uptime code does not work on FreeBSD with python 3

my current attempt to bring this into the new millenium:

import ctypes
import time
import errno

class timeval(ctypes.Structure):
    _fields_ = [
        ("tv_sec", ctypes.c_int64),
        ("tv_usec", ctypes.c_int64)
    ]

libc = ctypes.CDLL('/lib/libc.so.7', use_errno=True)
boottime = timeval()
if libc.sysctlbyname("kern.boottime", ctypes.byref(boottime), ctypes.sizeof(timeval), None, 0) == -1:
    print(errno.errorcode[ctypes.get_errno()])
    exit(1)

which results in ENOENT

which is rather confusing, given that `sysctl kern.boottime` returns
kern.boottime: { sec = 1573656128, usec = 384300 } Wed Nov 13 14:42:08 2019

soooooo!

there are two different issues here at play, which confused me a lot

Let's get the simplest one out of the way: ENOENT is caused by the fact that we're passing a Python String to a C function.

when using b"kern.boottime" + "\x00", it works as expected.

The issue in the original code is that kern.boottime is not an integer (any more… and has not been for a long time…)

There are two ways to unpack it: either by loading the value into a generic string buffer: https://github.com/Cairnarvon/uptime/blob/master/src/__init__.py#L135 and then using struct.unpack

or, as i tried above, by constructing a Structure of our own.

patch: https://github.com/canonical/cloud-init/pull/53

Fix committed for this bug in upstream cloud-init @ https://github.com/canonical/cloud-init/commit/c911afbfe5a38823971e9cdbd4d1848c6e5c16de

Tracked in Github Issues as https://github.com/canonical/cloud-init/issues/3499