Improvements for PMTU discovery and IPv4 packet fragmentation.
[oweals/tinc.git] / src / graph.c
1 /*
2     graph.c -- graph algorithms
3     Copyright (C) 2001-2003 Guus Sliepen <guus@sliepen.eu.org>,
4                   2001-2003 Ivo Timmermans <ivo@o2w.nl>
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
17     along with this program; if not, write to the Free Software
18     Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
19
20     $Id: graph.c,v 1.1.2.34 2003/12/22 11:04:16 guus Exp $
21 */
22
23 /* We need to generate two trees from the graph:
24
25    1. A minimum spanning tree for broadcasts,
26    2. A single-source shortest path tree for unicasts.
27
28    Actually, the first one alone would suffice but would make unicast packets
29    take longer routes than necessary.
30
31    For the MST algorithm we can choose from Prim's or Kruskal's. I personally
32    favour Kruskal's, because we make an extra AVL tree of edges sorted on
33    weights (metric). That tree only has to be updated when an edge is added or
34    removed, and during the MST algorithm we just have go linearly through that
35    tree, adding safe edges until #edges = #nodes - 1. The implementation here
36    however is not so fast, because I tried to avoid having to make a forest and
37    merge trees.
38
39    For the SSSP algorithm Dijkstra's seems to be a nice choice. Currently a
40    simple breadth-first search is presented here.
41
42    The SSSP algorithm will also be used to determine whether nodes are directly,
43    indirectly or not reachable from the source. It will also set the correct
44    destination address and port of a node if possible.
45 */
46
47 #include "system.h"
48
49 #include "avl_tree.h"
50 #include "connection.h"
51 #include "device.h"
52 #include "edge.h"
53 #include "logger.h"
54 #include "netutl.h"
55 #include "node.h"
56 #include "process.h"
57 #include "utils.h"
58
59 /* Implementation of Kruskal's algorithm.
60    Running time: O(EN)
61    Please note that sorting on weight is already done by add_edge().
62 */
63
64 void mst_kruskal(void)
65 {
66         avl_node_t *node, *next;
67         edge_t *e;
68         node_t *n;
69         connection_t *c;
70         int nodes = 0;
71         int safe_edges = 0;
72         bool skipped;
73
74         cp();
75         
76         /* Clear MST status on connections */
77
78         for(node = connection_tree->head; node; node = node->next) {
79                 c = node->data;
80                 c->status.mst = false;
81         }
82
83         /* Do we have something to do at all? */
84
85         if(!edge_weight_tree->head)
86                 return;
87
88         ifdebug(SCARY_THINGS) logger(LOG_DEBUG, "Running Kruskal's algorithm:");
89
90         /* Clear visited status on nodes */
91
92         for(node = node_tree->head; node; node = node->next) {
93                 n = node->data;
94                 n->status.visited = false;
95                 nodes++;
96         }
97
98         /* Starting point */
99
100         ((edge_t *) edge_weight_tree->head->data)->from->status.visited = true;
101
102         /* Add safe edges */
103
104         for(skipped = false, node = edge_weight_tree->head; node; node = next) {
105                 next = node->next;
106                 e = node->data;
107
108                 if(!e->reverse || e->from->status.visited == e->to->status.visited) {
109                         skipped = true;
110                         continue;
111                 }
112
113                 e->from->status.visited = true;
114                 e->to->status.visited = true;
115
116                 if(e->connection)
117                         e->connection->status.mst = true;
118
119                 if(e->reverse->connection)
120                         e->reverse->connection->status.mst = true;
121
122                 safe_edges++;
123
124                 ifdebug(SCARY_THINGS) logger(LOG_DEBUG, " Adding edge %s - %s weight %d", e->from->name,
125                                    e->to->name, e->weight);
126
127                 if(skipped) {
128                         skipped = false;
129                         next = edge_weight_tree->head;
130                         continue;
131                 }
132         }
133
134         ifdebug(SCARY_THINGS) logger(LOG_DEBUG, "Done, counted %d nodes and %d safe edges.", nodes,
135                            safe_edges);
136 }
137
138 /* Implementation of a simple breadth-first search algorithm.
