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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 "utils.h"
  57 #include "xalloc.h"
  58 #include "graph.h"
  59
  60 /* Implementation of Kruskal's algorithm.
  61    Running time: O(EN)
  62    Please note that sorting on weight is already done by add_edge().
  63 */
  64
  65 static void mst_kruskal(void) {
  66         /* Clear MST status on connections */
  67
  68         for list_each(connection_t, c, connection_list)
  69                 c->status.mst = false;
  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         /* Starting point */
  79
  80         for splay_each(edge_t, e, edge_weight_tree) {
  81                 if(e->from->status.reachable) {
  82                         e->from->status.visited = true;
  83                         break;
  84                 }
  85         }
  86
  87         /* Add safe edges */
  88
  89         bool skipped = false;
  90
  91         for splay_each(edge_t, e, edge_weight_tree) {
  92                 if(!e->reverse || (e->from->status.visited == e->to->status.visited)) {
  93                         skipped = true;
  94                         continue;
  95                 }
  96
  97                 e->from->status.visited = true;
  98                 e->to->status.visited = true;
  99
 100                 if(e->connection)
 101                         e->connection->status.mst = true;
 102
 103                 if(e->reverse->connection)
 104                         e->reverse->connection->status.mst = true;
 105
 106                 logger(DEBUG_SCARY_THINGS, LOG_DEBUG, " Adding edge %s - %s weight %d", e->from->name, e->to->name, e->weight);
 107
 108                 if(skipped) {
 109                         skipped = false;
 110                         next = edge_weight_tree->head;
 111                 }
 112         }
 113 }
 114
 115 /* Implementation of a simple breadth-first search algorithm.
 116    Running time: O(E)
 117 */
 118
 119 static void sssp_bfs(void) {
 120         list_t *todo_list = list_alloc(NULL);
 121
 122         /* Clear visited status on nodes */
 123
 124         for splay_each(node_t, n, node_tree) {
 125                 n->status.visited = false;
 126                 n->status.indirect = true;
 127                 n->distance = -1;
 128         }
 129
 130         /* Begin with myself */
 131
 132         myself->status.visited = true;
 133         myself->status.indirect = false;
 134         myself->nexthop = myself;
 135         myself->prevedge = NULL;
 136         myself->via = myself;
 137         myself->distance = 0;
 138         list_insert_head(todo_list, myself);
 139
 140         /* Loop while todo_list is filled */
 141
 142         for list_each(node_t, n, todo_list) {                   /* "n" is the node from which we start */
 143                 logger(DEBUG_SCARY_THINGS, LOG_DEBUG, " Examining edges from %s", n->name);
 144
 145                 if(n->distance < 0)
 146                         abort();
 147
 148                 for splay_each(edge_t, e, n->edge_tree) {       /* "e" is the edge connected to "from" */
 149                         if(!e->reverse)
 150                                 continue;
 151
 152                         /* Situation:
 153
 154                                    /
 155                                   /
 156                            ----->(n)---e-->(e->to)
 157                                   \
 158                                    \
 159
 160                            Where e is an edge, (n) and (e->to) are nodes.
 161                            n->address is set to the e->address of the edge left of n to n.
 162                            We are currently examining the edge e right of n from n:
 163
 164                            - If edge e provides for better reachability of e->to, update
 165                              e->to and (re)add it to the todo_list to (re)examine the reachability
 166                              of nodes behind it.
 167                          */
 168
 169                         bool indirect = n->status.indirect || e->options & OPTION_INDIRECT;
 170
 171                         if(e->to->status.visited
 172                            && (!e->to->status.indirect || indirect)
 173                            && (e->to->distance != n->distance + 1 || e->weight >= e->to->prevedge->weight))
 174                                 continue;
 175
 176                         e->to->status.visited = true;
 177                         e->to->status.indirect = indirect;
 178                         e->to->nexthop = (n->nexthop == myself) ? e->to : n->nexthop;
 179                         e->to->prevedge = e;
 180                         e->to->via = indirect ? n->via : e->to;
 181                         e->to->options = e->options;
 182                         e->to->distance = n->distance + 1;
 183
 184                         if(!e->to->status.reachable || (e->to->address.sa.sa_family == AF_UNSPEC && e->address.sa.sa_family != AF_UNKNOWN))
 185                                 update_node_udp(e->to, &e->address);
 186
 187                         list_insert_tail(todo_list, e->to);
 188                 }
 189
 190                 next = node->next; /* Because the list_insert_tail() above could have added something extra for us! */
 191                 list_delete_node(todo_list, node);
 192         }
 193
 194         list_free(todo_list);
 195 }
 196
 197 static void check_reachability(void) {
 198         /* Check reachability status. */
 199
 200         for splay_each(node_t, n, node_tree) {
 201                 if(n->status.visited != n->status.reachable) {
 202                         n->status.reachable = !n->status.reachable;
 203                         n->last_state_change = now.tv_sec;
 204
 205                         if(n->status.reachable) {
 206                                 logger(DEBUG_TRAFFIC, LOG_DEBUG, "Node %s (%s) became reachable",
 207                                            n->name, n->hostname);
 208                         } else {
 209                                 logger(DEBUG_TRAFFIC, LOG_DEBUG, "Node %s (%s) became unreachable",
 210                                            n->name, n->hostname);
 211                         }
 212
 213                         if(experimental && OPTION_VERSION(n->options) >= 2)
 214                                 n->status.sptps = true;
 215
 216                         /* TODO: only clear status.validkey if node is unreachable? */
 217
 218                         n->status.validkey = false;
 219                         if(n->status.sptps) {
 220                                 sptps_stop(&n->sptps);
 221                                 n->status.waitingforkey = false;
 222                         }
 223                         n->last_req_key = 0;
 224
 225                         n->status.udp_confirmed = false;
 226                         n->maxmtu = MTU;
 227                         n->minmtu = 0;
 228                         n->mtuprobes = 0;
 229
 230                         timeout_del(&n->mtutimeout);
 231
 232                         //TODO: callback to application to inform of this node going up/down
 233
 234                         if(!n->status.reachable) {
 235                                 update_node_udp(n, NULL);
 236                                 memset(&n->status, 0, sizeof n->status);
 237                                 n->options = 0;
 238                         } else if(n->connection) {
 239                                 if(n->status.sptps) {
 240                                         if(n->connection->outgoing)
 241                                                 send_req_key(n);
 242                                 } else {
 243                                         send_ans_key(n);
 244                                 }
 245                         }
 246                 }
 247         }
 248 }
 249
 250 void graph(void) {
 251         sssp_bfs();
 252         check_reachability();
 253         mst_kruskal();
 254 }