www.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         list_insert_head(todo_list, myself);
 145
 146         /* Loop while todo_list is filled */
 147
 148         for list_each(node_t, n, todo_list) {                   /* "n" is the node from which we start */
 149                 logger(DEBUG_SCARY_THINGS, LOG_DEBUG, " Examining edges from %s", n->name);
 150
 151                 if(n->distance < 0) {
 152                         abort();
 153                 }
 154
 155                 for splay_each(edge_t, e, &n->edge_tree) {       /* "e" is the edge connected to "from" */
 156                         if(!e->reverse || e->to == myself) {
 157                                 continue;
 158                         }
 159
 160                         /* Situation:
 161
 162                                    /
 163                                   /
 164                            ----->(n)---e-->(e->to)
 165                                   \
 166                                    \
 167
 168                            Where e is an edge, (n) and (e->to) are nodes.
 169                            n->address is set to the e->address of the edge left of n to n.
 170                            We are currently examining the edge e right of n from n:
 171
 172                            - If edge e provides for better reachability of e->to, update
 173                              e->to and (re)add it to the todo_list to (re)examine the reachability
 174                              of nodes behind it.
 175                          */
 176
 177                         bool indirect = n->status.indirect || e->options & OPTION_INDIRECT;
 178
 179                         if(e->to->status.visited
 180                                         && (!e->to->status.indirect || indirect)
 181                                         && (e->to->distance != n->distance + 1 || e->weight >= e->to->prevedge->weight)) {
 182                                 continue;
 183                         }
 184
 185                         // Only update nexthop if it doesn't increase the path length
 186
 187                         if(!e->to->status.visited || (e->to->distance == n->distance + 1 && e->weight < e->to->prevedge->weight)) {
 188                                 e->to->nexthop = (n->nexthop == myself) ? e->to : n->nexthop;
 189                         }
 190
 191                         e->to->status.visited = true;
 192                         e->to->status.indirect = indirect;
 193                         e->to->prevedge = e;
 194                         e->to->via = indirect ? n->via : e->to;
 195                         e->to->options = e->options;
 196                         e->to->distance = n->distance + 1;
 197
 198                         if(!e->to->status.reachable || (e->to->address.sa.sa_family == AF_UNSPEC && e->address.sa.sa_family != AF_UNKNOWN)) {
 199                                 update_node_udp(e->to, &e->address);
 200                         }
 201
 202                         list_insert_tail(todo_list, e->to);
 203                 }
 204
 205                 next = node->next; /* Because the list_insert_tail() above could have added something extra for us! */
 206                 list_delete_node(todo_list, node);
 207         }
 208
 209         list_free(todo_list);
 210 }
 211
 212 static void check_reachability(void) {
 213         /* Check reachability status. */
 214
 215         int reachable_count = 0;
 216         int became_reachable_count = 0;
 217         int became_unreachable_count = 0;
 218
 219         for splay_each(node_t, n, &node_tree) {
 220                 if(n->status.visited != n->status.reachable) {
 221                         n->status.reachable = !n->status.reachable;
 222                         n->last_state_change = now.tv_sec;
 223
 224                         if(n->status.reachable) {
 225                                 logger(DEBUG_TRAFFIC, LOG_DEBUG, "Node %s (%s) became reachable",
 226                                        n->name, n->hostname);
 227
 228                                 if(n != myself) {
 229                                         became_reachable_count++;
 230
 231                                         if(n->connection && n->connection->outgoing) {
 232                                                 if(!n->address_cache) {
 233                                                         n->address_cache = open_address_cache(n);
 234                                                 }
 235
 236                                                 add_recent_address(n->address_cache, &n->connection->address);
 237                                         }
 238                                 }
 239                         } else {
 240                                 logger(DEBUG_TRAFFIC, LOG_DEBUG, "Node %s (%s) became unreachable",
 241                                        n->name, n->hostname);
 242
 243                                 if(n != myself) {
 244                                         became_unreachable_count++;
 245                                 }
 246                         }
 247
 248                         if(experimental && OPTION_VERSION(n->options) >= 2) {
 249                                 n->status.sptps = true;
 250                         }
 251
 252                         /* TODO: only clear status.validkey if node is unreachable? */
 253
 254                         n->status.validkey = false;
 255
 256                         if(n->status.sptps) {
 257                                 sptps_stop(&n->sptps);
 258                                 n->status.waitingforkey = false;
 259                         }
 260
 261                         n->last_req_key = 0;
 262
 263                         n->status.udp_confirmed = false;
 264                         n->maxmtu = MTU;
 265                         n->maxrecentlen = 0;
 266                         n->minmtu = 0;
 267                         n->mtuprobes = 0;
 268
 269                         timeout_del(&n->udp_ping_timeout);
 270
 271                         char *name;
 272                         char *address;
 273                         char *port;
 274
 275                         environment_t env;
 276                         environment_init(&env);
 277                         environment_add(&env, "NODE=%s", n->name);
 278                         sockaddr2str(&n->address, &address, &port);
 279                         environment_add(&env, "REMOTEADDRESS=%s", address);
 280                         environment_add(&env, "REMOTEPORT=%s", port);
 281
 282                         execute_script(n->status.reachable ? "host-up" : "host-down", &env);
 283
 284                         xasprintf(&name, n->status.reachable ? "hosts/%s-up" : "hosts/%s-down", n->name);
 285                         execute_script(name, &env);
 286
 287                         free(name);
 288                         free(address);
 289                         free(port);
 290                         environment_exit(&env);
 291
 292                         subnet_update(n, NULL, n->status.reachable);
 293
 294                         if(!n->status.reachable) {
 295                                 update_node_udp(n, NULL);
 296                                 memset(&n->status, 0, sizeof(n->status));
 297                                 n->options = 0;
 298                         } else if(n->connection) {
 299                                 // Speed up UDP probing by sending our key.
 300                                 if(!n->status.sptps) {
 301                                         send_ans_key(n);
 302                                 }
 303                         }
 304                 }
 305
 306                 if(n->status.reachable && n != myself) {
 307                         reachable_count++;
 308                 }
 309         }
 310
 311         if(device_standby) {
 312                 if(reachable_count == 0 && became_unreachable_count > 0) {
 313                         device_disable();
 314                 } else if(reachable_count > 0 && reachable_count == became_reachable_count) {
 315                         device_enable();
 316                 }
 317         }
 318 }
 319
 320 void graph(void) {
 321         subnet_cache_flush_tables();
 322         sssp_bfs();
 323         check_reachability();
 324         mst_kruskal();
 325 }