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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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9
ntp_auth.h
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@@ -51,10 +51,6 @@ extern int NAU_GetSuggestedNtpVersion(NAU_Instance instance);
/* Perform operations necessary for NAU_GenerateRequestAuth() */
extern int NAU_PrepareRequestAuth(NAU_Instance instance);
/* Adjust a transmit timestamp for an estimated minimum time it takes to call
NAU_GenerateRequestAuth() */
extern void NAU_AdjustRequestTimestamp(NAU_Instance instance, struct timespec *ts);
/* Extend a request with data required by the authentication mode */
extern int NAU_GenerateRequestAuth(NAU_Instance instance, NTP_Packet *request,
NTP_PacketInfo *info);
@@ -66,11 +62,6 @@ extern int NAU_ParsePacket(NTP_Packet *packet, NTP_PacketInfo *info);
kod code is returned, a KoD response should be sent back. */
extern int NAU_CheckRequestAuth(NTP_Packet *request, NTP_PacketInfo *info, uint32_t *kod);
/* Adjust a transmit timestamp for an estimated minimum time it takes to call
NAU_GenerateResponseAuth() */
extern void NAU_AdjustResponseTimestamp(NTP_Packet *request, NTP_PacketInfo *info,
struct timespec *ts);
/* Extend a response with data required by the authentication mode. This
function can be called only if the previous call of NAU_CheckRequestAuth()
was on the same request. */