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sources: add option to limit selection of unreachable sources

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Add maxunreach option to NTP sources and refclocks to specify the
maximum number of polls that the source can stay selected for
synchronization when it is unreachable (i.e. no valid sample was
received in the last 8 polls).

It is an additional requirement to having at least one sample more
recent than the oldest sample of reachable sources.

The default value is 100000. Setting the option to 0 disables selection
of unreachable sources, which matches RFC 5905.
This commit is contained in:
Miroslav Lichvar
2025-08-05 16:08:40 +02:00
parent be7f5e8916
commit 9b183fe98f
16 changed files with 108 additions and 15 deletions
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33
sources.c
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@@ -106,13 +106,20 @@ struct SRC_Instance_Record {
/* Number of set bits in the reachability register */
int reachability_size;
/* Updates since last reference update */
/* Number of reachability updates with cleared register */
int unreachable_run;
/* Maximum number of reachability updates with cleared register to still
allow selection */
int max_unreachable_run;
/* Number of selection updates since last reference update */
int updates;
/* Updates left before allowing combining */
/* Number of selection updates left before allowing combining again */
int distant;
/* Updates with a status requiring source replacement */
/* Number of selection updates with a status requiring source replacement */
int bad;
/* Flag indicating the status of the source */
@@ -259,7 +266,8 @@ void SRC_Finalise(void)
SRC_Instance SRC_CreateNewInstance(uint32_t ref_id, SRC_Type type, int authenticated,
int sel_options, IPAddr *addr, int min_samples,
int max_samples, double min_delay, double asymmetry)
int max_samples, double min_delay, double asymmetry,
int max_unreach)
{
SRC_Instance result;
@@ -295,6 +303,7 @@ SRC_Instance SRC_CreateNewInstance(uint32_t ref_id, SRC_Type type, int authentic
result->authenticated = authenticated;
result->conf_sel_options = sel_options;
result->sel_options = sel_options;
result->max_unreachable_run = max_unreach;
result->active = 0;
SRC_SetRefid(result, ref_id, addr);
@@ -351,6 +360,7 @@ SRC_ResetInstance(SRC_Instance instance)
instance->updates = 0;
instance->reachability = 0;
instance->reachability_size = 0;
instance->unreachable_run = 0;
instance->distant = 0;
instance->bad = 0;
instance->status = SRC_BAD_STATS;
@@ -524,6 +534,13 @@ SRC_UpdateReachability(SRC_Instance inst, int reachable)
if (inst->reachability_size < SOURCE_REACH_BITS)
inst->reachability_size++;
if (inst->reachability == 0) {
if (inst->unreachable_run < INT_MAX)
inst->unreachable_run++;
} else {
inst->unreachable_run = 0;
}
/* Check if special reference update mode failed */
if (REF_GetMode() != REF_ModeNormal && special_mode_end()) {
REF_SetUnsynchronised();
@@ -545,6 +562,7 @@ SRC_ResetReachability(SRC_Instance inst)
{
inst->reachability = 0;
inst->reachability_size = 0;
inst->unreachable_run = 0;
SRC_UpdateReachability(inst, 0);
}
@@ -1059,8 +1077,11 @@ SRC_SelectSource(SRC_Instance updated_inst)
/* Reachability is not a requirement for selection. An unreachable source
can still be selected if its newest sample is not older than the oldest
sample from reachable sources. */
if (!sources[i]->reachability && max_reach_sample_ago < si->last_sample_ago) {
sample from reachable sources and the number of consecutive unreachable
updates does not exceed the configured maximum. */
if (sources[i]->reachability == 0 &&
(si->last_sample_ago > max_reach_sample_ago ||
sources[i]->unreachable_run > sources[i]->max_unreachable_run)) {
mark_source(sources[i], SRC_STALE);
continue;
}