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Retire the kill(SIGNULL) test in VSM
A bug was uncovered in the VSM code that checks if kill(SIGNULL) would work as a test of liveness of the master and worker processes. If the user running the utility has the required permissions to send signal to the worker process, but not the management process, the code would wrongly assume it could do kill on both. It would then end up in a connect loop never succeeding. Because kill() can not always be successfully run (a common scenario when the user running varnishlog is not the same UID as the cache processes), there is a fall back to using fstat to check for Varnish restarts. Since this fallback is active for most use cases anyways, it was decided to retire the kill() mechanism rather than to fix it. This way the behaviour does not change depending on what user the utility is run as. This change was OK'd by PHK after discussing it on IRC.
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