git.meshlink.io Git - meshlink/blob - src/graph.c

   1 /*
   2     graph.c -- graph algorithms
   3     Copyright (C) 2014 Guus Sliepen <guus@meshlink.io>
   4
   5     This program is free software; you can redistribute it and/or modify
   6     it under the terms of the GNU General Public License as published by
   7     the Free Software Foundation; either version 2 of the License, or
   8     (at your option) any later version.
   9
  10     This program is distributed in the hope that it will be useful,
  11     but WITHOUT ANY WARRANTY; without even the implied warranty of
  12     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13     GNU General Public License for more details.
  14
  15     You should have received a copy of the GNU General Public License along
  16     with this program; if not, write to the Free Software Foundation, Inc.,
  17     51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  18 */
  19
  20 /* We need to generate two trees from the graph:
  21
  22    1. A minimum spanning tree for broadcasts,
  23    2. A single-source shortest path tree for unicasts.
  24
  25    Actually, the first one alone would suffice but would make unicast packets
  26    take longer routes than necessary.
  27
  28    For the MST algorithm we can choose from Prim's or Kruskal's. I personally
  29    favour Kruskal's, because we make an extra AVL tree of edges sorted on
  30    weights (metric). That tree only has to be updated when an edge is added or
  31    removed, and during the MST algorithm we just have go linearly through that
  32    tree, adding safe edges until #edges = #nodes - 1. The implementation here
  33    however is not so fast, because I tried to avoid having to make a forest and
  34    merge trees.
  35
  36    For the SSSP algorithm Dijkstra's seems to be a nice choice. Currently a
  37    simple breadth-first search is presented here.
  38
  39    The SSSP algorithm will also be used to determine whether nodes are directly,
  40    indirectly or not reachable from the source. It will also set the correct
  41    destination address and port of a node if possible.
  42 */
  43
  44 #include "system.h"
  45
  46 #include "connection.h"
  47 #include "edge.h"
  48 #include "graph.h"
  49 #include "list.h"
  50 #include "logger.h"
  51 #include "netutl.h"
  52 #include "node.h"
  53 #include "protocol.h"
  54 #include "utils.h"
  55 #include "xalloc.h"
  56 #include "graph.h"
  57
  58 /* Implementation of Kruskal's algorithm.
  59    Running time: O(EN)
  60    Please note that sorting on weight is already done by add_edge().
  61 */
  62
  63 static void mst_kruskal(void) {
  64         /* Clear MST status on connections */
  65
  66         for list_each(connection_t, c, connection_list)
  67                 c->status.mst = false;
  68
  69         logger(DEBUG_SCARY_THINGS, LOG_DEBUG, "Running Kruskal's algorithm:");
  70
  71         /* Clear visited status on nodes */
  72
  73         for splay_each(node_t, n, node_tree)
  74                 n->status.visited = false;
  75
  76         /* Starting point */
  77
  78         for splay_each(edge_t, e, edge_weight_tree) {
  79                 if(e->from->status.reachable) {
  80                         e->from->status.visited = true;
  81                         break;
  82                 }
  83         }
  84
  85         /* Add safe edges */
  86
  87         bool skipped = false;
  88
  89         for splay_each(edge_t, e, edge_weight_tree) {
  90                 if(!e->reverse || (e->from->status.visited == e->to->status.visited)) {
  91                         skipped = true;
  92                         continue;
  93                 }
  94
  95                 e->from->status.visited = true;
  96                 e->to->status.visited = true;
  97
  98                 if(e->connection)
  99                         e->connection->status.mst = true;
 100
 101                 if(e->reverse->connection)
 102                         e->reverse->connection->status.mst = true;
 103
 104                 logger(DEBUG_SCARY_THINGS, LOG_DEBUG, " Adding edge %s - %s weight %d", e->from->name, e->to->name, e->weight);
 105
 106                 if(skipped) {
 107                         skipped = false;
 108                         next = edge_weight_tree->head;
 109                 }
 110         }
 111 }
 112
 113 /* Implementation of a simple breadth-first search algorithm.
