318                         } else {
 319                                 ifdebug(TRAFFIC) logger(LOG_DEBUG, "Node %s (%s) became unreachable",
 320                                            n->name, n->hostname);
 321                         }
 322
 323                         /* TODO: only clear status.validkey if node is unreachable? */
 324
 325                         n->status.validkey = false;
 326                         n->last_req_key = 0;
 327
 328                         n->maxmtu = MTU;
 329                         n->minmtu = 0;
 330                         n->mtuprobes = 0;
 331
 332                         if(timeout_initialized(&n->mtuevent))
 333                                 event_del(&n->mtuevent);
 334
 335                         xasprintf(&envp[0], "NETNAME=%s", netname ? : "");
 336                         xasprintf(&envp[1], "DEVICE=%s", device ? : "");
 337                         xasprintf(&envp[2], "INTERFACE=%s", iface ? : "");
 338                         xasprintf(&envp[3], "NODE=%s", n->name);
 339                         sockaddr2str(&n->address, &address, &port);
 340                         xasprintf(&envp[4], "REMOTEADDRESS=%s", address);
 341                         xasprintf(&envp[5], "REMOTEPORT=%s", port);
 342                         envp[6] = NULL;
 343
 344                         execute_script(n->status.reachable ? "host-up" : "host-down", envp);
 345
 346                         xasprintf(&name,
 347                                          n->status.reachable ? "hosts/%s-up" : "hosts/%s-down",
 348                                          n->name);
 349                         execute_script(name, envp);
 350
 351                         free(name);
 352                         free(address);
 353                         free(port);
 354
 355                         for(i = 0; i < 6; i++)
 356                                 free(envp[i]);
 357
 358                         subnet_update(n, NULL, n->status.reachable);
 359
 360                         if(!n->status.reachable)
 361                                 update_node_udp(n, NULL);
 362                         else if(n->connection)
 363                                 send_ans_key(n);
 364                 }
 365         }
 366 }
 367
 368 void graph(void) {
 369         subnet_cache_flush();
 370         sssp_dijkstra();
 371         check_reachability();
 372         mst_kruskal();
 373 }