git.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
  59 /* Implementation of Kruskal's algorithm.
  60    Running time: O(EN)
  61    Please note that sorting on weight is already done by add_edge().
  62 */
  63
  64 static void mst_kruskal(void) {
  65         /* Clear MST status on connections */
  66
  67         for list_each(connection_t, c, &connection_list) {
  68                 c->status.mst = false;
  69         }
  70
  71         logger(DEBUG_SCARY_THINGS, LOG_DEBUG, "Running Kruskal's algorithm:");
  72
  73         /* Clear visited status on nodes */
  74
  75         for splay_each(node_t, n, &node_tree) {
  76                 n->status.visited = false;
  77         }
  78
  79         /* Starting point */
  80
  81         for splay_each(edge_t, e, &edge_weight_tree) {
  82                 if(e->from->status.reachable) {
  83                         e->from->status.visited = true;
  84                         break;
  85                 }
  86         }
  87
  88         /* Add safe edges */
  89
  90         bool skipped = false;
  91
  92         for splay_each(edge_t, e, &edge_weight_tree) {
  93                 if(!e->reverse || (e->from->status.visited == e->to->status.visited)) {
  94                         skipped = true;
  95                         continue;
  96                 }
  97
  98                 e->from->status.visited = true;
  99                 e->to->status.visited = true;
 100
 101                 if(e->connection) {
 102                         e->connection->status.mst = true;
 103                 }
 104
 105                 if(e->reverse->connection) {
 106                         e->reverse->connection->status.mst = true;
 107                 }
 108
 109                 logger(DEBUG_SCARY_THINGS, LOG_DEBUG, " Adding edge %s - %s weight %d", e->from->name, e->to->name, e->weight);
 110
 111                 if(skipped) {
 112                         skipped = false;
 113                         next = edge_weight_tree.head;
 114                 }
 115         }
 116 }
 117
 118 /* Implementation of a simple breadth-first search algorithm.
 119    Running time: O(E)
 120 */
 121
 122 static void sssp_bfs(void) {
 123         list_t *todo_list = list_alloc(NULL);
 124
 125         /* Clear visited status on nodes */
 126
 127         for splay_each(node_t, n, &node_tree) {
 128                 n->status.visited = false;
 129                 n->status.indirect = true;
 130                 n->distance = -1;
 131         }
 132
 133         /* Begin with myself */
 134
 135         myself->status.visited = true;
 136         myself->status.indirect = false;
 137         myself->nexthop = myself;
 138         myself->prevedge = NULL;
 139         myself->via = myself;
 140         myself->distance = 0;
 141         list_insert_head(todo_list, myself);
 142
 143         /* Loop while todo_list is filled */
 144
 145         for list_each(node_t, n, todo_list) {                   /* "n" is the node from which we start */
 146                 logger(DEBUG_SCARY_THINGS, LOG_DEBUG, " Examining edges from %s", n->name);
 147
 148                 if(n->distance < 0) {
 149                         abort();
 150                 }
 151
 152                 for splay_each(edge_t, e, &n->edge_tree) {       /* "e" is the edge connected to "from" */
 153                         if(!e->reverse || e->to == myself) {
 154                                 continue;
 155                         }
 156
 157                         /* Situation:
 158
 159                                    /
 160                                   /
 161                            ----->(n)---e-->(e->to)
 162                                   \
 163                                    \
 164
 165                            Where e is an edge, (n) and (e->to) are nodes.
 166                            n->address is set to the e->address of the edge left of n to n.
 167                            We are currently examining the edge e right of n from n:
 168
 169                            - If edge e provides for better reachability of e->to, update
 170                              e->to and (re)add it to the todo_list to (re)examine the reachability
 171                              of nodes behind it.
