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   1 /*
   2     graph.c -- graph algorithms
   3     Copyright (C) 2001-2012 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 "splay_tree.h"
  48 #include "config.h"
  49 #include "connection.h"
  50 #include "device.h"
  51 #include "edge.h"
  52 #include "graph.h"
  53 #include "logger.h"
  54 #include "netutl.h"
  55 #include "node.h"
  56 #include "process.h"
  57 #include "protocol.h"
  58 #include "subnet.h"
  59 #include "utils.h"
  60 #include "xalloc.h"
  61 #include "graph.h"
  62
  63 /* Implementation of Kruskal's algorithm.
  64    Running time: O(E)
  65    Please note that sorting on weight is already done by add_edge().
  66 */
  67
  68 static void mst_kruskal(void) {
  69         splay_node_t *node, *next;
  70         edge_t *e;
  71         node_t *n;
  72         connection_t *c;
  73
  74         /* Clear MST status on connections */
  75
  76         for(node = connection_tree->head; node; node = node->next) {
  77                 c = node->data;
  78                 c->status.mst = false;
  79         }
  80
  81         logger(DEBUG_SCARY_THINGS, LOG_DEBUG, "Running Kruskal's algorithm:");
  82
  83         /* Clear visited status on nodes */
  84
  85         for(node = node_tree->head; node; node = node->next) {
  86                 n = node->data;
  87                 n->status.visited = false;
  88         }
  89
  90         /* Add safe edges */
  91
  92         for(node = edge_weight_tree->head; node; node = next) {
  93                 next = node->next;
  94                 e = node->data;
  95
  96                 if(!e->reverse || (e->from->status.visited && e->to->status.visited))
  97                         continue;
  98
  99                 e->from->status.visited = true;
 100                 e->to->status.visited = true;
 101
 102                 if(e->connection)
 103                         e->connection->status.mst = true;
 104
 105                 if(e->reverse->connection)
 106                         e->reverse->connection->status.mst = true;
 107
 108                 logger(DEBUG_SCARY_THINGS, LOG_DEBUG, " Adding edge %s - %s weight %d", e->from->name,
 109                                    e->to->name, e->weight);
 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         splay_node_t *node, *to;
 119         edge_t *e;
 120         node_t *n;
 121         list_t *todo_list;
 122         list_node_t *from, *todonext;
 123         bool indirect;
 124
 125         todo_list = list_alloc(NULL);
 126
 127         /* Clear visited status on nodes */
 128
 129         for(node = node_tree->head; node; node = node->next) {
 130                 n = node->data;
 131                 n->status.visited = false;
 132                 n->status.indirect = true;
 133                 n->distance = -1;
 134         }
 135
 136         /* Begin with myself */
 137
 138         myself->status.visited = true;
 139         myself->status.indirect = false;
 140         myself->nexthop = myself;
 141         myself->prevedge = NULL;
 142         myself->via = myself;
 143         myself->distance = 0;
 144         list_insert_head(todo_list, myself);
 145
 146         /* Loop while todo_list is filled */
 147
 148         for(from = todo_list->head; from; from = todonext) {    /* "from" is the node from which we start */
 149                 n = from->data;
 150                 if(n->distance < 0)
 151                         abort();
 152
 153                 for(to = n->edge_tree->head; to; to = to->next) {       /* "to" is the edge connected to "from" */
 154                         e = to->data;
 155
 156                         if(!e->reverse)
 157                                 continue;
 158
 159                         /* Situation:
 160
 161                                    /
 162                                   /
 163                            ----->(n)---e-->(e->to)
 164                                   \
 165                                    \
 166
 167                            Where e is an edge, (n) and (e->to) are nodes.
 168                            n->address is set to the e->address of the edge left of n to n.
 169                            We are currently examining the edge e right of n from n:
 170
 171                            - If edge e provides for better reachability of e->to, update
 172                              e->to and (re)add it to the todo_list to (re)examine the reachability
 173                              of nodes behind it.
