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   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 "edge.h"
  49 #include "graph.h"
  50 #include "list.h"
  51 #include "logger.h"
  52 #include "names.h"
  53 #include "netutl.h"
  54 #include "node.h"
  55 #include "protocol.h"
  56 #include "script.h"
  57 #include "subnet.h"
  58 #include "utils.h"
  59 #include "xalloc.h"
  60 #include "graph.h"
  61
  62 /* Implementation of Kruskal's algorithm.
  63    Running time: O(EN)
  64    Please note that sorting on weight is already done by add_edge().
  65 */
  66
  67 static void mst_kruskal(void) {
  68         /* Clear MST status on connections */
  69
  70         for list_each(connection_t, c, connection_list)
  71                 c->status.mst = false;
  72
  73         logger(DEBUG_SCARY_THINGS, LOG_DEBUG, "Running Kruskal's algorithm:");
  74
  75         /* Clear visited status on nodes */
  76
  77         for splay_each(node_t, n, node_tree)
  78                 n->status.visited = false;
  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                 if(e->reverse->connection)
 106                         e->reverse->connection->status.mst = true;
 107
 108                 logger(DEBUG_SCARY_THINGS, LOG_DEBUG, " Adding edge %s - %s weight %d", e->from->name, e->to->name, e->weight);
 109
 110                 if(skipped) {
 111                         skipped = false;
 112                         next = edge_weight_tree->head;
 113                 }
 114         }
 115 }
 116
 117 /* Implementation of a simple breadth-first search algorithm.
 118    Running time: O(E)
 119 */
 120
 121 static void sssp_bfs(void) {
 122         list_t *todo_list = list_alloc(NULL);
 123
 124         /* Clear visited status on nodes */
 125
 126         for splay_each(node_t, n, node_tree) {
 127                 n->status.visited = false;
 128                 n->status.indirect = true;
 129                 n->distance = -1;
 130         }
 131
 132         /* Begin with myself */
 133
 134         myself->status.visited = true;
 135         myself->status.indirect = false;
 136         myself->nexthop = myself;
 137         myself->prevedge = NULL;
 138         myself->via = myself;
 139         myself->distance = 0;
 140         list_insert_head(todo_list, myself);
 141
 142         /* Loop while todo_list is filled */
 143
 144         for list_each(node_t, n, todo_list) {                   /* "n" is the node from which we start */
 145                 logger(DEBUG_SCARY_THINGS, LOG_DEBUG, " Examining edges from %s", n->name);
 146
 147                 if(n->distance < 0)
 148                         abort();
 149
 150                 for splay_each(edge_t, e, n->edge_tree) {       /* "e" is the edge connected to "from" */
 151                         if(!e->reverse)
 152                                 continue;
 153
 154                         /* Situation:
 155
 156                                    /
 157                                   /
 158                            ----->(n)---e-->(e->to)
 159                                   \
 160                                    \
 161
 162                            Where e is an edge, (n) and (e->to) are nodes.
 163                            n->address is set to the e->address of the edge left of n to n.
 164                            We are currently examining the edge e right of n from n:
 165
 166                            - If edge e provides for better reachability of e->to, update
 167                              e->to and (re)add it to the todo_list to (re)examine the reachability
 168                              of nodes behind it.
 169                          */
 170
 171                         bool indirect = n->status.indirect || e->options & OPTION_INDIRECT;
 172
 173                         if(e->to->status.visited
 174                            && (!e->to->status.indirect || indirect)
 175                            && (e->to->distance != n->distance + 1 || e->weight >= e->to->prevedge->weight))
 176                                 continue;
 177
 178                         e->to->status.visited = true;
 179                         e->to->status.indirect = indirect;
 180                         e->to->nexthop = (n->nexthop == myself) ? e->to : n->nexthop;
 181                         e->to->prevedge = e;
 182                         e->to->via = indirect ? n->via : e->to;
 183                         e->to->options = e->options;
 184                         e->to->distance = n->distance + 1;
 185
 186                         if(!e->to->status.reachable || (e->to->address.sa.sa_family == AF_UNSPEC && e->address.sa.sa_family != AF_UNKNOWN))
 187                                 update_node_udp(e->to, &e->address);
 188
 189                         list_insert_tail(todo_list, e->to);
 190                 }
 191
 192                 next = node->next; /* Because the list_insert_tail() above could have added something extra for us! */
 193                 list_delete_node(todo_list, node);
 194         }
 195
 196         list_free(todo_list);
 197 }
 198
 199 static void check_reachability(void) {
 200         /* Check reachability status. */
 201
 202         for splay_each(node_t, n, node_tree) {
 203                 if(n->status.visited != n->status.reachable) {
 204                         n->status.reachable = !n->status.reachable;
 205                         n->last_state_change = now.tv_sec;
 206
 207                         if(n->status.reachable) {
 208                                 logger(DEBUG_TRAFFIC, LOG_DEBUG, "Node %s (%s) became reachable",
 209                                            n->name, n->hostname);
 210                         } else {
 211                                 logger(DEBUG_TRAFFIC, LOG_DEBUG, "Node %s (%s) became unreachable",
 212                                            n->name, n->hostname);
 213                         }
 214
 215                         if(experimental && OPTION_VERSION(n->options) >= 2)
 216                                 n->status.sptps = true;
 217
 218                         /* TODO: only clear status.validkey if node is unreachable? */
 219
 220                         n->status.validkey = false;
 221                         if(n->status.sptps) {
 222                                 sptps_stop(&n->sptps);
 223                                 n->status.waitingforkey = false;
 224                         }
 225                         n->last_req_key = 0;
 226
 227                         n->status.udp_confirmed = false;
 228                         n->maxmtu = MTU;
 229                         n->minmtu = 0;
 230                         n->mtuprobes = 0;
 231
 232                         timeout_del(&n->mtutimeout);
 233
 234                         char *name;
 235                         char *address;
 236                         char *port;
 237                         char *envp[8] = {NULL};
 238
 239                         xasprintf(&envp[0], "NETNAME=%s", netname ? : "");
 240                         xasprintf(&envp[3], "NODE=%s", n->name);
 241                         sockaddr2str(&n->address, &address, &port);
 242                         xasprintf(&envp[4], "REMOTEADDRESS=%s", address);
 243                         xasprintf(&envp[5], "REMOTEPORT=%s", port);
 244                         xasprintf(&envp[6], "NAME=%s", myself->name);
 245
 246                         execute_script(n->status.reachable ? "host-up" : "host-down", envp);
 247
 248                         xasprintf(&name, n->status.reachable ? "hosts/%s-up" : "hosts/%s-down", n->name);
 249                         execute_script(name, envp);
 250
 251                         free(name);
 252                         free(address);
 253                         free(port);
 254
 255                         for(int i = 0; i < 7; i++)
 256                                 free(envp[i]);
 257
 258                         subnet_update(n, NULL, n->status.reachable);
 259
 260                         if(!n->status.reachable) {
 261                                 update_node_udp(n, NULL);
 262                                 memset(&n->status, 0, sizeof n->status);
 263                                 n->options = 0;
 264                         } else if(n->connection) {
 265                                 if(n->status.sptps) {
 266                                         if(n->connection->outgoing)
 267                                                 send_req_key(n);
 268                                 } else {
 269                                         send_ans_key(n);
 270                                 }
 271                         }
 272                 }
 273         }
 274 }
 275
 276 void graph(void) {
 277         subnet_cache_flush();
 278         sssp_bfs();
 279         check_reachability();
 280         mst_kruskal();
 281 }