 172                          */
 173
 174                         bool indirect = n->status.indirect || e->options & OPTION_INDIRECT;
 175
 176                         if(e->to->status.visited
 177                                         && (!e->to->status.indirect || indirect)
 178                                         && (e->to->distance != n->distance + 1 || e->weight >= e->to->prevedge->weight)) {
 179                                 continue;
 180                         }
 181
 182                         // Only update nexthop if it doesn't increase the path length
 183
 184                         if(!e->to->status.visited || (e->to->distance == n->distance + 1 && e->weight >= e->to->prevedge->weight)) {
 185                                 e->to->nexthop = (n->nexthop == myself) ? e->to : n->nexthop;
 186                         }
 187
 188                         e->to->status.visited = true;
 189                         e->to->status.indirect = indirect;
 190                         e->to->prevedge = e;
 191                         e->to->via = indirect ? n->via : e->to;
 192                         e->to->options = e->options;
 193                         e->to->distance = n->distance + 1;
 194
 195                         if(!e->to->status.reachable || (e->to->address.sa.sa_family == AF_UNSPEC && e->address.sa.sa_family != AF_UNKNOWN)) {
 196                                 update_node_udp(e->to, &e->address);
 197                         }
 198
 199                         list_insert_tail(todo_list, e->to);
 200                 }
 201
 202                 next = node->next; /* Because the list_insert_tail() above could have added something extra for us! */
 203                 list_delete_node(todo_list, node);
 204         }
 205
 206         list_free(todo_list);
 207 }
 208
 209 static void check_reachability(void) {
 210         /* Check reachability status. */
 211
 212         int reachable_count = 0;
 213         int became_reachable_count = 0;
 214         int became_unreachable_count = 0;
 215
 216         for splay_each(node_t, n, &node_tree) {
 217                 if(n->status.visited != n->status.reachable) {
 218                         n->status.reachable = !n->status.reachable;
 219                         n->last_state_change = now.tv_sec;
 220
 221                         if(n->status.reachable) {
 222                                 logger(DEBUG_TRAFFIC, LOG_DEBUG, "Node %s (%s) became reachable",
 223                                        n->name, n->hostname);
 224
 225                                 if(n != myself) {
 226                                         became_reachable_count++;
 227                                 }
 228                         } else {
 229                                 logger(DEBUG_TRAFFIC, LOG_DEBUG, "Node %s (%s) became unreachable",
 230                                        n->name, n->hostname);
 231
 232                                 if(n != myself) {
 233                                         became_unreachable_count++;
 234                                 }
 235                         }
 236
 237                         if(experimental && OPTION_VERSION(n->options) >= 2) {
 238                                 n->status.sptps = true;
 239                         }
 240
 241                         /* TODO: only clear status.validkey if node is unreachable? */
 242
 243                         n->status.validkey = false;
 244
 245                         if(n->status.sptps) {
 246                                 sptps_stop(&n->sptps);
 247                                 n->status.waitingforkey = false;
 248                         }
 249
 250                         n->last_req_key = 0;
 251
 252                         n->status.udp_confirmed = false;
 253                         n->maxmtu = MTU;
 254                         n->maxrecentlen = 0;
 255                         n->minmtu = 0;
 256                         n->mtuprobes = 0;
 257
 258                         timeout_del(&n->udp_ping_timeout);
 259
 260                         char *name;
 261                         char *address;
 262                         char *port;
 263
 264                         environment_t env;
 265                         environment_init(&env);
 266                         environment_add(&env, "NODE=%s", n->name);
 267                         sockaddr2str(&n->address, &address, &port);
 268                         environment_add(&env, "REMOTEADDRESS=%s", address);
 269                         environment_add(&env, "REMOTEPORT=%s", port);
 270
 271                         execute_script(n->status.reachable ? "host-up" : "host-down", &env);
 272
 273                         xasprintf(&name, n->status.reachable ? "hosts/%s-up" : "hosts/%s-down", n->name);
 274                         execute_script(name, &env);
 275
 276                         free(name);
 277                         free(address);
 278                         free(port);
 279                         environment_exit(&env);
 280
 281                         subnet_update(n, NULL, n->status.reachable);
 282
 283                         if(!n->status.reachable) {
 284                                 update_node_udp(n, NULL);
 285                                 memset(&n->status, 0, sizeof(n->status));
 286                                 n->options = 0;
 287                         } else if(n->connection) {
 288                                 // Speed up UDP probing by sending our key.
 289                                 if(!n->status.sptps) {
 290                                         send_ans_key(n);
 291                                 }
 292                         }
 293                 }
 294
 295                 if(n->status.reachable && n != myself) {
 296                         reachable_count++;
 297                 }
 298         }
 299
 300         if(device_standby) {
 301                 if(reachable_count == 0 && became_unreachable_count > 0) {
 302                         device_disable();
 303                 } else if(reachable_count > 0 && reachable_count == became_reachable_count) {
 304                         device_enable();
 305                 }
 306         }
 307 }
 308
 309 void graph(void) {
 310         subnet_cache_flush_tables();
 311         sssp_bfs();
 312         check_reachability();
 313         mst_kruskal();
 314 }