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serval-dna/route_link.c

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/*
Serval DNA link state routing
Copyright (C) 2013 Serval Project Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*/
#include <assert.h>
#include "serval.h"
#include "conf.h"
#include "overlay_address.h"
#include "overlay_buffer.h"
#include "overlay_interface.h"
#include "overlay_packet.h"
#include "str.h"
#include "keyring.h"
#include "server.h"
#include "mdp_client.h"
#include "route_link.h"
/*
Link state routing;
- each node sends a packet on a heartbeat
- on recieving a packet, update a link cost calculation (initially up/down only)
- when the cost changes, update a version field
- every heartbeat interval, send link cost details
- send link cost for every neighbour, they need to know we can still hear them.
- after parsing incoming link details, if anything has changed, mark routes as dirty
*/
#define MAX_LINK_STATES 512
#define FLAG_HAS_INTERFACE (1<<0)
#define FLAG_NO_PATH (1<<1)
#define FLAG_BROADCAST (1<<2)
#define FLAG_UNICAST (1<<3)
#define FLAG_HAS_ACK (1<<4)
#define FLAG_HAS_DROP_RATE (1<<5)
#define ACK_WINDOW (16)
struct link{
struct link *_left;
struct link *_right;
struct subscriber *transmitter;
struct link *parent;
struct network_destination *destination;
struct subscriber *receiver;
// What's the last ack we've heard so we don't process nacks twice.
int last_ack_seq;
// neighbour path version when path scores were last updated
char path_version;
// link quality stats;
char link_version;
char drop_rate;
// calculated path score;
int hop_count;
int path_drop_rate;
// loop prevention;
char calculating;
};
// statistics of incoming half of network links
struct link_in{
struct link_in *_next;
// which of our interfaces did we hear it on?
overlay_interface *interface;
// which of their interfaces did they send it from?
int neighbour_interface;
// very simple time based link up/down detection;
// when will we consider the link broken?
time_ms_t link_timeout;
// unicast or broadcast?
int unicast;
int ack_sequence;
uint64_t ack_mask;
int ack_counter;
};
struct link_out{
struct link_out *_next;
time_ms_t timeout;
struct network_destination *destination;
};
struct neighbour{
struct neighbour *_next;
struct subscriber *subscriber;
// whenever we hear about a link change, update the version to mark all link path scores as dirty
char path_version;
// when do we assume the link is dead because they stopped hearing us or vice versa?
time_ms_t link_in_timeout;
// if a neighbour is telling the world that they are using us as a next hop, we need to send acks & nacks with high priority
// otherwise we don't care too much about packet loss.
char using_us;
// is this neighbour still sending selfacks?
char legacy_protocol;
// when a neighbour is using us as a next hop *and* they are using us to send packets to one of our neighbours,
// we must forward their broadcasts
time_ms_t routing_through_us;
// which of their mdp packets have we already heard and can be dropped as duplicates?
int mdp_ack_sequence;
uint64_t mdp_ack_mask;
// next link update
time_ms_t next_neighbour_update;
time_ms_t last_update;
int last_update_seq;
time_ms_t rtt;
// un-balanced tree of known link states
struct link *root;
// list of incoming link stats
struct link_in *links, *best_link;
// list of outgoing links
struct link_out *out_links;
};
// one struct per subscriber, where we track all routing information, allocated on first use
struct link_state{
// what is the current best hop count? (via subscriber->next_hop)
struct subscriber *next_hop;
struct subscriber *transmitter;
int hop_count;
int route_version;
// if a neighbour is free'd this link will point to invalid memory.
// don't use this pointer directly, call find_best_link instead
struct link *link;
char calculating;
// when do we need to send a new link state message.
time_ms_t next_update;
};
DEFINE_ALARM(link_send);
static int append_link(void **record, void *context);
static int neighbour_find_best_link(struct neighbour *n);
struct neighbour *neighbours=NULL;
unsigned neighbour_count=0;
int route_version=0;
struct network_destination * new_destination(struct overlay_interface *interface){
assert(interface);
struct network_destination *ret = emalloc_zero(sizeof(struct network_destination));
if (ret){
ret->_ref_count=1;
ret->interface = interface;
ret->resend_delay = 1000;
ret->last_tx = TIME_MS_NEVER_HAS;
ret->sequence_number = -1;
ret->last_ack_seq = -1;
}
return ret;
}
struct network_destination * create_unicast_destination(struct socket_address *addr, struct overlay_interface *interface){
if (!interface && addr->addr.sa_family == AF_INET)
interface = overlay_interface_find(addr->inet.sin_addr, 1);
if (!interface){
WHY("I don't know which interface to use");
return NULL;
}
if (interface->state!=INTERFACE_STATE_UP){
WHY("The interface is down.");
return NULL;
}
if (addr->addr.sa_family == AF_INET && (addr->inet.sin_addr.s_addr==0 || addr->inet.sin_port==0))
return NULL;
if (!interface->ifconfig.unicast.send)
return NULL;
struct network_destination *ret = new_destination(interface);
if (ret){
ret->address = *addr;
ret->unicast = 1;
overlay_destination_configure(ret, &interface->ifconfig.unicast);
}
return ret;
}
struct network_destination * add_destination_ref(struct network_destination *ref){
ref->_ref_count++;
return ref;
}
void release_destination_ref(struct network_destination *ref){
if (ref->_ref_count<=1){
free(ref);
}else{
ref->_ref_count--;
}
}
int set_destination_ref(struct network_destination **ptr, struct network_destination *ref){
if (ref==*ptr)
return 0;
if (ref)
add_destination_ref(ref);
if (*ptr)
release_destination_ref(*ptr);
*ptr = ref;
return 1;
}
static int NumberOfSetBits(uint32_t i)
{
i = i - ((i >> 1) & 0x55555555);
i = (i & 0x33333333) + ((i >> 2) & 0x33333333);
return (((i + (i >> 4)) & 0x0F0F0F0F) * 0x01010101) >> 24;
}
static struct link_state *get_link_state(struct subscriber *subscriber)
{
if (!subscriber->link_state){
subscriber->link_state = emalloc_zero(sizeof(struct link_state));
subscriber->link_state->route_version = route_version -1;
}
return subscriber->link_state;
}
static struct neighbour *get_neighbour(struct subscriber *subscriber, char create)
{
struct neighbour *n = neighbours;
while(n){
if (n->subscriber==subscriber)
return n;
n = n->_next;
}
if (create){
n = emalloc_zero(sizeof(struct neighbour));
n->subscriber = subscriber;
n->_next = neighbours;
n->last_update_seq = -1;
n->mdp_ack_sequence = -1;
// TODO measure min/max rtt
n->rtt = 120;
n->next_neighbour_update = gettime_ms() + 10;
neighbours = n;
neighbour_count++;
if (neighbour_count==1){
time_ms_t now = gettime_ms();
RESCHEDULE(&ALARM_STRUCT(link_send), now+10, now+10, now+30);
}
DEBUGF(linkstate, "LINK STATE; new neighbour %s", alloca_tohex_sid_t(n->subscriber->sid));
CALL_TRIGGER(nbr_change, subscriber, 1, neighbour_count);
}
return n;
}
static void free_links(struct link *link)
{
if (!link)
return;
free_links(link->_left);
link->_left=NULL;
free_links(link->_right);
link->_right=NULL;
if (link->destination)
release_destination_ref(link->destination);
free(link);
}
static struct link *find_link(struct neighbour *neighbour, struct subscriber *receiver, char create)
{
struct link **link_ptr=&neighbour->root, *link=neighbour->root;
while(1){
if (link==NULL){
if (create){
link = *link_ptr = emalloc_zero(sizeof(struct link));
link->receiver = receiver;
link->path_version = neighbour->path_version -1;
link->last_ack_seq = -1;
link->link_version = -1;
}
break;
}
if (receiver == link->receiver)
break;
link_ptr = (cmp_sid_t(&receiver->sid, &link->receiver->sid) < 0) ? &link->_left : &link->_right;
link = *link_ptr;
}
return link;
}
static struct link *get_parent(struct neighbour *neighbour, struct link *link)
{
// root of the routing table.
