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

[Tor Bug Tracker & Wiki]

#11553: Be more verbose when warning about not finding a circuit ID
-------------------------+-------------------------------------------------
     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:           |
-------------------------+-------------------------------------------------

Comment (by andrea):

 Begin code review:

  * New logging in bb9b4c37f8e7f5cf78918f382e90d8b11ff42551 looks okay, but
 perhaps we should consider resetting warn_circ_ids_exhausted if the number
 of circuits drops or if sufficient time elapses since it was set, so we
 don't block warnings on that channel forever even if the exhaustion
 condition is relieved later?

  * 0d75344b0e0eafc89db89a974e87b16564cd8f0a:
    - This code looks okay, but the possibility of occasional false
 positives on circuit ID exhaustion amplifies my above-stated concern about
 never letting the blockage on the log message age out.
    - We could be smarter about this with better data structures; suppose,
 for example, the circuit IDs in use per channel lived in a balanced tree
 with each node knowing how many nodes its subtree had.  Then we could know
 how many circuit IDs are available to assign (N = max_circ_id -
 num_circ_ids from the root), pick a random i with 0 <= i < n, and then
 walk down the tree adjusting i as appropriate for which circuit IDs are
 already in use.  This would assign a uniformly distributed random unused
 circuit ID in deterministic log time in the number of circuit IDs already
 assigned, and never fail.

  * 985deaaaf7b7397857e02206e89392e0ee101077 looks okay to me

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/11553#comment:14>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online