]> git.meshlink.io Git - meshlink/blob - src/graph.c
Fast retries and timeout of UDP probes.
[meshlink] / src / graph.c
1 /*
2     graph.c -- graph algorithms
3     Copyright (C) 2014 Guus Sliepen <guus@meshlink.io>
4
5     This program is free software; you can redistribute it and/or modify
6     it under the terms of the GNU General Public License as published by
7     the Free Software Foundation; either version 2 of the License, or
8     (at your option) any later version.
9
10     This program is distributed in the hope that it will be useful,
11     but WITHOUT ANY WARRANTY; without even the implied warranty of
12     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
13     GNU General Public License for more details.
14
15     You should have received a copy of the GNU General Public License along
16     with this program; if not, write to the Free Software Foundation, Inc.,
17     51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
18 */
19
20 /* We need to generate two trees from the graph:
21
22    1. A minimum spanning tree for broadcasts,
23    2. A single-source shortest path tree for unicasts.
24
25    Actually, the first one alone would suffice but would make unicast packets
26    take longer routes than necessary.
27
28    For the MST algorithm we can choose from Prim's or Kruskal's. I personally
29    favour Kruskal's, because we make an extra AVL tree of edges sorted on
30    weights (metric). That tree only has to be updated when an edge is added or
31    removed, and during the MST algorithm we just have go linearly through that
32    tree, adding safe edges until #edges = #nodes - 1. The implementation here
33    however is not so fast, because I tried to avoid having to make a forest and
34    merge trees.
35
36    For the SSSP algorithm Dijkstra's seems to be a nice choice. Currently a
37    simple breadth-first search is presented here.
38
39    The SSSP algorithm will also be used to determine whether nodes are
40    reachable from the source. It will also set the correct destination address
41    and port of a node if possible.
42 */
43
44 #include "system.h"
45
46 #include "connection.h"
47 #include "edge.h"
48 #include "graph.h"
49 #include "list.h"
50 #include "logger.h"
51 #include "meshlink_internal.h"
52 #include "netutl.h"
53 #include "node.h"
54 #include "protocol.h"
55 #include "utils.h"
56 #include "xalloc.h"
57 #include "graph.h"
58
59 /* Implementation of a simple breadth-first search algorithm.
60    Running time: O(E)
61 */
62
63 static void sssp_bfs(meshlink_handle_t *mesh) {
64         list_t *todo_list = list_alloc(NULL);
65
66         /* Clear visited status on nodes */
67
68         for splay_each(node_t, n, mesh->nodes) {
69                 n->status.visited = false;
70                 n->distance = -1;
71         }
72
73         /* Begin with mesh->self */
74
75         mesh->self->status.visited = mesh->threadstarted;
76         mesh->self->nexthop = mesh->self;
77         mesh->self->prevedge = NULL;
78         mesh->self->distance = 0;
79         list_insert_head(todo_list, mesh->self);
80
81         /* Loop while todo_list is filled */
82
83         for list_each(node_t, n, todo_list) {                   /* "n" is the node from which we start */
84                 logger(mesh, MESHLINK_DEBUG, " Examining edges from %s", n->name);
85
86                 if(n->distance < 0) {
87                         abort();
88                 }
89
90                 for splay_each(edge_t, e, n->edge_tree) {       /* "e" is the edge connected to "from" */
91                         if(!e->reverse) {
92                                 continue;
93                         }
94
95                         /* Situation:
96
97                                    /
98                                   /
99                            ----->(n)---e-->(e->to)
100                                   \
101                                    \
102
103                            Where e is an edge, (n) and (e->to) are nodes.
104                            n->address is set to the e->address of the edge left of n to n.
105                            We are currently examining the edge e right of n from n:
106
107                            - If edge e provides for better reachability of e->to, update
108                              e->to and (re)add it to the todo_list to (re)examine the reachability
109                              of nodes behind it.