if (link->receiver == neighbour->subscriber || link->transmitter == NULL)
return NULL;
if (!link->parent)
link->parent = find_link(neighbour, link->transmitter, 0);
return link->parent;
}
static void update_path_score(struct neighbour *neighbour, struct link *link){
if (link->path_version == neighbour->path_version)
return;
if (link->calculating)
return;
link->calculating = 1;
int hop_count = -1;
int drop_rate = 0;
if (link->transmitter == get_my_subscriber(1)){
if (link->receiver==neighbour->subscriber){
hop_count = 1;
}
}else{
struct link *parent = get_parent(neighbour, link);
if (parent && (!parent->calculating)){
update_path_score(neighbour, parent);
// TODO more interesting path cost metrics...
if (parent->hop_count>0){
hop_count = parent->hop_count+1;
drop_rate = parent->path_drop_rate;
}
}
}
// ignore occasional dropped packets due to collisions
if (link->drop_rate>2)
drop_rate += link->drop_rate;
if (hop_count != link->hop_count && IF_DEBUG(verbose))
DEBUGF(linkstate, "LINK STATE; path score to %s via %s version %d = %d",
alloca_tohex_sid_t(link->receiver->sid),
alloca_tohex_sid_t(neighbour->subscriber->sid),
neighbour->path_version,
hop_count);
link->hop_count = hop_count;
link->path_version = neighbour->path_version;
link->path_drop_rate = drop_rate;
link->calculating = 0;
}
// pick the best path to this network end point
static struct link * find_best_link(struct subscriber *subscriber)
{
IN();
if (subscriber->reachable & REACHABLE_SELF)
RETURN(NULL);
struct link_state *state = get_link_state(subscriber);
if (state->route_version == route_version)
RETURN(state->link);
if (state->calculating)
RETURN(NULL);
state->calculating = 1;
struct neighbour *neighbour = neighbours;
struct network_destination *destination = NULL;
int best_hop_count = 99;
int best_drop_rate = 99;
struct link *best_link = NULL;
struct subscriber *next_hop = NULL, *transmitter=NULL;
time_ms_t now = gettime_ms();
while (neighbour){
if (neighbour->link_in_timeout < now)
goto next;
struct link *link = find_link(neighbour, subscriber, 0);
if (!(link && link->transmitter))
goto next;
if (link->transmitter != get_my_subscriber(1)){
struct link_state *parent_state = get_link_state(link->transmitter);
find_best_link(link->transmitter);
if (parent_state->next_hop != neighbour->subscriber)
goto next;
}
update_path_score(neighbour, link);
if (link->hop_count>0){
if (link->path_drop_rate < best_drop_rate ||
(link->path_drop_rate == best_drop_rate && link->hop_count < best_hop_count)){
next_hop = neighbour->subscriber;
best_hop_count = link->hop_count;
best_drop_rate = link->path_drop_rate;
transmitter = link->transmitter;
destination = link->destination;
best_link = link;
}
}
next:
neighbour = neighbour->_next;
}
int changed =0;
if (state->transmitter != transmitter || state->link != best_link)
changed = 1;
state->next_hop = next_hop;
state->transmitter = transmitter;
state->hop_count = best_hop_count;
state->route_version = route_version;
state->calculating = 0;
state->link = best_link;
if (next_hop == subscriber)
next_hop = NULL;
if (set_reachable(subscriber, destination, next_hop, best_hop_count, transmitter))
changed = 1;
if (subscriber->identity && subscriber->reachable == REACHABLE_NONE){
subscriber->reachable=REACHABLE_SELF;
changed = 1;
best_link = NULL;
DEBUGF2(overlayrouting, linkstate, "REACHABLE via self %s", alloca_tohex_sid_t(subscriber->sid));
}
if (changed)
state->next_update = now+5;
RETURN(best_link);
}
static int append_link_state(struct overlay_buffer *payload, struct decode_context *context, char flags,
struct subscriber *transmitter, struct subscriber *receiver,
int interface, int version, int ack_sequence, uint32_t ack_mask,
int drop_rate)
{
if (interface!=-1)
flags|=FLAG_HAS_INTERFACE;
if (!transmitter)
flags|=FLAG_NO_PATH;
if (ack_sequence!=-1)
flags|=FLAG_HAS_ACK;
if (drop_rate!=-1)
flags|=FLAG_HAS_DROP_RATE;
size_t length_pos = ob_position(payload);
ob_append_byte(payload, 0);
ob_append_byte(payload, flags);
context->flags = DECODE_FLAG_EXTRA_BITS;
overlay_address_append(context, payload, receiver);
context->flags = 0;
ob_append_byte(payload, version);
if (transmitter)
overlay_address_append(context, payload, transmitter);
if (interface != -1)
ob_append_byte(payload, interface);
if (ack_sequence != -1){
ob_append_byte(payload, ack_sequence);
ob_append_ui32(payload, ack_mask);
}
if (drop_rate != -1)
ob_append_byte(payload, drop_rate);
// TODO insert future fields here
if (ob_overrun(payload))
return -1;
// patch the record length
size_t end_pos = ob_position(payload);
ob_set(payload, length_pos, end_pos - length_pos);
ob_checkpoint(payload);
return 0;
}
struct append_context{
struct overlay_buffer *payload;
struct decode_context context;
};
static int append_link(void **record, void *context)
{
struct subscriber *subscriber = *record;
if (subscriber == get_my_subscriber(1))
return 0;
struct link_state *state = get_link_state(subscriber);
struct link *best_link = find_best_link(subscriber);
if (!context)
return 0;
struct append_context *append_context = context;
time_ms_t now = gettime_ms();
if (subscriber->reachable==REACHABLE_SELF){
if (state->next_update - 20 <= now){
// Other entries in our keyring are always one hop away from us.