 174                          */
 175
 176                         indirect = n->status.indirect || e->options & OPTION_INDIRECT;
 177
 178                         if(e->to->status.visited
 179                            && (!e->to->status.indirect || indirect)
 180                            && (e->to->distance != n->distance + 1 || e->weight >= e->to->prevedge->weight))
 181                                 continue;
 182
 183                         e->to->status.visited = true;
 184                         e->to->status.indirect = indirect;
 185                         e->to->nexthop = (n->nexthop == myself) ? e->to : n->nexthop;
 186                         e->to->prevedge = e;
 187                         e->to->via = indirect ? n->via : e->to;
 188                         e->to->options = e->options;
 189                         e->to->distance = n->distance + 1;
 190
 191                         if(!e->to->status.reachable || (e->to->address.sa.sa_family == AF_UNSPEC && e->address.sa.sa_family != AF_UNKNOWN)
 192 )
 193                                 update_node_udp(e->to, &e->address);
 194
 195                         list_insert_tail(todo_list, e->to);
 196                 }
 197
 198                 todonext = from->next;
 199                 list_delete_node(todo_list, from);
 200         }
 201
 202         list_free(todo_list);
 203 }
 204
 205 static void check_reachability(void) {
 206         splay_node_t *node, *next;
 207         node_t *n;
 208         char *name;
 209         char *address, *port;
 210         char *envp[7];
 211         int i;
 212
 213         /* Check reachability status. */
 214
 215         for(node = node_tree->head; node; node = next) {
 216                 next = node->next;
 217                 n = node->data;
 218
 219                 if(n->status.visited != n->status.reachable) {
 220                         n->status.reachable = !n->status.reachable;
 221                         n->last_state_change = time(NULL);
 222
 223                         if(n->status.reachable) {
 224                                 logger(DEBUG_TRAFFIC, LOG_DEBUG, "Node %s (%s) became reachable",
 225                                            n->name, n->hostname);
 226                         } else {
 227                                 logger(DEBUG_TRAFFIC, LOG_DEBUG, "Node %s (%s) became unreachable",
 228                                            n->name, n->hostname);
 229                         }
 230
 231                         if(experimental && OPTION_VERSION(n->options) >= 2)
 232                                 n->status.sptps = true;
 233
 234                         /* TODO: only clear status.validkey if node is unreachable? */
 235
 236                         n->status.validkey = false;
 237                         n->last_req_key = 0;
 238
 239                         n->maxmtu = MTU;
 240                         n->minmtu = 0;
 241                         n->mtuprobes = 0;
 242
 243                         if(timeout_initialized(&n->mtuevent))
 244                                 event_del(&n->mtuevent);
 245
 246                         xasprintf(&envp[0], "NETNAME=%s", netname ? : "");
 247                         xasprintf(&envp[1], "DEVICE=%s", device ? : "");
 248                         xasprintf(&envp[2], "INTERFACE=%s", iface ? : "");
 249                         xasprintf(&envp[3], "NODE=%s", n->name);
 250                         sockaddr2str(&n->address, &address, &port);
 251                         xasprintf(&envp[4], "REMOTEADDRESS=%s", address);
 252                         xasprintf(&envp[5], "REMOTEPORT=%s", port);
 253                         envp[6] = NULL;
 254
 255                         execute_script(n->status.reachable ? "host-up" : "host-down", envp);
 256
 257                         xasprintf(&name,
 258                                          n->status.reachable ? "hosts/%s-up" : "hosts/%s-down",
 259                                          n->name);
 260                         execute_script(name, envp);
 261
 262                         free(name);
 263                         free(address);
 264                         free(port);
 265
 266                         for(i = 0; i < 6; i++)
 267                                 free(envp[i]);
 268
 269                         subnet_update(n, NULL, n->status.reachable);
 270
 271                         if(!n->status.reachable) {
 272                                 update_node_udp(n, NULL);
 273                         } else if(n->connection) {
 274                                 if(n->status.sptps) {
 275                                         if(n->connection->outgoing)
 276                                                 send_req_key(n);
 277                                 } else {
 278                                         send_ans_key(n);
 279                                 }
 280                         }
 281                 }
 282         }
 283 }
 284
 285 void graph(void) {
 286         subnet_cache_flush();
 287         sssp_bfs();
 288         check_reachability();
 289         mst_kruskal();
 290 }