Enable SCM_TIMESTAMPING control messages and the socket's error queue in
order to receive our transmitted packets with a more accurate transmit
timestamp. Add a new file for Linux-specific NTP I/O and implement
processing of these messages there.
Introduce a new structure for local timestamps that will hold the
timestamp with its estimated error and also its source (daemon, kernel
or HW). While at it, reorder parameters of the functions that accept the
timestamps.
Add new functions for processing of packets after they are actually
sent by the kernel or HW in order to get a more accurate transmit
timestamp. Rename old functions for processing of received packets and
their parameters to make the naming more consistent.
If all or most SHM/SOCK samples collected in a polling interval had the
same local timestamp, the dispersion could end up as nan, which could
trigger an assert failure later in the code.
Before accumulating a refclock sample, check if the timestamp is newer
than the previous one.
Use the ipi_addr field instead of ipi_spec_dst as the local address
after recvmsg() to be consistent with the processing of struct
in6_pktinfo. This may make a difference for messages from the error
queue.
When the smoothing process is updated with extremely small (e.g.
sub-nanosecond) values, both directions may give a negative length of
the 1st or 3rd stage due to numerical errors and the selection will fail
an in assertion. Rework the code to select the direction which gives a
smaller error.
When chronyd is starting, after the point where dump files are loaded,
remove all files in the dump directory that match the naming scheme used
for dump files. This prevents loading stale dump files that were not
saved in the latest run of chronyd.
Use empty string instead of "." (which is normally the root directory)
as the default value of dumpdir and logdir to indicate they are not
specified. Print warnings in syslog when trying to log or dump
measurements without dumpdir or logdir.
When the SO_TIMESTAMP socket option was enabled, the expected type of
control messages containing timestamps was SO_TIMESTAMP instead of
SCM_TIMESTAMP. This worked on Linux, where the two values are equal, but
not on the other supported systems. The timestamps were ignored and this
probably worsened the accuracy and stability of the synchronisation.
Include IP address instead of reference ID in the name of dump file
for NTP sources and for reference clocks format the reference ID as a
hexadecimal number instead of quad dotted notation.
Also, avoid dynamic memory allocation and improve warning messages.
Replace struct timeval with struct timespec as the main data type for
timestamps. This will allow the NTP code to work with timestamps in
nanosecond resolution.
Crypto-NAK is useful only with Autokey where it allows quick reset
of the association. There is no plan to support Autokey and NTS will
specify its own message for authentication errors.
Estimate asymmetry of network jitter on the path to the source as a
slope of offset against network delay in multiple linear regression. If
the asymmetry is significant and its sign doesn't change frequently, the
measured offsets (which are used later to estimate the offset and
frequency of the clock) are corrected to correspond to the minimum
network delay. This can significantly improve the accuracy and stability
of the estimated offset and frequency.
