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ntp: drop precompensation of TX timestamp

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The daemon transmit timestamps are precompensated for the time it takes
to generate a MAC using a symmetric key (as measured on chronyd start)
and also an average round-trip time of the Samba signing of MS-SNTP
responses. This improves accuracy of the transmit timestamp, but it
has some issues.

The correction has a random error which is changing over time due to
variable CPU frequency, system load, migration to a different machine,
etc. If the measured delay is too large, the correction may cause the
transmit timestamp to be later than the actual transmission. Also, the
delay is measured for a packet of a minimal length with no extension
fields, and there is no support for NTS.

Drop the precompensation in favor of the interleaved mode, which now
avoids the authentication delay even when no kernel/hardware timestamps
are available.
This commit is contained in:
Miroslav Lichvar
2020-07-02 15:34:22 +02:00
parent ff03b813b0
commit eae4b2abe5
9 changed files with 0 additions and 132 deletions
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34
ntp_auth.c
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@@ -96,24 +96,6 @@ check_symmetric_auth(NTP_Packet *packet, NTP_PacketInfo *info)
/* ================================================== */
static void
adjust_timestamp(NTP_AuthMode mode, uint32_t key_id, struct timespec *ts)
{
switch (mode) {
case NTP_AUTH_SYMMETRIC:
ts->tv_nsec += KEY_GetAuthDelay(key_id);
UTI_NormaliseTimespec(ts);
break;
case NTP_AUTH_MSSNTP:
ts->tv_nsec += NSD_GetAuthDelay(key_id);
UTI_NormaliseTimespec(ts);
default:
break;
}
}
/* ================================================== */
static int
is_zero_data(unsigned char *data, int length)
{
@@ -230,14 +212,6 @@ NAU_PrepareRequestAuth(NAU_Instance instance)
/* ================================================== */
void
NAU_AdjustRequestTimestamp(NAU_Instance instance, struct timespec *ts)
{
adjust_timestamp(instance->mode, instance->key_id, ts);
}
/* ================================================== */
int
NAU_GenerateRequestAuth(NAU_Instance instance, NTP_Packet *request, NTP_PacketInfo *info)
{
@@ -397,14 +371,6 @@ NAU_CheckRequestAuth(NTP_Packet *request, NTP_PacketInfo *info, uint32_t *kod)
/* ================================================== */
void
NAU_AdjustResponseTimestamp(NTP_Packet *request, NTP_PacketInfo *info, struct timespec *ts)
{
adjust_timestamp(info->auth.mode, info->auth.mac.key_id, ts);
}
/* ================================================== */
int
NAU_GenerateResponseAuth(NTP_Packet *request, NTP_PacketInfo *request_info,
NTP_Packet *response, NTP_PacketInfo *response_info,