e5f70902f95b0ca2b4650d212665ee01ec47f103
[tinc] / src / graph.c
1 /*
2     graph.c -- graph algorithms
3     Copyright (C) 2001-2012 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 "config.h"
48 #include "connection.h"
49 #include "device.h"
50 #include "edge.h"
51 #include "graph.h"
52 #include "list.h"
53 #include "logger.h"
54 #include "names.h"
55 #include "netutl.h"
56 #include "node.h"
57 #include "process.h"
58 #include "protocol.h"
59 #include "subnet.h"
60 #include "utils.h"
61 #include "xalloc.h"
62 #include "graph.h"
63
64 /* Implementation of Kruskal's algorithm.
65    Running time: O(EN)
66    Please note that sorting on weight is already done by add_edge().
67 */
68
69 static void mst_kruskal(void) {
70         /* Clear MST status on connections */
71
72         for list_each(connection_t, c, connection_list)
73                 c->status.mst = false;
74
75         logger(DEBUG_SCARY_THINGS, LOG_DEBUG, "Running Kruskal's algorithm:");
76
77         /* Clear visited status on nodes */
78
79         for splay_each(node_t, n, node_tree)
80                 n->status.visited = false;
81
82         /* Starting point */
83
84         for splay_each(edge_t, e, edge_weight_tree) {
85                 if(e->from->status.reachable) {
86                         e->from->status.visited = true;
87                         break;
88                 }
89         }
90
91         /* Add safe edges */
92
93         bool skipped = false;
94
95         for splay_each(edge_t, e, edge_weight_tree) {
96                 if(!e->reverse || (e->from->status.visited == e->to->status.visited)) {
97                         skipped = true;
98                         continue;
99                 }
100
101                 e->from->status.visited = true;
102                 e->to->status.visited = true;
103
104                 if(e->connection)
105                         e->connection->status.mst = true;
106
107                 if(e->reverse->connection)
108                         e->reverse->connection->status.mst = true;
109
110                 logger(DEBUG_SCARY_THINGS, LOG_DEBUG, " Adding edge %s - %s weight %d", e->from->name, e->to->name, e->weight);
111
112                 if(skipped) {
113                         skipped = false;
114                         next = edge_weight_tree->head;
115                 }
116         }
117 }
118
119 /* Implementation of a simple breadth-first search algorithm.
120    Running time: O(E)
121 */
122
123 static void sssp_bfs(void) {
124         list_t *todo_list = list_alloc(NULL);
125
126         /* Clear visited status on nodes */
127
128         for splay_each(node_t, n, node_tree) {
129                 n->status.visited = false;
130                 n->status.indirect = true;
131                 n->distance = -1;
132         }
133
134         /* Begin with myself */
135
136         myself->status.visited = true;
137         myself->status.indirect = false;
138         myself->nexthop = myself;
139         myself->prevedge = NULL;
140         myself->via = myself;
141         myself->distance = 0;
142         list_insert_head(todo_list, myself);
143
144         /* Loop while todo_list is filled */
145
146         for list_each(node_t, n, todo_list) {                   /* "n" is the node from which we start */
147                 logger(DEBUG_SCARY_THINGS, LOG_DEBUG, " Examining edges from %s", n->name);
148
149                 if(n->distance < 0)
150                         abort();
151
152                 for splay_each(edge_t, e, n->edge_tree) {       /* "e" is the edge connected to "from" */
153                         if(!e->reverse)
154                                 continue;
155
156                         /* Situation:
157
158                                    /
159                                   /
160                            ----->(n)---e-->(e->to)
161                                   \
162                                    \
163
164                            Where e is an edge, (n) and (e->to) are nodes.
165                            n->address is set to the e->address of the edge left of n to n.
166                            We are currently examining the edge e right of n from n:
167
168                            - If edge e provides for better reachability of e->to, update
169                              e->to and (re)add it to the todo_list to (re)examine the reachability
170                              of nodes behind it.
