(BSD) util.py:boottime: make finding libc platform independent

[igalic]

and slower.
and since we're making it slower, let's cache it, in case boottime gets
called more than once.

this should fix boottime() (again).

[igalic]

@goneri finally getting around to fixing this!

[OddBloke]

I know it's not called on Linux (so I won't block merge on this at all, in particular because it's broken on Linux in master), but do we expect boottime() to work here?

I see:

In [2]: boottime()                                                                                                                                                                                                                                                                        
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-2-cc4cfa1f18c8> in <module>
----> 1 boottime()

~/dev/cloud-init/cloudinit/util.py in boottime()
   1889     size.value = ctypes.sizeof(timeval)
   1890     buf = timeval()
-> 1891     if libc.sysctlbyname(b"kern.boottime" + NULL_BYTES, ctypes.byref(buf),
   1892                          ctypes.byref(size), None, 0) != -1:
   1893         return buf.tv_sec + buf.tv_usec / 1000000.0

/usr/lib/python3.8/ctypes/__init__.py in __getattr__(self, name)
    384         if name.startswith('__') and name.endswith('__'):
    385             raise AttributeError(name)
--> 386         func = self.__getitem__(name)
    387         setattr(self, name, func)
    388         return func

/usr/lib/python3.8/ctypes/__init__.py in __getitem__(self, name_or_ordinal)
    389 
    390     def __getitem__(self, name_or_ordinal):
--> 391         func = self._FuncPtr((name_or_ordinal, self))
    392         if not isinstance(name_or_ordinal, int):
    393             func.__name__ = name_or_ordinal

AttributeError: /lib/x86_64-linux-gnu/libc.so.6: undefined symbol: sysctlbyname

[OddBloke]

Thanks Mina! This LGTM, but I'll wait for a +1 from @goneri (or I'll just go ahead without on Monday, in case they're busy) before I Approve and land it.

[igalic]

sysctlbyname() exists on

• NetBSD https://netbsd.gw.com/cgi-bin/man-cgi?sysctlbyname++NetBSD-current
• FreeBSD https://www.freebsd.org/cgi/man.cgi?sysctlbyname
• and, uh, QNX: http://www.qnx.com/developers/docs/6.5.0SP1.update/com.qnx.doc.neutrino_lib_ref/s/sysctl.html

anyone planning to make QNX available in their cloud?

but anyway, we should add a try around the call, until OpenBSD implements that function, or exclude it with util.is_OpenBSD()

[OddBloke]

It's Monday, you know what that means.