 114    Running time: O(E)
 115 */
 116
 117 static void sssp_bfs(void) {
 118         list_t *todo_list = list_alloc(NULL);
 119
 120         /* Clear visited status on nodes */
 121
 122         for splay_each(node_t, n, node_tree) {
 123                 n->status.visited = false;
 124                 n->status.indirect = true;
 125                 n->distance = -1;
 126         }
 127
 128         /* Begin with myself */
 129
 130         myself->status.visited = true;
 131         myself->status.indirect = false;
 132         myself->nexthop = myself;
 133         myself->prevedge = NULL;
 134         myself->via = myself;
 135         myself->distance = 0;
 136         list_insert_head(todo_list, myself);
 137
 138         /* Loop while todo_list is filled */
 139
 140         for list_each(node_t, n, todo_list) {                   /* "n" is the node from which we start */
 141                 logger(DEBUG_SCARY_THINGS, LOG_DEBUG, " Examining edges from %s", n->name);
 142
 143                 if(n->distance < 0)
 144                         abort();
 145
 146                 for splay_each(edge_t, e, n->edge_tree) {       /* "e" is the edge connected to "from" */
 147                         if(!e->reverse)
 148                                 continue;
 149
 150                         /* Situation:
 151
 152                                    /
 153                                   /
 154                            ----->(n)---e-->(e->to)
 155                                   \
 156                                    \
 157
 158                            Where e is an edge, (n) and (e->to) are nodes.
 159                            n->address is set to the e->address of the edge left of n to n.
 160                            We are currently examining the edge e right of n from n:
 161
 162                            - If edge e provides for better reachability of e->to, update
 163                              e->to and (re)add it to the todo_list to (re)examine the reachability
 164                              of nodes behind it.
 165                          */
 166
 167                         bool indirect = n->status.indirect || e->options & OPTION_INDIRECT;
 168
 169                         if(e->to->status.visited
 170                            && (!e->to->status.indirect || indirect)
 171                            && (e->to->distance != n->distance + 1 || e->weight >= e->to->prevedge->weight))
 172                                 continue;
 173
 174                         e->to->status.visited = true;
 175                         e->to->status.indirect = indirect;
 176                         e->to->nexthop = (n->nexthop == myself) ? e->to : n->nexthop;
 177                         e->to->prevedge = e;
 178                         e->to->via = indirect ? n->via : e->to;
 179                         e->to->options = e->options;
 180                         e->to->distance = n->distance + 1;
 181
 182                         if(!e->to->status.reachable || (e->to->address.sa.sa_family == AF_UNSPEC && e->address.sa.sa_family != AF_UNKNOWN))
 183                                 update_node_udp(e->to, &e->address);
 184
 185                         list_insert_tail(todo_list, e->to);
 186                 }
 187
 188                 next = node->next; /* Because the list_insert_tail() above could have added something extra for us! */
 189                 list_delete_node(todo_list, node);
 190         }
 191
 192         list_free(todo_list);
 193 }
 194
 195 static void check_reachability(void) {
 196         /* Check reachability status. */
 197
 198         for splay_each(node_t, n, node_tree) {
 199                 if(n->status.visited != n->status.reachable) {
 200                         n->status.reachable = !n->status.reachable;
 201                         n->last_state_change = now.tv_sec;
 202
 203                         if(n->status.reachable) {
 204                                 logger(DEBUG_TRAFFIC, LOG_DEBUG, "Node %s (%s) became reachable",
 205                                            n->name, n->hostname);
 206                         } else {
 207                                 logger(DEBUG_TRAFFIC, LOG_DEBUG, "Node %s (%s) became unreachable",
 208                                            n->name, n->hostname);
 209                         }
 210
 211                         if(experimental && OPTION_VERSION(n->options) >= 2)
 212                                 n->status.sptps = true;
 213
 214                         /* TODO: only clear status.validkey if node is unreachable? */
 215
 216                         n->status.validkey = false;
 217                         if(n->status.sptps) {
 218                                 sptps_stop(&n->sptps);
 219                                 n->status.waitingforkey = false;
 220                         }
 221                         n->last_req_key = 0;
 222
 223                         n->status.udp_confirmed = false;
 224                         n->maxmtu = MTU;
 225                         n->minmtu = 0;
 226                         n->mtuprobes = 0;
 227
 228                         timeout_del(&n->mtutimeout);
 229
 230                         //TODO: callback to application to inform of this node going up/down
 231
 232                         if(!n->status.reachable) {
 233                                 update_node_udp(n, NULL);
 234                                 memset(&n->status, 0, sizeof n->status);
 235                                 n->options = 0;
 236                         } else if(n->connection) {
 237                                 if(n->status.sptps) {
 238                                         if(n->connection->outgoing)
 239                                                 send_req_key(n);
 240                                 } else {
 241                                         send_ans_key(n);
 242                                 }
 243                         }
 244                 }
 245         }
 246 }
 247
 248 void graph(void) {
 249         sssp_bfs();
 250         check_reachability();
 251         mst_kruskal();
 252 }