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   1 /*
   2     graph.c -- graph algorithms
   3     Copyright (C) 2001-2013 Guus Sliepen <guus@meshlink.io>,
   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 "utils.h"
  56 #include "xalloc.h"
  57 #include "graph.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         logger(DEBUG_SCARY_THINGS, LOG_DEBUG, "Running Kruskal's algorithm:");
  71
  72         /* Clear visited status on nodes */
  73
  74         for splay_each(node_t, n, node_tree)
  75                 n->status.visited = false;
  76
  77         /* Starting point */
  78
  79         for splay_each(edge_t, e, edge_weight_tree) {
  80                 if(e->from->status.reachable) {
  81                         e->from->status.visited = true;
  82                         break;
  83                 }
  84         }
  85
  86         /* Add safe edges */
  87
  88         bool skipped = false;
  89
  90         for splay_each(edge_t, e, edge_weight_tree) {
  91                 if(!e->reverse || (e->from->status.visited == e->to->status.visited)) {
  92                         skipped = true;
  93                         continue;
  94                 }
  95
  96                 e->from->status.visited = true;
  97                 e->to->status.visited = true;
  98
  99                 if(e->connection)
 100                         e->connection->status.mst = true;
 101
 102                 if(e->reverse->connection)
 103                         e->reverse->connection->status.mst = true;
 104
 105                 logger(DEBUG_SCARY_THINGS, LOG_DEBUG, " Adding edge %s - %s weight %d", e->from->name, e->to->name, e->weight);
 106
 107                 if(skipped) {
 108                         skipped = false;
 109                         next = edge_weight_tree->head;
 110                 }
 111         }
 112 }
 113
 114 /* Implementation of a simple breadth-first search algorithm.
 115    Running time: O(E)
 116 */
 117
 118 static void sssp_bfs(void) {
 119         list_t *todo_list = list_alloc(NULL);
 120
 121         /* Clear visited status on nodes */
 122
 123         for splay_each(node_t, n, node_tree) {
 124                 n->status.visited = false;
 125                 n->status.indirect = true;
 126                 n->distance = -1;
 127         }
 128
 129         /* Begin with myself */
 130
 131         myself->status.visited = true;
 132         myself->status.indirect = false;
 133         myself->nexthop = myself;
 134         myself->prevedge = NULL;
 135         myself->via = myself;
 136         myself->distance = 0;
 137         list_insert_head(todo_list, myself);
 138
 139         /* Loop while todo_list is filled */
 140
 141         for list_each(node_t, n, todo_list) {                   /* "n" is the node from which we start */
 142                 logger(DEBUG_SCARY_THINGS, LOG_DEBUG, " Examining edges from %s", n->name);
 143
 144                 if(n->distance < 0)
 145                         abort();
 146
 147                 for splay_each(edge_t, e, n->edge_tree) {       /* "e" is the edge connected to "from" */
 148                         if(!e->reverse)
 149                                 continue;
 150
 151                         /* Situation:
 152
 153                                    /
 154                                   /
 155                            ----->(n)---e-->(e->to)
 156                                   \
 157                                    \
 158
 159                            Where e is an edge, (n) and (e->to) are nodes.
 160                            n->address is set to the e->address of the edge left of n to n.
 161                            We are currently examining the edge e right of n from n:
 162
 163                            - If edge e provides for better reachability of e->to, update
 164                              e->to and (re)add it to the todo_list to (re)examine the reachability
 165                              of nodes behind it.
 166                          */
 167
 168                         bool indirect = n->status.indirect || e->options & OPTION_INDIRECT;
 169
 170                         if(e->to->status.visited
 171                            && (!e->to->status.indirect || indirect)
 172                            && (e->to->distance != n->distance + 1 || e->weight >= e->to->prevedge->weight))
 173                                 continue;
 174
 175                         e->to->status.visited = true;
 176                         e->to->status.indirect = indirect;
 177                         e->to->nexthop = (n->nexthop == myself) ? e->to : n->nexthop;
 178                         e->to->prevedge = e;
 179                         e->to->via = indirect ? n->via : e->to;
 180                         e->to->options = e->options;
 181                         e->to->distance = n->distance + 1;
 182
 183                         if(!e->to->status.reachable || (e->to->address.sa.sa_family == AF_UNSPEC && e->address.sa.sa_family != AF_UNKNOWN))
 184                                 update_node_udp(e->to, &e->address);
 185
 186                         list_insert_tail(todo_list, e->to);
 187                 }
 188
 189                 next = node->next; /* Because the list_insert_tail() above could have added something extra for us! */
 190                 list_delete_node(todo_list, node);
 191         }
 192
 193         list_free(todo_list);
 194 }
 195
 196 static void check_reachability(void) {
 197         /* Check reachability status. */
 198
 199         for splay_each(node_t, n, node_tree) {
 200                 if(n->status.visited != n->status.reachable) {
 201                         n->status.reachable = !n->status.reachable;
 202                         n->last_state_change = now.tv_sec;
 203
 204                         if(n->status.reachable) {
 205                                 logger(DEBUG_TRAFFIC, LOG_DEBUG, "Node %s (%s) became reachable",
 206                                            n->name, n->hostname);
 207                         } else {
 208                                 logger(DEBUG_TRAFFIC, LOG_DEBUG, "Node %s (%s) became unreachable",
 209                                            n->name, n->hostname);
 210                         }
 211
 212                         if(experimental && OPTION_VERSION(n->options) >= 2)
 213                                 n->status.sptps = true;
 214
 215                         /* TODO: only clear status.validkey if node is unreachable? */
 216
 217                         n->status.validkey = false;
 218                         if(n->status.sptps) {
 219                                 sptps_stop(&n->sptps);
 220                                 n->status.waitingforkey = false;
 221                         }
 222                         n->last_req_key = 0;
 223
 224                         n->status.udp_confirmed = false;
 225                         n->maxmtu = MTU;
 226                         n->minmtu = 0;
 227                         n->mtuprobes = 0;
 228
 229                         timeout_del(&n->mtutimeout);
 230
 231                         //TODO: callback to application to inform of this node going up/down
 232
 233                         if(!n->status.reachable) {
 234                                 update_node_udp(n, NULL);
 235                                 memset(&n->status, 0, sizeof n->status);
 236                                 n->options = 0;
 237                         } else if(n->connection) {
 238                                 if(n->status.sptps) {
 239                                         if(n->connection->outgoing)
 240                                                 send_req_key(n);
 241                                 } else {
 242                                         send_ans_key(n);
 243                                 }
 244                         }
 245                 }
 246         }
 247 }
 248
 249 void graph(void) {
 250         sssp_bfs();
 251         check_reachability();
 252         mst_kruskal();
 253 }