[tor-bugs] #32910 [Core Tor/Tor]: trace: Add tracepoints and userspace tracer support

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#32910: trace: Add tracepoints and userspace tracer support
--------------------------+------------------------------------
 Reporter:  dgoulet       |          Owner:  dgoulet
     Type:  enhancement   |         Status:  needs_review
 Priority:  Medium        |      Milestone:  Tor: 0.4.4.x-final
Component:  Core Tor/Tor  |        Version:
 Severity:  Normal        |     Resolution:
 Keywords:  tracing       |  Actual Points:
Parent ID:                |         Points:  3
 Reviewer:  nickm         |        Sponsor:
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Changes (by dgoulet):

 * status:  needs_revision => needs_review


Comment:

 (New rebased on latest master branch. Nothing has changed in the commit
 from _02 branch, just new commits have been added.)

 Branch: `ticket32910_044_03`
 PR: https://github.com/torproject/tor/pull/1790

 > Maybe we should disambiguate identifiers used as domains and event
 names. Prefixes, suffices, InitialCaps, and camelCase were all suggested
 as possibilities. So were TOR_TRACE, macros to create a single macro per
 event, and so on.

 See commit `cc1dd1bea88065a4`

 > Safety. In order to make sure this feature stays safe:

 See commit `a311da45004ab093` for the log warning
 See commit `973044b0334f9eac` for safety guidelines.

 > Documentation. We should make sure that you don't need to know the tor
 source code intimately to understand the event descriptions.

 I have a question on that one. Should I make a central file (maybe in
 Tracing.md) containing all tracepoints and a description? I'm suggesting
 that because of the different possible instrumentation (USDT, Lttng,...),
 there is not central point where a tracepoint is defined. And thus, we
 might want an "index" file explaining them all ?

 > Testing. How do we verify that this is working and we haven't broken it?
 We need some kind of test that actually makes sure events are happening
 and getting recorded.

 The only way I see for now is adding a build matrix in our CI that builds
 all instrumentation at once.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/32910#comment:16>
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