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

   1 /*
   2     graph.c -- graph algorithms
   3     Copyright (C) 2001-2013 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 "process.h"
  57 #include "protocol.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         logger(DEBUG_SCARY_THINGS, LOG_DEBUG, "Running Kruskal's algorithm:");
  75
  76         /* Clear visited status on nodes */
  77
  78         for splay_each(node_t, n, node_tree)
  79                 n->status.visited = false;
  80
  81         /* Starting point */
  82
  83         for splay_each(edge_t, e, edge_weight_tree) {
  84                 if(e->from->status.reachable) {
  85                         e->from->status.visited = true;
  86                         break;
  87                 }
  88         }
  89
  90         /* Add safe edges */
  91
  92         bool skipped = false;
  93
  94         for splay_each(edge_t, e, edge_weight_tree) {
  95                 if(!e->reverse || (e->from->status.visited == e->to->status.visited)) {
  96                         skipped = true;
  97                         continue;
  98                 }
  99
 100                 e->from->status.visited = true;
 101                 e->to->status.visited = true;
 102
 103                 if(e->connection)
 104                         e->connection->status.mst = true;
 105
 106                 if(e->reverse->connection)
 107                         e->reverse->connection->status.mst = true;
 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                 for splay_each(edge_t, e, n->edge_tree) {       /* "e" is the edge connected to "from" */
 152                         if(!e->reverse)
 153                                 continue;
 154
 155                         /* Situation:
 156
 157                                    /
 158                                   /
 159                            ----->(n)---e-->(e->to)
 160                                   \
 161                                    \
 162
 163                            Where e is an edge, (n) and (e->to) are nodes.
 164                            n->address is set to the e->address of the edge left of n to n.
 165                            We are currently examining the edge e right of n from n:
 166
 167                            - If edge e provides for better reachability of e->to, update
 168                              e->to and (re)add it to the todo_list to (re)examine the reachability
 169                              of nodes behind it.
 170                          */
 171
 172                         bool indirect = n->status.indirect || e->options & OPTION_INDIRECT;
 173
 174                         if(e->to->status.visited
 175                            && (!e->to->status.indirect || indirect)
 176                            && (e->to->distance != n->distance + 1 || e->weight >= e->to->prevedge->weight))
 177                                 continue;
 178
 179                         e->to->status.visited = true;
 180                         e->to->status.indirect = indirect;
 181                         e->to->nexthop = (n->nexthop == myself) ? e->to : n->nexthop;
 182                         e->to->prevedge = e;
 183                         e->to->via = indirect ? n->via : e->to;
 184                         e->to->options = e->options;
 185                         e->to->distance = n->distance + 1;
 186
 187                         if(!e->to->status.reachable || (e->to->address.sa.sa_family == AF_UNSPEC && e->address.sa.sa_family != AF_UNKNOWN))
 188                                 update_node_udp(e->to, &e->address);
 189
 190                         list_insert_tail(todo_list, e->to);
 191                 }
 192
 193                 next = node->next; /* Because the list_insert_tail() above could have added something extra for us! */
 194                 list_delete_node(todo_list, node);
 195         }
 196
 197         list_free(todo_list);
 198 }
 199
 200 static void check_reachability(void) {
 201         /* Check reachability status. */
 202
 203         for splay_each(node_t, n, node_tree) {
 204                 if(n->status.visited != n->status.reachable) {
 205                         n->status.reachable = !n->status.reachable;
 206                         n->last_state_change = now.tv_sec;
 207
 208                         if(n->status.reachable) {
 209                                 logger(DEBUG_TRAFFIC, LOG_DEBUG, "Node %s (%s) became reachable",
 210                                            n->name, n->hostname);
 211                         } else {
 212                                 logger(DEBUG_TRAFFIC, LOG_DEBUG, "Node %s (%s) became unreachable",
 213                                            n->name, n->hostname);
 214                         }
 215
 216                         if(experimental && OPTION_VERSION(n->options) >= 2)
 217                                 n->status.sptps = true;
 218
 219                         /* TODO: only clear status.validkey if node is unreachable? */
 220
 221                         n->status.validkey = false;
 222                         if(n->status.sptps) {
 223                                 sptps_stop(&n->sptps);
 224                                 n->status.waitingforkey = false;
 225                         }
 226                         n->last_req_key = 0;
 227
 228                         n->status.udp_confirmed = false;
 229                         n->maxmtu = MTU;
 230                         n->minmtu = 0;
 231                         n->mtuprobes = 0;
 232
 233                         timeout_del(&n->mtutimeout);
 234
 235                         char *name;
 236                         char *address;
 237                         char *port;
 238                         char *envp[7];
 239
 240                         xasprintf(&envp[0], "NETNAME=%s", netname ? : "");
 241                         xasprintf(&envp[1], "DEVICE=%s", device ? : "");
 242                         xasprintf(&envp[2], "INTERFACE=%s", iface ? : "");
 243                         xasprintf(&envp[3], "NODE=%s", n->name);
 244                         sockaddr2str(&n->address, &address, &port);
 245                         xasprintf(&envp[4], "REMOTEADDRESS=%s", address);
 246                         xasprintf(&envp[5], "REMOTEPORT=%s", port);
 247                         envp[6] = NULL;
 248
 249                         execute_script(n->status.reachable ? "host-up" : "host-down", envp);
 250
 251                         xasprintf(&name, n->status.reachable ? "hosts/%s-up" : "hosts/%s-down", n->name);
 252                         execute_script(name, envp);
 253
 254                         free(name);
 255                         free(address);
 256                         free(port);
 257
 258                         for(int i = 0; i < 6; i++)
 259                                 free(envp[i]);
 260
 261                         subnet_update(n, NULL, n->status.reachable);
 262
 263                         if(!n->status.reachable) {
 264                                 update_node_udp(n, NULL);
 265                                 memset(&n->status, 0, sizeof n->status);
 266                                 n->options = 0;
 267                         } else if(n->connection) {
 268                                 if(n->status.sptps) {
 269                                         if(n->connection->outgoing)
 270                                                 send_req_key(n);
 271                                 } else {
 272                                         send_ans_key(n);
 273                                 }
 274                         }
 275                 }
 276         }
 277 }
 278
 279 void graph(void) {
 280         subnet_cache_flush();
 281         sssp_bfs();
 282         check_reachability();
 283         mst_kruskal();
 284 }