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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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