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[FR] Use kernel timestamps for dnstap #888

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edmonds opened this issue May 15, 2023 · 1 comment
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[FR] Use kernel timestamps for dnstap #888

edmonds opened this issue May 15, 2023 · 1 comment

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@edmonds
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edmonds commented May 15, 2023

Hey @wcawijngaards @vvfedorenko, I see support was added for kernel timestamping of client queries in #882. Looks like it's conditionally enabled only if the new sock_queue_timeout option is enabled?

Any chance the kernel timestamp could be enabled and used (if available) instead of re-fetching the timestamp in the dnstap code?

unbound/dnstap/dnstap.c

Line 396 in 1fb78af

gettimeofday(&qtime, NULL);

The dnstap code is going to run some time after the client query packet hits the machine, potentially after many context switches, etc., so the accuracy of the dnstap timestamp can certainly suffer if the query is being re-timestamped after getting the packet from the kernel.

Thanks!
@wcawijngaards
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Hi Robert, I have implemented the feature in the commit. It changes the kernel timestamp handling, so that the timestamp is not modified by the checking code, it is left as it was when the packet entered. The wait_queue_time that is calculated is used instead to measure if the packet needs to be dropped. Then the kernel timestamp is passed to dnstap, and if such a timestamp is available that is used for logging the client queries.

I hope this provides more accurate time information! The commit is part of the code repository.

jedisct1 added a commit to jedisct1/unbound that referenced this issue May 25, 2023
@jedisct1
Merge remote-tracking branch 'nlnet/master'
cb8d41e 
* nlnet/master: (39 commits)
  - Fix unbound-dnstap-socket time fraction conversion for printout.
  - Fix unbound-dnstap-socket printout when no query is present.
  - Fix to remove unused variables from RPZ clientip data structure.
  - Fix RPZ removal of client-ip, nsip, nsdname triggers from IXFR.
  - Fix to print debug log for ancillary data with correct IP address.
  - Fix NLnetLabs#888: [FR] Use kernel timestamps for dnstap.
  - Fix warning in windows compile, in set_recvtimestamp.
  - Fix doxygen in addr_to_nat64 header definition.
  - Fix to remove unused whitespace from acx_nlnetlabs.m4 and config.h.
  - Fix NLnetLabs#885: Error: util/configlexer.c: No such file or directory,   adds error messages explaining to install flex and bison.
  Changelog entry for NLnetLabs#722: - Merge NLnetLabs#722 from David 'eqvinox' Lamparter: NAT64 support. - For NLnetLabs#722: minor fixes, formatting, refactoring.
  - For NLnetLabs#722: Minor fixes, formatting and refactoring.
  - Fix RPZ IP responses with trigger rpz-drop on cache entries, that   they are dropped.
  Changelog for NLnetLabs#860
  Remove msg_del_for_0ttl, call msg_cache_remove directly
  - Fix for NLnetLabs#882: document variable to stop doxygen warning.
  - Fix for NLnetLabs#882: small changes, date updated in Copyright for   util/timeval_func.c and util/timeval_func.h. Man page entries and   example entry.
  stats: add query max wait time metric
  stats: add counter for timed out queries
  config: add sock_queue_timeout configuration
  ...
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@edmonds @wcawijngaards