2 graph.c -- graph algorithms
3 Copyright (C) 2001-2017 Guus Sliepen <guus@tinc-vpn.org>,
4 2001-2005 Ivo Timmermans
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.
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.
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.
21 /* We need to generate two trees from the graph:
23 1. A minimum spanning tree for broadcasts,
24 2. A single-source shortest path tree for unicasts.
26 Actually, the first one alone would suffice but would make unicast packets
27 take longer routes than necessary.
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
37 For the SSSP algorithm Dijkstra's seems to be a nice choice. Currently a
38 simple breadth-first search is presented here.
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.
47 #include "connection.h"
58 #include "address_cache.h"
60 /* Implementation of Kruskal's algorithm.
62 Please note that sorting on weight is already done by add_edge().
65 static void mst_kruskal(void) {
66 /* Clear MST status on connections */
68 for list_each(connection_t, c, &connection_list) {
69 c->status.mst = false;
72 logger(DEBUG_SCARY_THINGS, LOG_DEBUG, "Running Kruskal's algorithm:");
74 /* Clear visited status on nodes */
76 for splay_each(node_t, n, &node_tree) {
77 n->status.visited = false;
82 for splay_each(edge_t, e, &edge_weight_tree) {
83 if(e->from->status.reachable) {
84 e->from->status.visited = true;
93 for splay_each(edge_t, e, &edge_weight_tree) {
94 if(!e->reverse || (e->from->status.visited == e->to->status.visited)) {
99 e->from->status.visited = true;
100 e->to->status.visited = true;
103 e->connection->status.mst = true;
106 if(e->reverse->connection) {
107 e->reverse->connection->status.mst = true;
110 logger(DEBUG_SCARY_THINGS, LOG_DEBUG, " Adding edge %s - %s weight %d", e->from->name, e->to->name, e->weight);
114 next = edge_weight_tree.head;
119 // Not putting it into header, the outside world doesn't need to know about it.
120 extern void sssp_bfs(void);
122 /* Implementation of a simple breadth-first search algorithm.
125 void sssp_bfs(void) {
126 list_t *todo_list = list_alloc(NULL);
128 /* Clear visited status on nodes */
130 for splay_each(node_t, n, &node_tree) {
131 n->status.visited = false;
132 n->status.indirect = true;
136 /* Begin with myself */
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);
146 /* Loop while todo_list is filled */
148 for list_each(node_t, n, todo_list) { /* "n" is the node from which we start */
149 logger(DEBUG_SCARY_THINGS, LOG_DEBUG, " Examining edges from %s", n->name);
151 if(n->distance < 0) {
155 for splay_each(edge_t, e, &n->edge_tree) { /* "e" is the edge connected to "from" */
156 if(!e->reverse || e->to == myself) {
164 ----->(n)---e-->(e->to)
168 Where e is an edge, (n) and (e->to) are nodes.
169 n->address is set to the e->address of the edge left of n to n.
170 We are currently examining the edge e right of n from n:
172 - If edge e provides for better reachability of e->to, update
173 e->to and (re)add it to the todo_list to (re)examine the reachability
177 bool indirect = n->status.indirect || e->options & OPTION_INDIRECT;
179 if(e->to->status.visited
180 && (!e->to->status.indirect || indirect)
181 && (e->to->distance != n->distance + 1 || e->weight >= e->to->prevedge->weight)) {
185 // Only update nexthop if it doesn't increase the path length
187 if(!e->to->status.visited || (e->to->distance == n->distance + 1 && e->weight < e->to->prevedge->weight)) {
188 e->to->nexthop = (n->nexthop == myself) ? e->to : n->nexthop;
191 e->to->status.visited = true;
192 e->to->status.indirect = indirect;
194 e->to->via = indirect ? n->via : e->to;
195 e->to->options = e->options;
196 e->to->distance = n->distance + 1;
198 if(!e->to->status.reachable || (e->to->address.sa.sa_family == AF_UNSPEC && e->address.sa.sa_family != AF_UNKNOWN)) {
199 update_node_udp(e->to, &e->address);
202 list_insert_tail(todo_list, e->to);
205 next = node->next; /* Because the list_insert_tail() above could have added something extra for us! */
206 list_delete_node(todo_list, node);
209 list_free(todo_list);
212 static void check_reachability(void) {
213 /* Check reachability status. */
215 int reachable_count = 0;
216 int became_reachable_count = 0;
217 int became_unreachable_count = 0;
219 for splay_each(node_t, n, &node_tree) {
220 if(n->status.visited != n->status.reachable) {
221 n->status.reachable = !n->status.reachable;
222 n->last_state_change = now.tv_sec;
224 if(n->status.reachable) {
225 logger(DEBUG_TRAFFIC, LOG_DEBUG, "Node %s (%s) became reachable",
226 n->name, n->hostname);
229 became_reachable_count++;
231 if(n->connection && n->connection->outgoing) {
232 if(!n->address_cache) {
233 n->address_cache = open_address_cache(n);
236 add_recent_address(n->address_cache, &n->connection->address);
240 logger(DEBUG_TRAFFIC, LOG_DEBUG, "Node %s (%s) became unreachable",
241 n->name, n->hostname);
244 became_unreachable_count++;
248 if(experimental && OPTION_VERSION(n->options) >= 2) {
249 n->status.sptps = true;
252 /* TODO: only clear status.validkey if node is unreachable? */
254 n->status.validkey = false;
256 if(n->status.sptps) {
257 sptps_stop(&n->sptps);
258 n->status.waitingforkey = false;
263 n->status.udp_confirmed = false;
269 timeout_del(&n->udp_ping_timeout);
276 environment_init(&env);
277 environment_add(&env, "NODE=%s", n->name);
278 sockaddr2str(&n->address, &address, &port);
279 environment_add(&env, "REMOTEADDRESS=%s", address);
280 environment_add(&env, "REMOTEPORT=%s", port);
282 execute_script(n->status.reachable ? "host-up" : "host-down", &env);
284 xasprintf(&name, n->status.reachable ? "hosts/%s-up" : "hosts/%s-down", n->name);
285 execute_script(name, &env);
290 environment_exit(&env);
292 subnet_update(n, NULL, n->status.reachable);
294 if(!n->status.reachable) {
295 update_node_udp(n, NULL);
296 memset(&n->status, 0, sizeof(n->status));
298 } else if(n->connection) {
299 // Speed up UDP probing by sending our key.
300 if(!n->status.sptps) {
306 if(n->status.reachable && n != myself) {
312 if(reachable_count == 0 && became_unreachable_count > 0) {
314 } else if(reachable_count > 0 && reachable_count == became_reachable_count) {
321 subnet_cache_flush_tables();
323 check_reachability();