WIP raw clock

kano_updater/monitor.py

@@ -9,6 +9,7 @@
 import subprocess
 from collections import defaultdict
 import sys
+from raw_clock import raw_clock
 import time
 import signal
 import os
@@ -103,12 +104,14 @@ def monitor(watchproc, timeout):
 
     spoll = SignalPoll(signal.SIGUSR1)
 
-    lastEvent = time.time()
+    raw_clk = raw_clock()
+
+    lastEvent = raw_clk.monotonic_time()
 
     pids = MonitorPids(watchpid)
 
     while True:
-        now = time.time()
+        now = raw_clk.monotonic_time()
         # check for child events
         changed = pids.is_changed()
         if watchproc.poll() is not None:

kano_updater/raw_clock.py

@@ -0,0 +1,36 @@
+# raw_clock.py
+#
+# Copyright (C) 2018 Kano Computing Ltd.
+# License: http://www.gnu.org/licenses/gpl-2.0.txt GNU GPL v2
+#
+# Module to obtain a clock value which is not disturbed by the boot process
+# when it obtains time from ntp.
+#
+# From http://stackoverflow.com/questions/1205722/how-do-i-get-monotonic-time-durations-in-python
+
+
+import ctypes
+import os
+
+
+class timespec(ctypes.Structure):
+    _fields_ = [
+        ('tv_sec', ctypes.c_long),
+        ('tv_nsec', ctypes.c_long)
+    ]
+
+
+class raw_clock:
+    CLOCK_MONOTONIC_RAW = 4  # see <linux/time.h>
+    def __init__(self):
+        self.librt = ctypes.CDLL('librt.so.1', use_errno=True)
+        self.clock_gettime = self.librt.clock_gettime
+        self.clock_gettime.argtypes = [ctypes.c_int, ctypes.POINTER(timespec)]
+
+
+    def monotonic_time(self):
+        t = timespec()
+        if self.clock_gettime(self.CLOCK_MONOTONIC_RAW, ctypes.pointer(t)) != 0:
+            errno_ = ctypes.get_errno()
+            raise OSError(errno_, os.strerror(errno_))
+        return t.tv_sec + t.tv_nsec * 1e-9