Move repeating MIN/MAX macros into dropin.h.
[tinc] / src / graph.c
1 /*
2     graph.c -- graph algorithms
3     Copyright (C) 2001-2017 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 "edge.h"
49 #include "graph.h"
50 #include "list.h"
51 #include "logger.h"
52 #include "netutl.h"
53 #include "node.h"
54 #include "protocol.h"
55 #include "script.h"
56 #include "subnet.h"
57 #include "xalloc.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 static void mst_kruskal(void) {
65         /* Clear MST status on connections */
66
67         for list_each(connection_t, c, &connection_list) {
68                 c->status.mst = false;
69         }
70
71         logger(DEBUG_SCARY_THINGS, LOG_DEBUG, "Running Kruskal's algorithm:");
72
73         /* Clear visited status on nodes */
74
75         for splay_each(node_t, n, &node_tree) {
76                 n->status.visited = false;
77         }
78
79         /* Starting point */
80
81         for splay_each(edge_t, e, &edge_weight_tree) {
82                 if(e->from->status.reachable) {
83                         e->from->status.visited = true;
84                         break;
85                 }
86         }
87
88         /* Add safe edges */
89
90         bool skipped = false;
91
92         for splay_each(edge_t, e, &edge_weight_tree) {
93                 if(!e->reverse || (e->from->status.visited == e->to->status.visited)) {
94                         skipped = true;
95                         continue;
96                 }
97
98                 e->from->status.visited = true;
99                 e->to->status.visited = true;
100
101                 if(e->connection) {
102                         e->connection->status.mst = true;
103                 }
104
105                 if(e->reverse->connection) {
106                         e->reverse->connection->status.mst = true;
107                 }
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
152                 for splay_each(edge_t, e, &n->edge_tree) {       /* "e" is the edge connected to "from" */
153                         if(!e->reverse || e->to == myself) {
154                                 continue;
155                         }
156
157                         /* Situation:
158
159                                    /
160                                   /
161                            ----->(n)---e-->(e->to)
162                                   \
163                                    \
164
165                            Where e is an edge, (n) and (e->to) are nodes.
166                            n->address is set to the e->address of the edge left of n to n.
167                            We are currently examining the edge e right of n from n:
168
169                            - If edge e provides for better reachability of e->to, update
170                              e->to and (re)add it to the todo_list to (re)examine the reachability
171                              of nodes behind it.
172                          */
173
174                         bool indirect = n->status.indirect || e->options & OPTION_INDIRECT;
175
176                         if(e->to->status.visited
177                                         && (!e->to->status.indirect || indirect)
178                                         && (e->to->distance != n->distance + 1 || e->weight >= e->to->prevedge->weight)) {
179                                 continue;
180                         }
181
182                         // Only update nexthop if it doesn't increase the path length
183
184                         if(!e->to->status.visited || (e->to->distance == n->distance + 1 && e->weight >= e->to->prevedge->weight)) {
185                                 e->to->nexthop = (n->nexthop == myself) ? e->to : n->nexthop;
186                         }
187
188                         e->to->status.visited = true;
189                         e->to->status.indirect = indirect;
190                         e->to->prevedge = e;
191                         e->to->via = indirect ? n->via : e->to;
192                         e->to->options = e->options;
193                         e->to->distance = n->distance + 1;
194
195                         if(!e->to->status.reachable || (e->to->address.sa.sa_family == AF_UNSPEC && e->address.sa.sa_family != AF_UNKNOWN)) {
196                                 update_node_udp(e->to, &e->address);
197                         }
198
199                         list_insert_tail(todo_list, e->to);
200                 }
201
202                 next = node->next; /* Because the list_insert_tail() above could have added something extra for us! */
203                 list_delete_node(todo_list, node);
204         }
205
206         list_free(todo_list);
207 }
208
209 static void check_reachability(void) {
210         /* Check reachability status. */
211
212         int reachable_count = 0;
213         int became_reachable_count = 0;
214         int became_unreachable_count = 0;
215
216         for splay_each(node_t, n, &node_tree) {
217                 if(n->status.visited != n->status.reachable) {
218                         n->status.reachable = !n->status.reachable;
219                         n->last_state_change = now.tv_sec;
220
221                         if(n->status.reachable) {
222                                 logger(DEBUG_TRAFFIC, LOG_DEBUG, "Node %s (%s) became reachable",
223                                        n->name, n->hostname);
224
225                                 if(n != myself) {
226                                         became_reachable_count++;
227                                 }
228                         } else {
229                                 logger(DEBUG_TRAFFIC, LOG_DEBUG, "Node %s (%s) became unreachable",
230                                        n->name, n->hostname);
231
232                                 if(n != myself) {
233                                         became_unreachable_count++;
234                                 }
235                         }
236
237                         if(experimental && OPTION_VERSION(n->options) >= 2) {
238                                 n->status.sptps = true;
239                         }
240
241                         /* TODO: only clear status.validkey if node is unreachable? */
242
243                         n->status.validkey = false;
244
245                         if(n->status.sptps) {
246                                 sptps_stop(&n->sptps);
247                                 n->status.waitingforkey = false;
248                         }
249
250                         n->last_req_key = 0;
251
252                         n->status.udp_confirmed = false;
253                         n->maxmtu = MTU;
254                         n->maxrecentlen = 0;
255                         n->minmtu = 0;
256                         n->mtuprobes = 0;
257
258                         timeout_del(&n->udp_ping_timeout);
259
260                         char *name;
261                         char *address;
262                         char *port;
263
264                         environment_t env;
265                         environment_init(&env);
266                         environment_add(&env, "NODE=%s", n->name);
267                         sockaddr2str(&n->address, &address, &port);
268                         environment_add(&env, "REMOTEADDRESS=%s", address);
269                         environment_add(&env, "REMOTEPORT=%s", port);
270
271                         execute_script(n->status.reachable ? "host-up" : "host-down", &env);
272
273                         xasprintf(&name, n->status.reachable ? "hosts/%s-up" : "hosts/%s-down", n->name);
274                         execute_script(name, &env);
275
276                         free(name);
277                         free(address);
278                         free(port);
279                         environment_exit(&env);
280
281                         subnet_update(n, NULL, n->status.reachable);
282
283                         if(!n->status.reachable) {
284                                 update_node_udp(n, NULL);
285                                 memset(&n->status, 0, sizeof(n->status));
286                                 n->options = 0;
287                         } else if(n->connection) {
288                                 // Speed up UDP probing by sending our key.
289                                 if(!n->status.sptps) {
290                                         send_ans_key(n);
291                                 }
292                         }
293                 }
294
295                 if(n->status.reachable && n != myself) {
296                         reachable_count++;
297                 }
298         }
299
300         if(device_standby) {
301                 if(reachable_count == 0 && became_unreachable_count > 0) {
302                         device_disable();
303                 } else if(reachable_count > 0 && reachable_count == became_reachable_count) {
304                         device_enable();
305                 }
306         }
307 }
308
309 void graph(void) {
310         subnet_cache_flush_tables();
311         sssp_bfs();
312         check_reachability();
313         mst_kruskal();
314 }