FileMonitor eventlet dies due to eventlet.monkey_patch introduced change

[Onong Tayeng]

One of the core modules patched by eventlet.monkey_patch() is select. Now, in select module it patches the select() function call and deletes a bunch of others. Here's the relevant snip from the eventlet code:

./eventlet/green/select.py:
__patched__ = ['select']
__deleted__ = ['devpoll', 'poll', 'epoll', 'kqueue', 'kevent']

As a result, if some code tries to invoke the poll() function, it throws an exception:

[root@overcloud-novacompute-1 heat-admin]# python
Python 2.7.5 (default, Aug 4 2017, 00:39:18)
[GCC 4.8.5 20150623 (Red Hat 4.8.5-16)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import eventlet
>>> import select
>>> eventlet.monkey_patch(thread=False)
>>> pollobj = select.poll()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'module' object has no attribute 'poll'
>>>

This is precisely what is happening with the FileMonitor eventlet:

2018-04-13 21:11:09.630 239485 DEBUG networking_vpp.utils.file_monitor [-] File Monitor [pynotify] entered run /usr/lib/python2.7/site-packages/networking_vpp/utils/file_monitor.py:96
2018-04-13 21:11:09.632 239485 DEBUG networking_vpp.utils.file_monitor [-] Current tracked files: [] run /usr/lib/python2.7/site-packages/networking_vpp/utils/file_monitor.py:99
2018-04-13 21:11:09.638 239485 ERROR networking_vpp.utils.file_monitor [-] 'module' object has no attribute 'poll'

So, this means that nova live migration will not work.

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/565621
Committed: https://git.openstack.org/cgit/openstack/networking-vpp/commit/?id=d7d7e1240ac12e63e2e39c339f5a9c253e95402e
Submitter: Zuul
Branch: master

commit d7d7e1240ac12e63e2e39c339f5a9c253e95402e
Author: Hareesh Puthalath <email address hidden>
Date: Tue May 1 17:30:38 2018 -0700

    Handle missing select.poll with eventlet 0.20.0 or more

    The missing select.poll in eventlet >= 0.20.0 causes problems for
    pyinotify which uses it. The poll object is not actually used by the
    Notifier object used for file monitoring, but rather select.select, so
    we provide a dummy poll object to let pyinotify's init method
    complete.

    Change-Id: Ib6aacb3566d602f2af485831162eb092a89892ca
    Closes-Bug: #1765470