2 graph.c -- graph algorithms
3 Copyright (C) 2001-2009 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 "splay_tree.h"
49 #include "connection.h"
60 /* Implementation of Kruskal's algorithm.
62 Please note that sorting on weight is already done by add_edge().
65 void mst_kruskal(void) {
66 splay_node_t *node, *next;
71 /* Clear MST status on connections */
73 for(node = connection_tree->head; node; node = node->next) {
75 c->status.mst = false;
78 ifdebug(SCARY_THINGS) logger(LOG_DEBUG, "Running Kruskal's algorithm:");
80 /* Clear visited status on nodes */
82 for(node = node_tree->head; node; node = node->next) {
84 n->status.visited = false;
89 for(node = edge_weight_tree->head; node; node = next) {
93 if(!e->reverse || (e->from->status.visited && e->to->status.visited))
96 e->from->status.visited = true;
97 e->to->status.visited = true;
100 e->connection->status.mst = true;
102 if(e->reverse->connection)
103 e->reverse->connection->status.mst = true;
105 ifdebug(SCARY_THINGS) logger(LOG_DEBUG, " Adding edge %s - %s weight %d", e->from->name,
106 e->to->name, e->weight);
110 /* Implementation of Dijkstra's algorithm.
114 void sssp_dijkstra(void) {
115 splay_node_t *node, *to;
119 list_node_t *lnode, *nnode;
122 todo_list = list_alloc(NULL);
124 ifdebug(SCARY_THINGS) logger(LOG_DEBUG, "Running Dijkstra's algorithm:");
126 /* Clear visited status on nodes */
128 for(node = node_tree->head; node; node = node->next) {
130 n->status.visited = false;
131 n->status.indirect = true;
135 /* Begin with myself */
137 myself->status.indirect = false;
138 myself->nexthop = myself;
139 myself->via = myself;
140 myself->distance = 0;
141 list_insert_head(todo_list, myself);
143 /* Loop while todo_list is filled */
145 while(todo_list->head) {
149 /* Select node from todo_list with smallest distance */
151 for(lnode = todo_list->head; lnode; lnode = lnode->next) {
153 if(!n || m->status.indirect < n->status.indirect || m->distance < n->distance) {
159 /* Mark this node as visited and remove it from the todo_list */
161 n->status.visited = true;
162 list_unlink_node(todo_list, nnode);
164 /* Update distance of neighbours and add them to the todo_list */
166 for(to = n->edge_tree->head; to; to = to->next) { /* "to" is the edge connected to "from" */
169 if(e->to->status.visited || !e->reverse)
176 ----->(n)---e-->(e->to)
180 Where e is an edge, (n) and (e->to) are nodes.
181 n->address is set to the e->address of the edge left of n to n.
182 We are currently examining the edge e right of n from n:
184 - If e->reverse->address != n->address, then e->to is probably
185 not reachable for the nodes left of n. We do as if the indirectdata
186 flag is set on edge e.
187 - If edge e provides for better reachability of e->to, update e->to.
190 if(e->to->distance < 0)
191 list_insert_tail(todo_list, e->to);
193 indirect = n->status.indirect || e->options & OPTION_INDIRECT || ((n != myself) && sockaddrcmp(&n->address, &e->reverse->address));
195 if(e->to->distance >= 0 && (!e->to->status.indirect || indirect) && e->to->distance <= n->distance + e->weight)
198 e->to->distance = n->distance + e->weight;
199 e->to->status.indirect = indirect;
200 e->to->nexthop = (n->nexthop == myself) ? e->to : n->nexthop;
201 e->to->via = indirect ? n->via : e->to;
202 e->to->options = e->options;
204 if(sockaddrcmp(&e->to->address, &e->address)) {
205 node = splay_unlink(node_udp_tree, e->to);
206 sockaddrfree(&e->to->address);
207 sockaddrcpy(&e->to->address, &e->address);
210 free(e->to->hostname);
212 e->to->hostname = sockaddr2hostname(&e->to->address);
215 splay_insert_node(node_udp_tree, node);
217 if(e->to->options & OPTION_PMTU_DISCOVERY) {
218 e->to->mtuprobes = 0;
221 if(e->to->status.validkey)
222 send_mtu_probe(e->to);
226 ifdebug(SCARY_THINGS) logger(LOG_DEBUG, " Updating edge %s - %s weight %d distance %d", e->from->name,
227 e->to->name, e->weight, e->to->distance);
231 list_free(todo_list);
234 /* Implementation of a simple breadth-first search algorithm.
