worker: disconnect dbus from NameOwnerChanged signal (POO #183833)

[AdamWill]

This avoids us piling up signals we never handle and eventually exceeding a dbus quota limit and causing all subsequent tap jobs to fail.

New Net::DBus instances are automatically connected to this signal on creation, you cannot change this. If the instance is kept around but nothing iterates the dbus event loop once in a while, that signal will just keep piling up messages indefinitely. We encountered this once before in os-autoinst and "solved" it by not persisting the dbus connection, but in this case it doesn't seem a good idea to re-initialize that connection every time we want to check on the status of a tap worker. So instead let's disconnect it from the signal.

The 1 here is a bit magical. The Net::DBus connect_to_signal method issues signal numbers on a first-come, first-served basis, starting at 1 (0 is never used), and returns the number it issued. When Net::DBus _new calls it, though, it doesn't record the return value. So we have to know/guess that this will always be the first signal connected.

Related ticket: https://progress.opensuse.org/issues/183833

[AdamWill]

I'm not 100% sure this is un-hacky enough to upstream, but figured I'd submit it at least. It'd be great if @berrange could comment. Relevant perl-net-dbus code areas:

• the signal connection in _new
• connect_to_signal's handling of signal IDs - note nothing else in the codebase touches this signal_id property AFAICT, which makes me feel like the assumption that the ID here will always be 1 is pretty solid, unless I'm missing something

[AdamWill]

The last time we ran into a very similar issue was https://progress.opensuse.org/issues/90872 , which we 'fixed' with os-autoinst/os-autoinst#1641 .

[berrange]

I'm not 100% sure this is un-hacky enough to upstream, but figured I'd submit it at least. It'd be great if @berrange could comment. Relevant perl-net-dbus code areas:

Yes it is a bit hacky, but at the same time I think it is likely the least worst option, given the constraints imposed by the perl-net-dbus implementation. Since the perl-net-dbus project is largely dormant, it is unlikely to see new changes that would invalidate the assumption made here.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.11%. Comparing base (371ad64) to head (7c71f3f).
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6578      +/-   ##
==========================================
- Coverage   99.11%   99.11%   -0.01%     
==========================================
  Files         399      399              
  Lines       40707    40714       +7     
==========================================
+ Hits        40347    40353       +6     
- Misses        360      361       +1     

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