[BUG] Linux, LinuxBridge and runtime plugins hangs when retrieving IP address of an FDU interface

[gabrik]

Describe the bug
The monitoring process of an FDU hangs when it tries to retrieve information from the DHCP about the IP Address of an FDU's interface

To Reproduce
Instantiate an FDU connected to a virtual network, with DHCP

Expected behavior
Should not hang

Desktop (please complete the following information):

• OS: Ubuntu
• Version 18.04, 16.04
• Involved pluging: Linux, LinuxBridge, any runtime plugin

Additional context
Seems that the LinuxPlugin hangs when trying to read data from the dnsmasq lease file, and so all the chain just hangs
Linux plugin output:

[2019-07-24 09:45:27,656] - [INFO] > < read_file() > Arguments: {'root': 'True', 'file_path': '/var/fos/linuxbridge/dhcp/net_6cc2aa30_leases', 'self': <__main__.Linux object at 0x7fa2ef274e48>}

LinuxBridge plugin:

[2019-07-24 09:45:27,655] - [INFO] > < get_address() > Linux Bridge Plugin - Getting IP address for  be:ef:be:ef:00:01

LXD plugin:

[2019-07-24 09:45:27,634] - [INFO] > < __monitor_instance() > [ INFO ] LXD Plugin - Updating status of 9c507cba-ba02-4b89-9abe-b23c2763a294 - c9c507cba-ba02-4b89-9abe-b23c2763a294

The LinuxPlugin acutally, as the parameter root is set to True, should execute this command: sudo cat /var/fos/linuxbridge/dhcp/net_6cc2aa30_leases

That should not hang, the code that hangs is:

if root:
                file_path = 'sudo cat {}'.format(file_path)
                process = subprocess.Popen(
                    file_path.split(), stdout=subprocess.PIPE)
                for line in iter(process.stdout.readline, ''):
                    data = data + '{}'.format(line)

That hangs also if executed in python interpreter

$ python3
Python 3.6.8 (default, Jan 14 2019, 11:02:34)
[GCC 8.0.1 20180414 (experimental) [trunk revision 259383]] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from subprocess import PIPE
>>> import subprocess
>>> cmd  = 'sudo cat  /var/fos/linuxbridge/dhcp/net_6cc2aa30_leases'
>>> p = subprocess.Popen(cmd.split(), stdout=subprocess.PIPE)
>>> data = ''
>>> for line in iter(p.stdout.readline, ''):
...     data = data + '{}'.format(line)
...

This suggest that we should find another way to read that file

[gabrik]

Quick update, seems that using psutil instead of subprocess solves the issue:

$ python3
Python 3.6.8 (default, Jan 14 2019, 11:02:34)
[GCC 8.0.1 20180414 (experimental) [trunk revision 259383]] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import psutil
>>> from subprocess import PIPE
>>> cmd  = 'sudo cat  /var/fos/linuxbridge/dhcp/net_6cc2aa30_leases'.split()
>>> p = psutil.Popen(cmd,stdout=PIPE)
>>> p.wait()
0
>>> r = ''
>>> for line in p.stdout:
...     r = r + line.decode()
...
>>> r
'1564040719 be:ef:be:ef:00:01 192.168.234.10 c9c507cba-ba02-4b89-9abe-b23c2763a294 01:be:ef:be:ef:00:01\n'
>>>

Also using direct python access to file solves the issue:

f = '/var/fos/linuxbridge/dhcp/net_6cc2aa30_leases'
>>> data = ''
>>> with open(f, 'r') as f:
...     data = f.read()
...
>>> data
'1564041966 be:ef:be:ef:00:01 192.168.234.10 cf009de5b-e6b5-43db-b400-985ad70f4407 01:be:ef:be:ef:00:01\n'

So we will use psutil instead of subprocess in case of root == True