[tor-bugs] #11553 [Tor]: Be more verbose when warning about not finding a circuit ID

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#11553: Be more verbose when warning about not finding a circuit ID
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     Reporter:  ra       |      Owner:
         Type:           |     Status:  needs_review
  enhancement            |  Milestone:  Tor: 0.2.5.x-final
     Priority:  major    |    Version:  Tor: 0.2.5.3-alpha
    Component:  Tor      |   Keywords:  tor-relay 024-backport 023-backport
   Resolution:           |  Parent ID:
Actual Points:           |
       Points:           |
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Comment (by ra):

 A few comments/questions from my side:
 a) The new log message should be fine.
 b) Limiting the number of iterations to find a usable circuit ID to 64
 instead of 2^15 or 2^31 sounds also good. Having non-predictable circuit
 IDs sounds like a wise move to me anyway. Nevertheless, although the
 chance of not finding a usuable circuit ID for a specific channel within
 64 tries is quite small, it will eventually happen and people will end up
 having warning messages in their log files; which is perfectly fine, as
 long as this happens very infrequently. I think it is really bad to have
 ignorable warning messages, but unfortunately I have no better suggestion
 at this time on how to handle this but stating in the log message that the
 warning can be ignored if it happens only very rarely.
 c) Defining MAX_CIRCID_ATTEMPTS 64 seems like a good choice to me. But
 there is a comment missing in the code explaining why the constant is 64
 and not 23, 42, 128 or 1024.
 d) Is a warning only printed once for a channel
 (chan->warned_circ_ids_exhausted)? If so, why?

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/11553#comment:11>
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