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

   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->address.sa.sa_family == AF_UNSPEC && e->address.sa.sa_family != AF_UNKNOWN)
 192                                 update_node_udp(e->to, &e->address);
 193
 194                         list_insert_tail(todo_list, e->to);
 195                 }
 196
 197                 todonext = from->next;
 198                 list_delete_node(todo_list, from);
 199         }
 200
 201         list_free(todo_list);
 202 }
 203
 204 static void check_reachability(void) {
 205         splay_node_t *node, *next;
 206         node_t *n;
 207         char *name;
 208         char *address, *port;
 209         char *envp[7];
 210         int i;
 211
 212         /* Check reachability status. */
 213
 214         for(node = node_tree->head; node; node = next) {
 215                 next = node->next;
 216                 n = node->data;
 217
 218                 if(n->status.visited != n->status.reachable) {
 219                         n->status.reachable = !n->status.reachable;
 220
 221                         if(n->status.reachable) {
 222                                 logger(DEBUG_TRAFFIC, LOG_DEBUG, "Node %s (%s) became reachable",
 223                                            n->name, n->hostname);
 224                         } else {
 225                                 logger(DEBUG_TRAFFIC, LOG_DEBUG, "Node %s (%s) became unreachable",
 226                                            n->name, n->hostname);
 227                         }
 228
 229                         /* TODO: only clear status.validkey if node is unreachable? */
 230
 231                         n->status.validkey = false;
 232                         n->last_req_key = 0;
 233
 234                         n->maxmtu = MTU;
 235                         n->minmtu = 0;
 236                         n->mtuprobes = 0;
 237
 238                         if(timeout_initialized(&n->mtuevent))
 239                                 event_del(&n->mtuevent);
 240
 241                         xasprintf(&envp[0], "NETNAME=%s", netname ? : "");
 242                         xasprintf(&envp[1], "DEVICE=%s", device ? : "");
 243                         xasprintf(&envp[2], "INTERFACE=%s", iface ? : "");
 244                         xasprintf(&envp[3], "NODE=%s", n->name);
 245                         sockaddr2str(&n->address, &address, &port);
 246                         xasprintf(&envp[4], "REMOTEADDRESS=%s", address);
 247                         xasprintf(&envp[5], "REMOTEPORT=%s", port);
 248                         envp[6] = NULL;
 249
 250                         execute_script(n->status.reachable ? "host-up" : "host-down", envp);
 251
 252                         xasprintf(&name,
 253                                          n->status.reachable ? "hosts/%s-up" : "hosts/%s-down",
 254                                          n->name);
 255                         execute_script(name, envp);
 256
 257                         free(name);
 258                         free(address);
 259                         free(port);
 260
 261                         for(i = 0; i < 6; i++)
 262                                 free(envp[i]);
 263
 264                         subnet_update(n, NULL, n->status.reachable);
 265
 266                         if(!n->status.reachable)
 267                                 update_node_udp(n, NULL);
 268                         else if(n->connection)
 269                                 send_ans_key(n);
 270                 }
 271         }
 272 }
 273
 274 void graph(void) {
 275         subnet_cache_flush();
 276         sssp_bfs();
 277         check_reachability();
 278         mst_kruskal();
 279 }