if (append_link_state(append_context->payload, &append_context->context, 0, get_my_subscriber(1), subscriber, -1, 1, -1, 0, 0)){
ALARM_STRUCT(link_send).alarm = now+5;
return 1;
}
// include information about this link every 5s
state->next_update = now + 5000;
}
} else {
if (subscriber->identity)
keyring_send_unlock(subscriber);
if (best_link && best_link->destination
&& !best_link->destination->ifconfig.route){
// never mention links we shouldn't advertise
state->next_update = TIME_MS_NEVER_WILL;
}else{
if (state->next_update - 20 <= now){
if (append_link_state(append_context->payload, &append_context->context, 0, state->transmitter, subscriber, -1,
best_link?best_link->link_version:-1, -1, 0, best_link?best_link->drop_rate:32)){
ALARM_STRUCT(link_send).alarm = now+5;
return 1;
}
// include information about this link every 5s
state->next_update = now + 5000;
}
}
}
if (state->next_update < ALARM_STRUCT(link_send).alarm)
ALARM_STRUCT(link_send).alarm = state->next_update;
return 0;
}
static void free_neighbour(struct neighbour **neighbour_ptr){
struct neighbour *n = *neighbour_ptr;
if (IF_DEBUG(verbose))
DEBUGF(linkstate, "LINK STATE; all links from neighbour %s have died", alloca_tohex_sid_t(n->subscriber->sid));
struct link_in *link = n->links;
while(link){
struct link_in *l=link;
link = l->_next;
free(l);
}
struct link_out *out = n->out_links;
while (out){
struct link_out *l=out;
out = l->_next;
release_destination_ref(l->destination);
free(l);
}
free_links(n->root);
n->root=NULL;
*neighbour_ptr = n->_next;
free(n);
}
static void clean_neighbours(time_ms_t now)
{
struct neighbour **n_ptr = &neighbours;
while (*n_ptr){
struct neighbour *n = *n_ptr;
struct subscriber *subscriber = n->subscriber;
// drop any inbound links that have expired
struct link_in **list = &n->links;
while(*list){
struct link_in *link = *list;
if (link->interface->state!=INTERFACE_STATE_UP || link->link_timeout < now){
DEBUGF(linkstate, "LINK STATE; link expired from neighbour %s on interface %s",
alloca_tohex_sid_t(subscriber->sid),
link->interface->name);
*list=link->_next;
free(link);
}else{
list = &link->_next;
}
}
// drop any outbound links that have expired
struct link_out **out = &n->out_links;
int alive=0;
while(*out){
struct link_out *link = *out;
if (link->destination->interface->state!=INTERFACE_STATE_UP){
*out = link->_next;
release_destination_ref(link->destination);
free(link);
}else{
if (link->timeout >= now)
alive=1;
out = &link->_next;
}
}
// when all links to a neighbour that we were directly routing to expire, force a routing calculation update
struct link_state *state = get_link_state(subscriber);
if (state->next_hop == subscriber &&
(n->link_in_timeout < now || !n->links || !alive) &&
state->route_version == route_version)
route_version++;
if (!n->links || !alive){
free_neighbour(n_ptr);
neighbour_count--;
CALL_TRIGGER(nbr_change, subscriber, 0, neighbour_count);
if (neighbour_count==0){
// one last re-scan of network paths to clean up the routing table
enum_subscribers(NULL, append_link, NULL);
RESCHEDULE(&ALARM_STRUCT(link_send),
TIME_MS_NEVER_WILL, TIME_MS_NEVER_WILL, TIME_MS_NEVER_WILL);
}
}else{
n_ptr = &n->_next;
}
}
}
static void link_status_html(struct strbuf *b, struct subscriber *n, struct link *link)
{
if (!link)
return;
link_status_html(b, n, link->_left);
int best=0;
if (link->receiver->next_hop==n)
best=1;
else if(link->receiver==n && n->reachable&REACHABLE_DIRECT)
best=1;
strbuf_sprintf(b, "%s* -%s H: %d, C: %d, via %s*<br>",
alloca_tohex_sid_t_trunc(link->receiver->sid, 16),
best?" *best*":"",
link->hop_count, link->path_drop_rate,
link->transmitter?alloca_tohex_sid_t_trunc(link->transmitter->sid, 16):"unreachable");
link_status_html(b, n, link->_right);
}
void link_neighbour_short_status_html(struct strbuf *b, const char *link_prefix)
{
struct neighbour *n = neighbours;
if (!n)
strbuf_puts(b, "No peers<br>");
while(n){
strbuf_sprintf(b, "<a href=\"%s/%s\">%s*</a>, seq=%d, mask=%08"PRIx64"<br>",
link_prefix,
alloca_tohex_sid_t(n->subscriber->sid),
alloca_tohex_sid_t_trunc(n->subscriber->sid, 16),
n->mdp_ack_sequence, n->mdp_ack_mask);
n=n->_next;
}
}
void link_neighbour_status_html(struct strbuf *b, struct subscriber *neighbour)
{
time_ms_t now = gettime_ms();
struct neighbour *n = neighbours;
while(n){
if (n->subscriber == neighbour){
strbuf_sprintf(b, "Neighbour %s*;<br>", alloca_tohex_sid_t_trunc(n->subscriber->sid, 16));
