We have a cache for sysctl values, so that we can log changes and
previous values.
When resetting the log level, we prune that cache, which is done by
_nm_logging_clear_platform_logging_cache(). That function is called
by nm_logging_setup(), which is guaranteed to only happen on the main
thread.
NMPlatform in general is not thread safe (meaning, that the same NMPlatform
instance cannot be used by multiple threads at the same time). There is however
a reasonable aim that you could use different NMPlatform instances on their
own threads.
That currently doesn't work, mainly due to nm-logging which always must
be done from the main thread -- unless we would set NM_THREAD_SAFE_ON_MAIN_THREAD
in all of NMPlatform (which would be too expensive for something we
don't actually need). That means also the sysctl getter must only be
called on the main thread an all was good already.
Still, we could have NMPlatform usable from multiple thread by setting
NM_THREAD_SAFE_ON_MAIN_THREAD. As we are almost there to have the code
thread-safe, make accessing the sysctl value cache thread-safe (even if
we currently don't actually access it from multiple thread).
Avoid dependencies but explicitly link the static library where it is
used.
This also fixes that we linked libnm-log-core into
libnm-settings-plugin-ifcfg-rh.so, which duplicated the symbols
while it should used them from NetworkManager.
"nm-test-utils.h" is a header-only, helper library for our unit tests.
It was somewhat unmotivated in "shared/nm-utils", because all tests use
it, but it was not part of a "module".
Move it to "src/libnm-glib-aux/". It fits there very well. They both
have (only) a dependency on glib.
