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

   1 /*
   2     graph.c -- graph algorithms
   3     Copyright (C) 2001-2017 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 "connection.h"
  48 #include "edge.h"
  49 #include "graph.h"
  50 #include "list.h"
  51 #include "logger.h"
  52 #include "netutl.h"
  53 #include "node.h"
  54 #include "protocol.h"
  55 #include "script.h"
  56 #include "subnet.h"
  57 #include "xalloc.h"
  58 #include "address_cache.h"
  59
  60 /* Implementation of Kruskal's algorithm.
  61    Running time: O(EN)
  62    Please note that sorting on weight is already done by add_edge().
  63 */
  64
  65 static void mst_kruskal(void) {
  66         /* Clear MST status on connections */
  67
  68         for list_each(connection_t, c, &connection_list) {
  69                 c->status.mst = false;
  70         }
  71
  72         logger(DEBUG_SCARY_THINGS, LOG_DEBUG, "Running Kruskal's algorithm:");
  73
  74         /* Clear visited status on nodes */
  75
  76         for splay_each(node_t, n, &node_tree) {
  77                 n->status.visited = false;
  78         }
  79
  80         /* Starting point */
  81
  82         for splay_each(edge_t, e, &edge_weight_tree) {
  83                 if(e->from->status.reachable) {
  84                         e->from->status.visited = true;
  85                         break;
  86                 }
  87         }
  88
  89         /* Add safe edges */
  90
  91         bool skipped = false;
  92
  93         for splay_each(edge_t, e, &edge_weight_tree) {
  94                 if(!e->reverse || (e->from->status.visited == e->to->status.visited)) {
  95                         skipped = true;
  96                         continue;
  97                 }
  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
 106                 if(e->reverse->connection) {
 107                         e->reverse->connection->status.mst = true;
 108                 }
 109
 110                 logger(DEBUG_SCARY_THINGS, LOG_DEBUG, " Adding edge %s - %s weight %d", e->from->name, e->to->name, e->weight);
 111
 112                 if(skipped) {
 113                         skipped = false;
 114                         next = edge_weight_tree.head;
 115                 }
 116         }
 117 }
 118
 119 // Not putting it into header, the outside world doesn't need to know about it.
 120 extern void sssp_bfs(void);
 121
 122 /* Implementation of a simple breadth-first search algorithm.
 123    Running time: O(E)
 124 */
 125 void sssp_bfs(void) {
 126         list_t *todo_list = list_alloc(NULL);
 127
 128         /* Clear visited status on nodes */
 129
 130         for splay_each(node_t, n, &node_tree) {
 131                 n->status.visited = false;
 132                 n->status.indirect = true;
 133                 n->distance = -1;
 134         }
 135
 136         /* Begin with myself */
 137
 138         myself->status.visited = true;
 139         myself->status.indirect = false;
 140         myself->nexthop = myself;
 141         myself->prevedge = NULL;
 142         myself->via = myself;
 143         myself->distance = 0;
 144         myself->weighted_distance = 0;
 145         list_insert_head(todo_list, myself);
 146
 147         /* Loop while todo_list is filled */
 148
 149         for list_each(node_t, n, todo_list) {                   /* "n" is the node from which we start */
 150                 logger(DEBUG_SCARY_THINGS, LOG_DEBUG, " Examining edges from %s", n->name);
 151
 152                 if(n->distance < 0) {
 153                         abort();
 154                 }
 155
 156                 for splay_each(edge_t, e, &n->edge_tree) {       /* "e" is the edge connected to "from" */
 157                         if(!e->reverse || e->to == myself) {
 158                                 continue;
 159                         }
 160
 161                         /* Situation:
 162
 163                                    /
 164                                   /
 165                            ----->(n)---e-->(e->to)
 166                                   \
 167                                    \
 168
 169                            Where e is an edge, (n) and (e->to) are nodes.
 170                            n->address is set to the e->address of the edge left of n to n.
 171                            We are currently examining the edge e right of n from n:
 172
 173                            - If edge e provides for better reachability of e->to, update
 174                              e->to and (re)add it to the todo_list to (re)examine the reachability
 175                              of nodes behind it.