strbuf_sprintf(b, "Seq=%d, mask=%08"PRIx64"<br>", n->mdp_ack_sequence, n->mdp_ack_mask);
rhizome_sync_status_html(b, n->subscriber);
struct link_in *link_in = n->links;
while(link_in){
strbuf_sprintf(b, "In: %s %s%s, seq=%d, mask=%08"PRIx64"<br>",
link_in->interface->name,
link_in->unicast?"unicast":"broadcast",
link_in == n->best_link?" *best":"",
link_in->ack_sequence,
link_in->ack_mask);
link_in = link_in->_next;
}
struct link_out *link_out = n->out_links;
while(link_out){
if (link_out->timeout >= now){
strbuf_sprintf(b, "Out: %s %s<br>",
link_out->destination->interface->name,
link_out->destination->unicast?"unicast":"broadcast");
}
link_out = link_out->_next;
}
strbuf_puts(b, "Links;<br>");
link_status_html(b, n->subscriber, n->root);
return;
}
n = n->_next;
}
strbuf_puts(b, "Not found<br>");
}
int link_has_neighbours()
{
return neighbours?1:0;
}
int link_interface_has_neighbours(struct overlay_interface *interface)
{
struct neighbour *n = neighbours;
while(n){
neighbour_find_best_link(n);
if (n->best_link && n->best_link->interface == interface)
return 1;
n=n->_next;
}
return 0;
}
int link_destination_has_neighbours(struct network_destination *dest)
{
struct neighbour *n = neighbours;
time_ms_t now = gettime_ms();
while(n){
struct link_out *l = n->out_links;
while(l){
if (l->destination == dest && l->timeout >= now)
return 1;
l=l->_next;
}
n=n->_next;
}
return 0;
}
static int send_legacy_self_announce_ack(struct neighbour *neighbour, struct link_in *link, time_ms_t now){
struct overlay_frame *frame=emalloc_zero(sizeof(struct overlay_frame));
frame->type = OF_TYPE_SELFANNOUNCE_ACK;
frame->ttl = 6;
frame->destination = neighbour->subscriber;
frame->source = get_my_subscriber(1);
if ((frame->payload = ob_new()) == NULL) {
op_free(frame);
return -1;
}
ob_append_ui32(frame->payload, neighbour->last_update);
ob_append_ui32(frame->payload, now);
ob_append_byte(frame->payload, link->neighbour_interface);
frame->queue=OQ_MESH_MANAGEMENT;
if (overlay_payload_enqueue(frame) == -1) {
op_free(frame);
return -1;
}
return 0;
}
// find our neighbour's best link from them to us.
// we only ack a single inbound link.
static int neighbour_find_best_link(struct neighbour *n)
{
// TODO compare other link stats to find the best...
struct link_in *best_link=n->links;
if (best_link){
struct link_in *link=best_link->_next;
while(link){
// find the link with the best interface
switch(overlay_interface_compare(best_link->interface, link->interface)){
case -1:
break;
case 0:
if (link->unicast < best_link->unicast)
break;
// fall through
case 1:
best_link = link;
}
link = link->_next;
}
}
if (n->best_link != best_link){
n->best_link = best_link;
n->next_neighbour_update = gettime_ms()+20;
if (best_link) {
DEBUGF(linkstate, "LINK STATE; best link from neighbour %s is %s on interface %s",
alloca_tohex_sid_t(n->subscriber->sid),
best_link->unicast?"unicast":"broadcast",
best_link->interface->name);
} else {
DEBUGF(linkstate, "LINK STATE; no best link from neighbour %s",
alloca_tohex_sid_t(n->subscriber->sid));
}
}
return 0;
}
static int neighbour_link_sent(struct overlay_frame *frame, struct network_destination *destination, int sequence, void *context)
{
frame->resend = -1;
struct subscriber *subscriber = context;
struct neighbour *neighbour = get_neighbour(subscriber, 0);
if (!neighbour)
return 0;
neighbour->last_update_seq = sequence;
if (IF_DEBUG(verbose) || IF_DEBUG(ack))
DEBUGF2(linkstate, ack, "LINK STATE; ack sent to neighbour %s via %s, in seq %d",
alloca_tohex_sid_t(subscriber->sid),
alloca_socket_address(&destination->address), sequence);
return 0;
}
static int send_neighbour_link(struct neighbour *n)
{
IN();
if (!n->best_link)
RETURN(-1);
time_ms_t now = gettime_ms();
if (n->legacy_protocol){
// send a self announce ack instead.
send_legacy_self_announce_ack(n, n->best_link, now);
n->last_update = now;
} else {
struct overlay_frame *frame = emalloc_zero(sizeof(struct overlay_frame));
frame->type=OF_TYPE_DATA;
frame->source=get_my_subscriber(1);
frame->ttl=1;
frame->queue=OQ_MESH_MANAGEMENT;
if ((frame->payload = ob_new()) == NULL) {
op_free(frame);
RETURN(-1);
}
frame->send_hook = neighbour_link_sent;
frame->send_context = n->subscriber;
frame->resend = -1;
if (n->subscriber->reachable & REACHABLE_DIRECT){
// let normal packet routing decisions pick the best link
frame->destination = n->subscriber;
}else{
// not an immediate neighbour yet? send this packet to all probable destinations.
