git.meshlink.io Git - meshlink/blob - 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 }