src/graph.c

   1 /*
   2     graph.c -- graph algorithms
   3     Copyright (C) 2001-2006 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
  17     along with this program; if not, write to the Free Software
  18     Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  19
  20     $Id$
  21 */
  22
  23 /* We need to generate two trees from the graph:
  24
  25    1. A minimum spanning tree for broadcasts,
  26    2. A single-source shortest path tree for unicasts.
  27
  28    Actually, the first one alone would suffice but would make unicast packets
  29    take longer routes than necessary.
  30
  31    For the MST algorithm we can choose from Prim's or Kruskal's. I personally
  32    favour Kruskal's, because we make an extra AVL tree of edges sorted on
  33    weights (metric). That tree only has to be updated when an edge is added or
  34    removed, and during the MST algorithm we just have go linearly through that
  35    tree, adding safe edges until #edges = #nodes - 1. The implementation here
  36    however is not so fast, because I tried to avoid having to make a forest and
  37    merge trees.
  38
  39    For the SSSP algorithm Dijkstra's seems to be a nice choice. Currently a
  40    simple breadth-first search is presented here.
  41
  42    The SSSP algorithm will also be used to determine whether nodes are directly,
  43    indirectly or not reachable from the source. It will also set the correct
  44    destination address and port of a node if possible.
  45 */
  46
  47 #include "system.h"
  48
  49 #include "avl_tree.h"
  50 #include "connection.h"
  51 #include "device.h"
  52 #include "edge.h"
  53 #include "logger.h"
  54 #include "netutl.h"
  55 #include "node.h"
  56 #include "process.h"
  57 #include "subnet.h"
  58 #include "utils.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 void mst_kruskal(void)
  66 {
  67         avl_node_t *node, *next;
  68         edge_t *e;
  69         node_t *n;
  70         connection_t *c;
  71         int nodes = 0;
  72         int safe_edges = 0;
  73         bool skipped;
  74
  75         cp();
  76
  77         /* Clear MST status on connections */
  78
  79         for(node = connection_tree->head; node; node = node->next) {
  80                 c = node->data;
  81                 c->status.mst = false;
  82         }
  83
  84         /* Do we have something to do at all? */
  85
  86         if(!edge_weight_tree->head)
  87                 return;
  88
  89         ifdebug(SCARY_THINGS) logger(LOG_DEBUG, "Running Kruskal's algorithm:");
  90
  91         /* Clear visited status on nodes */
  92
  93         for(node = node_tree->head; node; node = node->next) {
  94                 n = node->data;
  95                 n->status.visited = false;
  96                 nodes++;
  97         }
  98
  99         /* Starting point */
 100
 101         ((edge_t *) edge_weight_tree->head->data)->from->status.visited = true;
 102
 103         /* Add safe edges */
 104
 105         for(skipped = false, node = edge_weight_tree->head; node; node = next) {
 106                 next = node->next;
 107                 e = node->data;
 108
 109                 if(!e->reverse || e->from->status.visited == e->to->status.visited) {
 110                         skipped = true;
 111                         continue;
 112                 }
 113
 114                 e->from->status.visited = true;
 115                 e->to->status.visited = true;
 116
 117                 if(e->connection)
 118                         e->connection->status.mst = true;
 119
 120                 if(e->reverse->connection)
 121                         e->reverse->connection->status.mst = true;
 122
 123                 safe_edges++;
 124
 125                 ifdebug(SCARY_THINGS) logger(LOG_DEBUG, " Adding edge %s - %s weight %d", e->from->name,
 126                                    e->to->name, e->weight);
 127
 128                 if(skipped) {
 129                         skipped = false;
 130                         next = edge_weight_tree->head;
 131                         continue;
 132                 }
 133         }
 134
 135         ifdebug(SCARY_THINGS) logger(LOG_DEBUG, "Done, counted %d nodes and %d safe edges.", nodes,
 136                            safe_edges);
 137 }
 138
 139 /* Implementation of a simple breadth-first search algorithm.
 140    Running time: O(E)
 141 */
 142
 143 void sssp_bfs(void)
 144 {
 145         avl_node_t *node, *next, *to;
 146         edge_t *e;
 147         node_t *n;
 148         list_t *todo_list;
 149         list_node_t *from, *todonext;
 150         bool indirect;
 151         char *name;
 152         char *address, *port;
 153         char *envp[7];
 154         int i;
 155
 156         cp();
 157
 158         todo_list = list_alloc(NULL);
 159
 160         /* Clear visited status on nodes */
 161
 162         for(node = node_tree->head; node; node = node->next) {
 163                 n = node->data;
 164                 n->status.visited = false;
 165                 n->status.indirect = true;
 166         }
 167
 168         /* Begin with myself */
 169
 170         myself->status.visited = true;
 171         myself->status.indirect = false;
 172         myself->nexthop = myself;
 173         myself->via = myself;
 174         list_insert_head(todo_list, myself);
 175
 176         /* Loop while todo_list is filled */
 177
 178         for(from = todo_list->head; from; from = todonext) {    /* "from" is the node from which we start */
 179                 n = from->data;
 180
 181                 for(to = n->edge_tree->head; to; to = to->next) {       /* "to" is the edge connected to "from" */
 182                         e = to->data;
 183
 184                         if(!e->reverse)
 185                                 continue;
 186
 187                         /* Situation:
 188
 189                                    /
 190                                   /
 191                            ----->(n)---e-->(e->to)
 192                                   \
 193                                    \
 194
 195                            Where e is an edge, (n) and (e->to) are nodes.
 196                            n->address is set to the e->address of the edge left of n to n.