if (IF_DEBUG(verbose) || IF_DEBUG(ack))
DEBUGF2(linkstate, ack, "Sending link state ack to all possibilities");
struct link_out *out = n->out_links;
while(out){
if (out->timeout >= now)
frame->destinations[frame->destination_count++].destination = add_destination_ref(out->destination);
out = out->_next;
}
}
ob_limitsize(frame->payload, 400);
overlay_mdp_encode_ports(frame->payload, MDP_PORT_LINKSTATE, MDP_PORT_LINKSTATE);
char flags=0;
if (n->best_link->unicast)
flags|=FLAG_UNICAST;
else
flags|=FLAG_BROADCAST;
DEBUGF(ack, "LINK STATE; Sending ack to %s for seq %d", alloca_tohex_sid_t(n->subscriber->sid), n->best_link->ack_sequence);
struct decode_context context;
bzero(&context, sizeof context);
context.sender = get_my_subscriber(1);
append_link_state(frame->payload, &context, flags, n->subscriber, context.sender, n->best_link->neighbour_interface, 1,
n->best_link->ack_sequence, n->best_link->ack_mask, -1);
if (overlay_payload_enqueue(frame) == -1)
op_free(frame);
n->best_link->ack_counter = ACK_WINDOW;
n->last_update = now;
}
{
struct overlay_interface *i = n->best_link->interface;
int delay = 0;
if (n->best_link->unicast && i->ifconfig.unicast.tick_ms>0)
delay = i->ifconfig.unicast.tick_ms;
if (delay==0)
delay = i->destination->ifconfig.tick_ms;
n->next_neighbour_update = n->last_update + delay;
}
DEBUGF(ack, "Next update for %s in %"PRId64"ms", alloca_tohex_sid_t(n->subscriber->sid), n->next_neighbour_update - gettime_ms());
OUT();
return 0;
}
static int link_send_neighbours()
{
time_ms_t now = gettime_ms();
clean_neighbours(now);
struct neighbour *n = neighbours;
while (n){
neighbour_find_best_link(n);
if (n->next_neighbour_update <= now)
send_neighbour_link(n);
if (n->next_neighbour_update < ALARM_STRUCT(link_send).alarm)
ALARM_STRUCT(link_send).alarm = n->next_neighbour_update;
struct link_out *out = n->out_links;
while(out){
if (out->destination->ifconfig.tick_ms>0 && out->destination->unicast){
if (out->destination->last_tx + out->destination->ifconfig.tick_ms < now)
overlay_send_tick_packet(out->destination);
if (out->destination->last_tx + out->destination->ifconfig.tick_ms < ALARM_STRUCT(link_send).alarm){
time_ms_t next_tick = out->destination->last_tx + out->destination->ifconfig.tick_ms;
time_ms_t next_allowed = limit_next_allowed(&out->destination->transfer_limit);
ALARM_STRUCT(link_send).alarm = next_tick < next_allowed ? next_allowed : next_tick ;
}
}
out=out->_next;
}
n = n->_next;
}
return 0;
}
// send link details
void link_send(struct sched_ent *alarm)
{
if (!neighbours)
return;
alarm->alarm=TIME_MS_NEVER_WILL;
// TODO use a separate alarm?
link_send_neighbours();
struct append_context context;
bzero(&context, sizeof(context));
context.payload = ob_new();
if (!context.payload){
WHY("Cannot send link details");
alarm->alarm = gettime_ms()+20;
}else{
struct internal_mdp_header header;
bzero(&header, sizeof(header));
context.context.sender = header.source = get_my_subscriber(1);
header.source_port = MDP_PORT_LINKSTATE;
header.destination_port = MDP_PORT_LINKSTATE;
header.ttl = 1;
header.qos = OQ_MESH_MANAGEMENT;
header.crypt_flags = MDP_FLAG_NO_CRYPT|MDP_FLAG_NO_SIGN;
header.resend = -1;
ob_limitsize(context.payload, 400);
ob_checkpoint(context.payload);
size_t pos = ob_position(context.payload);
enum_subscribers(NULL, append_link, &context);
ob_rewind(context.payload);
if (ob_position(context.payload) != pos){
ob_flip(context.payload);
overlay_send_frame(&header, context.payload);
}
ob_free(context.payload);
}
time_ms_t allowed=gettime_ms()+5;
if (alarm->alarm < allowed)
alarm->alarm = allowed;
alarm->deadline = alarm->alarm;
schedule(alarm);
}
static void update_alarm(struct __sourceloc __whence, time_ms_t limit)
{
if (limit == 0)
FATALF("limit == 0");
if (ALARM_STRUCT(link_send).alarm>limit){
RESCHEDULE(&ALARM_STRUCT(link_send), limit, limit, limit+20);
}
}
int link_stop_routing(struct subscriber *subscriber)
{
if (subscriber->reachable!=REACHABLE_SELF)
return 0;
subscriber->reachable = REACHABLE_NONE;
subscriber->identity=NULL;
if (serverMode && subscriber->link_state){
struct link_state *state = get_link_state(subscriber);
state->next_update = gettime_ms();
update_alarm(__WHENCE__, state->next_update);
}
return 0;
}
struct link_in * get_neighbour_link(struct neighbour *neighbour, struct overlay_interface *interface, int sender_interface, int unicast)
{
struct link_in *link = neighbour->links;
if (unicast){
if (interface->ifconfig.prefer_unicast)
unicast=1;
else
unicast=-1;
}
while(link){
if (link->interface == interface
&& link->neighbour_interface == sender_interface
&& link->unicast == unicast)
return link;
link=link->_next;
}
link = emalloc_zero(sizeof(struct link_in));
link->interface = interface;
link->unicast = unicast;
link->neighbour_interface = sender_interface;
link->ack_sequence = -1;
link->ack_mask = 0;
link->_next = neighbour->links;
DEBUGF(linkstate, "LINK STATE; new possible %s link from neighbour %s on interface %s/%d",
unicast?"unicast":"broadcast",
alloca_tohex_sid_t(neighbour->subscriber->sid),
interface->name,
sender_interface);
neighbour->links = link;
return link;
}
int link_add_destinations(struct overlay_frame *frame)
{
if (frame->destination){
struct subscriber *next_hop = frame->destination;
// if the destination is unreachable, but we have a reachable directory service
// forward it through the directory service
if (next_hop->reachable==REACHABLE_NONE
&& directory_service
&& next_hop!=directory_service
&& directory_service->reachable&REACHABLE)
next_hop = directory_service;
if (next_hop->reachable==REACHABLE_NONE && frame->destination_count==0){
// if the destination is a network neighbour, but we haven't established any viable route yet
// we need to add all likely links so that we can send ack's and bootstrap the routing table
struct neighbour *n = get_neighbour(frame->destination, 0);
if (n){
struct link_out *out = n->out_links;
time_ms_t now = gettime_ms();
while(out){
if (out->timeout>=now && frame->destination_count < MAX_PACKET_DESTINATIONS)
frame_add_destination(frame, next_hop, out->destination);
out = out->_next;
}
}
}
if (next_hop->reachable==REACHABLE_NONE && frame->destination_count==0){
// check config for a hardcoded address
struct network_destination *destination = load_subscriber_address(frame->destination);
if (destination){
frame_add_destination(frame, next_hop, destination);
release_destination_ref(destination);
}
}
if ((next_hop->reachable&REACHABLE)==REACHABLE_INDIRECT)
next_hop = next_hop->next_hop;
if (next_hop->reachable&REACHABLE_DIRECT){
unsigned i;
for (i=frame->destination_count;i>0;i--){
// do nothing if this packet is already going the right way
if (frame->destinations[i-1].destination == next_hop->destination)
return 0;
// remove any stale destinations where the initial packet was not acked
frame_remove_destination(frame, i-1);
}
frame_add_destination(frame, next_hop, next_hop->destination);
}
}else if (frame->destination_count==0){
char added_interface[OVERLAY_MAX_INTERFACES];
bzero(added_interface, sizeof(added_interface));
struct neighbour *neighbour = neighbours;
for(;neighbour;neighbour = neighbour->_next){
if (neighbour->subscriber->reachable&REACHABLE_DIRECT){
struct network_destination *dest = neighbour->subscriber->destination;
// TODO move packet version flag to destination struct?
