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                 next = node->next; /* Because the list_insert_tail() above could have added something extra for us! */
 130                 list_delete_node(todo_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                         n->session_id = n->prevedge->reverse->session_id;
 149
 150                         if(n->utcp) {
 151                                 utcp_abort_all_connections(n->utcp);
 152                         }
 153
 154                         if(n->status.visited == n->status.reachable) {
 155                                 /* This session replaces the previous one without changing reachability status.
 156                                  * We still need to reset the UDP SPTPS state.
 157                                  */
 158                                 n->status.validkey = false;
 159                                 sptps_stop(&n->sptps);
 160                                 n->status.waitingforkey = false;
 161                                 n->last_req_key = 0;
 162
 163                                 n->status.udp_confirmed = false;
 164                                 n->maxmtu = MTU;
 165                                 n->minmtu = 0;
 166                                 n->mtuprobes = 0;
 167
 168                                 timeout_del(&mesh->loop, &n->mtutimeout);
 169                         }
 170                 }
 171
 172                 if(n->status.visited != n->status.reachable) {
 173                         n->status.reachable = !n->status.reachable;
 174                         n->status.dirty = true;
 175
 176                         if(!n->status.blacklisted) {
 177                                 if(n->status.reachable) {
 178                                         logger(mesh, MESHLINK_DEBUG, "Node %s became reachable", n->name);
 179                                         bool first_time_reachable = !n->last_reachable;
 180                                         n->last_reachable = time(NULL);
 181
 182                                         if(first_time_reachable) {
 183                                                 if(!node_write_config(mesh, n)) {
 184                                                         logger(mesh, MESHLINK_WARNING, "Could not write host config file for node %s!\n", n->name);
 185
 186                                                 }
 187                                         }
 188                                 } else {
 189                                         logger(mesh, MESHLINK_DEBUG, "Node %s became unreachable", n->name);
 190                                         n->last_unreachable = time(NULL);
 191                                 }
 192                         }
 193
 194                         /* TODO: only clear status.validkey if node is unreachable? */
 195
 196                         n->status.validkey = false;
 197                         sptps_stop(&n->sptps);
 198                         n->status.waitingforkey = false;
 199                         n->last_req_key = 0;
 200
 201                         n->status.udp_confirmed = false;
 202                         n->maxmtu = MTU;
 203                         n->minmtu = 0;
 204                         n->mtuprobes = 0;
 205
 206                         timeout_del(&mesh->loop, &n->mtutimeout);
 207
 208                         if(!n->status.blacklisted) {
 209                                 update_node_status(mesh, n);
 210                         }
 211
 212                         if(!n->status.reachable) {
 213                                 update_node_udp(mesh, n, NULL);
 214                                 n->status.broadcast = false;
 215                         } else if(n->connection) {
 216                                 if(n->connection->status.initiator) {
 217                                         send_req_key(mesh, n);
 218                                 }
 219                         }
 220
 221                         if(n->utcp) {
 222                                 utcp_offline(n->utcp, !n->status.reachable);
 223                         }
 224                 }
 225         }
 226
 227         if(mesh->reachable != reachable) {
 228                 if(!reachable) {
 229                         mesh->last_unreachable = mesh->loop.now.tv_sec;
 230
 231                         if(mesh->threadstarted) {
 232                                 timeout_set(&mesh->loop, &mesh->periodictimer, &(struct timespec) {
 233                                         0, prng(mesh, TIMER_FUDGE)
 234                                 });
 235                         }
 236                 }
 237
 238                 mesh->reachable = reachable;
 239         }
 240 }
 241
 242 void graph(meshlink_handle_t *mesh) {
 243         sssp_bfs(mesh);
 244         check_reachability(mesh);
 245 }