Don't waste time with processing messages that don't fit in the receive
buffer as they most likely wouldn't pass the format check due to an
invalid length of an extension field.
Add a new directive to specify interfaces which should be used for HW
timestamping. Extend the Linux ntp_io initialization to enable HW
timestamping, configure the RX filter using the SIOCSHWTSTAMP ioctl,
open their PHC devices, and track them as hwclock instances. When
messages with HW timestamps are received, use the PTP_SYS_OFFSET ioctl
to make PHC samples for hwclock.
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.
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 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.
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.
Replace SCH_*InputFileHandler() functions with more general
SCH_*FileHandler(), where events are specified as a new parameter and
which will later support other file events, e.g. file ready for ouput
and exception.
The file handlers have two new parameters: file descriptor and event.
Server sockets are now explicitly opened and closed for normal NTP
server, NTP broadcast and NTP peering. This will allow closing the
NTP port when not needed.
Switch to NTP for presend as the echo service (RFC 862) is rarely
enabled. When presend is active, send an NTP client packet to the
server/peer and ignore the reply.
This also fixes presend with separate client sockets. The destination
port can't be changed on connected sockets, so the echo packet was sent
to the NTP port instead of the echo port.
With separate client sockets, allow the initial connect() to fail (e.g.
when the network is not reachable yet) and try to connect later when
sending the packet.
Also, reconnect the socket when the local address has changed.