if (frame->packet_version > neighbour->subscriber->max_packet_version)
frame->packet_version = neighbour->subscriber->max_packet_version;
if (!dest->unicast){
// make sure we only add each broadcast interface once
unsigned id = dest->interface - overlay_interfaces;
if (added_interface[id])
continue;
added_interface[id]=1;
}
frame_add_destination(frame, NULL, dest);
}else if(!(neighbour->subscriber->reachable & REACHABLE)){
// send broadcast packets to neighbours before link establishment
struct link_out *out = neighbour->out_links;
time_ms_t now = gettime_ms();
while(out){
if (out->timeout>=now)
frame_add_destination(frame, NULL, out->destination);
out = out->_next;
}
}
}
}
return 0;
}
// do we need to forward any broadcast packets transmitted by this neighbour?
int link_state_should_forward_broadcast(struct subscriber *transmitter)
{
struct neighbour *neighbour = get_neighbour(transmitter, 0);
if (!neighbour)
return 1;
time_ms_t now = gettime_ms();
// it's only safe to drop broadcasts if we know we are in this neighbours routing table,
// and we know we are not vital to reach someone else.
// if we aren't in their routing table as an immediate neighbour, we may be hearing this broadcast packet over an otherwise unreliable link.
// since we're going to process it now and assume that any future copies are duplicates, its better to be safe and forward it.
if (neighbour->using_us && neighbour->routing_through_us < now)
return 0;
return 1;
}
// when we receive a packet from a neighbour with ourselves as the next hop, make sure we send an ack soon(ish)
int link_state_ack_soon(struct subscriber *subscriber)
{
IN();
struct neighbour *neighbour = get_neighbour(subscriber, 0);
if (!neighbour)
RETURN(0);
time_ms_t now = gettime_ms();
if (neighbour->using_us
&& subscriber->reachable & REACHABLE_DIRECT
&& subscriber->destination){
time_ms_t update_time = now + subscriber->destination->resend_delay/3;
if (neighbour->next_neighbour_update > update_time){
neighbour->next_neighbour_update = update_time;
DEBUGF(ack, "Asking for next ACK Real Soon Now");
}
update_alarm(__WHENCE__, neighbour->next_neighbour_update);
}
OUT();
return 0;
}
// our neighbour is sending a duplicate frame, did we see the original?
int link_received_duplicate(struct decode_context *context, int payload_seq)
{
struct neighbour *neighbour = get_neighbour(context->sender, 0);
if (!neighbour)
return 0;
if (neighbour->mdp_ack_sequence == -1){
neighbour->mdp_ack_sequence = payload_seq;
return 0;
}
if (neighbour->mdp_ack_sequence == payload_seq)
return 1;
int offset = (neighbour->mdp_ack_sequence - 1 - payload_seq)&0xFF;
if (offset < 64){
if (neighbour->mdp_ack_mask & (1ull<<offset)){
return 1;
}
neighbour->mdp_ack_mask |= (1ull<<offset);
}else{
int offset = (payload_seq - neighbour->mdp_ack_sequence - 1)&0xFF;
if (offset>=64){
neighbour->mdp_ack_mask = 0;
DEBUGF(ack, "Jump in neighbour mdp seq (%d -> %d)",neighbour->mdp_ack_sequence,payload_seq);
}else{
neighbour->mdp_ack_mask = (neighbour->mdp_ack_mask << 1) | 1;
neighbour->mdp_ack_mask = neighbour->mdp_ack_mask << offset;
}
neighbour->mdp_ack_sequence = payload_seq;
}
return 0;
}
// remote peer has confirmed hearing a recent unicast packet
int link_unicast_ack(struct subscriber *UNUSED(subscriber), struct overlay_interface *UNUSED(interface), struct socket_address *UNUSED(addr))
{
// NOOP, the packet arrival has already been tracked
return 0;
}
static struct link_out *create_out_link(struct neighbour *neighbour, overlay_interface *interface, struct socket_address *addr, char unicast)
{
struct network_destination *dest = NULL;
if (unicast)
dest = create_unicast_destination(addr, interface);
else
dest = add_destination_ref(interface->destination);
if (!dest)
return NULL;
struct link_out *ret=emalloc_zero(sizeof(struct link_out));
if (!ret)
return NULL;
ret->_next=neighbour->out_links;
neighbour->out_links=ret;
ret->destination=dest;
DEBUGF(linkstate, "LINK STATE; Create possible %s link_out for neighbour %s on interface %s",
unicast?"unicast":"broadcast",
alloca_tohex_sid_t(neighbour->subscriber->sid),
interface->name);
time_ms_t now = gettime_ms();
ret->timeout = now + ret->destination->ifconfig.reachable_timeout_ms;
update_alarm(__WHENCE__, now + 5);
return ret;
}
static void create_out_links(struct neighbour *neighbour, overlay_interface *interface, struct socket_address *addr){
struct link_out *l = neighbour->out_links;
while(l){
if (l->destination->interface==interface)
return;
l=l->_next;
}
// if this packet arrived in an IPv4 packet, assume we need to send them unicast packets
create_out_link(neighbour, interface, addr, 1);
// if this packet arrived from the same IPv4 subnet, or a different type of network, assume they can hear our broadcasts
if (!addr || addr->addr.sa_family!=AF_INET ||
(addr->inet.sin_addr.s_addr & interface->netmask.s_addr)
== (interface->address.inet.sin_addr.s_addr & interface->netmask.s_addr))
create_out_link(neighbour, interface, addr, 0);
}
// track stats for receiving packets from this neighbour
int link_received_packet(struct decode_context *context, int sender_seq, uint8_t unicast)
{
if (!context->sender)
return 0;
struct neighbour *neighbour = get_neighbour(context->sender, 1);
// get stats about incoming packets
struct link_in *link=get_neighbour_link(neighbour, context->interface, context->sender_interface, unicast);
time_ms_t now = gettime_ms();
create_out_links(neighbour, context->interface, &context->addr);
// for now we'll use a simple time based link up/down flag + dropped packet count
if (sender_seq >=0){
if (link->ack_sequence != -1){
int offset = (link->ack_sequence - 1 - sender_seq)&0xFF;
if (offset < 64){
if (link->ack_mask & (1ull<<offset)){
// received duplicate frame?