110                          */
111
112                         if(e->to->status.visited
113                                         && (e->to->distance != n->distance + 1 || e->weight >= e->to->prevedge->weight)) {
114                                 continue;
115                         }
116
117                         e->to->status.visited = true;
118                         e->to->nexthop = (n->nexthop == mesh->self) ? e->to : n->nexthop;
119                         e->to->prevedge = e;
120                         e->to->distance = n->distance + 1;
121
122                         if(!e->to->status.reachable || (e->to->address.sa.sa_family == AF_UNSPEC && e->address.sa.sa_family != AF_UNKNOWN)) {
123                                 update_node_udp(mesh, e->to, &e->address);
124                         }
125
126                         list_insert_tail(todo_list, e->to);
127                 }
128
129                 list_next = list_node->next; /* Because the list_insert_tail() above could have added something extra for us! */
130                 list_delete_node(todo_list, list_node);
131         }
132
133         list_free(todo_list);
134 }
135
136 static void check_reachability(meshlink_handle_t *mesh) {
137         /* Check reachability status. */
138
139         int reachable = -1; /* Don't count ourself */
140
141         for splay_each(node_t, n, mesh->nodes) {
142                 if(n->status.visited) {
143                         reachable++;
144                 }
145
146                 /* Check for nodes that have changed session_id */
147                 if(n->status.visited && n->prevedge && n->prevedge->reverse->session_id != n->session_id) {
148                         logger(mesh, MESHLINK_DEBUG, "Node %s has a new session ID", n->name);
149
150                         n->session_id = n->prevedge->reverse->session_id;
151
152                         if(n->utcp) {
153                                 utcp_reset_all_connections(n->utcp);
154                         }
155
156                         n->status.validkey = false;
157                         sptps_stop(&n->sptps);
158                         n->status.waitingforkey = false;
159                         n->last_req_key = -3600;
160
161                         n->status.udp_confirmed = false;
162                         n->maxmtu = MTU;
163                         n->minmtu = 0;
164                         n->mtuprobes = 0;
165                 }
166
167                 if(n->status.visited != n->status.reachable) {
168                         n->status.reachable = !n->status.reachable;
169                         n->status.dirty = true;
170
171                         if(!n->status.blacklisted) {
172                                 if(n->status.reachable) {
173                                         logger(mesh, MESHLINK_DEBUG, "Node %s became reachable", n->name);
174                                         bool first_time_reachable = !n->last_reachable;
175                                         n->last_reachable = time(NULL);
176
177                                         if(first_time_reachable) {
178                                                 if(!node_write_config(mesh, n, false)) {
179                                                         logger(mesh, MESHLINK_WARNING, "Could not write host config file for node %s!\n", n->name);
180
181                                                 }
182                                         }
183                                 } else {
184                                         logger(mesh, MESHLINK_DEBUG, "Node %s became unreachable", n->name);
185                                         n->last_unreachable = time(NULL);
186                                 }
187                         }
188
189                         n->status.udp_confirmed = false;
190                         n->maxmtu = MTU;
191                         n->minmtu = 0;
192                         n->mtuprobes = 0;
193
194                         timeout_del(&mesh->loop, &n->udp_ping_timeout);
195
196                         if(!n->status.blacklisted) {
197                                 update_node_status(mesh, n);
198                         }
199
200                         if(!n->status.reachable) {
201                                 update_node_udp(mesh, n, NULL);
202                                 n->status.broadcast = false;
203                         }
204
205                         if(n->utcp) {
206                                 utcp_offline(n->utcp, !n->status.reachable);
207                         }
208                 }
209         }
210
211         if(mesh->reachable != reachable) {
212                 if(!reachable) {
213                         mesh->last_unreachable = mesh->loop.now.tv_sec;
214
215                         if(mesh->threadstarted && mesh->periodictimer.cb) {
216                                 timeout_set(&mesh->loop, &mesh->periodictimer, &(struct timespec) {
217                                         0, prng(mesh, TIMER_FUDGE)
218                                 });
219                         }
220                 }
221
222                 mesh->reachable = reachable;
223         }
224 }
225
226 void graph(meshlink_handle_t *mesh) {
227         sssp_bfs(mesh);
228         check_reachability(mesh);
229 }