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