 176                          */
 177
 178                         bool indirect = n->status.indirect || e->options & OPTION_INDIRECT;
 179
 180                         if(e->to->status.visited
 181                                         && (!e->to->status.indirect || indirect)
 182                                         && (e->to->distance != n->distance + 1 || e->to->weighted_distance <= n->weighted_distance + e->weight)) {
 183                                 continue;
 184                         }
 185
 186                         // Only update nexthop if it doesn't increase the path length
 187
 188                         if(!e->to->status.visited || (e->to->distance == n->distance + 1 && e->to->weighted_distance > n->weighted_distance + e->weight)) {
 189                                 e->to->nexthop = (n->nexthop == myself) ? e->to : n->nexthop;
 190                                 e->to->weighted_distance = n->weighted_distance + e->weight;
 191                         }
 192
 193                         e->to->status.visited = true;
 194                         e->to->status.indirect = indirect;
 195                         e->to->prevedge = e;
 196                         e->to->via = indirect ? n->via : e->to;
 197                         e->to->options = e->options;
 198                         e->to->distance = n->distance + 1;
 199
 200                         if(!e->to->status.reachable || (e->to->address.sa.sa_family == AF_UNSPEC && e->address.sa.sa_family != AF_UNKNOWN)) {
 201                                 update_node_udp(e->to, &e->address);
 202                         }
 203
 204                         list_insert_tail(todo_list, e->to);
 205                 }
 206
 207                 next = node->next; /* Because the list_insert_tail() above could have added something extra for us! */
 208                 list_delete_node(todo_list, node);
 209         }
 210
 211         list_free(todo_list);
 212 }
 213
 214 static void check_reachability(void) {
 215         /* Check reachability status. */
 216
 217         int reachable_count = 0;
 218         int became_reachable_count = 0;
 219         int became_unreachable_count = 0;
 220
 221         for splay_each(node_t, n, &node_tree) {
 222                 if(n->status.visited != n->status.reachable) {
 223                         n->status.reachable = !n->status.reachable;
 224                         n->last_state_change = now.tv_sec;
 225
 226                         if(n->status.reachable) {
 227                                 logger(DEBUG_TRAFFIC, LOG_DEBUG, "Node %s (%s) became reachable",
 228                                        n->name, n->hostname);
 229
 230                                 if(n != myself) {
 231                                         became_reachable_count++;
 232
 233                                         if(n->connection && n->connection->outgoing) {
 234                                                 if(!n->address_cache) {
 235                                                         n->address_cache = open_address_cache(n);
 236                                                 }
 237
 238                                                 add_recent_address(n->address_cache, &n->connection->address);
 239                                         }
 240                                 }
 241                         } else {
 242                                 logger(DEBUG_TRAFFIC, LOG_DEBUG, "Node %s (%s) became unreachable",
 243                                        n->name, n->hostname);
 244
 245                                 if(n != myself) {
 246                                         became_unreachable_count++;
 247                                 }
 248                         }
 249
 250                         if(experimental && OPTION_VERSION(n->options) >= 2) {
 251                                 n->status.sptps = true;
 252                         }
 253
 254                         /* TODO: only clear status.validkey if node is unreachable? */
 255
 256                         n->status.validkey = false;
 257
 258                         if(n->status.sptps) {
 259                                 sptps_stop(&n->sptps);
 260                                 n->status.waitingforkey = false;
 261                         }
 262
 263                         n->last_req_key = 0;
 264
 265                         n->status.udp_confirmed = false;
 266                         n->maxmtu = MTU;
 267                         n->maxrecentlen = 0;
 268                         n->minmtu = 0;
 269                         n->mtuprobes = 0;
 270
 271                         timeout_del(&n->udp_ping_timeout);
 272
 273                         char *name;
 274                         char *address;
 275                         char *port;
 276
 277                         environment_t env;
 278                         environment_init(&env);
 279                         environment_add(&env, "NODE=%s", n->name);
 280                         sockaddr2str(&n->address, &address, &port);
 281                         environment_add(&env, "REMOTEADDRESS=%s", address);
 282                         environment_add(&env, "REMOTEPORT=%s", port);
 283
 284                         execute_script(n->status.reachable ? "host-up" : "host-down", &env);
 285
 286                         xasprintf(&name, n->status.reachable ? "hosts/%s-up" : "hosts/%s-down", n->name);
 287                         execute_script(name, &env);
 288
 289                         free(name);
 290                         free(address);
 291                         free(port);
 292                         environment_exit(&env);
 293
 294                         subnet_update(n, NULL, n->status.reachable);
 295
 296                         if(!n->status.reachable) {
 297                                 update_node_udp(n, NULL);
 298                                 memset(&n->status, 0, sizeof(n->status));
 299                                 n->options = 0;
 300                         } else if(n->connection) {
 301                                 // Speed up UDP probing by sending our key.
 302                                 if(!n->status.sptps) {
 303                                         send_ans_key(n);
 304                                 }
 305                         }
 306                 }
 307
 308                 if(n->status.reachable && n != myself) {
 309                         reachable_count++;
 310                 }
 311         }
 312
 313         if(device_standby) {
 314                 if(reachable_count == 0 && became_unreachable_count > 0) {
 315                         device_disable();
 316                 } else if(reachable_count > 0 && reachable_count == became_reachable_count) {
 317                         device_enable();
 318                 }
 319         }
 320 }
 321
 322 void graph(void) {
 323         subnet_cache_flush_tables();
 324         sssp_bfs();
 325         check_reachability();
 326         mst_kruskal();
 327 }