[tor-bugs] #11016 [Tor]: Add support for systemd watchdog protocol

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#11016: Add support for systemd watchdog protocol
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     Reporter:  misc         |      Owner:
         Type:  enhancement  |     Status:  needs_revision
     Priority:  minor        |  Milestone:  Tor: 0.2.5.x-final
    Component:  Tor          |    Version:
   Resolution:               |   Keywords:  tor-relay systemd
Actual Points:               |  Parent ID:
       Points:               |
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Changes (by nickm):

 * status:  needs_review => needs_revision


Comment:

 note 1: does PKG_PROG_PKG_CONFIG exist everywhere?  If not, do we need to
 add it to our m4/ directory?

 note 2: Maybe the configure.in logic should check for the presence of the
 systemd headers.  On some systems, the headers get installed separately
 from the libraries, and that confuses some users.  They want to build Tor
 but wonder "why can't I build with systemd?  I installed systemd!"

 note 3: The systemd libs should really only get linked with the program
 (tor) that needs them. The stuff in tools doesn't need to link against
 libsystemd.

 note 4: The control.c module should not be interacting with anything other
 than the controller.  If we want to do something else once we are
 bootstrapped, we should have a new intermediate function (in status.c
 maybe?) that calls both control_event_bootstrap and
 systemd_event_bootstrap.  I'm happy to make this change myself if you
 don't want to.

 note 5: There should be a comment on why we divide watchdog_delay by 2.

 note 6: Can watchdog_delay be 2 seconds or greater?  If so, you can't
 divide by 2 and put it in tv_usec; libevent requires that timeout values
 be well-formed (with tv_usec between 0 and 999999).

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/11016#comment:4>
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