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 "device.h"
  49 #include "edge.h"
  50 #include "graph.h"
  51 #include "list.h"
  52 #include "logger.h"
  53 #include "names.h"
  54 #include "netutl.h"
  55 #include "node.h"
  56 #include "protocol.h"
  57 #include "script.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(EN)
  65    Please note that sorting on weight is already done by add_edge().
  66 */
  67
  68 static void mst_kruskal(void) {
  69         /* Clear MST status on connections */
  70
  71         for list_each(connection_t, c, connection_list) {
  72                 c->status.mst = false;
  73         }
  74
  75         logger(DEBUG_SCARY_THINGS, LOG_DEBUG, "Running Kruskal's algorithm:");
  76
  77         /* Clear visited status on nodes */
  78
  79         for splay_each(node_t, n, node_tree) {
  80                 n->status.visited = false;
  81         }
  82
  83         /* Starting point */
  84
  85         for splay_each(edge_t, e, edge_weight_tree) {
  86                 if(e->from->status.reachable) {
  87                         e->from->status.visited = true;
  88                         break;
  89                 }
  90         }
  91
  92         /* Add safe edges */
  93
  94         bool skipped = false;
  95
  96         for splay_each(edge_t, e, edge_weight_tree) {
  97                 if(!e->reverse || (e->from->status.visited == e->to->status.visited)) {
  98                         skipped = true;
  99                         continue;
 100                 }
 101
 102                 e->from->status.visited = true;
 103                 e->to->status.visited = true;
 104
 105                 if(e->connection) {
 106                         e->connection->status.mst = true;
 107                 }
 108
 109                 if(e->reverse->connection) {
 110                         e->reverse->connection->status.mst = true;
 111                 }
 112
 113                 logger(DEBUG_SCARY_THINGS, LOG_DEBUG, " Adding edge %s - %s weight %d", e->from->name, e->to->name, e->weight);
 114
 115                 if(skipped) {
 116                         skipped = false;
 117                         next = edge_weight_tree->head;
 118                 }
 119         }
 120 }
 121
 122 /* Implementation of a simple breadth-first search algorithm.
 123    Running time: O(E)
 124 */
 125
 126 static void sssp_bfs(void) {
 127         list_t *todo_list = list_alloc(NULL);
 128
 129         /* Clear visited status on nodes */
 130
 131         for splay_each(node_t, n, node_tree) {
 132                 n->status.visited = false;
 133                 n->status.indirect = true;
 134                 n->distance = -1;
 135         }
 136
 137         /* Begin with myself */
 138
 139         myself->status.visited = true;
 140         myself->status.indirect = false;
 141         myself->nexthop = myself;
 142         myself->prevedge = NULL;
 143         myself->via = myself;
 144         myself->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->weight >= e->to->prevedge->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->weight >= e->to->prevedge->weight)) {
 189                                 e->to->nexthop = (n->nexthop == myself) ? e->to : n->nexthop;
 190                         }
 191
 192                         e->to->status.visited = true;
 193                         e->to->status.indirect = indirect;
 194                         e->to->prevedge = e;
 195                         e->to->via = indirect ? n->via : e->to;
 196                         e->to->options = e->options;
 197                         e->to->distance = n->distance + 1;
 198
 199                         if(!e->to->status.reachable || (e->to->address.sa.sa_family == AF_UNSPEC && e->address.sa.sa_family != AF_UNKNOWN)) {
 200                                 update_node_udp(e->to, &e->address);
 201                         }
 202
 203                         list_insert_tail(todo_list, e->to);
 204                 }
 205
 206                 next = node->next; /* Because the list_insert_tail() above could have added something extra for us! */
 207                 list_delete_node(todo_list, node);
 208         }
 209
 210         list_free(todo_list);
 211 }
 212
 213 static void check_reachability(void) {
 214         /* Check reachability status. */
 215
 216         int reachable_count = 0;
 217         int became_reachable_count = 0;
 218         int became_unreachable_count = 0;
 219
 220         for splay_each(node_t, n, node_tree) {
 221                 if(n->status.visited != n->status.reachable) {
 222                         n->status.reachable = !n->status.reachable;
 223                         n->last_state_change = now.tv_sec;
 224
 225                         if(n->status.reachable) {
 226                                 logger(DEBUG_TRAFFIC, LOG_DEBUG, "Node %s (%s) became reachable",
 227                                        n->name, n->hostname);
 228
 229                                 if(n != myself) {
 230                                         became_reachable_count++;
 231                                 }
 232                         } else {
 233                                 logger(DEBUG_TRAFFIC, LOG_DEBUG, "Node %s (%s) became unreachable",
 234                                        n->name, n->hostname);
 235
 236                                 if(n != myself) {
 237                                         became_unreachable_count++;
 238                                 }
 239                         }
 240
 241                         if(experimental && OPTION_VERSION(n->options) >= 2) {
 242                                 n->status.sptps = true;
 243                         }
 244
 245                         /* TODO: only clear status.validkey if node is unreachable? */
 246
 247                         n->status.validkey = false;
 248
 249                         if(n->status.sptps) {
 250                                 sptps_stop(&n->sptps);
 251                                 n->status.waitingforkey = false;
 252                         }
 253
 254                         n->last_req_key = 0;
 255
 256                         n->status.udp_confirmed = false;
 257                         n->maxmtu = MTU;
 258                         n->maxrecentlen = 0;
 259                         n->minmtu = 0;
 260                         n->mtuprobes = 0;
 261
 262                         timeout_del(&n->udp_ping_timeout);
 263
 264                         char *name;
 265                         char *address;
 266                         char *port;
 267
 268                         environment_t env;
 269                         environment_init(&env);
 270                         environment_add(&env, "NODE=%s", n->name);
 271                         sockaddr2str(&n->address, &address, &port);
 272                         environment_add(&env, "REMOTEADDRESS=%s", address);
 273                         environment_add(&env, "REMOTEPORT=%s", port);
 274
 275                         execute_script(n->status.reachable ? "host-up" : "host-down", &env);
 276
 277                         xasprintf(&name, n->status.reachable ? "hosts/%s-up" : "hosts/%s-down", n->name);
 278                         execute_script(name, &env);
 279
 280                         free(name);
 281                         free(address);
 282                         free(port);
 283                         environment_exit(&env);
 284
 285                         subnet_update(n, NULL, n->status.reachable);
 286
 287                         if(!n->status.reachable) {
 288                                 update_node_udp(n, NULL);
 289                                 memset(&n->status, 0, sizeof(n->status));
 290                                 n->options = 0;
 291                         } else if(n->connection) {
 292                                 // Speed up UDP probing by sending our key.
 293                                 if(!n->status.sptps) {
 294                                         send_ans_key(n);
 295                                 }
 296                         }
 297                 }
 298
 299                 if(n->status.reachable && n != myself) {
 300                         reachable_count++;
 301                 }
 302         }
 303
 304         if(device_standby) {
 305                 if(reachable_count == 0 && became_unreachable_count > 0) {
 306                         device_disable();
 307                 } else if(reachable_count > 0 && reachable_count == became_reachable_count) {
 308                         device_enable();
 309                 }
 310         }
 311 }
 312
 313 void graph(void) {
 314         subnet_cache_flush();
 315         sssp_bfs();
 316         check_reachability();
 317         mst_kruskal();
 318 }