src/graph.c

   1 /*
   2     graph.c -- graph algorithms
   3     Copyright (C) 2001-2013 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 "connection.h"
  48 #include "device.h"
  49 #include "edge.h"
  50 #include "graph.h"
  51 #include "list.h"
  52 #include "logger.h"
  53 #include "names.h"
  54 #include "netutl.h"
  55 #include "node.h"
  56 #include "protocol.h"
  57 #include "script.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(EN)
  65    Please note that sorting on weight is already done by add_edge().
  66 */
  67
  68 static void mst_kruskal(void) {
  69         /* Clear MST status on connections */
  70
  71         for list_each(connection_t, c, connection_list)
  72                 c->status.mst = false;
  73
  74         logger(DEBUG_SCARY_THINGS, LOG_DEBUG, "Running Kruskal's algorithm:");
  75
  76         /* Clear visited status on nodes */
  77
  78         for splay_each(node_t, n, node_tree)
  79                 n->status.visited = false;
  80
  81         /* Starting point */
  82
  83         for splay_each(edge_t, e, edge_weight_tree) {
  84                 if(e->from->status.reachable) {
  85                         e->from->status.visited = true;
  86                         break;
  87                 }
  88         }
  89
  90         /* Add safe edges */
  91
  92         bool skipped = false;
  93
  94         for splay_each(edge_t, e, edge_weight_tree) {
  95                 if(!e->reverse || (e->from->status.visited == e->to->status.visited)) {
  96                         skipped = true;
  97                         continue;
  98                 }
  99
 100                 e->from->status.visited = true;
 101                 e->to->status.visited = true;
 102
 103                 if(e->connection)
 104                         e->connection->status.mst = true;
 105
 106                 if(e->reverse->connection)
 107                         e->reverse->connection->status.mst = true;
 108
 109                 logger(DEBUG_SCARY_THINGS, LOG_DEBUG, " Adding edge %s - %s weight %d", e->from->name, e->to->name, e->weight);
 110
 111                 if(skipped) {
 112                         skipped = false;
 113                         next = edge_weight_tree->head;
 114                 }
 115         }
 116 }
 117
 118 /* Implementation of a simple breadth-first search algorithm.
 119    Running time: O(E)
 120 */
 121
 122 static void sssp_bfs(void) {
 123         list_t *todo_list = list_alloc(NULL);
 124
 125         /* Clear visited status on nodes */
 126
 127         for splay_each(node_t, n, node_tree) {
 128                 n->status.visited = false;
 129                 n->status.indirect = true;
 130                 n->distance = -1;
 131         }
 132
 133         /* Begin with myself */
 134
 135         myself->status.visited = true;
 136         myself->status.indirect = false;
 137         myself->nexthop = myself;
 138         myself->prevedge = NULL;
 139         myself->via = myself;
 140         myself->distance = 0;
 141         list_insert_head(todo_list, myself);
 142
 143         /* Loop while todo_list is filled */
 144
 145         for list_each(node_t, n, todo_list) {                   /* "n" is the node from which we start */
 146                 logger(DEBUG_SCARY_THINGS, LOG_DEBUG, " Examining edges from %s", n->name);
 147
 148                 if(n->distance < 0)
 149                         abort();
 150
 151                 for splay_each(edge_t, e, n->edge_tree) {       /* "e" is the edge connected to "from" */
 152                         if(!e->reverse)
 153                                 continue;
 154
 155                         /* Situation:
 156
 157                                    /
 158                                   /
 159                            ----->(n)---e-->(e->to)
 160                                   \
 161                                    \
 162
 163                            Where e is an edge, (n) and (e->to) are nodes.
 164                            n->address is set to the e->address of the edge left of n to n.
 165                            We are currently examining the edge e right of n from n:
 166
 167                            - If edge e provides for better reachability of e->to, update
 168                              e->to and (re)add it to the todo_list to (re)examine the reachability
 169                              of nodes behind it.
