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 directly,
40 indirectly or not reachable from the source. It will also set the correct
41 destination address 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;
70 logger(mesh, MESHLINK_DEBUG, "Running Kruskal's algorithm:");
72 /* Clear visited status on nodes */
74 for splay_each(node_t, n, mesh->nodes)
75 n->status.visited = false;
79 for splay_each(edge_t, e, mesh->edges) {
80 if(e->from->status.reachable) {
81 e->from->status.visited = true;
90 for splay_each(edge_t, e, mesh->edges) {
91 if(!e->reverse || (e->from->status.visited == e->to->status.visited)) {
96 e->from->status.visited = true;
97 e->to->status.visited = true;
100 e->connection->status.mst = true;
102 if(e->reverse->connection)
103 e->reverse->connection->status.mst = true;
105 logger(mesh, MESHLINK_DEBUG, " Adding edge %s - %s weight %d", e->from->name, e->to->name, e->weight);
109 next = mesh->edges->head;
114 /* Implementation of a simple breadth-first search algorithm.
118 static void sssp_bfs(meshlink_handle_t *mesh) {
119 list_t *todo_list = list_alloc(NULL);
121 /* Clear visited status on nodes */
123 for splay_each(node_t, n, mesh->nodes) {
124 n->status.visited = false;
125 n->status.indirect = true;
129 /* Begin with mesh->self */
131 mesh->self->status.visited = true;
132 mesh->self->status.indirect = false;
133 mesh->self->nexthop = mesh->self;
134 mesh->self->prevedge = NULL;
135 mesh->self->via = mesh->self;
136 mesh->self->distance = 0;
137 list_insert_head(todo_list, mesh->self);
139 /* Loop while todo_list is filled */
141 for list_each(node_t, n, todo_list) { /* "n" is the node from which we start */
142 logger(mesh, MESHLINK_DEBUG, " Examining edges from %s", n->name);
147 for splay_each(edge_t, e, n->edge_tree) { /* "e" is the edge connected to "from" */
155 ----->(n)---e-->(e->to)
159 Where e is an edge, (n) and (e->to) are nodes.
160 n->address is set to the e->address of the edge left of n to n.
161 We are currently examining the edge e right of n from n:
163 - If edge e provides for better reachability of e->to, update
164 e->to and (re)add it to the todo_list to (re)examine the reachability
168 bool indirect = n->status.indirect || e->options & OPTION_INDIRECT;
170 if(e->to->status.visited
171 && (!e->to->status.indirect || indirect)
172 && (e->to->distance != n->distance + 1 || e->weight >= e->to->prevedge->weight))
175 e->to->status.visited = true;
176 e->to->status.indirect = indirect;
177 e->to->nexthop = (n->nexthop == mesh->self) ? e->to : n->nexthop;
179 e->to->via = indirect ? n->via : e->to;
180 e->to->options = e->options;
181 e->to->distance = n->distance + 1;
183 if(!e->to->status.reachable || (e->to->address.sa.sa_family == AF_UNSPEC && e->address.sa.sa_family != AF_UNKNOWN))
184 update_node_udp(mesh, e->to, &e->address);
186 list_insert_tail(todo_list, e->to);
189 next = node->next; /* Because the list_insert_tail() above could have added something extra for us! */
190 list_delete_node(todo_list, node);
193 list_free(todo_list);
196 static void check_reachability(meshlink_handle_t *mesh) {
197 /* Check reachability status. */
199 for splay_each(node_t, n, mesh->nodes) {
200 if(n->status.visited != n->status.reachable) {
201 n->status.reachable = !n->status.reachable;
202 n->last_state_change = mesh->loop.now.tv_sec;
204 if(n->status.reachable) {
205 logger(mesh, MESHLINK_DEBUG, "Node %s (%s) became reachable",
206 n->name, n->hostname);
208 logger(mesh, MESHLINK_DEBUG, "Node %s (%s) became unreachable",
209 n->name, n->hostname);
212 /* TODO: only clear status.validkey if node is unreachable? */
214 n->status.validkey = false;
215 sptps_stop(&n->sptps);
216 n->status.waitingforkey = false;
219 n->status.udp_confirmed = false;
224 timeout_del(&mesh->loop, &n->mtutimeout);
226 update_node_status(mesh, n);
228 if(!n->status.reachable) {
229 update_node_udp(mesh, n, NULL);
230 memset(&n->status, 0, sizeof n->status);
232 } else if(n->connection) {
233 if(n->connection->outgoing)
234 send_req_key(mesh, n);
240 void graph(meshlink_handle_t *mesh) {
242 check_reachability(mesh);