2 graph.c -- graph algorithms
3 Copyright (C) 2014 Guus Sliepen <guus@meshlink.io>
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.
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.
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.
20 /* We need to generate two trees from the graph:
22 1. A minimum spanning tree for broadcasts,
23 2. A single-source shortest path tree for unicasts.
25 Actually, the first one alone would suffice but would make unicast packets
26 take longer routes than necessary.
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
36 For the SSSP algorithm Dijkstra's seems to be a nice choice. Currently a
37 simple breadth-first search is presented here.
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.
46 #include "connection.h"
51 #include "meshlink_internal.h"
59 /* Implementation of Kruskal's algorithm.
61 Please note that sorting on weight is already done by add_edge().
64 static void mst_kruskal(meshlink_handle_t *mesh) {
65 /* Clear MST status on connections */
67 for list_each(connection_t, c, mesh->connections) {
68 c->status.mst = false;
71 logger(mesh, MESHLINK_DEBUG, "Running Kruskal's algorithm:");
73 /* Clear visited status on nodes */
75 for splay_each(node_t, n, mesh->nodes) {
76 n->status.visited = false;
81 for splay_each(edge_t, e, mesh->edges) {
82 if(e->from->status.reachable) {
83 e->from->status.visited = true;
92 for splay_each(edge_t, e, mesh->edges) {
93 if(!e->reverse || (e->from->status.visited == e->to->status.visited)) {
98 e->from->status.visited = true;
99 e->to->status.visited = true;
102 e->connection->status.mst = true;
105 if(e->reverse->connection) {
106 e->reverse->connection->status.mst = true;
109 logger(mesh, MESHLINK_DEBUG, " Adding edge %s - %s weight %d", e->from->name, e->to->name, e->weight);
113 next = mesh->edges->head;
118 /* Implementation of a simple breadth-first search algorithm.
122 static void sssp_bfs(meshlink_handle_t *mesh) {
123 list_t *todo_list = list_alloc(NULL);
125 /* Clear visited status on nodes */
127 for splay_each(node_t, n, mesh->nodes) {
128 n->status.visited = false;
132 /* Begin with mesh->self */
134 mesh->self->status.visited = true;
135 mesh->self->nexthop = mesh->self;
136 mesh->self->prevedge = NULL;
137 mesh->self->distance = 0;
138 list_insert_head(todo_list, mesh->self);
140 /* Loop while todo_list is filled */
142 for list_each(node_t, n, todo_list) { /* "n" is the node from which we start */
143 logger(mesh, MESHLINK_DEBUG, " Examining edges from %s", n->name);
145 if(n->distance < 0) {
149 for splay_each(edge_t, e, n->edge_tree) { /* "e" is the edge connected to "from" */
158 ----->(n)---e-->(e->to)
162 Where e is an edge, (n) and (e->to) are nodes.
163 n->address is set to the e->address of the edge left of n to n.
164 We are currently examining the edge e right of n from n:
166 - If edge e provides for better reachability of e->to, update
167 e->to and (re)add it to the todo_list to (re)examine the reachability
171 if(e->to->status.visited
172 && (e->to->distance != n->distance + 1 || e->weight >= e->to->prevedge->weight)) {
176 e->to->status.visited = true;
177 e->to->nexthop = (n->nexthop == mesh->self) ? e->to : n->nexthop;
179 e->to->distance = n->distance + 1;
181 if(!e->to->status.reachable || (e->to->address.sa.sa_family == AF_UNSPEC && e->address.sa.sa_family != AF_UNKNOWN)) {
182 update_node_udp(mesh, e->to, &e->address);
185 list_insert_tail(todo_list, e->to);
188 next = node->next; /* Because the list_insert_tail() above could have added something extra for us! */
189 list_delete_node(todo_list, node);
192 list_free(todo_list);
195 static void check_reachability(meshlink_handle_t *mesh) {
196 /* Check reachability status. */
198 for splay_each(node_t, n, mesh->nodes) {
199 if(n->status.visited != n->status.reachable) {
200 n->status.reachable = !n->status.reachable;
201 n->last_state_change = mesh->loop.now.tv_sec;
203 if(n->status.reachable) {
204 logger(mesh, MESHLINK_DEBUG, "Node %s became reachable", n->name);
206 logger(mesh, MESHLINK_DEBUG, "Node %s became unreachable", n->name);
209 /* TODO: only clear status.validkey if node is unreachable? */
211 n->status.validkey = false;
212 sptps_stop(&n->sptps);
213 n->status.waitingforkey = false;
216 n->status.udp_confirmed = false;
221 timeout_del(&mesh->loop, &n->mtutimeout);
223 if(!n->status.blacklisted) {
224 update_node_status(mesh, n);
227 if(!n->status.reachable) {
228 update_node_udp(mesh, n, NULL);
229 n->status.broadcast = false;
230 } else if(n->connection) {
231 if(n->connection->status.initiator) {
232 send_req_key(mesh, n);
237 utcp_offline(n->utcp, !n->status.reachable);
243 void graph(meshlink_handle_t *mesh) {
245 check_reachability(mesh);