139    Running time: O(E)
140 */
141
142 void sssp_bfs(void)
143 {
144         avl_node_t *node, *from, *next, *to;
145         edge_t *e;
146         node_t *n;
147         avl_tree_t *todo_tree;
148         bool indirect;
149         char *name;
150         char *address, *port;
151         char *envp[7];
152         int i;
153
154         cp();
155
156         todo_tree = avl_alloc_tree(NULL, NULL);
157
158         /* Clear visited status on nodes */
159
160         for(node = node_tree->head; node; node = node->next) {
161                 n = node->data;
162                 n->status.visited = false;
163                 n->status.indirect = true;
164         }
165
166         /* Begin with myself */
167
168         myself->status.visited = true;
169         myself->status.indirect = false;
170         myself->nexthop = myself;
171         myself->via = myself;
172         node = avl_alloc_node();
173         node->data = myself;
174         avl_insert_top(todo_tree, node);
175
176         /* Loop while todo_tree is filled */
177
178         while(todo_tree->head) {
179                 for(from = todo_tree->head; from; from = next) {        /* "from" is the node from which we start */
180                         next = from->next;
181                         n = from->data;
182
183                         for(to = n->edge_tree->head; to; to = to->next) {       /* "to" is the edge connected to "from" */
184                                 e = to->data;
185
186                                 if(!e->reverse)
187                                         continue;
188
189                                 /* Situation:
190
191                                            /
192                                           /
193                                    ----->(n)---e-->(e->to)
194                                           \
195                                            \
196
197                                    Where e is an edge, (n) and (e->to) are nodes.
198                                    n->address is set to the e->address of the edge left of n to n.
199                                    We are currently examining the edge e right of n from n:
200
201                                    - If e->reverse->address != n->address, then e->to is probably
202                                      not reachable for the nodes left of n. We do as if the indirectdata
203                                      flag is set on edge e.
204                                    - If edge e provides for better reachability of e->to, update
205                                      e->to and (re)add it to the todo_tree to (re)examine the reachability
206                                      of nodes behind it.
207                                  */
208
209                                 indirect = n->status.indirect || e->options & OPTION_INDIRECT
210                                         || ((n != myself) && sockaddrcmp(&n->address, &e->reverse->address));
211
212                                 if(e->to->status.visited
213                                    && (!e->to->status.indirect || indirect))
214                                         continue;
215
216                                 e->to->status.visited = true;
217                                 e->to->status.indirect = indirect;
218                                 e->to->nexthop = (n->nexthop == myself) ? e->to : n->nexthop;
219                                 e->to->via = indirect ? n->via : e->to;
220                                 e->to->options = e->options;
221
222                                 if(sockaddrcmp(&e->to->address, &e->address)) {
223                                         node = avl_unlink(node_udp_tree, e->to);
224                                         sockaddrfree(&e->to->address);
225                                         sockaddrcpy(&e->to->address, &e->address);
226
227                                         if(e->to->hostname)
228                                                 free(e->to->hostname);
229
230                                         e->to->hostname = sockaddr2hostname(&e->to->address);
231                                         avl_insert_node(node_udp_tree, node);
232
233                                         if(e->to->options & OPTION_PMTU_DISCOVERY) {
234                                                 e->to->mtuprobes = 0;
235                                                 e->to->minmtu = 0;
236                                                 e->to->maxmtu = MTU;
237                                                 if(e->to->status.validkey)
238                                                         send_mtu_probe(e->to);
239                                         }
240                                 }
241
242                                 node = avl_alloc_node();
243                                 node->data = e->to;
244                                 avl_insert_before(todo_tree, from, node);
245                         }
246
247                         avl_delete_node(todo_tree, from);
248                 }
249         }
250
251         avl_free_tree(todo_tree);
252
253         /* Check reachability status. */
254
255         for(node = node_tree->head; node; node = next) {
256                 next = node->next;
257                 n = node->data;
258
259                 if(n->status.visited != n->status.reachable) {
260                         n->status.reachable = !n->status.reachable;
261
262                         if(n->status.reachable) {
263                                 ifdebug(TRAFFIC) logger(LOG_DEBUG, _("Node %s (%s) became reachable"),
264                                            n->name, n->hostname);
265                         } else {
266                                 ifdebug(TRAFFIC) logger(LOG_DEBUG, _("Node %s (%s) became unreachable"),
267                                            n->name, n->hostname);
268                         }
269
270                         n->status.validkey = false;
271                         n->status.waitingforkey = false;
272
273                         n->maxmtu = MTU;
274                         n->minmtu = 0;
275                         n->mtuprobes = 0;
276
277                         asprintf(&envp[0], "NETNAME=%s", netname ? : "");
278                         asprintf(&envp[1], "DEVICE=%s", device ? : "");
279                         asprintf(&envp[2], "INTERFACE=%s", iface ? : "");
280                         asprintf(&envp[3], "NODE=%s", n->name);
281                         sockaddr2str(&n->address, &address, &port);
282                         asprintf(&envp[4], "REMOTEADDRESS=%s", address);
283                         asprintf(&envp[5], "REMOTEPORT=%s", port);
284                         envp[6] = NULL;
285
286                         asprintf(&name,
287                                          n->status.reachable ? "hosts/%s-up" : "hosts/%s-down",
288                                          n->name);
289                         execute_script(name, envp);
290
291                         free(name);
292                         free(address);
293                         free(port);
294
295                         for(i = 0; i < 7; i++)
296                                 free(envp[i]);
297                 }
298         }
299 }
300
301 void graph(void)
302 {
303         mst_kruskal();
304         sssp_bfs();
305 }