if (IF_DEBUG(verbose))
DEBUGF(linkstate, "LINK STATE; duplicate seq %d from %s on %s",
sender_seq, alloca_tohex_sid_t(context->sender->sid), context->interface->name);
return 1;
}
// packets were re-ordered?
if (IF_DEBUG(verbose))
DEBUGF(linkstate, "LINK STATE; late seq %d from %s on %s",
sender_seq, alloca_tohex_sid_t(context->sender->sid), context->interface->name);
link->ack_mask |= (1ull<<offset);
}else{
link->ack_mask = (link->ack_mask << 1) | 1;
while(1){
link->ack_sequence = (link->ack_sequence+1)&0xFF;
if (link->ack_sequence == sender_seq)
break;
// missed a packet? send a link state soon
if (IF_DEBUG(verbose) || IF_DEBUG(ack))
DEBUGF2(linkstate, ack, "LINK STATE; missed seq %d from %s on %s",
link->ack_sequence, alloca_tohex_sid_t(context->sender->sid), context->interface->name);
link->ack_mask = link->ack_mask << 1;
link->ack_counter --;
// we need to nack promptly
if (neighbour->using_us && link==neighbour->best_link){
neighbour->next_neighbour_update = now + 5;
}
}
}
}else
link->ack_sequence = sender_seq;
}
// force an update when we start hearing a new neighbour link
if (link->link_timeout < now){
if (neighbour->next_neighbour_update > now + 10)
neighbour->next_neighbour_update = now + 10;
}
link->link_timeout = now + context->interface->destination->ifconfig.reachable_timeout_ms;
link->ack_counter --;
// force an update soon when we need to promptly ack packets
if (neighbour->using_us && link->ack_counter <=0){
neighbour_find_best_link(neighbour);
if (link == neighbour->best_link)
send_neighbour_link(neighbour);
}
update_alarm(__WHENCE__, neighbour->next_neighbour_update);
return 0;
}
// parse incoming link details
DEFINE_BINDING(MDP_PORT_LINKSTATE, link_receive);
static int link_receive(struct internal_mdp_header *header, struct overlay_buffer *payload)
{
IN();
if (header->source->reachable == REACHABLE_SELF)
RETURN(0);
struct subscriber *myself = get_my_subscriber(1);
struct neighbour *neighbour = get_neighbour(header->source, 1);
struct decode_context context;
bzero(&context, sizeof(context));
context.interface = header->receive_interface;
context.sender = header->source;
time_ms_t now = gettime_ms();
char changed = 0;
while(ob_remaining(payload)>0){
struct subscriber *receiver=NULL, *transmitter=NULL;
struct overlay_interface *interface = NULL;
size_t start_pos = ob_position(payload);
int length = ob_get(payload);
if (length <=0)
break;
int flags = ob_get(payload);
if (flags<0)
break;
// If the link is dead, and we don't understand the SID, don't ask about it.
// We don't want or need to know.
context.flags = (flags & FLAG_NO_PATH)?DECODE_FLAG_DONT_EXPLAIN:0;
if (overlay_address_parse(&context, payload, &receiver))
break;
int version = ob_get(payload);
if (version < 0)
break;
if (!(flags & FLAG_NO_PATH)){
if (overlay_address_parse(&context, payload, &transmitter))
break;
}
int interface_id = -1;
if (flags & FLAG_HAS_INTERFACE){
interface_id = ob_get(payload);
if (interface_id < 0)
break;
if (interface_id >= OVERLAY_MAX_INTERFACES)
continue;
}
int ack_seq = -1;
uint32_t ack_mask = 0;
int drop_rate = 0;
if (flags & FLAG_HAS_ACK){
ack_seq = ob_get(payload);
ack_mask = ob_get_ui32(payload);
drop_rate = 15 - NumberOfSetBits((ack_mask & 0x7FFF));
// we can deal with low packet loss, and with fast packet transmission rates we're going to see lots of broadcast collisions.
// we only want to force a link update when packet loss due to interference is high. Otherwise ignore it.
if (drop_rate <=3)
drop_rate = 0;
}
if (flags & FLAG_HAS_DROP_RATE){
drop_rate = ob_get(payload);
if (drop_rate <0)
break;
}
// jump to the position of the next record, even if there's more data we don't understand
payload->position = start_pos + length;
if (context.flags & DECODE_FLAG_INVALID_ADDRESS)
continue;
if (IF_DEBUG(verbose) || IF_DEBUG(ack))
DEBUGF2(linkstate, ack, "LINK STATE; record - %d, %s, %s, %d, %d, %x, %d",
flags,
receiver?alloca_tohex_sid_t(receiver->sid):"NULL",
transmitter?alloca_tohex_sid_t(transmitter->sid):"NULL",
interface_id,
ack_seq,
ack_mask,
drop_rate);
if (transmitter && transmitter!=myself && transmitter->reachable==REACHABLE_SELF){
// Our neighbour is talking about a path *from* a secondary SID of ours? Impossible.
// Maybe we decoded an abbreviation incorrectly and this indicates a SID collision.
// TODO add a test for this case!
transmitter->send_full=1;
continue;
}
if (receiver == myself){
// track if our neighbour is using us as an immediate neighbour, if they are we need to ack / nack promptly
neighbour->using_us = (transmitter==header->source?1:0);
// for routing, we can completely ignore any links that our neighbour is using to route to us.
