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
  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 // Not putting it into header, the outside world doesn't need to know about it.
 119 extern void sssp_bfs(void);
 120
 121 /* Implementation of a simple breadth-first search algorithm.
 122    Running time: O(E)
 123 */
 124 void sssp_bfs(void) {
 125         list_t *todo_list = list_alloc(NULL);
 126
 127         /* Clear visited status on nodes */
 128
 129         for splay_each(node_t, n, &node_tree) {
 130                 n->status.visited = false;
 131                 n->status.indirect = true;
 132                 n->distance = -1;
 133         }
 134
 135         /* Begin with myself */
 136
 137         myself->status.visited = true;
 138         myself->status.indirect = false;
 139         myself->nexthop = myself;
 140         myself->prevedge = NULL;
 141         myself->via = myself;
 142         myself->distance = 0;
 143         list_insert_head(todo_list, myself);
 144
 145         /* Loop while todo_list is filled */
 146
 147         for list_each(node_t, n, todo_list) {                   /* "n" is the node from which we start */
 148                 logger(DEBUG_SCARY_THINGS, LOG_DEBUG, " Examining edges from %s", n->name);
 149
 150                 if(n->distance < 0) {
 151                         abort();
 152                 }
 153
 154                 for splay_each(edge_t, e, &n->edge_tree) {       /* "e" is the edge connected to "from" */
 155                         if(!e->reverse || e->to == myself) {
 156                                 continue;
 157                         }
 158
 159                         /* Situation:
 160
 161                                    /
 162                                   /
 163                            ----->(n)---e-->(e->to)
 164                                   \
 165                                    \
 166
 167                            Where e is an edge, (n) and (e->to) are nodes.
 168                            n->address is set to the e->address of the edge left of n to n.
 169                            We are currently examining the edge e right of n from n:
 170
 171                            - If edge e provides for better reachability of e->to, update
 172                              e->to and (re)add it to the todo_list to (re)examine the reachability
 173                              of nodes behind it.
 174                          */
 175
 176                         bool indirect = n->status.indirect || e->options & OPTION_INDIRECT;
 177
 178                         if(e->to->status.visited
 179                                         && (!e->to->status.indirect || indirect)
 180                                         && (e->to->distance != n->distance + 1 || e->weight >= e->to->prevedge->weight)) {
 181                                 continue;
 182                         }
 183
 184                         // Only update nexthop if it doesn't increase the path length
 185
 186                         if(!e->to->status.visited || (e->to->distance == n->distance + 1 && e->weight < e->to->prevedge->weight)) {
 187                                 e->to->nexthop = (n->nexthop == myself) ? e->to : n->nexthop;
 188                         }
 189
 190                         e->to->status.visited = true;
 191                         e->to->status.indirect = indirect;
 192                         e->to->prevedge = e;
 193                         e->to->via = indirect ? n->via : e->to;
 194                         e->to->options = e->options;
 195                         e->to->distance = n->distance + 1;
 196
 197                         if(!e->to->status.reachable || (e->to->address.sa.sa_family == AF_UNSPEC && e->address.sa.sa_family != AF_UNKNOWN)) {
 198                                 update_node_udp(e->to, &e->address);
 199                         }
 200
 201                         list_insert_tail(todo_list, e->to);
 202                 }
 203
 204                 next = node->next; /* Because the list_insert_tail() above could have added something extra for us! */
 205                 list_delete_node(todo_list, node);
 206         }
 207
 208         list_free(todo_list);
 209 }
 210
 211 static void check_reachability(void) {
 212         /* Check reachability status. */
 213
 214         int reachable_count = 0;
 215         int became_reachable_count = 0;
 216         int became_unreachable_count = 0;
 217
 218         for splay_each(node_t, n, &node_tree) {
 219                 if(n->status.visited != n->status.reachable) {
 220                         n->status.reachable = !n->status.reachable;
 221                         n->last_state_change = now.tv_sec;
 222
 223                         if(n->status.reachable) {
 224                                 logger(DEBUG_TRAFFIC, LOG_DEBUG, "Node %s (%s) became reachable",
 225                                        n->name, n->hostname);
 226
 227                                 if(n != myself) {
 228                                         became_reachable_count++;
 229                                 }
 230                         } else {
 231                                 logger(DEBUG_TRAFFIC, LOG_DEBUG, "Node %s (%s) became unreachable",
 232                                        n->name, n->hostname);
 233
 234                                 if(n != myself) {
 235                                         became_unreachable_count++;
 236                                 }
 237                         }
 238
 239                         if(experimental && OPTION_VERSION(n->options) >= 2) {
 240                                 n->status.sptps = true;
 241                         }
 242
 243                         /* TODO: only clear status.validkey if node is unreachable? */
 244
 245                         n->status.validkey = false;
 246
 247                         if(n->status.sptps) {
 248                                 sptps_stop(&n->sptps);
 249                                 n->status.waitingforkey = false;
 250                         }
 251
 252                         n->last_req_key = 0;
 253
 254                         n->status.udp_confirmed = false;
 255                         n->maxmtu = MTU;
 256                         n->maxrecentlen = 0;
 257                         n->minmtu = 0;
 258                         n->mtuprobes = 0;
 259
 260                         timeout_del(&n->udp_ping_timeout);
 261
 262                         char *name;
 263                         char *address;
 264                         char *port;
 265
 266                         environment_t env;
 267                         environment_init(&env);
 268                         environment_add(&env, "NODE=%s", n->name);
 269                         sockaddr2str(&n->address, &address, &port);
 270                         environment_add(&env, "REMOTEADDRESS=%s", address);
 271                         environment_add(&env, "REMOTEPORT=%s", port);
 272
 273                         execute_script(n->status.reachable ? "host-up" : "host-down", &env);
 274
 275                         xasprintf(&name, n->status.reachable ? "hosts/%s-up" : "hosts/%s-down", n->name);
 276                         execute_script(name, &env);
 277
 278                         free(name);
 279                         free(address);
 280                         free(port);
 281                         environment_exit(&env);
 282
 283                         subnet_update(n, NULL, n->status.reachable);
 284
 285                         if(!n->status.reachable) {
 286                                 update_node_udp(n, NULL);
 287                                 memset(&n->status, 0, sizeof(n->status));
 288                                 n->options = 0;
 289                         } else if(n->connection) {
 290                                 // Speed up UDP probing by sending our key.
 291                                 if(!n->status.sptps) {
 292                                         send_ans_key(n);
 293                                 }
 294                         }
 295                 }
 296
 297                 if(n->status.reachable && n != myself) {
 298                         reachable_count++;
 299                 }
 300         }
 301
 302         if(device_standby) {
 303                 if(reachable_count == 0 && became_unreachable_count > 0) {
 304                         device_disable();
 305                 } else if(reachable_count > 0 && reachable_count == became_reachable_count) {
 306                         device_enable();
 307                 }
 308         }
 309 }
 310
 311 void graph(void) {
 312         subnet_cache_flush_tables();
 313         sssp_bfs();
 314         check_reachability();
 315         mst_kruskal();
 316 }