 170                          */
 171
 172                         bool indirect = n->status.indirect || e->options & OPTION_INDIRECT;
 173
 174                         if(e->to->status.visited
 175                            && (!e->to->status.indirect || indirect)
 176                            && (e->to->distance != n->distance + 1 || e->weight >= e->to->prevedge->weight))
 177                                 continue;
 178
 179                         // Only update nexthop if it doesn't increase the path length
 180
 181                         if(!e->to->status.visited || (e->to->distance == n->distance + 1 && e->weight >= e->to->prevedge->weight))
 182                                 e->to->nexthop = (n->nexthop == myself) ? e->to : n->nexthop;
 183
 184                         e->to->status.visited = true;
 185                         e->to->status.indirect = indirect;
 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                                 update_node_udp(e->to, &e->address);
 193
 194                         list_insert_tail(todo_list, e->to);
 195                 }
 196
 197                 next = node->next; /* Because the list_insert_tail() above could have added something extra for us! */
 198                 list_delete_node(todo_list, node);
 199         }
 200
 201         list_free(todo_list);
 202 }
 203
 204 static void check_reachability(void) {
 205         /* Check reachability status. */
 206
 207         int reachable_count = 0;
 208         int became_reachable_count = 0;
 209         int became_unreachable_count = 0;
 210         for splay_each(node_t, n, node_tree) {
 211                 if(n->status.visited != n->status.reachable) {
 212                         n->status.reachable = !n->status.reachable;
 213                         n->last_state_change = now.tv_sec;
 214
 215                         if(n->status.reachable) {
 216                                 logger(DEBUG_TRAFFIC, LOG_DEBUG, "Node %s (%s) became reachable",
 217                                            n->name, n->hostname);
 218                                 if (n != myself)
 219                                         became_reachable_count++;
 220                         } else {
 221                                 logger(DEBUG_TRAFFIC, LOG_DEBUG, "Node %s (%s) became unreachable",
 222                                            n->name, n->hostname);
 223                                 if (n != myself)
 224                                         became_unreachable_count++;
 225                         }
 226
 227                         if(experimental && OPTION_VERSION(n->options) >= 2)
 228                                 n->status.sptps = true;
 229
 230                         /* TODO: only clear status.validkey if node is unreachable? */
 231
 232                         n->status.validkey = false;
 233                         if(n->status.sptps) {
 234                                 sptps_stop(&n->sptps);
 235                                 n->status.waitingforkey = false;
 236                         }
 237                         n->last_req_key = 0;
 238
 239                         n->status.udp_confirmed = false;
 240                         n->maxmtu = MTU;
 241                         n->minmtu = 0;
 242                         n->mtuprobes = 0;
 243
 244                         timeout_del(&n->mtutimeout);
 245
 246                         char *name;
 247                         char *address;
 248                         char *port;
 249                         char *envp[8] = {NULL};
 250
 251                         xasprintf(&envp[0], "NETNAME=%s", netname ? : "");
 252                         xasprintf(&envp[1], "DEVICE=%s", device ? : "");
 253                         xasprintf(&envp[2], "INTERFACE=%s", iface ? : "");
 254                         xasprintf(&envp[3], "NODE=%s", n->name);
 255                         sockaddr2str(&n->address, &address, &port);
 256                         xasprintf(&envp[4], "REMOTEADDRESS=%s", address);
 257                         xasprintf(&envp[5], "REMOTEPORT=%s", port);
 258                         xasprintf(&envp[6], "NAME=%s", myself->name);
 259
 260                         execute_script(n->status.reachable ? "host-up" : "host-down", envp);
 261
 262                         xasprintf(&name, n->status.reachable ? "hosts/%s-up" : "hosts/%s-down", n->name);
 263                         execute_script(name, envp);
 264
 265                         free(name);
 266                         free(address);
 267                         free(port);
 268
 269                         for(int i = 0; i < 7; i++)
 270                                 free(envp[i]);
 271
 272                         subnet_update(n, NULL, n->status.reachable);
 273
 274                         if(!n->status.reachable) {
 275                                 update_node_udp(n, NULL);
 276                                 memset(&n->status, 0, sizeof n->status);
 277                                 n->options = 0;
 278                         }
 279                 }
 280
 281                 if(n->status.reachable && n != myself)
 282                         reachable_count++;
 283         }
 284
 285         if (device_standby) {
 286                 if (reachable_count == 0 && became_unreachable_count > 0)
 287                         device_disable();
 288                 else if (reachable_count > 0 && reachable_count == became_reachable_count)
 289                         device_enable();
 290         }
 291 }
 292
 293 void graph(void) {
 294         subnet_cache_flush();
 295         sssp_bfs();
 296         check_reachability();
 297         mst_kruskal();
 298 }