238 void sssp_bfs(void) {
239 splay_node_t *node, *to;
243 list_node_t *from, *todonext;
246 todo_list = list_alloc(NULL);
248 /* Clear visited status on nodes */
250 for(node = node_tree->head; node; node = node->next) {
252 n->status.visited = false;
253 n->status.indirect = true;
256 /* Begin with myself */
258 myself->status.visited = true;
259 myself->status.indirect = false;
260 myself->nexthop = myself;
261 myself->via = myself;
262 list_insert_head(todo_list, myself);
264 /* Loop while todo_list is filled */
266 for(from = todo_list->head; from; from = todonext) { /* "from" is the node from which we start */
269 for(to = n->edge_tree->head; to; to = to->next) { /* "to" is the edge connected to "from" */
279 ----->(n)---e-->(e->to)
283 Where e is an edge, (n) and (e->to) are nodes.
284 n->address is set to the e->address of the edge left of n to n.
285 We are currently examining the edge e right of n from n:
287 - If e->reverse->address != n->address, then e->to is probably
288 not reachable for the nodes left of n. We do as if the indirectdata
289 flag is set on edge e.
290 - If edge e provides for better reachability of e->to, update
291 e->to and (re)add it to the todo_list to (re)examine the reachability
295 indirect = n->status.indirect || e->options & OPTION_INDIRECT
296 || ((n != myself) && sockaddrcmp(&n->address, &e->reverse->address));
298 if(e->to->status.visited
299 && (!e->to->status.indirect || indirect))
302 e->to->status.visited = true;
303 e->to->status.indirect = indirect;
304 e->to->nexthop = (n->nexthop == myself) ? e->to : n->nexthop;
305 e->to->via = indirect ? n->via : e->to;
306 e->to->options = e->options;
308 if(e->to->address.sa.sa_family == AF_UNSPEC && e->address.sa.sa_family != AF_UNKNOWN)
309 update_node_udp(e->to, &e->address);
311 list_insert_tail(todo_list, e->to);
314 todonext = from->next;
315 list_delete_node(todo_list, from);
318 list_free(todo_list);
321 void check_reachability() {
322 splay_node_t *node, *next;
325 char *address, *port;
329 /* Check reachability status. */
331 for(node = node_tree->head; node; node = next) {
335 if(n->status.visited != n->status.reachable) {
336 n->status.reachable = !n->status.reachable;
338 if(n->status.reachable) {
339 ifdebug(TRAFFIC) logger(LOG_DEBUG, "Node %s (%s) became reachable",
340 n->name, n->hostname);
342 ifdebug(TRAFFIC) logger(LOG_DEBUG, "Node %s (%s) became unreachable",
343 n->name, n->hostname);
346 /* TODO: only clear status.validkey if node is unreachable? */
348 n->status.validkey = false;
349 n->status.waitingforkey = false;
355 event_del(&n->mtuevent);
357 xasprintf(&envp[0], "NETNAME=%s", netname ? : "");
358 xasprintf(&envp[1], "DEVICE=%s", device ? : "");
359 xasprintf(&envp[2], "INTERFACE=%s", iface ? : "");
360 xasprintf(&envp[3], "NODE=%s", n->name);
361 sockaddr2str(&n->address, &address, &port);
362 xasprintf(&envp[4], "REMOTEADDRESS=%s", address);
363 xasprintf(&envp[5], "REMOTEPORT=%s", port);
366 execute_script(n->status.reachable ? "host-up" : "host-down", envp);
369 n->status.reachable ? "hosts/%s-up" : "hosts/%s-down",
371 execute_script(name, envp);
377 for(i = 0; i < 6; i++)
380 subnet_update(n, NULL, n->status.reachable);
382 if(!n->status.reachable)
383 update_node_udp(n, NULL);
389 subnet_cache_flush();
391 check_reachability();