#!/usr/bin/python3
#
# systemd/journalctl show timestamps in a container that come from
# the monotonic system clock, which is not namesapced.  This means
# that the output is not terribly useful for determining boot time
# of a container.
#
# /proc/uptime in lxd shows a timestamp relative to the start of
# the container.
#
# So, we can figure out at what monontonic time this container
# started by subtracting the value in /proc/uptime from time.monotonic()
#
# Then, we can filter the output of journalctl --output=short-monotonic
# and adjust the timestamps to get information useful in a container.
# It works in a non-container also because uptime and monotonic will
# be close-enough that we throw away numbers < 1.
#
# Usage for this tool is simple:
#   lxd-journalctl [journalctl [arguments]]
#
import subprocess
import sys
import time

with open("/proc/uptime") as fp:
   uptime_s, _idle = fp.read().split()
mono = time.monotonic()
delta = mono - float(uptime_s)
if delta < 1:
    delta = 0
print("delta is %03f" % (mono - float(uptime_s)))

out = subprocess.check_output(
    ['journalctl', '--no-pager', '--output=short-monotonic'] + sys.argv[1:])

for line in out.splitlines():
    if line.startswith(b'['):
        end_time = line.index(b']')
        fmt = b"[%%%df]" % (end_time - 2)
        ts = float(line[1:end_time])
        line = fmt % (ts - delta) + line[end_time+1:]
    sys.stdout.buffer.write(line + b'\n')