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#!/usr/bin/env python3
# SPDX-License-Identifier: GPL-2.0
"""Sets sysctl values and writes a file that restores them.
The arguments are of the form "<proc-file>=<val>" separated by spaces.
The program first reads the current value of the proc-file and creates
a shell script named "/tmp/sysctl_restore_${PACKETDRILL_PID}.sh" which
restores the values when executed. It then sets the new values.
PACKETDRILL_PID is set by packetdrill to the pid of itself, so a .pkt
file could restore sysctls by running `/tmp/sysctl_restore_${PPID}.sh`
at the end.
"""
import os
import subprocess
import sys
filename = '/tmp/sysctl_restore_%s.sh' % os.environ['PACKETDRILL_PID']
# Open file for restoring sysctl values
restore_file = open(filename, 'w')
print('#!/bin/bash', file=restore_file)
for a in sys.argv[1:]:
sysctl = a.split('=')
# sysctl[0] contains the proc-file name, sysctl[1] the new value
# read current value and add restore command to file
cur_val = subprocess.check_output(['cat', sysctl[0]], universal_newlines=True)
print('echo "%s" > %s' % (cur_val.strip(), sysctl[0]), file=restore_file)
# set new value
cmd = 'echo "%s" > %s' % (sysctl[1], sysctl[0])
os.system(cmd)
os.system('chmod u+x %s' % filename)
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