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 a simple breadth-first search algorithm.
63 static void sssp_bfs(meshlink_handle_t *mesh) {
64 list_t *todo_list = list_alloc(NULL);
66 /* Clear visited status on nodes */
68 for splay_each(node_t, n, mesh->nodes) {
69 n->status.visited = false;
73 /* Begin with mesh->self */
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);
81 /* Loop while todo_list is filled */
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);
90 for splay_each(edge_t, e, n->edge_tree) { /* "e" is the edge connected to "from" */
99 ----->(n)---e-->(e->to)
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:
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
112 if(e->to->status.visited
113 && (e->to->distance != n->distance + 1 || e->weight >= e->to->prevedge->weight)) {
117 e->to->status.visited = true;
118 e->to->nexthop = (n->nexthop == mesh->self) ? e->to : n->nexthop;
120 e->to->distance = n->distance + 1;
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);
126 list_insert_tail(todo_list, e->to);
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);
133 list_free(todo_list);
136 static void check_reachability(meshlink_handle_t *mesh) {
137 /* Check reachability status. */
139 int reachable = -1; /* Don't count ourself */
141 for splay_each(node_t, n, mesh->nodes) {
142 if(n->status.visited) {
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);
150 n->session_id = n->prevedge->reverse->session_id;
153 utcp_abort_all_connections(n->utcp);
156 n->status.validkey = false;
157 sptps_stop(&n->sptps);
158 n->status.waitingforkey = false;
159 n->last_req_key = -3600;
161 n->status.udp_confirmed = false;
166 timeout_del(&mesh->loop, &n->mtutimeout);
169 if(n->status.visited != n->status.reachable) {
170 n->status.reachable = !n->status.reachable;
171 n->status.dirty = true;
173 if(!n->status.blacklisted) {
174 if(n->status.reachable) {
175 logger(mesh, MESHLINK_DEBUG, "Node %s became reachable", n->name);
176 bool first_time_reachable = !n->last_reachable;
177 n->last_reachable = time(NULL);
179 if(first_time_reachable) {
180 if(!node_write_config(mesh, n, false)) {
181 logger(mesh, MESHLINK_WARNING, "Could not write host config file for node %s!\n", n->name);
186 logger(mesh, MESHLINK_DEBUG, "Node %s became unreachable", n->name);
187 n->last_unreachable = time(NULL);
191 n->status.udp_confirmed = false;
196 timeout_del(&mesh->loop, &n->mtutimeout);
198 if(!n->status.blacklisted) {
199 update_node_status(mesh, n);
202 if(!n->status.reachable) {
203 update_node_udp(mesh, n, NULL);
204 n->status.broadcast = false;
208 utcp_offline(n->utcp, !n->status.reachable);
213 if(mesh->reachable != reachable) {
215 mesh->last_unreachable = mesh->loop.now.tv_sec;
217 if(mesh->threadstarted && mesh->periodictimer.cb) {
218 timeout_set(&mesh->loop, &mesh->periodictimer, &(struct timespec) {
219 0, prng(mesh, TIMER_FUDGE)
224 mesh->reachable = reachable;
228 void graph(meshlink_handle_t *mesh) {
230 check_reachability(mesh);