aspect of time stamp configuration per interface rather than per BPF
descriptor. Prior to this, the order in which BPF devices were opened and the
per descriptor time stamp configuration settings could cause non-deterministic
and unintended behaviour with respect to time stamping. With the new scheme, a
BPF attached interface's tscfg sysctl entry can be set to "default", "none",
"fast", "normal" or "external". Setting "default" means use the system default
option (set with the net.bpf.tscfg.default sysctl), "none" means do not
generate time stamps for tapped packets, "fast" means generate time stamps for
tapped packets using a hz granularity system clock read, "normal" means
generate time stamps for tapped packets using a full timecounter granularity
system clock read and "external" (currently unimplemented) means use the time
stamp provided with the packet from an underlying source.
- Utilise the recently introduced sysclock_getsnapshot() and
sysclock_snap2bintime() KPIs to ensure the system clock is only read once per
packet, regardless of the number of BPF descriptors and time stamp formats
requested. Use the per BPF attached interface time stamp configuration to
control if sysclock_getsnapshot() is called and whether the system clock read
is fast or normal. The per BPF descriptor time stamp configuration is then
used to control how the system clock snapshot is converted to a bintime by
sysclock_snap2bintime().
- Remove all FAST related BPF descriptor flag variants. Performing a "fast"
read of the system clock is now controlled per BPF attached interface using
the net.bpf.tscfg sysctl tree.
- Update the bpf.4 man page.
Committed on behalf of Julien Ridoux and Darryl Veitch from the University of
Melbourne, Australia, as part of the FreeBSD Foundation funded "Feed-Forward
Clock Synchronization Algorithms" project.
For more information, see http://www.synclab.org/radclock/
In collaboration with: Julien Ridoux (jridoux at unimelb edu au)
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