// we can always send packets to ourself :)
continue;
}
if (receiver->reachable == REACHABLE_SELF){
if (transmitter && transmitter!=myself){
// An alternative path to a secondary SID, that isn't via me? Impossible.
// Maybe we decoded an abbreviation incorrectly and this indicates a SID collision.
// TODO add a test for this case!
receiver->send_full=1;
continue;
}
}
struct network_destination *destination=NULL;
if (receiver == header->source){
// ignore other incoming links to our neighbour
if (transmitter!=myself || interface_id==-1)
continue;
interface = &overlay_interfaces[interface_id];
// ignore any links claiming to be from an interface we aren't using
if (interface->state != INTERFACE_STATE_UP)
continue;
struct link_out *out = neighbour->out_links;
char unicast = flags&FLAG_UNICAST?1:0;
while(out){
if (out->destination->interface==interface
&& out->destination->unicast==unicast)
break;
out=out->_next;
}
if (!out){
if (flags&FLAG_UNICAST)
continue;
out = create_out_link(neighbour, interface, NULL, 0);
if (!out)
continue;
}
// start sending sequence numbers when our neighbour has acked a packet
if (out->destination->sequence_number<0)
out->destination->sequence_number=0;
out->timeout=now + out->destination->ifconfig.reachable_timeout_ms;
destination = out->destination;
}else if(transmitter == myself){
// if our neighbour starts using us to reach this receiver, we have to treat the link in our routing table as if it just died.
transmitter = NULL;
if (receiver->reachable != REACHABLE_SELF){
// also we should forward this neighbours broadcast packets to ensure they reach this receiver.
// since we won't remember this link for routing purposes, we'll just use a simple timer.
neighbour->routing_through_us = now + 2500;
}
}
struct link *link = find_link(neighbour, receiver, transmitter?1:0);
if (!link)
continue;
if (transmitter == myself && receiver == header->source && interface_id != -1 && destination){
// they can hear us? we can route through them!
version = link->link_version;
// which network destination can they hear us from?
if (set_destination_ref(&link->destination, destination)){
changed = 1;
version++;
}
if (neighbour->link_in_timeout < now || version<0){
changed = 1;
version++;
}
neighbour->link_in_timeout = now + interface->destination->ifconfig.reachable_timeout_ms;
if (drop_rate != link->drop_rate || transmitter != link->transmitter)
version++;
// process acks / nacks
if (ack_seq!=-1){
// track the latest ack from any neighbour
if (destination->last_ack_seq==-1 || ((ack_seq - destination->last_ack_seq)&0xFF) <= 127){
destination->last_ack_seq = ack_seq;
}
overlay_queue_ack(header->source, destination, ack_mask, ack_seq);
// did they miss our last ack?
if (neighbour->last_update_seq!=-1){
int seq_delta = (ack_seq - neighbour->last_update_seq)&0xFF;
if (seq_delta <= 32 && (seq_delta==0 || ack_mask&(1ull<<(seq_delta-1)))){
neighbour->last_update_seq = -1;
}else if(seq_delta < 128){
// send another ack soon
DEBUGF(ack, "LINK STATE; neighbour %s missed ack %d, queue another",
alloca_tohex_sid_t(header->source->sid), neighbour->last_update_seq);
neighbour->next_neighbour_update=now+10;
update_alarm(__WHENCE__, neighbour->next_neighbour_update);
}
}
}
link->last_ack_seq = ack_seq;
}else{
set_destination_ref(&link->destination, NULL);
}
if (link->transmitter != transmitter || link->link_version != version){
changed = 1;
link->transmitter = transmitter;
link->link_version = version & 0xFF;
link->drop_rate = drop_rate;
// TODO other link attributes...
}
}
send_please_explain(&context, myself, header->source);
if (changed){
route_version++;
neighbour->path_version ++;
if (ALARM_STRUCT(link_send).alarm>now+5){
RESCHEDULE(&ALARM_STRUCT(link_send), now+5, now+5, now+25);
}
}
OUT();
return 0;
}
// if a neighbour asks for a subscriber explaination, make sure we repeat relevant link information immediately.
void link_explained(struct subscriber *subscriber)
{
time_ms_t now = gettime_ms();
struct link_state *state = get_link_state(subscriber);
state->next_update = now + 5;
update_alarm(__WHENCE__, now + 5);
}
static void link_interface_change(struct overlay_interface *UNUSED(interface))
{
clean_neighbours(gettime_ms());
}
DEFINE_TRIGGER(iupdown, link_interface_change);
/* if an ancient node on the network uses their old protocol to tell us that they can hear us;
- send the same format back at them
- treat the link as up.
- but we aren't going to use this link in either routing protocol
*/
int link_state_legacy_ack(struct overlay_frame *frame, time_ms_t now)
{
if (frame->payload->sizeLimit<9)
return WHY("selfannounce ack packet too short");
ob_get_ui32(frame->payload);
ob_get_ui32(frame->payload);
int iface=ob_get(frame->payload);
overlay_interface *interface = &overlay_interfaces[iface];
// record that we have a possible link to this neighbour
struct neighbour *neighbour = get_neighbour(frame->source, 1);
struct link *link = find_link(neighbour, frame->source, 1);
int changed = 0;
if (!neighbour->legacy_protocol){
changed = 1;
DEBUGF(linkstate, "LINK STATE; new legacy neighbour %s", alloca_tohex_sid_t(frame->source->sid));
}
if (neighbour->link_in_timeout < now)
changed = 1;
if (link->transmitter != get_my_subscriber(1))
changed = 1;
link->transmitter = get_my_subscriber(1);
link->link_version = 1;
link->destination = interface->destination;
// give this link a high cost, we aren't going to route through it anyway...
link->drop_rate = 32;
// track the incoming link so we remember to send broadcasts
struct link_in *nl = get_neighbour_link(neighbour, frame->interface, iface, 0);
nl->link_timeout = now + (link->destination->ifconfig.reachable_timeout_ms);
neighbour->legacy_protocol = 1;
neighbour->link_in_timeout = now + link->destination->ifconfig.reachable_timeout_ms;
if (changed){
route_version++;
neighbour->path_version ++;
if (ALARM_STRUCT(link_send).alarm>now+5){
RESCHEDULE(&ALARM_STRUCT(link_send), now+5, now+5, now+25);
}
}
return 0;
}
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