util: move uptime's else branch into its own boottime function (#53)

Also fix bugs:
- pass binary instead of string to sysctlbyname(), and
- unpack the "return value" in a struct, rather than in single integer.

LP: #1853160

Co-Authored-By: Ryan Harper <ryan.harper@canonical.com>

1 files changed, 29 insertions, 10 deletions

diff --git a/cloudinit/util.py b/cloudinit/util.py
index 830c8e54..76d7db78 100644
--- a/cloudinit/util.py
+++ b/cloudinit/util.py
@@ -10,7 +10,6 @@
 
 import contextlib
 import copy as obj_copy
-import ctypes
 import email
 import glob
 import grp
@@ -1807,6 +1806,33 @@ def time_rfc2822():
     return ts
 
 
+def boottime():
+    """Use sysctlbyname(3) via ctypes to find kern.boottime
+
+    kern.boottime is of type struct timeval. Here we create a
+    private class to easier unpack it.
+
+    @return boottime: float to be compatible with linux
+    """
+    import ctypes
+
+    NULL_BYTES = b"\x00"
+
+    class timeval(ctypes.Structure):
+        _fields_ = [
+            ("tv_sec", ctypes.c_int64),
+            ("tv_usec", ctypes.c_int64)
+        ]
+    libc = ctypes.CDLL('/lib/libc.so.7')
+    size = ctypes.c_size_t()
+    size.value = ctypes.sizeof(timeval)
+    buf = timeval()
+    if libc.sysctlbyname(b"kern.boottime" + NULL_BYTES, ctypes.byref(buf),
+                         ctypes.byref(size), None, 0) != -1:
+        return buf.tv_sec + buf.tv_usec / 1000000.0
+    raise RuntimeError("Unable to retrieve kern.boottime on this system")
+
+
 def uptime():
     uptime_str = '??'
     method = 'unknown'
@@ -1818,15 +1844,8 @@ def uptime():
                 uptime_str = contents.split()[0]
         else:
             method = 'ctypes'
-            libc = ctypes.CDLL('/lib/libc.so.7')
-            size = ctypes.c_size_t()
-            buf = ctypes.c_int()
-            size.value = ctypes.sizeof(buf)
-            libc.sysctlbyname("kern.boottime", ctypes.byref(buf),
-                              ctypes.byref(size), None, 0)
-            now = time.time()
-            bootup = buf.value
-            uptime_str = now - bootup
+            # This is the *BSD codepath
+            uptime_str = str(time.time() - boottime())
 
     except Exception:
         logexc(LOG, "Unable to read uptime using method: %s" % method)