Fix crash in runtime if PSK secret is missing

./Beremiz_service.py -s $PWD/psk2.txt -n beremiz /tmp/beremiz
Beremiz_service: 1.2-1378c18402c3+

Traceback (most recent call last):
File "./Beremiz_service.py", line 511, in <module>
ensurePSK(servicename, PSKpath)
File "/home/developer/WorkData/PLC/beremiz/beremiz/runtime/Stunnel.py", line 32, in ensurePSK
PSKgen(ID, PSKpath)
File "/home/developer/WorkData/PLC/beremiz/beremiz/runtime/Stunnel.py", line 23, in PSKgen
call(restart_stunnel_cmdline)
File "/home/developer/WorkData/PLC/beremiz/beremiz/runtime/spawn_subprocess.py", line 116, in call
pid = posix_spawn.posix_spawnp(cmd[0], cmd)
File "/home/developer/.local/lib/python2.7/site-packages/posix_spawn/_impl.py", line 120, in posix_spawnp
return _posix_spawn(lib.posix_spawnp, *args, **kwargs)
File "/home/developer/.local/lib/python2.7/site-packages/posix_spawn/_impl.py", line 111, in _posix_spawn
_check_error(res, path)
File "/home/developer/.local/lib/python2.7/site-packages/posix_spawn/_impl.py", line 10, in _check_error
raise OSError(errno, os.strerror(errno), path)
OSError: [Errno 2] No such file or directory: '/etc/init.d/S50stunnel'

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#!/usr/bin/env python

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# -*- coding: utf-8 -*-

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#

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# See COPYING.Runtime file for copyrights details.

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#

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from __future__ import absolute_import

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from ctypes import CDLL, RTLD_GLOBAL, pointer, c_int, POINTER, c_char, create_string_buffer

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def TryPreloadXenomai():

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    """

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    Xenomai 3 (at least for version <= 3.0.6) do not handle properly dlclose

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    of shared objects whose dlopen did trigger xenomai_init.

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    As a workaround, this pre-loads xenomai libraries that need to be

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    initialized and call xenomai_init once for all.

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    Xenomai auto init of libs MUST be disabled (see --auto-init-solib in xeno-config)

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    """

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    try:

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        for name in ["cobalt", "modechk", "copperplate", "alchemy"]:

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            globals()[name] = CDLL("lib"+name+".so", mode=RTLD_GLOBAL)

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        cobalt.xenomai_init(pointer(c_int(0)), pointer((POINTER(c_char)*2)(create_string_buffer("prog_name"), None)))

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    except Exception:

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        pass