171                          */
172
173                         bool indirect = n->status.indirect || e->options & OPTION_INDIRECT;
174
175                         if(e->to->status.visited
176                            && (!e->to->status.indirect || indirect)
177                            && (e->to->distance != n->distance + 1 || e->weight >= e->to->prevedge->weight))
178                                 continue;
179
180                         e->to->status.visited = true;
181                         e->to->status.indirect = indirect;
182                         e->to->nexthop = (n->nexthop == myself) ? e->to : n->nexthop;
183                         e->to->prevedge = e;
184                         e->to->via = indirect ? n->via : e->to;
185                         e->to->options = e->options;
186                         e->to->distance = n->distance + 1;
187
188                         if(!e->to->status.reachable || (e->to->address.sa.sa_family == AF_UNSPEC && e->address.sa.sa_family != AF_UNKNOWN))
189                                 update_node_udp(e->to, &e->address);
190
191                         list_insert_tail(todo_list, e->to);
192                 }
193
194                 next = node->next; /* Because the list_insert_tail() above could have added something extra for us! */
195                 list_delete_node(todo_list, node);
196         }
197
198         list_free(todo_list);
199 }
200
201 static void check_reachability(void) {
202         /* Check reachability status. */
203
204         for splay_each(node_t, n, node_tree) {
205                 if(n->status.visited != n->status.reachable) {
206                         n->status.reachable = !n->status.reachable;
207                         n->last_state_change = time(NULL);
208
209                         if(n->status.reachable) {
210                                 logger(DEBUG_TRAFFIC, LOG_DEBUG, "Node %s (%s) became reachable",
211                                            n->name, n->hostname);
212                         } else {
213                                 logger(DEBUG_TRAFFIC, LOG_DEBUG, "Node %s (%s) became unreachable",
214                                            n->name, n->hostname);
215                         }
216
217                         if(experimental && OPTION_VERSION(n->options) >= 2)
218                                 n->status.sptps = true;
219
220                         /* TODO: only clear status.validkey if node is unreachable? */
221
222                         n->status.validkey = false;
223                         if(n->status.sptps) {
224                                 sptps_stop(&n->sptps);
225                                 n->status.waitingforkey = false;
226                         }
227                         n->last_req_key = 0;
228
229                         n->status.udp_confirmed = false;
230                         n->maxmtu = MTU;
231                         n->minmtu = 0;
232                         n->mtuprobes = 0;
233
234                         timeout_del(&n->mtutimeout);
235
236                         char *name;
237                         char *address;
238                         char *port;
239                         char *envp[7];
240
241                         xasprintf(&envp[0], "NETNAME=%s", netname ? : "");
242                         xasprintf(&envp[1], "DEVICE=%s", device ? : "");
243                         xasprintf(&envp[2], "INTERFACE=%s", iface ? : "");
244                         xasprintf(&envp[3], "NODE=%s", n->name);
245                         sockaddr2str(&n->address, &address, &port);
246                         xasprintf(&envp[4], "REMOTEADDRESS=%s", address);
247                         xasprintf(&envp[5], "REMOTEPORT=%s", port);
248                         envp[6] = NULL;
249
250                         execute_script(n->status.reachable ? "host-up" : "host-down", envp);
251
252                         xasprintf(&name, n->status.reachable ? "hosts/%s-up" : "hosts/%s-down", n->name);
253                         execute_script(name, envp);
254
255                         free(name);
256                         free(address);
257                         free(port);
258
259                         for(int i = 0; i < 6; i++)
260                                 free(envp[i]);
261
262                         subnet_update(n, NULL, n->status.reachable);
263
264                         if(!n->status.reachable) {
265                                 update_node_udp(n, NULL);
266                                 memset(&n->status, 0, sizeof n->status);
267                                 n->options = 0;
268                         } else if(n->connection) {
269                                 if(n->status.sptps) {
270                                         if(n->connection->outgoing)
271                                                 send_req_key(n);
272                                 } else {
273                                         send_ans_key(n);
274                                 }
275                         }
276                 }
277         }
278 }
279
280 void graph(void) {
281         subnet_cache_flush();
282         sssp_bfs();
283         check_reachability();
284         mst_kruskal();
285 }