 197                            We are currently examining the edge e right of n from n:
 198
 199                            - If e->reverse->address != n->address, then e->to is probably
 200                              not reachable for the nodes left of n. We do as if the indirectdata
 201                              flag is set on edge e.
 202                            - If edge e provides for better reachability of e->to, update
 203                              e->to and (re)add it to the todo_list to (re)examine the reachability
 204                              of nodes behind it.
 205                          */
 206
 207                         indirect = n->status.indirect || e->options & OPTION_INDIRECT
 208                                 || ((n != myself) && sockaddrcmp(&n->address, &e->reverse->address));
 209
 210                         if(e->to->status.visited
 211                            && (!e->to->status.indirect || indirect))
 212                                 continue;
 213
 214                         e->to->status.visited = true;
 215                         e->to->status.indirect = indirect;
 216                         e->to->nexthop = (n->nexthop == myself) ? e->to : n->nexthop;
 217                         e->to->via = indirect ? n->via : e->to;
 218                         e->to->options = e->options;
 219
 220                         if(sockaddrcmp(&e->to->address, &e->address)) {
 221                                 node = avl_unlink(node_udp_tree, e->to);
 222                                 sockaddrfree(&e->to->address);
 223                                 sockaddrcpy(&e->to->address, &e->address);
 224
 225                                 if(e->to->hostname)
 226                                         free(e->to->hostname);
 227
 228                                 e->to->hostname = sockaddr2hostname(&e->to->address);
 229
 230                                 if(node)
 231                                         avl_insert_node(node_udp_tree, node);
 232
 233                                 if(e->to->options & OPTION_PMTU_DISCOVERY) {
 234                                         e->to->mtuprobes = 0;
 235                                         e->to->minmtu = 0;
 236                                         e->to->maxmtu = MTU;
 237                                         if(e->to->status.validkey)
 238                                                 send_mtu_probe(e->to);
 239                                 }
 240                         }
 241
 242                         list_insert_tail(todo_list, e->to);
 243                 }
 244
 245                 todonext = from->next;
 246                 list_delete_node(todo_list, from);
 247         }
 248
 249         list_free(todo_list);
 250
 251         /* Check reachability status. */
 252
 253         for(node = node_tree->head; node; node = next) {
 254                 next = node->next;
 255                 n = node->data;
 256
 257                 if(n->status.visited != n->status.reachable) {
 258                         n->status.reachable = !n->status.reachable;
 259
 260                         if(n->status.reachable) {
 261                                 ifdebug(TRAFFIC) logger(LOG_DEBUG, _("Node %s (%s) became reachable"),
 262                                            n->name, n->hostname);
 263                                 avl_insert(node_udp_tree, n);
 264                         } else {
 265                                 ifdebug(TRAFFIC) logger(LOG_DEBUG, _("Node %s (%s) became unreachable"),
 266                                            n->name, n->hostname);
 267                                 avl_delete(node_udp_tree, n);
 268                         }
 269
 270                         n->status.validkey = false;
 271                         n->status.waitingforkey = false;
 272
 273                         n->maxmtu = MTU;
 274                         n->minmtu = 0;
 275                         n->mtuprobes = 0;
 276
 277                         asprintf(&envp[0], "NETNAME=%s", netname ? : "");
 278                         asprintf(&envp[1], "DEVICE=%s", device ? : "");
 279                         asprintf(&envp[2], "INTERFACE=%s", iface ? : "");
 280                         asprintf(&envp[3], "NODE=%s", n->name);
 281                         sockaddr2str(&n->address, &address, &port);
 282                         asprintf(&envp[4], "REMOTEADDRESS=%s", address);
 283                         asprintf(&envp[5], "REMOTEPORT=%s", port);
 284                         envp[6] = NULL;
 285
 286                         asprintf(&name,
 287                                          n->status.reachable ? "hosts/%s-up" : "hosts/%s-down",
 288                                          n->name);
 289                         execute_script(name, envp);
 290
 291                         free(name);
 292                         free(address);
 293                         free(port);
 294
 295                         for(i = 0; i < 6; i++)
 296                                 free(envp[i]);
 297
 298                         subnet_update(n, NULL, n->status.reachable);
 299                 }
 300         }
 301 }
 302
 303 void graph(void)
 304 {
 305         mst_kruskal();
 306         sssp_bfs();
 307 }